Strategic Analysis of Farm-Based Renewable Energy Opportunities in Vermont

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Strategic Analysis of Farm-based Renewable Energy Opportunities in Vermont

Vermont Agency of Agriculture

2012

Vermont Agency of Agriculture, Food & Markets 116 State Street Montpelier, VT 05620-2901

Point of Contact: Dan Scruton Email: [email protected]

Prepared for the Vermont Agency of Agriculture under VTREAP/AIC Grant number 02200-12001 by:

Dr. Ben Luce Assistant Professor of Physics Lyndon State College Lyndonville, VT 05851 Email: [email protected]

Project Development and oversight (Vermont Agency of Agriculture): Chuck Ross (Vermont Secretary of Agriculture), Dan Scruton (Dairy Programs Section Chief), Stephanie Congo (Agricultural Engineer), and Rob Achilles (P.E.).

Acknowledgements: Special thanks to the following individuals and organizations for their helpful input: James Ashley (Green Mountain Geothermal), Gaelen Brown (Compost Power), Gail Busch (Algepower Inc), Reg Chaput (Chaput Family Farm), Andi Colnes (Energy Action Network), Dr. Anju Dahiya (University of Vermont), Ed Delhagen (Vermont Department of Public Service), David Dunn (Central Vermont Public Service), Aaron Emerson (Lyndon State College), Robert Foster (Composting Association of Vermont), Johannes Lehmann & Largus Angenan &Alfred M Center (Cornell University), Anne Margolis (Department of Public Service), Michael Miller (Enviro Energy LLC), Johanna Miller (Vermont Natural Resources Council/Vermont Energy Community Action Network), Martin Orio (Northeast Geo), Jenn Osgood (Program manager for Ag, Efficiency Vermont), Scott Sawyer (Vermont Sustainable Jobs Fund), Harvey Smith (Smith Family Farm), Gabrielle Stebbins (Renewable Energy Vermont), Gaye Symington (Vermont Community Foundation), and Netaka White (Vermont Sustainable Jobs Fund).

Table of Contents Executive Summary ...... 4 Oilseed Biofuels ...... 7 Grassy Biomass Production and Utilization ...... 14 Cellulosic Ethanol ...... 17 Pyrolysis & Gasification Reactors ...... 21 Algae ...... 28 Advanced Anaerobic Digesters ...... 34 Utilization of BioChar/Biogas/Bio-oil/Syngas ...... 38 Biological Fuel Cells ...... 46 Geothermal Heat Pumps ...... 49 Air Source Heat Pumps ...... 54 Solar Hot Water ...... 57 Heating with Aerobic breakdown of Biomass ...... 60 Thermal Energy Storage Technologies ...... 62 Thermal Energy Utilization ...... 73 Micro-hydropower ...... 86 Photovoltaics ...... 92 Electrical Energy Storage ...... 100 Wind Power ...... 111 Solar/Battery Powered Farm Equipment ...... 112 Energy Efficiency ...... 116

Executive Summary This report presents a broad strategic analysis of potential renewable energy development opportunities for Vermont farms, to determine which technologies are or may be of interest in the coming decade. For a variety of reasons the past decade has witnessed an unprecedented level of research and development, leading to a plethora of new opportunities. Prioritizing among these will be difficult, and will require constant attention to new developments. This report will hopefully help initiate and contribute to that effort.

Some of more exciting new technologies and/or developments include:  Second & Third Generation Biofuels, and Biochar: The wide range of emerging production routes for second and third generation biofuels presents an enormous opportunity for both Vermont and the world as a whole. These routes include the gasification, pyrolysis, or enzymatic breakdown of cellulosic biomass provided by high yield crops such as switchgrass, and the production of algae biofuels. This is perhaps the most difficult set of technologies to evaluate due to the rapidly changing status of these technologies. But the very high potential yield of these approaches, and the R&D progress that has been made to date, clearly indicate that these routes should be a primary focus of attention. In particular, there appears to exist a special opportunity to develop fast pyrolysis processes in Vermont initially for biochar and then expand into bio-oil production as a market for the latter develops.  Grass Energy: Recent R&D suggests that cultivation of high yield perennial grasses looks promising in Vermont, and could become a major source of both biofuel feedstock and heating fuel.  Solar power (Photovoltaics): PV technology has undergone a dramatic decrease in cost recently. Modules are now selling below $1/watt, and further reductions in cost can be expected. Solar power also has an enormous resource potential, good scalability, and other positive attributes. Vermont farms in particular have the potential to generate much or most of Vermont’s power requirements with this technology using a very small percentage of open farmland.  Ground Source (Geothermal) and Air Source Heat Pumps, and Solar Hot Water: These technologies have improved substantially recently, and offer a cost effective means to tap into enormous reserves of renewable heat. In the long run these may evolve into dominant sources of thermal energy (worldwide). Development of these will likely be greatly enhanced with new opportunities for large-scale thermal energy storage, and also low energy growing techniques, such as pioneered by grower Eliot Coleman.  Advanced Anaerobic & Aerobic Digestion: Anaerobic digestion at dairies with renewable electricity generation has already become established at some larger Vermont dairies. Significant potential exists for expanding this base to more and also smaller farms, possibly with assistance of new technology for ambient (low) temperature digestion, which can provide greater stability, more thermal energy for other uses, and shorter processing times. It also appears to be possible to produce a significant amount of thermal energy for greenhouses and other applications through the aerobic breakdown of compost and manure, and several organizations in Vermont and elsewhere have been perfecting technology for this.

There are many other exciting possibilities as well. A more systematic description of results appears in this section below, and full discussions appear in the remainder of the report.

A major theme in coming years will likely be the synergistic integration of many different technologies and cultivation practices, wherein the products and by-products of a given process feed another, and so on, in

4 more or less closed cycles that minimize conventional energy inputs and maximize productivity. Some possible integration synergies are discussed in this report where relevant.

The following bullets provide a more systematic summary of results, in the order in which they are covered in the remainder of the report:  We report on significant and exciting progress on the cultivation and processing of oilseed crops for biofuels. While biodiesel production is already well established, significant further reductions in costs seem likely with improved oilseed crop cultivation techniques, new uses of oilseed meal and glycerin by- products, and with new reactor technologies such as ultrasound and mixing reactors. The latter have the potential to not only save time and reduce costs, but also reduce methanol requirements. Potential for replacement of fossil methanol or avoidance of methanol altogether also exists.  We report on recent progress in the cultivation of and processing of tall perennial grasses for energy. It appears that, although further research is needed, tall grass cultivation will become a viable practice in Vermont. It also appears that technical hurdles for the creation and combustion of grass products have already largely been surmounted.  We describe the array of emerging biomass pyrolysis and gasification reactors, and the use of the outputs of these devices. Pyrolysis of biomass for the production of bio-oil and biochar in particular appears to be an emerging process with great economic and technical promise for the production of third generation biofuels, sue to the high energy density of bio-oil, and the positive attributes of biochar. Production of biofuels from syngas obtained from gasification of biomass also appears promising, and include both catalytic and fermentation routes.  We report on the status of algae biofuel production, which appears to be potentially viable in Vermont if: o High algae yields can be achieved, which new discoveries in the metabolism of algae would appear to support, and: o If sufficiently innovative (inexpensive) photobioreactors can be developed, perhaps along the lines that some Vermont companies are already pursuing. New advances in this area also suggest that direct production of ethanol from blue-green algae may be possible.  We discuss prospects for cellulosic ethanol production, which appears to have advanced greatly and may now be on the verge of successful large-scale commercialization. Development of modular cellulosic production technology may also enable smaller-scale production appropriate for Vermont.  We discuss the current status of anaerobic digesters, such as those currently utilized at over ten Vermont dairies. We discuss prospects for these to be scaled down, and also the potential use of low (ambient temperature) anaerobic digestion, which appears to offer greater stability and more waste heat for other applications.  We report on the current status of Biological Fuel Cells (BFCs) which are an interesting and potentially useful emerging technology for production of electricity from biomass.  We discuss the current status and issues associated with the use of air source and ground source heat pumps, both of which have improved significantly recently and are likely to become major sources of renewable heat for society, and also key components in many different kinds of integrated thermal energy capture, storage, and delivery systems.

 We report on the status of solar hot water systems, which continue to offer strong potential for providing cost effective renewable heat, and may find use in integrated systems involving heat pumps and large thermal storage systems.  We report on new technologies for utilizing heat from the aerobic digestion of biomass, including low tech approaches for utilizing compost heat, and higher tech approaches for utilizing large amounts of manure and other biomass.  We discuss emerging thermal storage technologies, including new large scale technologies now available in Vermont, and the progress of very large seasonal thermal energy storage experiments in Europe.  We also discuss the utilization of thermal energy from many of the above mentioned sources, including the integration of renewable heat strategies with low energy growing techniques (such as those pioneered by grower Eliot Coleman), aquaponics, and other uses.  We report on the current status of photovoltaics, which have recently achieved remarkable reductions in cost recently and have good prospects for further cost reductions and increases in efficiency.  We discuss micro-hydro generation, which is already a well-established but still evolving technology, and which can offer farms with the right hydro resource a cost effective means to generation renewable electricity.  We discuss the current status and prospects for wind energy, which offer farms with the right wind resources another potentially cost effective means to generate renewable electricity.  We discuss prospects for electric powered farm equipment, which presently appear good for equipment up to about 100 hp, and possibly beyond if electrical energy storage technologies achieve large cost reductions.  Finally, we review the current status and prospects for energy efficiency improvements at farms.

Disclaimer: An attempt has been made to utilize the best available scientific and commercial sources of information that could be located within the time allotted for the report’s development, with preference given to those sources which are publically accessible, and to which links can be provided. The scope is ambitious, however, and time and funding finite, so it will undoubtedly be the case that some technologies and/or key projects and/or individuals have been overlooked. We apologize for such lapses in advance, and stress that such omissions in no way imply a negative value judgment on that which has been omitted.

Oilseed Biofuels  Technology Description: o Production of first generation liquid biofuels for transportation from seed oil (“vegetable oil”) obtained from crops including soybeans, canola, sunflowers, and others. The vegetable oil may be used directly in modified diesel engines, or refined into fuels such as biodiesel.

 Technology Special Benefits: o A local, potentially competitive, and stably priced source of renewable fuel. Estimates suggest that oilseed biofuels may be able to provide full coverage of VT on-farm diesel fuel (up to 6 million gal/year of biodiesel) and up to 50% of VT feed meal demand. o A local supply of oilseed meal for uses including livestock feed and/or soil amendments.

 Overall Prospects for Successful Deployment: o Economic prospects for oilseed biofuels appear to be promising, with possible biodiesel production costs in the neighborhood of $3/gal or less, if oilseed yields can be kept sufficiently high (~1500 lbs/acre), and if oilseed meal can be sold (or offset other costs) at a sufficiently high cost (>$200/ton). o Research suggests that oilseed biofuels can have energy paybacks up to around 2.5, which is potentially acceptable but not as high as potentially obtainable from second and third generation biofuels such as cellulosic ethanol and algae biofuels, respectively. On the other hand, oilseed biofuels are already fairly cost effective and new reactor technologies and other opportunities, as described below, offer the potential for substantial improvements to the economics and sustainability of oilseed biofuels.

 Development Status: o Despite substantial progress, biodiesel still makes up a very small fraction of diesel consumption by Vermont farms, and challenges for oilseed cultivation remain. The long-term economic viability of widespread, small-scale biodiesel production in Vermont is also still somewhat uncertain due to the many potential emerging pathways for biofuel production. o Oilseed biofuel production is already a mature process, but can be further improved, including improvements in cultivation, seed processing, biodiesel processing (and production of other fuels such as bioethanol), and in end-use of by-products. Cultivation and fuel production are intimately linked: The true long-term average production costs of seed oil, which will only become completely apparent with further experience, will play a decisive factor in the economic viability of biodiesel, as will the economics for uses of biodiesel production by-products, such as the leftover oilseed meal and crude glycerin. o Vermont already possesses a well-developed oilseed biofuels research and production base: . A spreadsheet tool called the Vermont Oilseed Cost Calculator is now available1. . Eight Vermont farms already possess seed presses and/or biodiesel production facilities (604,000 gal/year of production capacity).

1 http://www.callahan.eng.pro/blog/index.php/2011/07/03/oilseed-cost-and-profit-calculator/

. At least eight Vermont farms now have oilseed pressing and processing equipment and expertise with a production capacity of around 604,000 gal/year, enough to support 10,000 acres of oilseed cultivation2. . Vermont has an active “Biofuels Initiative3” organized by the Vermont Sustainable Jobs Fund. . Vermont has an active biofuel’s research community4, and a significant amount of educational and research information has been published5. . The University of Vermont now has a biofuel curriculum6, which enjoys direct involvement by many in the Vermont biofuel research community and local growers. . Vermont is the ninth state to adopt a mandatory requirement for biodiesel in home heating fuel7. . At least one Vermont biofuel farm (State Line Farm) is exploring on-farm production of ethanol (from sweet sorghum) to eliminate the need for fossil based methanol in the biodiesel production process8.

 Barriers & Opportunities: o Oilseed Crop Cultivation Knowledge: This is increasing rapidly and research in Vermont has already provided many specific insights on how to maintain yield. Further research is needed on predation control techniques, planting and harvesting times, rotation possibilities, fertilization requirements, and no-till cultivation. UVM Professor Heather Darby9 and coworkers have been actively conducting research at sites such as the Borderview Farm research site10 in Vermont to develop the specific information needed for Vermont. Reports summarizing the results of this research can be found at http://www.uvm.edu/extension/cropsoil/oilseeds#reports. o No-Till Approach: Some growers in the Northeast are exploring no-till techniques for oilseed crops, which it appears might substantially lower production costs11. o Oilseed Pellets: Research at Borderview Farm in Vermont also found that the meal can be processed into extremely stable pellets when pressed at least twice, and the study remarked that pelleting after pressing may result in a pellet that has a longer shelf life than unpelleted meals12. o Processing Scale Issues: Greater oilseed production per existing press needed (greater acres/press), and greater shared use of biodiesel production facilities and bulk purchase of methanol has been identified as a means to keeping production costs sufficiently low13. Additional and/or better seed presses and biodiesel processers, including mobile units, and new reactor technologies (see below) may help.

2 http://www.vsjf.org/project-details/11/oilseeds--biodiesel 3 http://www.vsjf.org/project-details/4/bioenergy-initiative-overview--history 4 http://www.vsjf.org/project-details/11/oilseeds--biodiesel 5 http://www.extension.org/pages/28783/farm-energy-biodiesel-table-of-contents 6 http://learn.uvm.edu/?Page=biomass_to_biofuels.html 7 http://www.biodieselmagazine.com/articles/7817/vermont-heating-oil-to-contain-biodiesel 8 http://extension.psu.edu/susag/news/2011/June-2011/4-biodiesel 9 http://www.uvm.edu/extension/faculty/?Page=darby.html 10 http://www.vsjf.org/case-studies/17/grantee-borderview-research-farm 11 See comments attributed to Dorn Cox with GreenStart: http://www.uvm.edu/extension/cropsoil/wp- content/uploads/Oilseed_Producer_meeting_notes_2011.pdf 12 http://www.vsjf.org/assets/files/VBI/FFP_Final_Report_2008.pdf, Page 58. 13 http://www.uvm.edu/extension/cropsoil/wp-content/uploads/Oilseed_Producer_meeting_notes_2011.pdf

o Oilseed Meal Usage: Potential barriers to using the meal for livestock feed and fertilizer have been identified in the past, including inconsistency and high fat content for oilseeds from on-farm seed presses, and potential crop damage at excessive levels of application. Recent R&D appears to suggest that the outlook for using certain on-farm produced oilseed meals in livestock feed is nonetheless promising, and fertilizer applications appear to be a viable alternative in general used properly, but may offer less in terms of monetary payback. Further R&D is needed on these topics. Recent actual trials of using oilseed meal that is specifically from or like that coming from biodiesel operations, particularly in the form of pelletized meal, have been conducted for various types of livestock (outside of Vermont) and seem to have promising results. Examples of just a few of these for canola are: . A collaboration of Chinese and US researchers recently found no significant negative effects using up to at least 25% canola meal for “broilers” (chickens raised for meat) compared with control diets of soybean meal14. . A study by University of Minnesota and North Dakota State University researchers found that adding 7% canola meal pellets to feed for lactating Holsteins did not seem to have negative effects15. . A Chinese graduate student at an aquaculture center in Norway found that tilapia could be raised with large percentages of canola meal16. o Advanced biodiesel reactor technology: These offer very good potential for improving fuel quality while greatly reducing the time, energy, and amounts of catalysts and/or methanol required. New technologies include continuous flow reactors, ultrasound assisted production, supercritical reactors, static mixers, reactive distillation, and enzymatic biodiesel production (as an alternative to conventional sodium methoxide based approach). Several of these approaches, particularly ultrasound assisted production, static mixers, and reactive distillation, may enable mobile biodiesel processing units that can process seed oil much faster than more conventional batch reactors: . Batch Processing: This approach is presently widely used, relatively simple and cheap, and tolerant to impurities. The reactants are simply combined in a reactor, along with a catalyst, agitated in some way until the reaction is complete. Disadvantages include the fact that the capacity is directly proportional to processor size, and mixing is not as efficient as some other approaches, leading to a greater use of methanol. A catalyst is also generally required. . Continuous-Flow Reactors: These are similar to batch reactors in some respects, but the reactants and products are continuously fed in and removed, respectively, and the reactor size is not proportional to capacity. These generally require more careful design, complex controls and quality monitoring. A two-stage design can improve quality and reduce the amount of methanol used. . Ultrasonic Assisted Production: Ultrasonic assisted production utilizes the rapid mixing provided by ultrasonic cavitation effects (the continuous creation and collapse of micro-bubbles). Ultrasound can

14 Min Y.N., Z. Wang, C. Coto, F. Yan, S. Cerrate, F.Z. Liu and P.W. Waldroup. 2011. Evaluation of canola meal from biodiesel production as a feed ingredient for broilers. 2011. International Journal of Poultry Science 10 (10): 782-785. Link: http://www.pjbs.org/ijps/fin2084.pdf. 15 Maiga et. al., Effect of pelleted high-oil canola meal from on-farm biodiesel production on rumen fermentation in lactating Holstein dairy cows, The Professional Animal Scientist 27 (2011):29–34. 16 Chinese PhD student Youling Gao at the Aquaculture Protein Centre (APC), a Norwegian Centre of Excellence that is affiliated with the Norwegian University of Life Science (UMB). See http://sciencenordic.com/biodiesel-product-tilapia- farming.

reportedly reduce the typical 1-4 hours of processing time required in batch processing to less than 30 seconds. It also reduces separation time, which typically takes up to 10 hours, down to 1 hour17. Another related major advantage of this technique is that it can enable continuous flow processing. Although sonication requires electricity, the overall energy consumption is significantly reduced. The processors also take up less space, and are potentially safer. One possible problem with ultrasonic processing is that the flow rates need to be carefully tailored to the feedstock18. A database of information on different feedstocks might solve this problem. Ultrasonic reactors for biodiesel production were introduced by Hielscher Ultrasonics in the early 2000s. The company’s website indicates that the company “offers ultrasonic mixing reactors for the production of biodiesel at any scale,” although they also recommend it for capacities of 80 liters/hour and up. Other manufactures of ultrasonic equipment for biodiesel production now also exist. . Supercritical Reactors: These operate at high temperatures and pressure (typically 300°C and 5800 psi or higher), above the critical point of the oil, in which phase regime the oil exhibits a combination of liquid and vapor phase properties. In this state the oil completely dissolves in methanol, and the reaction proceeds very rapidly, and does not require a catalyst. The process is tolerant of water and free fatty acids, and eliminates soap formation. A disadvantage is that the equipment to achieve the high pressures and temperatures may not be cost effective for many small scale producers. . Static Mixers: These have no moving parts: The internal structure causes the reactant flows to combine effectively. These have been shown to be effective for biodiesel production19, although apparently have not been commercialized for this purpose. . Reactive Distillation: This approach combines reaction and separation steps. The UVM extension reports that this approach may be quite promising for biodiesel production20: “According to research conducted at the University of Idaho sponsored by the National Institute of Advanced Transportation Technologies (NIATT) (He et al., 2005, 2006, 2007), the RD reactor system showed three major advantages over the batch and traditional continuous-flow processes: 1) shorter reaction time (10 to 15 min) and higher unit productivity (7 to 9 gallons per gallon reactor volume per hour), which is highly desirable in commercial production units; 2) much lower excess alcohol requirement (approximately 3.5:1 molar), which greatly reduces the effort of downstream alcohol recovery and operating costs; and 3) lower capital costs due to its smaller size and the reduced need for alcohol recovery equipment.” o Alternative to Conventional (salt) Catalysts: Most biodiesel production that employs catalysts (e.g. batch reactors) use sodium or potassium methoxide (usually from dissolving sodium or potassium hydroxide in the methanol in the case of small scale producers). The need for a catalyst adds cost and complexity, and the left over salts in the glycerin by-product can be problematic for use of the glycerin, for example in livestock feed (although the use of potassium instead of sodium is potentially helpful). Some of the newer reactor designs eliminate the need for catalysts entirely. Another emerging option is use of enzymes. The company Piedmont recently announced a new plant using this approach21.

17 http://www.biodieselmagazine.com/articles/4202/ultrasonic-biodiesel-processing 18 http://www.biodieselmagazine.com/articles/4202/ultrasonic-biodiesel-processing 19 https://elibrary.asabe.org/abstract.asp?aid=22389&t=2&redir=&redirType= 20 http://www.extension.org/pages/26630/reactors-for-biodiesel-production 21 http://www.biodieselmagazine.com/articles/8547/piedmont-to-hold-enzymatic-biodiesel-plant-ribbon-cutting-june-22

o Alternatives to Fossil Fuel Methanol: Fossil methanol can be avoided by replacing it with anhydrous ethanol. A feasibility study of this approach was conducted in 201022, and at least one Vermont biofuel farm (State Line Farm) is exploring this possibility through the cultivation of sorghum23. The feasibility study also suggested that this could be done with high yield on marginal land. Biodiesel websites indicate that small producers are in fact successful at producing “ethanol biodiesel”, although the control requirements, such as maximum water content of the oil, are significantly more stringent24. Another route may be to develop a source of biomethanol produced from syngas obtained via gasification of cellulosic biomass (perhaps at a centralized facility). o Mobile Processing: The economic analysis of biodiesel production above clearly shows that keeping the production cost low is critical to economic feasibility. One possibility for achieving lower costs, and also helping to provide expertise to farmers unfamiliar with biodiesel production, would be to deploy mobile processing units around the state. A feasibility study of this idea has been performed as well25, which suggests that two such units could cover the entire state (in terms of geography and cost effectiveness, if not ultimate future demand). Both seeding pressing and biodiesel reactor services could be provided in separate units or combined in a single unit. Such biodiesel trailers already exist, such as the trailer by GreenStart26. o Discussion of Biodiesel Processing Options: The foregoing material indicates that there are several promising newer reactor designs that could be helpful to small-scale producers in Vermont. In particular, ultrasound, static mixer, and reactive distillation all appear to offer means to lower costs through various combinations of reduced requirements for time, methanol, energy, and catalysts, without needing to achieve the high temperatures and pressures required for supercritical operation. All three would appear to be potentially applicable to mobile processing units as well. Being able to significantly reduce processing time would be a real boon for a mobile unit that needs to be shared by many different farmers. Another boon would be producing glycerin with a much smaller methanol level, as the methanol in the glycerin often results from the use of more methanol than is chemically needed to drive the reaction to completion, and the subsequent failure to remove a significant amount of the methanol. This might have a number of benefits, as the next section on glycerin describes. Or, as was described above, it may be possible to eliminate the use of methanol entirely by switching to anhydrous ethanol. o Synergestic relationships such as the use thermal energy from other processes (e.g. anaerobic digestion, solar hot water, geothermal heat pumps, pyrolysis and/or gasification reactors, etc) might also be used to enhance the environmental attributes of oilseed biofuels and lower the costs of drying and processing oil seeds. o Disposal of Glycerin from Biodiesel Processing: . Glycerin may also be useful as an additive to anaerobic digesters. Presently, the methanol content of crude glycerin from biodiesel production presents regulatory hurdles to transporting (significant quantities of) crude glycerin. But recent R&D suggests that crude glycerin can be successfully utilized

22 http://www.callahan.eng.pro/blog/wp-content/uploads//REAP-On-Farm-Ethanol-Report-Final-2010-08-20-Public.pdf 23 http://extension.psu.edu/susag/news/2011/June-2011/4-biodiesel 24 http://journeytoforever.org/ethanol_link.html#ethylester 25 http://www.callahan.eng.pro/blog/index.php/2008/12/15/mobile-oilseed-processing-biodiesel-production/ 26 http://www.greenstartnh.org/index.php?option=com_content&view=article&id=70&Itemid=125

in anaerobic digesters, so anaerobic digestion provides one possible disposal route for glycerin produced on-site in this way. . New reactor technology may also be capable of reducing methanol levels sufficiently to enable transport, although (new) special regulatory treatment may be necessary. Glycerin may also be de- methylated, but lowering methanol levels with new reactor technology might prove more cost effective due to the additional advantages of utilizing new reactor technologies (reduced time, energy, etc). . One group of researchers in the Midwest has found that crude glycerin blended with woodchips can be gasified effectively in a downdraft gasifier27. They conclude “Though further testing is suggested, downdraft gasifiers could be run well with hardwood chips blending with liquid crude glycerol up to 20 (wt%).” . One company (AlterHeat Company, LLC) is now selling burners which they claim can combust crude glycerin directly28. . Another study determined that it appears that controlled amounts of crude glycerin can be utilized in anaerobic digesters29. If newer biodiesel reactor designs can reduce the amount of methanol as well, then this might allow both a greater level of glycerin consumption by AD and help lead to the removal of regulatory barriers to the transport of glycerin to AD sites. . If salts are removed, glycerin can be used to fuel modified diesel generators via the “McNeil cycle”30. It was seen above the some of the new reactor designs avoid the use of catalysts (salts), and the catalysts can potentially be replaced with enzymes. . Other studies have found that hydrothermal reforming (steam reforming) of crude glycerol, potentially using the wastewater from biodiesel production, appears to be a controllable and potentially viable means to produce hydrogen31,32. . Another study found that gasification (glycerol plus air) was a viable way to produce syngas (carbon monoxide plus hydrogen)33, which can be used for applications using as power generation, or synthesis of fuels such as dimethyl ether. . Another study found that crude glycerin is a promising fuel source for microbial fuel cells34. See the chapter on microbial (biological) fuel cells.

27 Co-gasification of hardwood chips and crude glycerol in a pilot scale downdraft gasifier, Wei L, Pordesimo LO, Haryanto A, Wooten J, Bioresour Technol 2011, 102:6266-6272. http://www.sciencedirect.com/science/article/pii/S0960852411003154 28 http://glycerinburners.com/glycerin_burner.php 29 Anaerobic digestion of glycerol derived from biodiesel manufacturing, López JÁS, Santos MDM, Pérez AFC, Martín AM, Bioresour Technol 2009, 100:5609-5615. http://www.sciencedirect.com/science/article/pii/S0960852409006762 30 http://www.biodieselmagazine.com/articles/3076/technology-allows-glycerin-to-power-diesel-generator/ 31 Steam reforming of biodiesel by-product to make renewable hydrogen, Slinn M, Kendall K, Mallo C, Andrews J, Bioresour Technol 2008, 99:5851-5858. http://www.sciencedirect.com/science/article/pii/S0960852407008401 32 Steam reforming of crude glycerol with in situ CO2 sorption, Dou B, Rickett GL, Dupont V, Williams PT, Chen H, Ding Y: Bioresour Technol 2010, 101:2436-2442. http://www.sciencedirect.com/science/article/pii/S0960852409014990 33 Gasification of biodiesel by-product with air or oxygen to make syngas, Yoon SJ, Choi Y, Son Y, Lee SH, Lee JG, Bioresour Technol 2010, 101:1227-1232. http://www.sciencedirect.com/science/article/pii/S0960852409012450

. Another found that producing ethanol from crude glycerin through fermentation may be a viable option to add value to biodiesel production35. . There are also many studies that look at possible uses of crude glycerin in livestock feed, and these might conceivably become relevant to Vermont as local biodiesel production practices improve, especially if methanol content can be reduced with newer reactor designs, and possibly with new or no catalysts. For example, recent joint research by Texas AgriLife Research and West Texas A&M University suggests that up to 7.5% of cattle forage diet can consist of glycerin that meets certain quality standards36.

34 Treatment of biodiesel production wastes with simultaneous electricity generation using a single-chamber microbial fuel cell, Feng Y, Yang Q, Wang X, Liu Y, Lee H, Ren N.,Bioresour Technol 2011, 102:411-415. http://www.sciencedirect.com/science/article/pii/S0960852410009168 35 Anaerobic fermentation of glycerol in Paenibacillus macerans: metabolic pathways and environmental determinants, Applied and Environmental Microbiology, September 2009, p. 5871-5883, Vol. 75, No. 18. http://aem.asm.org/content/75/18/5871.full 36 http://www.biodieselmagazine.com/articles/8463/feed-and-fuel

Grassy Biomass Production and Utilization  Technology Description: o Production of combustible pellets, briquettes, or cubes for space heating applications, or second generation liquid biofuels such as cellulosic ethanol or biofuels produced from pyrolysis or gasification products, from perennial grasses including but not limited to switchgrass, miscanthus, reed canarygrass, and hay. (Cultivation of perennial grass and space heating applications are considered here: See other sections for further information on cellulosic ethanol and pyrolysis/gasification routes).

 Technology Special Benefits: o A local source of renewable heating and transportation fuel, the production of which will not necessarily encroach significantly on food production. o High energy yield per acre, and high energy payback ratio (~10:1), compared with first generation biofuels such as oil seed biofuels. o Lower and more stable heating costs for farmers and Vermont homes and businesses. o Additional revenue for farmers from marginal land. o Grass crops are perennials that require small amounts of fertilizer input and maintenance, and can often be grown in marginal soils.

 Overall Prospects for Successful Deployment: o Prospects are good for both cultivation and energy production if high yields can be consistently achieved with low energy inputs (as initial research suggests). o Some estimates suggest that switchgrass can be produced with a long-term average cost of approximately $90/ton, stored and then delivered for processing at a total cost of about $120/ton, and that grass pellets can be produced at roughly $200/ton or less37. This compares favorably with wood pellet prices (~$280/ton) and very favorably with oil prices (~$340/ton equivalent for heating oil at $3/gallon, assuming that one ton of grass pellets offsets approximately 114 gallons of oil).

 Development Status: o Very little production/consumption currently exists in VT except for hay. o The viability of cultivation of several different tall grasses looks promising according to research to date in VT, although more research is needed. o Technical and economic viability for production of pure grass pellets, including mobile production, has recently been demonstrated (see below). o Vermont has well established grass energy R&D base: . The Vermont Grass Energy Partnership: This is a collaborative effort between the Vermont Biomass Energy Resource Center (BERC), University of Vermont Extension, and the Vermont Sustainable Jobs Fund. For more information, see http://www.vsjf.org/project-details/3/grass--biomass-energy. The Partnership has conducted crucial research on grass energy, including the 2011 “Technical

37 https://www.extension.iastate.edu/agdm/crops/html/a1-22.html: Estimates quoted here are converted to 2012 dollars.

Assessment of Grass Pellets as Boiler Fuel in Vermont38”. This report and other publications by BERC can be found at http://www.biomasscenter.org/resources/publications.html. . Grass Energy in the Northeast: A website providing discussions about grass energy between a variety of people and groups in Vermont and other Northeast States: http://grassenergy.wordpress.com/ . Northeast Biomass Heating Expo: http://www.heatne.com/program.html . Research at University of Vermont: http://pss.uvm.edu/vtcrops/?Page=energycrops.html . Cornell Grass Energy Site: http://www.forages.org/bioenergy/

 Barriers & Opportunities: o Greatest potential opportunity: This may lie with production of grass energy products for large space heating applications such as grass capable boilers. For example, a single farm supplying the heating fuel for a single school. The establishment of local grass pelletizing facilities, either producing pure or wood blended pellets, could rapidly broaden the potential market in Vermont for grass energy products to a much wider range of pellet stoves and boilers. o Further research is needed on harvesting techniques to both decrease chlorine level to the extent that is actually needed (standards for grass pellets have not yet been established) and to reduce pelletizing difficulties (such as high pelletizing energy inputs) while maintaining energy content. Issues include, for example: . Overwintering switchgrass can substantially decrease chlorine, but it appears this may unduly reduce energy content and cause pelletizing problems. . De-chlorination of canary grass can also be challenging because this cold season plant reaches maturity at the peak of the growing season, so the new shoots come up quickly through cuttings that are left in the field for leaching purposes. o Relatively pure grass stands can be difficult to establish due to weed encroachment, especially for warm season grasses like switchgrass. Further research and growing trials are still needed in general, including with respect to identifying the most viable grasses for both cultivation and end uses. o Invasive species issues should be considered carefully. For example, reed canary grass is presently on the Vermont watch list. o Pelletizing grasses (for pure grass pellets) has been difficult in the past, but this appears to have been (largely) overcome by both Enviro Energy LLC39 and the Hudson Valley Grass Energy group40. The latter has successfully developed a mobile grass pelletizer. Enviro Energy LLC still reports difficulties (large energy inputs) with switchgrass not harvested in the fall41. o Combustion of Pure (100%) Grass Pellets: Pure grass pellets have high ash content, and reducing chlorine content can be difficult without significant energy loss (see next bullet). These factors have prevented the use of pure grass pellets in wood pellet stoves to date, although research performed in Vermont suggests that wood/grass blends with up to at least 20% grass can be used. Various sources also suggest that some stoves, such as the Harmon Corn Stove, are capable of burning pure grass

38 http://www.biomasscenter.org/images/stories/grasspelletrpt_0111.pdf 39 http://www.enviroenergyny.com/ 40 http://hvgenergy.wordpress.com/2011/02/07/research-and-design-of-a-mobile-grass-pellet-mill/ 41 Direct correspondence, July 2012.

pellets without significant operational problems, although the longer term corrosive impacts on these stoves is not yet clear. The grass pellet maker Enviro Energy LLC reports that the company Europa also sells a grass pellet capable stove, that some small coal stoves appear to work well, and that larger grass pellet capable furnaces include the “Maxim” by Central Boiler (with the air flow adjusted to minimum) and a furnace by LEI Industries42. o Grass Briquettes and Cubes: BHS Energy LLC, a manufacturer of the “Slugger” grass briquette press, reports that compared with making pellets making briquettes is more reliable and repeatable, more tolerant to different moisture levels, more energy efficient, and requires less pre-processing of the raw material. The manufacturer also provides a list of boilers capable of utilizing its briquettes43. One of the boilers listed is the Goliath boiler by New Horizon Crop44, a boiler which is widely referred to on grass energy sites and discussions with few or no mention of problems. Cornell University scientist Jerry Cherney states ”Industrial sized ceramic-lined boilers (1 million BTU or more) are currently capable of burning grasses45.” It should also be noted that grass briquettes can simply be burned in wood stoves, although it may be necessary to avoid catalytic wood stoves due to chlorine impacts on the catalysts. o Status of Grass “Field Cuber”: Use of grass cubes in coal stokers requires high density grass cubes. University of Wisconsin researchers attempted to develop a field cuber for grasses (“cellulosic biomass”) for producing high density grass cubes46. They first determined that reducing moisture was a key factor in producing durable cubes (dense cubes with low relaxation), and then found that applying a few pounds of lime per ton of biomass (to bind with moisture), heated water, and using lower die temperature improved the quality of the cubes considerably, although the resulting process was still inconsistent.

42 Direct correspondence, July 2012. 43 http://bhsenergy.com/briquettes.html 44 http://www.biomass-heat.com/products/90-goliath-biomass-boiler.aspx 45 http://www.extension.umn.edu/forages/pdfs/grass_for_bioheat_on_farms_21309.pdf 46 http://ncsungrant.sdstate.org/upload/UW-Sun-Grant-KJS-2012.pdf

Cellulosic Ethanol  Technology Description: o Cellulosic Ethanol (CE), a second generation biofuel, is produced via the breakdown of cellulosic biomass including corn stover, grasses, woody biomass, and other agricultural residues. There are multiple possible routes: . Enzymatic breakdown of biomass, followed by fermentation of the resulting sugars into ethanol. . Gasification of biomass to produce syngas, followed by fermentation or catalytic conversion of the syngas into ethanol (or possibly other fuels in the case of catalytic conversion). This would allow use of the lignin as well as cellulose for ethanol production47. . Pyrolysis of biomass into bio-oil and syngas, and refining of these products into biofuel. This section is concerned only with the enzymatic and gasification routes for ethanol production in particular. See other sections on gasification and pyrolysis and use of products of these for discussion of other cellulosic biofuel production routes.

 Technology Special Benefits: o A local source of renewable transportation fuel, the production of which will not necessarily encroach significantly on food production. o Estimates suggest that 30-60 million gallons of cellulosic ethanol might be produced from about 60,000 acres of land devoted to hay (with yields of 5-10 tons hay/acre/year). o Cellulosic biofuels in general are potentially capable of supplying much of the World’s transportation fuel. o High energy yield per acre, and potentially high energy payback ratio (~10:1), compared with first generation biofuels such as oil seed biofuels. o Lower and stable fuel costs for farmers and Vermont residents (if cost effectiveness is achieved). o Additional revenue for farmers from a wide range of cellulosic biomass sources, including grasses grown on marginal land.

 Overall Prospects for Successful Deployment: o Uncertain, but with positive signs. This technology is still evolving extremely rapidly, and it is still too early to say if cost effectiveness will be achieved, and how scalable the ultimate technologies will be. Estimates by the Department of Energy suggest that production costs of around $2/gallon may be possible, and recent R&D in both enzymatic and gasification routes appears to be consistent with this.

 Development Status: o No production of cellulosic ethanol currently exists in Vermont. o Cellulosic ethanol production is still not proven to be cost competitive at a commercial scale, although some US pilot plants have reportedly been successful recently at demonstrating cost effective production, and a 13 million gal/year plant in Italy has reportedly been operating successfully since 2009.

47 http://web.anl.gov/PCS/acsfuel/preprint%20archive/Files/38_3_CHICAGO_08-93_0855.pdf

o There are now 33 CE plants that exist in the US and Canada (although production from these is still very small). These include over 100 million gals/year of capacity from four plants planned or under construction by Dupont, BP, Abengoa Bioenergy and Poet-DSM Advanced Biofuels48. Some, such as the plant under construction by Poet (“Project Liberty” in Iowa) are being watched especially closely. POET’s development is taking place via a collaboration called “POET-DSM Advanced Biofuels” with another company, Royal DSM, that has expertise with enzymes. DSM claims it is the only company that can “co- ferment all C6 and C5 sugars (xylose & arabinose)”49. o The company Syntec is attempting to commercialize using specialized catalysts to convert the resulting syngas to ethanol50. The company claims its CE approach costs roughly $1/gallon. Two other companies, Chinook Energy51 and Enerkem52 are pursuing at similar approach. Enerkem is currently constructing a commercial scale facility, and has two existing facilities in Quebec. o The Federal Renewable Fuels Standard is a crucial driver of cellulosic ethanol development at present, and the political future of this and other important policies is currently uncertain. In particular, the CE industry is greatly concerned about the potential for cancellation of the Renewable Fuels Standard and by new proposed requirements requiring flex fuel vehicle makers to prove usage of biofuels by vehicle operators.

 Barriers & Opportunities o CE in Vermont? Depending on the performance of projects currently under development elsewhere, it is possible that significant cellulosic ethanol development in Vermont may be possible and justified within the coming decade. Both the Enzymatic breakdown and gasification routes appear viable, and are each perhaps suited to different feedstocks and situations. A 2006 paper by the Vermont Sustainable Jobs Fund53 states that “the Vermont Alternative Energy Corporation (VAEC) has calculated that a ten million gallon a year facility (equal to about 3 percent of 2004 gasoline consumption) is possible based on Vermont’s feedstocks, at a cost of $44 million. Burning lignin at the facility would also generate 2100 kilowatts of electricity.” It also stated “VAEC’s cellulosic ethanol feasibility study concludes that wood, lumber, forest residue, and grass straw would make up the most likely ethanol feedstocks in Vermont. VAEC believes that 10 million gallons of cellulosic ethanol can be produced with about 60,000 acres of land devoted to hay.” o Scale-Down Potential: There may be potential for scaling down CE production to farm-scale or at least local scale: At least one company, Easy Energy Systems54, is offering modular CE systems with capacities as little as 0.5 million gallons/year. Such a system could produce 50 gallons per ton of biomass. If a biomass yield of 5 tons/acre is assumed, then such a plant could be supported by biomass cultivation on just 2000 acres. Conventional wisdom holds that bigger is better with fuel production plants. This may not actually prove to the be the case with CE plants in the long run, because of the costs of transporting

48 http://www.ethanolproducer.com/articles/8862/cellulosic-ethanol-here-today 49 http://www.poetdsm.com/ 50 http://www.syntecbiofuel.com/thermochemical_process.php 51 http://www.chinookenergy.com 52 http://www.enerkem.com/en/home.html 53 http://www.vsjf.org/assets/files/VBI/Cellulosic_Ethanol.pdf 54 http://easyenergysystems.com

and storing relatively low energy density (undensified) biomass. For these reasons, EES’s CEO has said "Our feeling is the answer will be distributed ethanol plants that are fully automatic and economic to build.55” o Enzymatic Research Advances: Significant R&D advances have occurred over the past decade, including apparent progress in reducing the cost of enzymatic breakdown using specially engineered enzymes. Most R&D on enzymes for CE production appear to have focused on the fungus Trichoderma reesei, although there may be alternatives56. This fungus has the capacity to secrete large amounts of cellulases and hemicellulases, which are the key enzymes in the production of cellulosic ethanol by enzymatic hydrolysis. Trichoderma reesei was first famously identified as the organism responsible for rapidly degrading uniforms and tents of military personnel during World War II. Its DNA structure has now been fully sequenced57, and many companies are attempting to engineer the organism to optimize it for CE production. A 2010 presentation by Novozyme reports that collaborative work with the Department of Energy (NREL, etc) led to a 30-fold decrease in enzyme costs by 2005, due in part to a breakthrough by NREL involving a pre-treatment for corn stover, and in part due to other enzyme process improvements. It also gave a middle range cost for CE of about $3/gallon in 2010. In February 2012 Novozymes announced a new enzyme, Cellic CTec3, that it claims now reduce the cost of CE to between $2 to $2.50 a gallon58, which is in line with an old cost projection for CE by NREL. In April 2012, the company announced an agreement with a Chinese company to produce CE in China. In May 2012, the company also announced a new $200 million enzyme manufacturing for biofuel enzymes in Nebraska59. o Technologies for Fermentation of Sugars to Ethanol: Baker’s yeast (Saccharomyces cerevisiae), has traditionally been used to produce ethanol from hexoses (six-carbon sugars). Lignocellulosic biomass also possesses a significant amount of xylose and arabinose, which are five-carbon sugars derived from the hemicellulose portion of the lignocellulose. Companies are therefore also attempting to develop microorganisms that can ferment the entire range of sugars resulting from the enzymatic breakdown of lignocelluloses. Besides Saccharomyces cerevisiae, microorganisms such as Zymomonas mobilis60 and Escherichia coli61 have been targeted through metabolic engineering for cellulosic ethanol production. o Pretreatment techniques, a key step for CE production, have advanced considerably. Chemical pretreatment techniques under consideration at this time appear to include dilute acid pretreatment, steam explosion, lime, near-neutral pH control, ammonia fiber expansion, organosolvation, alkaline wet oxidation, ozone pretreatment, and sulfite pretreatment. Dilute acid pretreatment has emerged as a likely best route.

55 http://www.ethanolproducer.com/articles/5871/chu-examines-modular-cellulosic-ethanol-production-facility/ 56 “Alternatives to Trichoderma reesei in biofuel production”, Trends in Biotechnology, Volume 29, Issue 9, 419-425, 24 May 2011. http://www.cell.com/trends/biotechnology/abstract/S0167-7799(11)00070-9 57 http://www.thebioenergysite.com/news/617/the-discovery-of-trichoderma-reesei 58 http://green.blogs.nytimes.com/2012/02/22/new-enzyme-could-cut-cost-of-ethanol-made-from-waste/ 59 http://www.novozymes.com/en/news/news-archive/Pages/Novozymes-inaugurates-largest-enzyme-plant-dedicated- to-biofuels-in-United-States.aspx 60 http://www1.eere.energy.gov/vehiclesandfuels/pdfs/success/zmobilis_mar_2001.pdf 61 http://www.treehugger.com/renewable-energy/genetically-engineered-ecoli-process-to-generate-ethanol-from- woodag-waste-by-2006.html

o Direct Conversion Potential: Some species of bacteria have been found capable of direct conversion of a cellulose substrate into ethanol. One example is Clostridium thermocellum62, which uses a complex cellulosome to break down cellulose and synthesize ethanol.

62 http://rochester.technologypublisher.com/technology/2966

Pyrolysis & Gasification Reactors  Technology Description: o When exposed to high temperatures organic matter can be thermally decomposed, and the outputs processed to provide energy in the form of direct heat, solid fuel, liquid fuels, and gaseous fuels, along with a number of useful by-products. . Pyrolysis consists of the heating of biomass in an environment with very little (essentially no) oxygen to produce mainly biochar or bio-oil. . Gasification involves heating of biomass with controlled amounts of oxygen to produce mainly syngas. o Three basic categories of reactors are: . Slow Pyrolysis Reactors: These are generally batch reactors that operate at relatively lower temperatures (below about 450oC or 842oF) and produce mainly biochar, which is useful as a soil amendment and for sequestering carbon and/or water filtration, or as a solid heating fuel (i.e. charcoal). Reactors range from small stove units (for cooking applications) up through large industrial scale units, and from low tech constructions through highly sophisticated systems. . Fast Pyrolysis Reactors: These are continuous process reactors which operate at low to mid-range temperatures (below 450 up to about 800oC, that is, below 842 up to about 1472oF), and produce either biochar (at lower temperatures), or a vapor (at higher temperatures) that can be separated into bio-oil and a non-condensable syngas, or both (at intermediate temperatures). The syngas and bio-oil can be combusted or processed into fuel. . Gasification Reactors: The heating of biomass with controlled amounts of oxygen to produce mainly syngas, which can be combusted for heating (for example with “close-coupled” burners fed directly off the gasifier) or for electricity production or processed into biofuel. Specific reactor types are discussed below. Usage of outputs of pyrolysis and gasification are considered under the section “Utilization of Biochar/Biogas/Bio-oil/Syngas.”

 Technology Special Benefits: o Slow pyrolysis reactors offer a cost effective, proven, and self-supporting technology for the production of biochar. Biochar has very substantial carbon sequestration and environment clean-up potential. Small pyrolysis stoves can also be used to provide cooking heat, and waste heat from pyrolysis reactors in general, although modest, can be utilized for many possible end uses. o Fast pyrolysis and gasification reactors offer continuous, efficient, and very highly controlled processing for heating, biofuel, and electricity production. Recent advances in fast pyrolysis reactors in particular offer new opportunities for farm-scale operation and have substantial potential to become a valuable source of income for Vermont farms due to the projected economics of bio-oil as a bio-fuel feedstock.

 Overall Prospects for Successful Deployment: o Gasification and slow pyrolysis reactors are already well understood, and prospects for these depend primarily on the overall economics of their use. Fast pyrolysis reactors are still largely in the R&D and initial deployment stage, and their economics are hence less well understood, but the experience to date and economic projections appear promising.

 Development Status: o Gasification reactors are available from many vendors. o Significant R&D and initial commercialization of fast pyrolysis reactors has occurred, and some vendors offer fast pyrolysis reactors at various scales. o UVM is studying the potential use of biochar for intercepting pollution inputs (phosphorous, E. Coli, etc) into Lake Champlain while simultaneously producing fertilizer. o At least one farm is currently selling inoculated biochar in Vermont made from wood waste.

 Barriers & Opportunities o Bio-oil Issues: The development of a market for bio-oil may prove challenging in the near-term. This is discussed further in the section on utilization of products from pyrolysis and gasification. o Slow Pyrolysis Reactor: These reactors, of which there are various kinds, are usually used to produce Biochar. Recovery of heat and other by-products occurs occasionally. In the past, the wood distillation industry produced large volumes of methanol from one of the resulting liquids (pyroligneous water) that results from the slow pyrolysis of wood. Slow pyrolysis reactors are typically “batch reactors” in which the biomass is loaded, the pyrolysis process ignited, and then the biomass is heated, cooled, and then unloaded at the proper time. These processes take anywhere from minutes to days depending on reactor type and scale. The heat transfer rates in slow pyrolysis are much slower than in fast pyrolysis reactors. This slow rate results from a combination of the relatively low operating temperatures and the relatively larger size of the biomass particles. In general, any reactor utilizing particles greater than about 2 mm in some diameter can be considered a slow pyrolysis reactor, and even entire logs can loaded whole in some traditional slow pyrolysis reactors. o Common terminology for three basic types of slow pyrolysis reactors are: . Kilns: These were traditionally earthen or brick or cement structures, although steel is used in many modern versions. These include most of the reactors used in traditional and some modern biochar production. They are generally used for biomass over 100 mm long and 25 mm in diameter (including logs and pile-wood), and cannot convert smaller particles like wood chips. Among these are the rotating kilns, which are rotating cylinders that are slightly elevated at one end. Recovery of pyrolysis vapors is possible in some designs, but rare. . Retorts: These reactors often take the form of sealed steel containers and are often capable of recovering and/or using some fraction of the pyrolysis vapors. Like kilns, they are generally used for biomass over 100 mm long and 25 mm in diameter (including logs and pile-wood), and cannot convert smaller particles like wood chips. . Convertors: These reactors are capable of pyrolyzing pellets, wood chips, and other finely chopped biomass, and of recovering and/or using the pyrolysis vapors. These usually take the form of steel containers. Recovery and/or use of pyrolysis vapors are rare with batch reactors. This is largely because the flow rates are not constant. For example, whatever volatiles produced from biochar production that were not combusted were usually released directly to the atmosphere. This was true even of the very substantial charcoal industry in the United States, most of which was located in Missouri, until the Missouri Air Conservation Commission recently adopted regulations requiring the use of afterburners

on charcoal kilns. Over the years, many new slow pyrolysis reactor designs have been developed to either capture volatiles for other uses such as heating, or to increase the efficiency of the Biochar manufacturing process. Some of these new slow pyrolysis reactors may be of interest to Vermont. Some of these include: . Kilns that still utilize fairly primitive construction materials but that re-route volatiles to a fire box to increase efficiency and reduce emissions. A real-world example is the “Adam Retort” or “Improved Charcoal Production Systems” developed by the Adam+ Partner Group for use in third world countries63. . Metal retorts where the vapors are redirected to the reactor and combusted to indirectly heat the biomass. This kind of idea has been carried quite far. Real-world examples range from simple designs using oil barrels to large commercial operations such as the French SIFIC, the Lurgi processes, and others 64. These appear to work quite well and could find new applications in Vermont. . Multiple retorts set up to feed a single vapor collection system, to create a more steady vapor stream that can utilized more effectively (say, for gasifying to provide heat). A real-world example is the CML process developed by CIRAD and Innov-energies65. This also appears to work well, and could find new applications in Vermont. . “Semi-batch” reactors that utilize multiple, moveable retorts in a system whereby the heat from the vapors from one retort is trapped in the thermal mass inside a retort housing structure and re-used to help heat the next retort that is inserted into the structure. A real-world example is the “Carbo- Twin Retort” system, which is claimed to have double the efficiency relative to traditional approaches66. . Reactors with a condenser and liquid storage unit on the output to capture and condense liquid by- products: o Slow Pyrolysis with Fine Particles: There have also been attempts to create reactors that can convert more finely (but not very finely) ground biomass particles such as wood chips via slow pyrolysis. Reactors that can deal with these particles generally must provide some sort of continuous agitation in order to achieve uniform and adequate heat transfer rates. Some of these designs, all of which have potential applications in Vermont, and which are also potentially applicable to fast pyrolysis as well (say, if smaller particles are utilized), include: . Auger Reactors: These can be used for either slow or fast pyrolysis. This promising design is discussed further below in the section on fast pyrolysis.

63 http://www.biocoal.org/3.html 64 For example, see www.lambiott.com and www.biocharengineering.com. 65 “Methods for Producing Biochar and Advanced Biofuels in Washington State: Part I: Literature Review of Pyrolysis Reactors”, pages 16-17. https://fortress.wa.gov/ecy/publications/publications/1107017.pdf 66 “Charcoal Production with Reduced Emissions”, P.J. Reumerman and B. Frederiks, 12th European Conference on Biomass for Energy, Industry, and Climate Protection, Amsterdam, 2002. http://www.cleanfuels.nl/Projects%20&%20publications/Charcoal%20Production%20with%20Reduced%20Emissions%20 (paper).pdf

. Multiple Hearth Furnace: In this reactor, biomass particles progresses downward through a series of circular “hearths”, each about 1 meter high, while undergoing continuous mechanical agitation inside. These reactors are quite expensive, but appear to be effective. . Rotary Drum Reactors/Rotary Kilns: In this reactor the biomass moves from one end of a rotating and nearly horizontal cylinder to the other. The cylinder can be heated indirectly through the walls, or by heated gases injected from the output end and moving counter to the biomass. These reactors are well developed and effective. An advanced version are the so-called “two stage” rotary kilns. . Pyrolysis Stoves: A number of groups, such as Biochar-International67 and the Biomass Energy Foundation68 have been promoting a variety of small biochar and heat producing gasifiers (stoves). An introduction to these is the presentation by BEF’s Paul Anderson69, and a very complete review of the whole field now exists in the publication “Micro-gasification: Cooking with gas from biomass. An introduction to the concept and the applications of wood-gas burning technologies for cooking70”. These stoves have substantial potential to replace charcoal stoves in many regions of the world, and might be used effectively in Vermont, for example, in lieu of charcoal/gas grills. Among these is the Top-Lit Updraft (TLUD) Gasifier: There are many varieties of TLUDs, but a primary distinction is between natural draft TLUDs and fan-forced TLUDs. This small, top-lit gasifier operates by creating a downward moving pyrolytic front that is oxygen starved enough to leave behind charcoal and combustible gases. The gases move upward and are mixed with air at the top and are combusted, providing cooking heat with very low emissions. o Fast Pyrolysis Reactors: Advantages of (most) fast pyrolysis machines include operation at atmospheric pressure, speed, high degree of control, and high yield. The primary types of fast pyrolysis reactors are described below. Diagrams and/or discussion of most of these can be found at “An Introduction to Biomass Thermochemical Conversion”, Richard L. Bain, National Renewable Energy Laboratory71, at “Fast Pyrolysis and Bio-Oil Upgrading”, Robert C. Brown and Jennifer Holmgren, Iowa state University72, and “Methods for Producing Biochar and Advanced Biofuels in Washington State: Part I: Literature Review of Pyrolysis Reactors73: . (Bubbling) Fluidized Bed: Particles of biomass are blown up through a bed of hot sand agitated by an upward flow of an inert carrier gas (e.g. nitrogen). The heat (from combusting either the char or volatiles) can applied externally to conduct through the reactor walls, or through heat exchange pipes, or by re-heating of the inert carrier gas. The volatiles and char all exit the top of the reactor, and the char is separated from the gas with a “cyclone”. The bio-oil can then be recovered in a condenser.  Inert gas need: high  Feed size: small  Complexity: medium

67 http://www.biochar-international.org/technology/production 68 http://biomassenergyfndn.org/ 69 http://www.vrac.iastate.edu/ethos/files/ethos2011/Anderson_TLUDs2011ClassificationStoves.pdf 70 http://www.gtz.de/de/dokumente/giz2011-en-micro-gasification.pdf 71 http://www.nrel.gov/docs/gen/fy04/36831e.pdf 72 http://www.ascension-publishing.com/BIZ/HD50.pdf 73 https://fortress.wa.gov/ecy/publications/publications/1107017.pdf

 Can (probably) be scaled up easily.  Note: This is most widely known and used reactor design, and has good temperature control, but is somewhat costly to construct and operate due to usage of continuously flowing inert gas. . Circulating Fluidized Bed: The mixture of volatiles, sand, and char exiting fluidized bed reactor (from which sand can emerge) are fed through a “cyclone” separator. The sand and char are separated off and re-routed to a combustion chamber, where some the char is combusted. The resulting hot sand is then re-routed back to the fluidized bed reactor.  Inert gas need: high  Feed size: medium  Complexity high  Can be scaled up easily  Note: These reactors are also very well understood, but are more complicated to operate, and necessarily tend to degrade the char more. . Rotating Cone: Biomass and hot sand are injected on a rotating conical surface, and interact as the slide toward the bottom.  Inert gas need: none  Feed size: very small  Complexity high  Does not scale up well  Note: This design can be made very compact. . Ablative pyrolyzer: Biomass is pressed against a hot rotating plate either by centrifugal or mechanical force, and bio-oil is formed on the plate surface.  Inert gas need: low  Feed size: large  Complexity high  Does not scale up well . Vacuum Pyrolyzer: Biomass falls downward through a series of rotating “scrappers”, encountering higher and higher temperatures as it falls. This is a high complexity reactor. Employs little carrier gas and can use large particles, but the vacuum pump is expensive and the process does not scale well.  Inert gas need: none  Feed size: large  Complexity high  Does not scale up well  Note: As mentioned above, operating with vacuum results in increased production of levoglucosan, an important precursor of glucose, and therefore important for bio-ethanol production. . Auger Reactor: Two versions are possible. In one, hot sand is mixed with biomass particles, which then travel down an auger through the retort chamber. In another, a hot inert gas is delivered to the biomass as it travels down the auger. The biochar falls out at the end of the auger. Requires hot sand or inert gas circulating and heating system. This is a low complexity reactor. Suitable for small scale and can scale up easily.  Inert gas need: low (with sand). High (with inert gas heating)

 Feed size: small  Complexity: low  Scale up might be easy  Note: This is a relatively new but promising reactor design, and one that can be used for either or fast pyrolysis. R&D is being carried out by a number of companies and universities. For example see International Tech Corp (http://www.internationaltechcorp.net), and Iowa State University Professor Robert C. Brown’s site at http://www.cset.iastate.edu/research/current- research/alternative-pyrolyzer-design-auger-reactor/. Possible downsides include moving parts in the hot zone and relatively low bio-oil yields. . Solar Thermal Reactor: It has been pointed out that concentrated solar energy can also be used to potentially pyrolyze biomass. This approach would likely not be economical in Vermont, but is nonetheless potentially promising for sunnier areas. See http://www.colorado.edu/che/TeamWeimer/ResearchInterests/BiomassGasification.htm. o Comparison of Pyrolysis Reactors: Overall, auger reactors would appear to be quite promising for use in Vermont, due to their suitability for small scale, scalability, and low complexity. For larger operations, the fluidized bed reactors look promising. o Advanced gasification reactors: . Fixed Bed Updraft Gasifier: In these units, a fixed bed of carbonaceous material at the bottom reacts with the gasification agent (air, oxygen, steam, or hydrogen), which flows through the grate at the bottom of the gasifier. As it ascends, the resulting gas pyrolyzes the biomass. The biomass used in this design must be “non-caking” so that the bed remains permeable. Tar and methane build up is significant, in comparison with downdraft and fluidized bed designs, due to the relatively low operation temperature of this design. Extensive cleaning of gas is therefore required before it is useable in other than close-coupled operation. . Fixed Bed Downdraft Gasifier: In this design the gasification agent (air, steam, or oxygen) is fed downward in the same direction as the fuel. Relatively high temperatures in this design help to reduce tars as the evolving syngas passes down through the hot bed. Differences between the updraft and downdraft designs result from the direction in which the process takes place, and the effects the operational flow has on the reactions taking place during gasification. . Fluidized Bed Gasifier: In a fluidized bed gasifier, the gasification agent rises through the grate with substantial speed where it fluidizes a heat transfer medium (sand or limestone) that meets and gasifies small biomass particles. o Comparison of gasifier types: Updraft and downdraft gasifiers are less complex than fluidized bed gasifiers, but don’t produce syngas with as high an energy content, and are more restricted in terms of type and condition of feedstock. Fluidized bed gasifiers are most useful for fuels, such as biomass, that normally would form corrosive ash. o Catalysts and Gasifiers: Special catalysts can sometimes be used in gasifiers to lower operating temperatures, increase or reduce certain products, etc. The University of Minnesota has reported that it succeeded in developing catalytically assisted gasification that is much more efficient (and fast), and

produces syngas with very low tar levels74. For more information on gasification and catalsysts, also see the useful web pages by the National Energy Technology Laboratory on this topic75,76.

74 http://www.license.umn.edu/Products/Syngas-from-Renewable-Hydrogen-and-Carbon-Monoxide-Gases-Using-a- Biomass-Gasification-Process__Z07080.aspx 75 http://www.netl.doe.gov/technologies/coalpower/gasification/gasifipedia/4-gasifiers/4-1-4-4_catalytic.html 76 http://www.netl.doe.gov/technologies/coalpower/gasification/gasifipedia/5-support/5-14_gas-catalysts.html

Algae  Technology Description: o Production of third generation biofuel from oil produced by photosynthetic algae. The oil can potentially be used as fuel directly or processed into other fuels such as biodiesel. The leftover greenwaste (proteins) can be used to produce other biofuels, or used for bioplastics, livestock and aquaculture feed, etc. Possible algae biofuels include vegetable oil, biodiesel, bioethanol, methane, biogasoline, biomethanol, and biobutanol. A least three distinct routes for algae biofuel production exist, depending on algae type, including a route that uses algae to produce algae oil from terrestrial biomass. o Types of Algae: Although the precise taxonomies are complex, algae can be thought of as a very large and diverse group of simple plant-like organisms that range from microscopic “microalgae” to large “macroalgae” such as seaweeds like giant kelp, and also the “blue-green algae”, or “cyanobacteria”, which are not “true algae” according to modern classifications. There are both unicellular and multicellular forms of algae. Many are photosynthetic and hence “autotrophic” or “photoautotropic” (self-feeding), producing biomass from carbon dioxide, nutrients, water, and sunlight. Others are “heterotrophic” (not self-feeding), and subsist on sugar and starches in the water instead of photosynthesis. Some are “mixotrophic”, that is, both photoautotropic and heterotrophic. Both photoautotrophic and heterotrophic types are of interest for energy production: The former can create its biomass directly with sunlight, the latter can utilize sugars and starches obtained from terrestrial biomass to transform those sugars into algal oil. o Algae can be grown in brackish water, seawater, and other wastewater unsuitable for cultivating agricultural crops. Besides sunlight and water, photoautotrophic algae generally require certain nutrients as well including nitrogen and phosphorous. If wastewaster is used, algae can potentially utilize the nutrients in and in the process help purify the water. o Photoautotrophic microalgae can be cultivated in “open ponds”, or in enclosed “photobioreactors”. These systems generally require the input of a concentrated (enriched) CO2 gas stream to achieve high yields. In principle, the CO2 can be obtained from the flue gases from generators or power plants or the combustion of fossil fuels or biomass for heating, or even from CO2 extracted directly from the atmosphere. Seaweeds (macroalgae) can also be cultivated in seawater for algae biofuels, typically in near-shore systems. Open ocean cultivation is also possible.

 Technology Special Benefits: o Algae are capable of very high photosynthetic efficiency and in theory can produce yields of 10 to 100 times that of other second generation biofuels77. Very high yield per unit acre (upwards of 6000 gals/acre) relative to conventional biofuels (potentially 100x greater). o Algae can be produced on non-arable land. o Production be integrated synergistically with other operations: . Algae can consume CO2 emitted from various farm based operations, including digesters, pyrolysis, gasification, pellet production, etc.

77 Greenwell et al (2010) Placing microalgae on the biofuels priority list: a review of the technological challenges J. R. Soc. Interface 6 May 2010 vol. 7 no. 46 703–726: http://rsif.royalsocietypublishing.org/content/7/46/703.full

. Algae can utilize and purify nutrient rich effluent water from digesters or aquaculture. . Greenwaste can be utilize as livestock or aquaculture feed, or fertilizer, or utilized to produce biomethane in anaerobic digesters, or syngas through gasification, or biochar/bio-oil through pyrolysis. . Butanol produced from left-over algae greenwaste can be also used in place of gasoline with no modifications.

 Overall Prospects for Successful Deployment: o The economic prospects for algae biofuel production are challenging, but overall appear promising, and the technology is still rapidly evolving. Recent scientific advances may significantly improve prospects.

 Development Status: o Economic viability has not been definitively proven, although the economic factors are well understood and a pathway to cost effectiveness has been charted. o Vermont Development: Vermont possesses an algae R&D base and several companies: . Vermont Sustainable Jobs Fund Biomass Initiative: http://www.vsjf.org/project-details/12/algae-to- biofuels: VSJFB has been coordinating assistance to Vermont algae biofuel companies and R&D efforts. . University of Vermont Professor & Algaepreneur Anju Dahiya: http://www.uvm.edu/~adahiya/#research: Dr. Dahiya conducts research on algae biofuels, and co- organized the conference on Algae & Energy in the Northeast, co-hosted by the University of Vermont, the Vermont Sustainable Jobs Fund, and VT EPSCoR held at the University of Vermont in Burlington on March 17 & 18, 2010. In addition to her biofuels teaching and research activities at UVM, Dr. Dahiya has also co-founded General Systems Research, which is working to isolate native species for wastewater treatment and CO2 capture, a rapid screening method quantification of lipids, and has been conducting research supported by EPA on cost-effective algae biomass production for oil integrated with dairy manure and industrial wastewater treatment, and producing valued byproducts78. . Algepower Inc: www.algepower.com: This Montpelier company, led by company president and algaepreneur Gail Busch, has developed a patented photobioreactor system consisting of series of cradles for growing algae, and is focusing on algal production utilizing the nutrient rich wastewater, heat, and CO2 from anaerobic digestion, and also integrated with aquaculture. Algepower believes it can achieve costs under $2.50/gallon given already existing supplies of heat, CO2, and wastewater from an anaerobic digester. See also: http://www.wcax.com/story/10719142/algae- power?clienttype=printable . Carbon Harvest Energy: http://carbonharvestenergy.com/: This company is also focusing on algal production utilizing the nutrient rich wastewater, heat, and CO2 from anaerobic digestion, and also in conjunction with aquaculture. The company has active projects in Vermont, and has been conducting R&D on the effects of flue gas on different microalgae species.

78 http://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.abstractDetail/abstract/9478

. University of Vermont College of Engineering Professor Jeffrey Marshall: According to the Vermont Sustainable Jobs Fund79, Dr. Marshall “is designing novel flow control devices in order to optimize algae growth rate through enhanced vertical mixing without increasing the energy cost necessary to produce the flow.” . Green Mountain Spark: According to the Vermont Sustainable Jobs Fund80, which awarded this firm $65 K in 2010, this Burlington company “proposes to use a photochemical process to separate oil from algae and turn that oil into a biofuel in the same photobioreactor”. o Algae Biofuel Industry at Large: A growing number of algae biofuel companies exist (more than can be comprehensively listed here) and some of the larger firms have accumulated significant experience growing. Some examples that include the use of true photoautotropic algae, blue-green algae, and heterotropic true algae, and also harvesting and extraction equipment, are (not including the Vermont companies mentioned above): . Saffire Energy: http://www.sapphireenergy.com: Saffire is a 150 employee company founded in 2007 that is attempting to commercialize algae biofuels grown in open ponds in the American Southwest. The company has produced several hundred barrels of algae oil to date, and claims the fuels produced from the oil has performed well in tests. Saffire is presently developing a 300 acre facility that is currently producing a barrel a day at present (which is equivalent to an annual yield of about 51 gallons/year/acre). The company projects they will eventually produce 5000-10,000 barrel per day by 2018 (apparently not just from the 300 acre facility). Saffire’s development can be considered an attempt to achieve the kinds of cost reductions for the open pond scenario described in the prior section. . Algenol: http://www.algenolbiofuels.com: This company utilizes a (specially prepared) plastic film covered bioreactor to cultivate “enhanced blue-green algae or cyanobacteria to convert sugar (pyruvate) made from carbon dioxide and saltwater by photosynthesis into ethanol.” The design is a “no harvest, no-kill” approach: The ethanol is collected via condensation on the photobioreactor surface. The company states that its patented technology “enables the production of ethanol for less than $1.00 per gallon using sunlight, carbon dioxide and saltwater and targets commercial production of 6,000 gallons of ethanol per acre per year.” . Solazyme: http://solazyme.com: This company specializes in using heterotrophic (non- photosynthetic) algae to produce algal oil from feedstocks including corn and stover, switchgrass, miscanthus, forest residues, sugarcane, and other waste streams. The company claims its algae achieve 80% lipid content. It claims to have been running commercial scale fermentations since 2007, and recently commissioned a new production in Peoria, Illinois. The company further states it has delivered “over 80,000 liters of algal-derived marine diesel and jet fuel to the U.S. Navy.” . OriginOil: http://www.originoil.com: This company is developing a special “one-step” harvesting and extraction process using electromagnetic waves. . Evodos: http://www.evodos.eu: This company offers specially designed centrifugal de-watering machines (for manure as well as algae). . BioProcess Algae: http://www.bioprocessalgae.com/

79 http://www.vsjf.org/project-details/12/algae-to-biofuels 80 http://www.vsjf.org/project-details/12/algae-to-biofuels

. Heliae LLC: http://heliae.com/

 Barriers & Opportunities: o Potential for Production in Vermont: There are a number of specific challenges facing algae biofuel production in Vermont in comparison with sunbelt regions: . Relatively small production scales, funding, and R&D services. . Less solar insolation compared with the Southwestern US. . Cold winter temperatures . Geographic constraints (mountains vs. flat open land) Vermont also has some helpful attributes: . Abundant water (especially wastewater) . A significant number (10+) anaerobic digester/generator systems at large dairies that provide a steady stream of CO2, heat, and nutrient rich water. . Generators at landfills that provide a steady stream of CO2 and heat. . Enthusiasm for self-reliance and experimentation. o Production Issues: Numerous techno-economic studies suggest that biofuel production from “true algae”, with the yields that are currently obtainable today, are not yet cost competitive if produced with purchased inputs of CO2, electricity, and fertilizer, especially if produced with the more expensively designed “photobioreactors” and algae harvesting and processing techniques. Cost effective production may be possible in Vermont, however, even with today’s yields, using more cost effectively designed photobioreactors or open pond systems, and if implemented in the context of synergistic efficiencies, for example, at livestock farms, power generation facilities, water treatment facilities, and landfills, where a free supply of CO2 and sometimes nutrients are available, where the water purifying effects of algae potentially have value, and where the by-products can be used effectively. Such is the approach of at least three Vermont companies (Algepower, Carbon Harvest Energy, and General Systems Research): . The photobioreactor of Algepower is open raceway arranged in vertical racks that it is housed in a positive pressure, translucent, greenhouse like structure. The company is also directly pursuing integration with farm digesters and aquaculture. The company has built and run trials with its system, but is still in the development stage and requires further funding to continue. It states it has developed a system “for growing algae at a cost competitive with fossil fuel.” . Another Vermont company, Carbon Harvest Energy, has their own photobioreactor design, and is also pursuing integration with digesters and aquaculture, and also landfill gas. o Three Different Routes: Two production routes based on “true algae” and “blue-green algae”, or “cyanobacteria” routes produce algae oil from carbon dioxide, water, nutrients, and sunlight. Both are potentially promising. The cyanobacteria route offers the potential to produce ethanol without needing to harvest (kill) the algae to obtain the oil. A third possible route is the conversion of terrestrial biomass using non-photosynthetic (heterotrophic) algae. This is essentially an alternative route to the fermentation of sugars and starches with the yeasts that have been traditionally used for bioethanol. This is also a potential alternative to other enzyme-based cellulosic ethanol production approaches. o Algae Cultivation Issues: Selection and cultivation strategies are crucial and interrelated areas of ongoing R&D. Algae oil yield depend strongly on both the algae’s lipid percentage and biomass growth rate, both of which can be measured in milligrams per liter per day (mg/L/d). Yields exceeding 200

mg/L/d for lipid production and 300 mg/L/d for biomass are generally deemed high, and lipid percentages can exceed 60% for some strains under the right conditions. Other cultivation issues are prevention of culture crashes and maintenance of production from highly mono-cultured strains. There are also hundreds of thousands of algae species, of which only several tens of thousands have so far been identified and studied, and algae can be genetically engineered relatively easily (a fact which also raises GMO concerns). o Advances in True-Algae Biofuel Production Science: Recent research has shown that algae can be encouraged to continue to produce more oil when fed nutrients and more carbon, overturning the long- standing belief that algae must be starved to encourage oil production. A common growth strategy up till recently had been to initially grow (true) algae in a nutrient (nitrogen) rich environment, and then starve the algae of nutrients prior to harvest to increase yield: The starvation is thought to inhibit certain metabolic pathways that forces the algae to produce oil instead of starch. But there is a downside to the starvation route: Starving the algae of nitrogen also arrests growth, so boosting lipid content with nitrogen starvation comes at the expense of maintaining rapid growth rates. Very recently, research at Brookhaven National Lab has suggested that algae can be encouraged to continue to produce more oil when fed more and more carbon without nutrient starvation, that is, by instead simply saturating the starch formation mechanism81. (The idea is very similar to what happens when human beings eat more calories than they can utilize at the moment.) This discovery may be a major breakthrough, but more research will be needed before it is known how applicable this is to algae strains used for biofuel production. o Advances in Cyanobacteria Production Science: Cyanobacteria can potentially be used to produce a number of biofuels, including biodiesel, methane, hydrogen and ethanol. In particular, in 1991 it was found that a number of cyanobacteria strains naturally excrete ethanol82. In 1999 another strain was genetically engineered to excrete ethanol83, and more have followed. The fact that the ethanol is excreted means that harvesting (killing) of the cyanobacteria is not needed to obtain the ethanol. Some researchers suggest that much more work to optimize the metabolic pathways of cyanobacteria still needs to occur. Nonetheless, some companies such as Algenol are now attempting to commercialize this route and are claiming that commercial success is near. A more recent breakthrough84 in the understanding of cyanobacterial metabolism may now also allow genetic engineering of cyanobateria to produce butanediol – a precursor useful for the production of

81 “Oil accumulation is controlled by carbon precursor supply for fatty acid synthesis in Chlamydomonas reinhardtii”. Fan J, Yan C, Andre C, Shanklin J, Schwender J, Xu C, Biology Department, Brookhaven National Laboratory, Upton, NY 11973. http://www.ncbi.nlm.nih.gov/pubmed/22642988. Also see: http://www.bnl.gov/bnlweb/pubaf/pr/PR_display.asp?prID=1424 82 “Renewable energy from Cyanobacteria: energy production optimization by metabolic pathway engineering”: N. Quintana et. al, Appl Mircrobiol Biotechnecnol 2011 August: 91(3): 471-490: www.ncbi.nlm.nih.gov/pmc/articles/PMC3136707 83 “Ethanol Synthesis by Genetic Engineering in Cyanobacteria”, M. Deng and J.R. Coleman, Appl. Environ. Microbiol., February 1999 vol. 65 no. 2: 523-528: http://aem.asm.org/content/65/2/523.full 84 http://www.sciencedaily.com/releases/2011/12/111215141613.htm

biofuels. The breakthrough over-turned a long-held belief that cyanobacteria are missing a particular enzyme in their metabolic process that would be crucial for this. o Invasive Species and Genetic Engineering Issues: Many companies are presently engaged in genetic engineering of algal strains, so the GMO aspect is a pressing issue that needs to be considered. Another serious and related consideration is the potential consequences of and means to reduce the risk the escape and spread of invasive algae species. In 2012 the National Wildlife Federation published a summary of invasive species risks associated with biofuel production85, and specifically pointed out some of the risks of algae biofuel production. The report states: “Given the vast number of algae species in existence and the rapid pace of algae research and genetic modification, very little known about the invasion potential of the species that are currently being cultivated in labs and commercial facilities. However, several traits specific to algae suggest the potential for invasiveness. For example, microalgae can easily aerosolize and spread, leading to a high potential for such algae to escape from a biomass production facility; indeed, and there have already been cases of algae escaping into the environment from research labs.” And also “complete containment of algae is completely impossible.”

85 “Growing Risk. Addressing the Invasive Potential of Bioenergy Feedstocks,” Aviva Glaser and Patty Glick: http://www.nwf.org/~/media/PDFs/Wildlife/Growing%20Risk-2-FINAL-LOW-RES.ashx

Advanced Anaerobic Digesters  Technology Description: o Biogas (biomethane) is produced via the anaerobic digestion (AD) of manure, and then combusted onsite either for space heating and/or electricity generation. Electricity generation is accomplished with a reciprocating engine, and possibly via other types of engines in the future. Waste heat can be used to either support the digester or for other uses. The digestate (leftover material) can often be used for applications such as soil amendments or livestock bedding, and the nutrient rich wastewater can also often be utilized for plant cultivation or in aquaculture. o Over a century of research has already greatly clarified the four-step biochemical process of AD: 1. The input biomass is broken down via “bacterial hydrolysis” into sugars, amino acids, and fatty acides to render them available for other bacteria. 2. “Acidogenic bacteria” convert the sugars and amino acids into hydrogen, carbon dioxide, ammonia, and organic acids. 3. “Acetogenic bacteria” convert the resulting organic acids into acetic acid, along with additional ammonia, hydrogen, and carbon dioxide. 4. Microbes called “methanogens” convert these products to methane and carbon dioxide. Studies show that “methanogenic archaea” populations in particular play a critical role in anaerobic wastewater treatments86. In short: Hydrolysis > Fermentation > Acetogenesis > Methogenesis o Types of Anaerobic Digestion Systems: AD systems are classified according to the following temperature range categories: . Psychrophilic (5-25°C or 41-77oF) – Essential ambient temperature operation . Mesophilic (35-45°C or 95-113oF) - The type used at AD systems in Vermont presently . Thermophilic (50-60°C or 122-140oF) o In general, lower temperature systems require less process heat, are more stable and hence easier to manage in principle, but with conventional digester designs have taken longer to process biomass, which essentially means the digesters need to be larger to achieve the same biogas production rate, and may have less sterile output. See discussion below for more information about new and faster technology for psychrophilic (ambient) temperature in Vermont. o In Vermont, all of the existing AD systems are currently mesophilic: These operate at a temperature of about 100oF to promote the growth of “mesophilic microbes”, and produce biogas containing about 60% methane, 40% carbon dioxide, along with small amounts of hydrogen sulfide and water. o Wet (5-15% solids) versus dry (over 15% solids) systems: Most so-called “wet systems” utilize pumpable slurry, where “dry systems” much generally rely more on gravity. Wet systems tend to have lower capital costs.

86 “Importance of the methanogenic archaea populations in anaerobic wastewater treatments,”Meisam Tabatabaei, Raha Abdul Rahim, André-Denis G. Wright, Yoshihito Shirai, Norhani Abdullah, Alawi Sulaiman, Kenji Sakai and Mohd Ali Hassan, 2010, Process Biochemistry- 45(8), pp: 1214-1225: http://www.sciencedirect.com/science/article/pii/S1359511310001984

o Continuous flow or batch: Most AD systems are continuous flow, although multiple batch systems can be utilized to maintain more uniform biogas production rates, similar to the use of multiple batch slow pyrolysis reactors. o Common digester types include covered lagoons, plug-flow reactors, and completely mixed reactors. Lagoons are appropriate for very dilute feedstocks, while the others can handle larger solid concentrations (~10%). Plug-flow reactors, through which the material moves as a whole from one to the other (in theory) were developed to lower costs (compared to completely mixed reactors) and impose more uniformity on retention times (in theory). o Single, double and multiple stage digesters: Multiple stage digesters can produce greater biogas output but generally have higher capital costs. o Vertical tank or horizontal (plug) flow: Horizontal plug flow systems provide more control over residence times.

 Technology Special Benefits: o Production of baseload renewable electricity (typical several times greater than the farm’s own level of consumption) and thermal energy: . Electricity Production Capacity density: About 130 watts/cow. . Thermal Energy Production density: About 82 BTUs/day/cow. o Dramatic odor reduction. o Effective destruction of fecal bacteria. o Production of solid effluent enough to cover full demand of farm’s cow bedding needs. o Production of good soil amendments (same material as used for cow bedding). o Production of high quality fertilizer (liquid effluent).

 Overall Prospects for Successful Deployment: o Very Good for larger (500+ animal) dairies and swine operations. Uncertain although under active exploration for smaller dairies. Prospects for more stable, low (ambient) temperature digestion are also good.

 Development Status: o As a technology, AD is well over a century old, and is well-established for both agricultural and waste treatment applications. An NREL Casebook provides an informative account of AD history up through 199887. o USDA’s AGstar Program reports that anaerobic digesters were operating at about 171 livestock operations in the US as of 2011, and some 30 million small-scale digesters are in operation throughout the world (mainly in the tropics). o Vermont now has a significant number of anaerobic digesters (10+) with electricity generation. Most of these are located at dairies with 500 or more cows. A few smaller dairies are piloting smaller systems.

87 “Methane Recovery from Animal Manures The Current Opportunities Casebook,” Paul Lusk, September 1998, NREL/SR- 580-25145: http://agrienvarchive.ca/bioenergy/download/methane.pdf

o A new low (ambient) temperature process has been fairly well tested by the company Bio-Terre Systems Inc (see below). o Attempts to deploy innovative approaches for smaller dairies already underway by Avatar Inc. in Vermont.

 Barriers & Opportunities: o Key barriers to additional AD development in Vermont include: . Initial investments of time during project development and start-up are substantial. . Smaller dairies have fewer available personnel, and many have pastured cows, such that collecting sufficient manure may not be feasible. . An incentive of upwards of 50% of capital costs, and a good electricity purchase price (at or above retail electricity costs) has been and is still likely needed to enable AD projects, even for large dairies. . Identification of new sources of off-farm organic material could enhance the economics for smaller farms greatly. Possible sources include fish or chicken processing waste liquids, additional manure from other farms within several miles, greenwaste from algae facilities, and oilseed meals and/or glycerin from oilseed biofuel facilities. o Potential for Ambient Temperature Digestion: The current AD systems in Vermont utilize “mesophilic digestion”, which operates at temperatures of 95oF to 113oF and requires thermal energy inputs in cold weather (often supplied from the waste heat of the associated electricity generation). The Canada based company Bio-Terre Systems, however, appears to have developed new technology that allows for “psychrophilic digestion" or ambient (or simply lower) temperature operation. This could provide more stable operation, free up more thermal energy from AD digesters for operations such as greenhouses, and possibly help with scaling down AD for smaller dairies. Founded by research scientist Dr. Daniel Masse of Agriculture and Agri-Food Canada, the company has been pioneering their approach since the 1990s. It now claims to been operating several large installations successfully for close to a decade. The technology is a two-stage batch reactor technology with a (short) 7 day total retention time, with special inoculations. A description in an article about the Bio-Terre system states88: “…Bio-Terre refined the sequential operation of the system, identifying the certain period of time the rich organic effluent needs to remain to allow the natural bacteria to develop. It consists of two vessels – one rests while the other is fed. Within the vessels, nutrient-rich sediment that has yet to be degraded settles naturally to the bottom of the tanks. The top layer, which is mostly liquid and degraded material, is removed from the vessels. The vessels are not mixed. This sequential batch process creates a longer solid retention time without increasing the hydraulic retention time. The average length of stay in each vessel is 3.5 days for a total seven-day cycle, compared to the 22-day hydraulic retention time in other digesters.” o Vermont Development of Smaller AD Systems: The Vermont based company Avatar appears to making progress in scaling down AD for smaller dairies. o Co-Location Synergies: Use of biogas in operations such as co-located greenhouses without electricity generation may help with the economics of AD for smaller dairies. AgSTAR recommends that digester systems in general should cost no more than about $1500/cow, which suggests that a 100 cow farm, for

88 http://www.progressivedairy.com/index.php?option=com_content&view=article&id=6297:new-digester-operates-at- low-temperatures&catid=48:new-technology&Itemid=74

example, should seek to achieve a total capital cost of no more than $150,000. Some research has suggested that it is generally more economical not to generate electricity if all of the biogas can be used on-farm for heating purposes (Bracmort et al., 2008; Bishop and Shumway, 2009). o Thermal Storage: Large thermal energy storage technologies may be useful for enabling efficient use of the waste heat. See the section of Thermal Storage Technologies for more information. o Performance Monitoring: Better scientific monitoring of AD systems may be useful, especially where new technologies and scale-down attempts are concerned: Scientific standards for digesters have recently been defined by the USDA, called the “Protocol for Quantifying and Reporting the Performance of Anaerobic Digestion Systems for Livestock Manures”, and some reports using this protocol are now available. This protocol allows a standardized comparison between different digester designs with criteria including changes in chemical oxygen destruction (a measure of the degree of breakdown of organic material in the manure), methane production, and the breakdown of fecal pathogens. The protocol also recommends a standard cash-flow analysis for determining annual net costs.

Utilization of BioChar/Biogas/Bio-oil/Syngas  Technology Description: o This section explores some of various opportunities for the use of products from anaerobic digestion, pyrolysis, and gasification processes for production of biofuels and heat. The section on Utilization of Thermal Energy extends this exploration further. The products under consideration here include: . Biochar: The leftover charcoal like material from (slow or fast) pyrolysis of biomass, and is mostly composed of carbon. It can be used as a soil amendment, or potentially combusted for heat. . Biogas (biomethane): A mixture of gases primarily consisting of methane and some carbon dioxide, which is produced by the anaerobic digestion of wet biomass, such as manure and algae, and in principle any properly prepared biomass feedstock with a high percentage by weight of water. . Bio-oil: A dark brown oil that results from the fast pyrolysis of finely ground biomass. This liquid is combustible and can be utilized in some burners for heating applications, and can be refined to provide third generation biofuels. . Syngas: A mixture of gases produced by the pyrolysis (as one of several outputs) or gasification of biomass that typically consists of hydrogen, carbon monoxide, carbon dioxide, methane, and nitrogen. o For further information on the reactor technologies that produce these products, see the (prior) section on Pyrolysis and Gasification Reactors.

 Technology Special Benefits: o Biochar: Production of biochar with slow pyrolysis reactors can provide a very effective soil amendment, an effective carbon sequestration method, and a potential water filtration technology. Biochar can also be inoculated to help revitalize soil microbial activity. Biochar has a number of particular and beneficial attributes as a soil amendment: . It contains important micro-nutrients, including selenium. . It can function as a form of activated carbon and reduce the leaching of nutrients out of the soil. . It is disinfected by pyrolysis and so does not introduce potentially harmful microbes into the soil and water table, and it can be inoculated with beneficial microbes as well. . It increases soil carbon, and can be potentially implemented on a very large scale for carbon sequestration. . It can increase soil water retention. o Biogas (biomethane): This gas is useful for electricity generation and/or as a source of thermal energy. Its use is straightforward. o Bio-oil: Production of bio-oil with fast pyrolysis reactors, and the sale of the bio-oil to centralized refining facilities, could provide a major new revenue source for Vermont farmers, and a large local source of cost effective biofuels for Vermont. A key attribute of fast pyrolysis is that the high energy density of the bio-oil relative to unprocessed biomass, or even pelletized biomass, enables the transportation costs of the energy to centralized refining facilities to be lowered to the point that biofuel produced from the bio-oil can potentially be competitive with other forms of biofuel, even when the higher costs of “farm-scale” reactors (~5 tons/day) relative to large scale reactors (~100 tons/day) are taken into account.

The volumetric potential for bio-oil production in Vermont is also very significant, even relative to the total amount of gasoline consumed annually in Vermont: Roughly 120 gallons of transportation fuel (refined from bio-oil) can be produced from a single ton of biomass89. If 4 tons/acre of switchgrass can be produced on average (based on the recent switchgrass trials in Vermont) then approximately 500 gallons/acre of fuel could be produced, which is a factor of 5-10 greater than can be produced from oilseed biofuels. It follows that if 100,000 acres of switchgrass cultivation were eventually devoted to bio-oil production, then 50 million gallons per year of fuel could be produced. If another 500,000 tons per year of forest biomass were utilized, then another 60 million gallons of fuel could be produced. The total 110 million gallons per year would then provide a 33% of the approximately 3.3 billion gallons of gasoline used in Vermont (all usage sectors) as of 201090. Use of other sources of organic waste could increase this percentage yet further. o Syngas: Production of high quality syngas with biomass gasifiers can provide a use fuel for the generation of heat, electricity, and biofuels. A key advantage of syngas is its potentially high quality and (as with bio-oil) the wide range of possible production feedstocks.

 Overall Prospects for Successful Deployment: o Biochar: Progress with pyrolysis reactors in recent years, particularly auger reactors, suggest that the economic prospects for producing and utilizing biochar at Vermont farms in the near term are promising, although actual costs are not yet well understood. o Biogas: This is already successfully produced and utilized at anaerobic digesters in Vermont. Possible advances in anaerobic digesters improve the prospects for further biogas production and use (see the section on Advanced Anaerobic Digestion for more information). o Bio-oil: As discussed above, the high energy density of bio-oil can justify transportation over long distances to refineries, and potential yields per acre are also high. More specifically, studies suggest that the most economical route may be the use of “farm-scale” pyrolysis reactors of around 5 tons/hour supported by several hundred acres of cultivation apiece that supply bio-oil to a large centralized facility91. In addition, a number of “techno-economic” analysis of pyrolysis bio-oil scenarios have been conducted, and although these are difficult to compare due to differences in feedstock, feedstock costs, reactor designs, etc, all suggest that bio-oil can be produced for costs of around or slightly above $1/gal92. It is less clear presently when transportation fuels produced from bio-oil will become competitive with fossil fuels, due to the early stage of the refinement processes. The processing chain is also potentially complex, although perhaps no more than already well-established fossil fuel refining processes. Refining

89 Advancement of Bio-oil Utilization for Refinery Feedstock. D. Elliot, Washington Bioenergy Research Symposium. November 8, 2010. http://www.pacificbiomass.org/documents/Elliott%20(C1).pdf 90 Energy Information Administration (multiply number of barrels by 42 gal/barrel): http://205.254.135.7/state/seds/sep_fuel/html/pdf/fuel_mg.pdf 91 “Distributed processing of biomass to bio-oil for subsequent production of Fischer-Tropsch liquids,” Mark M. Wright and Robert C. Brown, and Akwasi A. Boateng, Published online April 14, 2008 in Wiley Interscience (www.interscience.wiley.com); DOI: 10.1002/bbb.73;Biofuels, Bioprod. Bioref. 2:229–238 (2008) http://naldc.nal.usda.gov/download/32752/PDF 92 “Techno-Economic Analysis of Biomass Fast Pyrolysis to Transportation Fuels”, NREL/TP-6A20-46586, November 2010: http://www.nrel.gov/docs/fy11osti/46586.pdf. See page 1.

will likely adds substantial cost, perhaps as much or more than producing the bio-oil itself, and certainly much more so for “pioneer refineries”. Despite this, a comprehensive review by the Department of Energy’s Office of the Biomass Program, based on various techno-economic analyses, predicts that the pyrolysis/bio-oil route to biofuel production can still become competitive with many other biofuel routes and fossil fuels, and, in particular, capable of achieving production costs as low as $2/gallon93. R&D advances have been rapidly paving the way for both the production of bio-oil and the conversion of bio-oil into renewable fuels as green gasoline, biodiesel, and bioethanol. In light of these developments, a recent (2011) review of methods of biochar and bio-oil production by Washington State University optimistically concluded “that development of the pyrolysis industry is viable within the next ten years.94” Various refining routes for bio-oil are discussed further below. o Syngas: Various gasification companies appear to be having success at producing high quality syngas. The economics of the end uses will be likely play a critical role. Electricity generation with syngas appears quite promising on fundamental grounds. It is not yet clear whether syngas biofuel production routes will be economical in comparison with bio-oil (pyrolysis) routes, especially given the DOE appears to think bio-oil routes may be more economical, although the syngas route might still prove competitive at least in certain settings and types of feedstock, and some companies are making strong claims (see below).

 Development Status: o Experimentation and research on biochar is beginning in Vermont. UVM is conducting research at Shelburne Farms95, and at least one farm is already marketing biochar96. o Gasification is already widespread in certain kinds of wood boilers, but use of syngas for applications other than heating is rare or nonexistent. o Use of fast pyrolysis reactors for bio-oil production has not developed in Vermont, and bio-oil refineries do not yet exist in the area.  Barriers & Opportunities: o Initial Development Path for Bio-oil Production (Bio-oil): A promising near-term scenario for Vermont may be operation of fast pyrolysis reactors for the production of biochar (initially) and then bio-oil later via a change in the operating parameters (e.g. temperature) of pyrolysis reactors. Alternatively, it may be possible to develop sufficient near-term markets for co-firing bio-oil at area biomass power plants, or for use in special boilers, for example at large institutions such as schools. Although it is inexpensive to transport, bio-oil is difficult to store for long periods of time: It is highly acidic (2-4 pH), tends to phase separate, and become less viscous and volatile with time. It is also miscible with water and does not mix with readily with hydrocarbon fuels. It is also not suitable for direct use in internal combustion engines, either gasoline or diesel. For this reason it needs to be utilized quickly after production.

93 “Biofuels Design Cases”, DOE Office of Biomass Program, April 2012: http://www.usbiomassboard.gov/pdfs/tac_design_case_haq.pdf 94 “Methods for Producing Biochar and Advanced Biofuels in Washington State”, page 2. https://fortress.wa.gov/ecy/publications/publications/1107017.pdf 95 http://www.vpr.net/news_detail/87888/shelburne-farms-experiments-biochar/ 96 http://vermontbiochar.com/biochar/

o Pre-Treatment Technology for Bio-oil Production: Recent R&D has showed that pre-treatment of biomass feedstocks can significantly improve the quality of the resulting bio-oil. A few of the (many) results to date are: . Biomass washing using water or acid-removal techniques can significantly reduce alkali content in biomass. For example, one study that NREL cites found that97 “in the temperature range 200–500°C, washing with water reduces the alkali emission from wood waste and wheat straw by 5–30%, while acid leaching is more effective and reduces the emission by around 70%. Above 600°C where the vaporization of alkali compounds from untreated wheat straws increases sharply, the washing procedures are sufficient for a reduction in the measured alkali release by more than 90%. Experiments with pure cellulose (ash content 0.07%) indicate that the washing methods are ineffective in removing alkali bound to the organic structure of the biomass.” . Pretreatments may be useful for elevating the levels of levoglucosan and other important components vis a vis fuel production.98 o Bio-oil Refining Routes: There are at least two routes for producing fuel from bio-oil under consideration at present: The hydrotreating-hydocracking route, which is analogous to existing petroleum refining, and fermentation of bio-oil and/or syngas to produce ethanol or butanol. . Hydrotreating-Hydrocracking Bio-Oil Refining Route: Serious attention has been paid to this route over the past decade by many companies, and national laboratories including the National Renewable Energy Laboratory (NREL), the National Energy Technology Laboratory (NETL) and the Pacific Northwest National Laboratory (PNNL). The technical results from these efforts appear to be very promising, and a first large-scale bio-oil refinement demonstration plant in the US is now under development in Hawaii99. The Department of Energy now seems to clearly believe that producing fuel from pyrolyzed biomass via the hydrotreating-hydrocracking route will be cost competitive with both petroleum fuels and many other biofuel routes, including the production of gasoline via “Methanol-to-Liquids” route100. (MTL involves the gasification of biomass, the conversion of the resulting syngas to methanol, and the synthesis of gasoline from the methanol.) As far as the science is concerned, much of the fundamental chemistry research for the hydrotreating-hydrocracking route appears to have already been done, so that the R&D task is mainly a matter of working out and implementing the refining process, as opposed to making fundamental breakthroughs. PNNL scientist Doug Elliot concluded that: “Improved understanding of process steps and product

97 “The Effects of Fuel Washing Techniques on Alkali Release from Biomass,” Davidsson, K. O., Korsgren, J. G., Pettersson, J. B. C., Jäglid, U. Fuel; Vol. 81(2), 2002; pp. 137-142. : http://www.sciencedirect.com/science/article/pii/S0016236101001326 98 “Pre-treatment of biomass with phosphoric acid prior to fast pyrolysis: A promising method for obtaining 1,6- anhydrosaccharides in high yields,” G Dobele, T Dizhbite, G Rossinskaja, G Telysheva, D Meier, S Radtke, O Faix, Journal of Analytical and Applied Pyrolysis, Volumes 68–69, August 2003, Pages 197-211: http://www.sciencedirect.com/science/article/pii/S0165237003000639 99 http://energy.gov/articles/secretary-chu-checks-biomass-pilot-scale-facility 100 “Biofuels Design Cases”, DOE Office of Biomass Program, April 2012: http://www.usbiomassboard.gov/pdfs/tac_design_case_haq.pdf. See slide 5.

properties is developing. Process economics are promising in the current economic environment. Scale-up is envisioned in the near term.101” . Fermentation Bio-Oil Refining Route: There seems to be less focus on the fermentation route overall, and the literature shows that the bio-oil must be detoxified and distilled prior to fermentation to alcohols (fuels), and the use of specially engineered microbes may also be required102. Nonetheless, this might prove to be a simpler and cheaper route than hydrocracking, and possibly one that could be scaled down more easily. o Production of Biofuels from Syngas – Fischer-Tropsch, Catalytic and Fermentation Routes: It may also prove economical in some cases to refine, ferment or catalytically convert syngas (instead of bio-oil) to biofuels. For example, syngas can be used to produce diesel via the “Fischer–Tropsch process”, fermented to produce ethanol, or converted into methane, methanol, or dimethyl ether in various catalytic processes. In particular, “renewable gasoline” can also be produced via the so-called “Methanol-To-Liquids” (MTL) route, which involves conversion of syngas to methanol, and the synthesis of gasoline from the methanol. As mentioned above, the MTL route is thought by DOE to be more costly than the conversion of pyrolysis derived bio-oil to fuel103, but as the foregoing paragraph indicates, MTL is only one possible route. o Syngas Routes versus Bio-oil Routes: Gasification converts a large fraction of the biomass to syngas, as discussed above, fermentation of bio-oil requires detoxification and distillation. On the other hand, bio- oil is inexpensive to transport due to the high energy density of bio-oil, and catalysis and fermentation processes often usually require some kind of gas clean-up, depending on feedstock, to avoid or reduce chemical poisoning of catalysts or enzymes. The tradeoffs involved are complex and depend very much on the feedstocks available and hauling distances involved. Several companies and organizations are exploring the syngas routes: . Cornell University has launched a project called “Village Scale Pyrolysis for Liquid Biofuels” in 2009104, to explore the fermentation route, specifically in the context of small-scale, rural, production. Cornell confirms that this project (which is perhaps using gasification as opposed to pyrolysis, or some combination of these) is focusing on the syngas fermentation route and is still in process, and that some results may be published soon105. . Ineos Bio, the subsidiary of a major international chemical firm, broke ground in 2011 on a plant that will produce ethanol by fermenting syngas106. The company claims it has been able to produce 100 gallons of ethanol per dry ton of waste from the bacteria, which naturally occurs in chicken waste.

101 http://www.pacificbiomass.org/documents/Elliott%20(C1).pdf 102 “Hybrid thermochemical processing: fermentation of pyrolysis-derived bio-oil”, Jarboe LR, Wen Z, Choi D, Brown RC, Appl Microbiol Biotechnol. 2011 Sep;91(6):1519-23: http://www.ncbi.nlm.nih.gov/pubmed/217894900 103 “Biofuels Design Cases”, DOE Office of Biomass Program, April 2012: http://www.usbiomassboard.gov/pdfs/tac_design_case_haq.pdf. See slide 5. 104 http://www.css.cornell.edu/faculty/lehmann/village_pyrolysis/people.html 105 Direct correspondence with Cornell, July 2012. 106 http://www.ineos.com/new_item.php?id_press=283, http://green.blogs.nytimes.com/2011/02/10/yet-another-route- to-cellulosic-ethanol/?ref=earth

. The companies Syntec107, Chinook Energy108 and Enerkem109 are among those pursuing catalytic conversion of syngas to ethanol. Enerkem is currently constructing a commercial scale facility, and has two existing facilities in Quebec. o Comparison of Bio-oil and Syngas Routes with Enzyme Based Cellulosic Ethanol: Syngas routes may have a fundamental advantage over enzyme based cellulosic ethanol routes (those that use enzymes to breakdown the original biomass) in that gasifiers and pyrolyzers are able to convert a very wide range of feedstocks in syngas. Many gasification and pyrolysis providers stresse that they can utilize virtually any organic feedstock. On the other hand, significant progress has occurred with enzyme based cellulosic ethanol, and it is too early to definitively compare these. o Direct Use of Syngas in Engines: Syngas can and has been used directly for vehicle fuel. This involves the use of a gasifying right on the vehicle. FEMA has even published a guide to home-made gasification units for emergency fueling of tractors.110 o Electricity Generation with Biogas: Besides the reciprocating (internal combustion) engines used to generate electricity from biogas today, possible technologies to produce electricity with biogas include microturbines and heat driven engines such as stirling engines, rankine cycle engines, steam engines, and hot air engines. Biogas can be used to fuel natural gas or propane engines of the type typically used in generators with proper modifications. Biogas can also be used to fuel engine-driven refrigeration compressor and irrigation pumps. o Heat Generation with Biogas: Burners can be modified to effectively combust biogas for heating applications. Burners need to be specifically configured to utilized bio-gas, just as with reciprocating engines, due to the relatively low energy content of bio-gas. A detailed discussion of this subject appears on page 82 of chapter 5 of “Biomethane from Dairy Waste: A Sourcebook for the Production and Use of Renewable Natural Gas in California111”, from which we mention only a few highlights here: . As far as the actual equipment to use, the Sourcebook mentions that for hot water, “a modified commercial cast-iron natural-gas boiler can be used to produce hot water for most on-farm applications”. But it also mentions that “All metal surfaces of the housing should be painted. Flame- tube boilers may be used if the exhaust temperature is maintained above 300° F to minimize condensation. The high concentration of H S in the gas may result in clogging of the flame tubes.” 2 . For space heating, “Hot-air furnaces can be fueled by surplus biogas from a covered lagoon,“ but adds later that “Corrosion-resistant models are not available; therefore, the gas should be pretreated to remove H S and water.” 2 . Finally, the Sourcebook mentions that: “Direct-fired heating is commonly used in hog farrowing and nursery rooms …Commercial models of this equipment can be operated using treated biogas. Burner orifices should be enlarged for low Btu gas....Biogas would be burned directly in the room for heat; therefore, the biogas would need to be treated to remove H S and water.” 2

107 http://www.syntecbiofuel.com/thermochemical_process.php 108 http://www.chinookenergy.com 109 http://www.enerkem.com/en/home.html 110 http://www.woodgas.net/files/FEMA_emergency_gassifer.pdf 111 http://www.suscon.org/cowpower/biomethanesourcebook/chapter_5.pdf

o Carbon Black By-Products from Pyrolysis: A 2010 study by the State of Washington on the use of pyrolysis reactors concluded that producing Biochar, carbon black, and syngas is a promising scenario to “maximize use of carbonaceous materials112”. In this scenario the output of a pyrolysis reactor would be routed to a special high temperature (1200+ oC) “carbon black” reactor, essentially a gasifier, that would reduce the pyrolysis vapor to a mixture of soot (carbon black), water, and syngas. The Washington Study also noted that worldwide production of carbon black, which is presently created from non- renewable source, is projected to reach 13 million metric tons by 2015. Major manufacturers of products such as tires from carbon black do in fact appear to be interested in production of carbon black from biomass: A 2012 press release from Bridgestone states that one of their research groups, as part of the companies quest to become more sustainable, “has developed a technology that allows carbon black to be retrieved from intermediate materials created from biomass materials113.” The Washington Study also pointed out that this possibility has essentially been realized already as part of the “Choren Process”, which was developed by now-defunct Choren Industries. In this process, the volatiles are converted to carbon black with a high temperature reactor as described above, and then the carbon black and the Biochar are together gasified to create a very high quality syngas. Choren actually used this process to produce a fuel that was marketed briefly as “SunDiesel”. It is reported that Choren successfully operated their pilot system for “thousands of hours”114, and that a new entity acquired the rights to the process in 2012115. o Generation of Electricity with Syngas: Combusting the syngas directly in an engine of some kind for electricity generation may be attractive. Using heat engines in particular (hot air turbines, steam engines or stirling engines) are less efficient but can have advantages in terms of longevity, maintenance, and the ability to deal with syngas irregularities. There are challenges to utilizing syngas from biomass: . In the past, conversion of biomass to syngas has typically been fairly low-yield. . The precise composition of syngas varies depending on feedstock, feedstock pretreatment, and process. Contaminants in syngas, especially tar and moisture, or high hydrogen percentages (hydrogen burns quickly) can create problems for engines. . Syngas is also very poisonous (it contains large percentages of CO) and exits the gasifier as a hot, combustible gas, which creates safety issues. Syngas handling systems must therefore be designed and constructed carefully. It is therefore not surprising that a 2010 review found that direct use of syngas in engines was still rare at that time, although not entirely unheard of, and practically nonexistent in the US116. But this situation appears to be changing. For example: The company Ensyn, as a company white-paper describes117, and

112 “Methods for Producing Biochar and Advanced Biofuels in Washington State: Part I: Literature Review of Pyrolysis Reactors”, https://fortress.wa.gov/ecy/publications/publications/1107017.pdf, page 20. 113 http://www.bridgestone.com/corporate/news/2012052301.html 114 http://www.consumerenergyreport.com/2011/07/08/what-happened-at-choren/ 115 http://www.dieselnet.com/news/2012/02linde.php 116 “Status of Existing Biomass Gasification and Pyrolysis Facilities in North America”, Theodore S. Pytlar, Jr., Proceedings of the 18th Annual North American Waste-to-Energy Conference, NAWTEC18, May 11-13, 2010, Orlando, Florida, USA http://www.seas.columbia.edu/earth/wtert/sofos/nawtec/nawtec18/nawtec18-3521.pdf 117 http://www.ensyn.com/wp-content/uploads/rich-widget/file/Envergent_Electricity_5406_EN_WP_10v2.pdf

companies such as Nexterra are marketing systems for direct use of biomass syngas for electricity generation. The Ensyn white paper claims that their process can produce electricity much more efficiently than by simply combusting the biomass and using the drive a steam cycle for electricity production. Companies such as Clark Energy and GE are marketing engines which they claim have sophisticated control systems to deal with possible irregularities in Syngas118. Instead of using internal combustion engines, it may also make sense in some cases to use micro-turbines, or gas turbines. In the future it may be possible instead to return to a thermal route, and combust the syngas to drive hot air turbines, steam engines or stirling engines. The latter three are all heat driven, and are discussed further in the chapter on thermal energy utilization. Some of these systems may have lower efficiency, and may have higher capital costs, but can have advantages in terms of longevity, maintenance, and the ability to deal with syngas irregularities.

118 http://www.clarke-energy.com/gas-type/synthesis-gas-syngas/

Biological Fuel Cells  Technology Description: o Biological Fuel Cells (BFCs), also called Microbial Fuel Cells (MFCs), are an emerging technology based on the ability of certain organisms, including microbes (termed exoelectrogens), or certain plants, to generate electricity via direct contact with electrodes. Traditional fuel cells use chemical catalysts (e.g. platinum) that oxidize fuel (such as hydrogen) at anodes, and reduce atmospheric oxygen at cathodes to produce water. BFCs are a technology can be thought of as fuel cells with a regenerative, living microbial or plant catalyst, instead of a chemical catalyst. Essentially, BFCs utilize the oxidizing effects of microbial consumption of biomass to produce a supply of electrons and protons. A Proton Exchange Membrane (PEM) is then used in conjunction with a circuit to produce electricity and water. o How BFCs work: In a conventional hydrogen fuel cell, hydrogen is decomposed on a catalyst surface into protons and electrons. The positively charged protons can then diffuse through a PEM to another catalyst surface on which oxygen atoms are weakly attached. The electrons cannot penetrate the PEM easily due to the structure of the PEM material, but are provided an alternative path in the form of an electrical circuit, by which they can reach the other catalyst surface. Along the way the electrons deliver energy to the load on the circuit, which might be a light bulb, a motor, a battery, or some other load. Once they arrive at the catalyst with the oxygen, the protons and electrons combine with oxygen to form water molecules, which then break away from the catalyst surface. More oxygen attaches to the catalyst surface in the process repeats. The formation of water drives the process. One can think of the formation of water as effectively pulling the electrons and protons through the electric circuit and the PEM, respectively. The final products are primarily carbon dioxide, water, and electricity. Microbial fuel cells work in a similar fashion, except that in this case the hydrogen, that is, the electrons and protons are provided by the electrochemical (oxidizing) action of microbes on the biomass feedstock. More specifically, in the presence of oxygen, microbes break down carbohydrates into carbon dioxide and water. But when deprived of oxygen the microbes lack the oxygen needed to make both carbon dioxide and water, and instead produce carbon dioxide and hydrogen, the latter of which can also be output as protons and electrons. This effect is very general, and virtually any organic feedstock can be used in principal to fuel BFC's. Possible sources of biomass include wastewater from water treatment plants, algae119, breweries and other sources of biomass. o Categories of BFCs: There are two basic classes of BFC's: the mediator BFC's, and the mediator–less BFC's. In mediator BFC's, the electron transfer from microbial cells to the cathode is facilitated by chemical mediators such as thionine, methyl blue, humic acid, etc. These are generally costly and toxic. Mediator less BFC's utilize electrochemically active bacteria that are capable of directly transferring electrons to the cathode.

 Technology Special Benefits: o Low emissions o A wide range of possible biomass feedstocks o Quiet operation o Good prospects for scaling down to farm-size facilities

119 http://www.engr.psu.edu/ce/enve/logan/publications/2009-Velasquez-Orta-etal-B%26B.pdf

 Overall Prospects for Successful Deployment: o Little short-term potential for deployment. The fundamental science suggests that the long-term prospects might be good, and developments could proceed very quickly given the already advanced stage of fuel cell development.

 Development Status: o The first scientific work on BFCs was conducted by M. C. Potter in 1911. A series of researchers continued work on BFCs over the decades, leading up to a 10 liter prototype that converts brewery wastewater was constructed in 2007 by the University of Queensland, Australia (the results of which could not be located). o A significant research community has now developed around the concept of BFC's, and “bioelectrochemical systems” in general, and a research society calling itself the International Society of Microbial Electrochemical Technologies (ISMET) has emerged120. Hundreds of research publications are listed (many accessible) on organization’s website. o European and North American branches of the ISMET have now also formed: The North American branch will have its first meeting in October 2012 at Cornell University in Ithaca, NY. o The potential of BFCs for energy production is still largely unknown. But certain energy related results can at least be found: o In 2007 another group found that electricity generation might be maximized/sustained by adjusting the so-called “anode potential121”. o In 2011, some researchers have at least begun to develop methodologies for conducting life cycle assessments of BFCs for energy production122. o In 2011 an NREL affiliated group reported that carbon nano-tubes make effective electrodes for BFCs.123 o NPR Article: http://www.vpr.net/npr/147356660/: Grant Burgess, a marine biotechnologist at Newcastle University, discusses some of the possibilities and challenges of BFCs. o Wastewater Treatment Example: http://www.popsci.com/scitech/article/2009-08/microbial-fuel cell- cleans-wastewater-desalinates-seawater-and-generates-power. o The relatively recent dates on these references clearly indicate that BFCs are still in the early stage of development, and also indicates that R&D does appear to be continuing.

120 http://www.microbialfuelcell.org. 121 “The anode potential regulates bacterial activity in microbial fuel cells”, Peter Aelterman, Stefano Freguia, Jurg Keller, Willy Verstraete, and Korneel Rabaey, Appl Microbiol Biotechnol (2008) 78:409–418: http://www.microbialfuelcell.org/Publications/LabMET/2008%20-%20Aelterman%20- %20%20The%20anode%20potential%20regulates%20bacterial%20activity%20in%20microbial%20fuel%20cells.pdf 122 “An introduction to the life cycle assessment (LCA) of bioelectrochemical systems (BES) for sustainable energy and product generation: Relevance and key aspects,” Deepak Pant, Anoop Singh, Gilbert Van Bogaert, Yolanda Alvarez Gallego, Ludo Diels, Karolien Vanbroekhoven, Volume 15, Issue 2, February 2011, pages 1305–1313. http://www.sciencedirect.com/science/article/pii/S136403211000345X 123 “Carbon nanotube modified air-cathodes for electricity production in microbial fuel cells”, Heming Wang, Zhuangchun Wu, Atousa Plaseied, Peter Jenkins, Lin Simpson, Chaiwat Engtrakul, Zhiyong Ren: Volume 196, Issue 18, 15 September 2011, Pages 7465–7469: http://www.sciencedirect.com/science/article/pii/S0378775311009694

 Barriers & Opportunities: o There are potentially thousands of different microbes that might be useful for BFCs, and little knowledge of even how many of these can be grown. It will likely require many years for the best possibilities to be sorted out and applications developed. o One class of BFCs using microbes utilize chemical “mediators” to facilitate electron transfer from microbial cells to the electrode. These mediators are generally expensive and toxic. Fortunately, mediator-less BFCs using electrochemically active microbes and/or plants are also possible.

Geothermal Heat Pumps  Technology Description: o Geothermal or “ground-source” heat pump systems (GHPs) can be used to heat and/or cool buildings or provide low temperature thermal energy for many other applications. If equipped with a so-called “desuperheater”, they can also contribute substantially to domestic hot water heating. In heating mode, thermal energy is absorbed from the ground, either by a fluid circulating in a closed loop (close system), or via extraction and reinjection of well or pond water (open system). The heat pump, which is similar to the refrigerator, then utilizes a refrigerant cycle to elevate the temperature of the thermal energy to above storage tank temperature (or air temperature), so that the thermal energy can be delivered. These systems can also be used for cooling. o GHPs can be thought of as drawing up solar energy that is stored in the ground (because the energy removed from the ground by the system will be continually replaced mostly with thermal energy diffusing downward from the surface). As such they are drawing on an enormous and ubiquitous source of renewable energy, and could become a major and possibly even dominant source of renewable energy in the future. o In a broad sense, heat pumps (either air or water source) are devices which can be used to “upgrade heat”, that is, to increase the temperature of thermal energy, whenever this function is needed. They may be also thought of as energy multipliers that, for example, devices that effectively multiply a kilowatt-hour of photovoltaic electrical energy into many more kilowatt-hours of usable thermal energy. Heat pumps therefore have very wide potential wide utility. o Although heat pumps have not been widely utilized in Vermont in the past, heat pump technology in general will likely become a ubiquitous part of many thermal energy handling systems in the future, and moreover will likely be just one part of systems that integrate heat pumps with various types of thermal energy storage, solar thermal systems and photovoltaic systems, and other sources of renewable heat. o There are two basic categories of geothermal systems, closed loop and open loop systems: . Open Systems: These include “Standing Column Well” and (open) “Pond” systems. In these systems, water is drawn from and returned to the water body, for example, from the bottom of a standing column well, and returned to the top of the well. In this example, as the returned water travels downwards, it exchanges heat with the surrounding bedrock. Water can also be returned to a recharge well, or in some cases discharged on the surface. Standing column well systems often employ a “bleed” whereby a (small) percentage of the well water is diverted and discharged to the surface, which causes other groundwater to diffuse towards the well, which hence increases the temperature in the well. This increases the efficiency of the system, and also helps prevent freezing (there is no anti-freeze in these systems). The well water thus diverted can also be used in the domestic water supply for the building. See diagrams below. . Closed Systems: These include “Horizontal”, “Vertical”, (closed) “Pond”, and “Direct Exchange” systems. Water, with or without antifreeze, is circulated in a closed loop underground or in a pond to collect geothermal heat in cold months and disperse heat to the ground in warmer months. The underground piping can be laid out horizontally in trenches at least four feet deep, often in a coiled or “slinky” fashion so as to make maximum use of the trenches, or the piping can be laid out vertically in holes 100-400 feet deep, with U-joints at the bottom, spaced roughly 20 feet apart.

Piping can also be placed in ponds, if such a water body exists nearby. See diagrams below. In so- called “Direct Exchange” or “DX” closed loop systems, the refrigerant is circulated directly in the ground in copper or steel pipes, which enables a high efficiency (but requires lots of refrigerant and metal piping). o Closed versus Open Systems: In general, open systems, which draw water directly into the system, are fundamentally more efficient than closed systems (except perhaps for DX systems), because heat does not need to conduct through the walls of a collector loop, leading to higher Coefficients of Performance (COPs) – the ratio of heat delivered to electricity used to operate the system. Open systems are also often cheaper to install because they require less piping and excavation. Moreover, standing column wells either exist or can be drilled at many farms in Vermont. But not all sites can accommodate open systems, for example due to hydro-geological reasons, and in some ways closed loop systems can be simpler to install, for example because hydro-geological assessments are not needed. In any case, open loop systems should be considered first, closed loop systems second. This is contrary to the general trend in the Southern US, where many closed loop systems are installed for mainly cooling purposes. o Lifetime: The Department of Energy estimates system life at 25 years for the inside components and 50+ years for the ground loop.

 Technology Special Benefits: o If properly installed, GHPs can provide seasonally averaged Coefficients of Performance (COPs) of 3.5-5. o As a rule of thumb, GHPs can cut the heating cost of home roughly in half relative to oil heating, with a payback time of 10-20 years.

o Relative to heating with oil, a geothermal system in Vermont today can decrease CO2 emissions by at least 45%, even when the emissions associated with the increased electricity use of the system is factored in, and much more if a renewable electricity source is utilized. o There are few other technologies with such a large (essentially infinite) thermal energy resource potential. o Vermont has strong potential for many (open loop) standing-column well based GHP systems (which as mentioned above are more efficient than closed systems).

 Overall Prospects for Successful Deployment: o Very good for open systems with proper hydrological/geological characteristics. Moderately good in some cases for closed systems. o For a typical home at a site with optimal characteristics, a geothermal system in Vermont can save roughly $1000 to $2000 per year in heating costs, and have a “simple payback time” of between 10-20 years. o Detailed Cost Considerations: The heat pump unit itself, fully installed, and not counting drilling or excavation costs and the external piping, will cost approximately $2500 per ton of capacity, depending on installation details. So for example, the heat pump for a home with a 3 ton will cost approximately $7500. Drilling or excavation costs tend to run anywhere between about $10,000 to $30,000 depending on the design capacity of the system, the type of system, the geology of the site, and the hydrogeology of the site. The higher the installation cost – which depends in detail on the installation type and site

characteristics - the longer the payback time. If the site has an existing well that is suitable for a geothermal system, then a geothermal can be extremely cost effective. . In general, vertical closed loop systems require somewhat more and/or deeper boreholes than do open, standing column well systems, due to the relatively low thermal conductivity of the plastic piping through which heat must conduct in a closed system. For example, a closed system with a 3 ton capacity might require one to three 300 ft boreholes, whereas an open system might do the same drawing from a single well with a 300 foot standing water column. . Likewise, horizontal closed loop systems, at least those utilizing plastic pining, require very significant lengths of piping, again due to the relatively low thermal conductivity of the plastic piping. This implies significant excavation and piping costs. For example, a 3 ton system might require 600 feet of piping (200 ft/ton). Excavation for horizontal systems tends to cost roughly half of what drilling for vertical systems cost per foot, so a horizontal system may be preferable over a vertical closed loop system where adequate land area with soil at least 4 feet deep is available. The cost of horizontal systems can also be lowered in many cases by using a trencher instead of an excavator.

 Development Status: o Industry Status: Many companies offer GHPs, and industry sources suggest that 50,000+ heat pumps are being installed in the US annually. o Local Installers: Although geothermal heating is not widespread in Vermont, there already exists a significant base of installers. A database which can be accessed to find accredited installers in Vermont can be found on the website of the International Ground Source Heat Pump Association (IGSHPA): http://www.igshpa.okstate.edu/geothermal/geothermal.htm o Installation Success: Some geothermal heat pump systems have been deployed in Vermont, and are known to be performing well124. o Relationship to Hydronic Heating Technology: GHPs benefitted greatly by the introduction of modern hydronic heating technology, and have improved substantially over the past two decades. o R&D Status: There are ongoing R&D efforts underway to improve GHPs. For example, see Chua et. al125.

 Barriers & Opportunities: o Public Awareness: There is less public awareness of this technology than for many other renewable energy technologies. o Open Systems in Particular Offer an Opportunity: As mentioned above, open systems generally have significantly higher Coefficients of Performance (COP). Open systems can be particularly economical for those that already have a well. o Partial or Multi-Stage Operation: COPs are significantly higher when heat pumps are operated at partial capacity. This suggests that the COP can be increased in many cases by somewhat oversizing the system

124 Direct inspection by the author. 125 “Advances in heat pump systems: A review,” K.J. Chua, S.K. Chou, and W.M. Yang, Applied Energy, Volume 87, Issue 12, December 2010, Pages 3611–3624: http://www.sciencedirect.com/science/article/pii/S030626191000228X

capacity. Another helpful approach is to utilize multistage or variable stage units that can better adapt to changes in heat demand. o Solar Charging: Another approach to increasing the COP may be to inject additional heat into the ground using a solar thermal collector that supplies heat to the ground using the same underground heat exchange system as the heat pump. This is a form of Seasonal Thermal Storage: See the section on the Thermal Energy Storage Technologies for more information. o Good/Installation is Essential: Initial installation is capital intensive, and care should be taken to avoid excessive upfront costs by careful design. For example, to ensure that pumping loads will not be too high, air ducts are properly designed. Some of the installation options and considerations that need to be taken into account include: . Air Duct Issues: Geothermal systems can supply space heating via “air handlers” retrofit into existing forced air distribution systems (duct work). It is possible to leave the original furnace intact for back up heat. Caution should be taken however to ensure that the ductwork is of adequate cross- sectional area. There are specific rules governing this that a professional installer can follow, and it can be well worth investing in improvements to the duct work itself. It is also essential to ensure that any duct work that is not strictly within the “thermal envelope” of the building is very well sealed and insulated. Existing insulation may very well not be adequate. Significant losses in the duct work can greatly compromise a geothermal system because geothermal heat is generally delivered in a steady way, that is, the system is delivering much of the time, so that significant losses will be able to have a significant adverse effect. In some buildings, especially small structures with few rooms, it may make sense to have an air handler simply deliver hot air to the building right at the location of the air handler, without duct work. The heat pump compressor can produce significant sound output, and should generally be well isolated from living space. . Hydrological/Geological Issues: Standing column well systems are particularly convenient where bedrock is at or close to the surface and/or where land area is limited. Information on existing wells in Vermont is now provided on the Vermont Renewable Energy Atlas (http://www.vtenergyatlas.com). A standing column well system is typically not appropriate in locations where the geology is mostly clay, silt, or sand. More specifically, if the bedrock is deeper than 200 feet from the surface, the cost of the well casing needed may become prohibitive. Likewise, if the water table is at a depth of 100 feet or more, then pumping loads may become prohibitive for systems that will utilize a significant level of “bleed”, that is, discharge to the surface to help maintain groundwater temperatures. As a rough rule of thumb, approximately 100 feet of standing water column is needed per ton of capacity for open systems. The precise value must be determined from an evaluation of the geology at a site. The thermal conductivity of the bedrock in particular is a critical parameter. How much of a “bleed” a standing column well system will depend on the production capacity of the well. Generally speaking, bleeds rates of about 5% to 15% of the system’s flow rates can be desirable for maintaining temperatures. Each ton of heat pump capacity will require roughly 3-5 gallons per minute (gpm) of flow, which implies bleed rates of .2-.6 gpm. So, for example, a 3 ton system would require a bleed rate of between about 1-2 gpm. If the system is running continuously, and is utilizing bleed say, 50% of the time, then this would result in the withdrawal of 700-1400 gallons per day. A well must be able to easily support this level of

withdrawal for significant durations during the heating season (if the system is going to utilize bleeding). . Excavation Cost Tradeoffs: Excavation for horizontal systems tends to cost roughly half of what drilling for vertical systems cost, so a horizontal system may be preferable over a vertical closed loop system where adequate land area with soil at least 4 feet deep is available. . Water quality Issues: Limescale may build up on the inside walls of the piping and require periodic acid cleaning. If the water contains especially high levels of minerals, salts, iron bacteria or hydrogen sulfide, a closed loop system is usually preferable. . Performance Evaluation: A good practice is to insure that a system can be monitored effectively by having “P/T Ports”, that is, pressure-temperature ports, installed where the ground loop water enters and leaves the heat pump. This will allow “stab-in” type pressure and temperature gauges to be quickly inserted, from which the rate of heat delivery can be easily determined.

Air Source Heat Pumps  Technology Description: o Air source heat pumps (ASHPs) can be used for a variety of heating or cooling applications. For heating, ASHPs transfer thermal energy from the outside (ambient) air to the inside air or to water, and vice versa for cooling. In other words, these devices "pump" heat into or out of the structure or thermal storage tank. There are “air to air” ASHPs, and “air to water” ASHPs. In the past, heating applications were limited to moderate ambient temperatures, but advances have now extended applications to sub- freezing temperatures. o How ASHPs work: In heating mode, thermal energy is absorbed from the ambient air into the heat pump’s refrigerant. The heat pump’s compressor then elevates the temperature of the refrigerant to above room temperature (or above the hot water tank’s temperature), so that the thermal energy can be delivered.

 Technology Special Benefits: o Although less efficient than geothermal heat pump systems for winter heating applications, ASHPs are relatively inexpensive. The critical issue is operating cost. Despite advances, ASHPs are still most efficient at moderate as opposed to low ambient temperatures. Specifically, ASHPs can provide Coefficients of Performance (COPs), that is, the ratio of thermal energy delivered to electrical energy consumed, at around 2-2.5 at low ambient air temperatures and greater than 4 at moderate to high ambient temperatures. o The performance of ASHPs has been gradually improving. According to the Department of Energy, “The efficiency and performance of today's air-source heat pumps is one-and-a-half to two times greater than those available 30 years ago.”, and the DOE lists the following improvements126: . Thermostatic expansion valves for more precise control of the refrigerant flow to the indoor coil. . Variable speed blowers, which are more efficient and can compensate for some of the adverse effects of restricted ducts, dirty filters, and dirty coils. . Improved coil design. . Improved electric motor and two-speed compressor designs. . Copper tubing, grooved inside to increase surface area.

 Overall Prospects for Successful Deployment: o Very good for certain applications, particularly well insulated spaces. See the section on Thermal Energy Utilization for a general discussion of thermal energy uses.

 Development Status: o It appears that little if any deployment of ASHPs has occurred at farms in Vermont, but as described in this section, higher COPs can now be achieved, and this should justify the use of ASHPs in certain applications.

 Barriers & Opportunities:

126 http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12620

o Cold Climate Operation: In the past, ASHPs were limited to moderate weather applications only (temperatures above about 40oF). Certain ASHP products by Fujitsu and Mitsubishi exist which can now be credibly classified as Cold Climate Heat Pumps (CCHPs). For example, one installer writes these units “work down to minus 17 degrees [Fahrenheit] and will create heat efficiently all winter in Maine,” and for “an entire heating season in Maine will average a COP of about 2.7127.” The same installer also points to the “Bright Built Barn” project as an example of such an installation128. Recent tests by NREL and Purdue University essentially support these claims129. In particular, these tests showed that the Fujitsu 12RLS and Mitsubishi FE12NA, two “mini-split” heat pumps (where the heat exchangers are split into two separate units, one inside, and one outside), and in conformance with their manufacturer’s specifications, can operate down to at least -5oF or somewhat lower. The tests also showed that the units can achieve COPs ranging from about 5 at an outside temperature of 70oF down to about 2 at 0oF, which are roughly consistent with the claim of an Avg COP of 2.7 for Maine. Another company that offers a heat pump system that is claimed to work down to low temperatures (- 5oF) effectively is Daikin130, and there may be additional ASHPs on the market with similar characteristics. It is worth noting that two Maine companies, first Nyle Systems, and then later Hallowell International LLC, attempted to develop a particular CCHP product. According to the Hallowell131, this heat pump featured a two-speed, two-cylinder compressor, along with back-up booster compressor that allowed the system to operate efficiently down to 15°F; and a plate heat exchanger called an "economizer" that further extends the performance of the heat pump to well below 0°F. Hallowell International LLC actually marketed several thousand of these CCHPs, but the units unfortunately experienced very high failure rates, leading to the company’s untimely and very public collapse in 2011132. Not all customers were unhappy with the performance of the units, however133, and following the collapse a retired engineer diagnosed the problem and found that the units could be fixed by installing a new $30 controller134. He and others then created a website to disseminate the fix (http://www.savemyacadia.org/) . o Capacity Issues: It is worth noting, that the NREL tests mentioned above do show significant loss of capacity at low ambient temperatures: For an ambient temperature decrease from 40oF down to 0oF, the capacities on the Fujitsu and Mitsubishi units fell by roughly 25% and 35%, respectively, which might be problematic for some applications. o Defrost Cycle Issues: It is also worth noting that these units, if used by themselves as air-to-air units, need to occasionally execute a defrost cycle to melt any ice that has accumulated on the outside heat exchanger (the “evaporator” unit) from condensation. In this mode, the pumps reverse operation and actually blow cool air into the building for a short time (the lower the ambient temperature, the longer).

127 http://www.revisionheat.com/renewable-heating-products/efficient-electric-heating-systems/air-source-heat-pumps/ 128 http://www.brightbuiltbarn.com/our-brightbuilt/about/ 129 http://www.nrel.gov/docs/fy11osti/52175.pdf 130 http://www.daikinac.com 131 http://www.energysavers.gov/your_home/space_heating_cooling/index.cfm/mytopic=12620 132http://greenenergymaine.com/news/efficiency-conservation-posts/heat-pump-maker-hallowell-out-business 133 http://bangordailynews.com/2011/02/01/business/heat-pump-company-draws-complaints/ 134 http://bangordailynews.com/2011/08/07/business/nh-man-has-fix-for-failed-heat-pumps-made-by-defunct-bangor- manufacturer/

“Reverse Cycle Chillers” (see next) avoid this problem by using stored thermal energy to melt the ice instead of heat from the building. o Reverse Cycle Chillers (RCC): These devices combine ASHPs with small insulated thermal storage tanks (usually 20 – 40 gallons). (The odd name derives from the fact that in Canada heat pumps are known as "reverse cycle air conditioners"). RCC units are often sold as integrated units containing both the heat pump and the water tank in a single package. These can be used directly to supply hot water to radiant floor systems or forced air systems equipped with fan coils. These also eliminate the need for periodic blowing of cool air into the building during the defrost cycle and according to the DOE are more efficient. The RCC can be equipped with a refrigeration heat reclaimer (RHR) to provide hot water from either excess heating capacity in the winter or by reusing the heat it extracts to cool the building in summer. The combined RCC and RHR system reportedly cost about 25% more than a standard heat pump of similar size. The technology applied in the Reverse Cycle Chiller is not new. Larger scale RCC systems have been in operation for decades in large institutions, but up until recently were not packaged for residential scale applications. o RCC Company Examples: www.aquaproducts.us , www.multiaqua.com, www.multiaqua.com o Potential for Future Enhancements: Even higher average COPs for the Northeast are possible in principle, and likely in practice. Purdue University researchers are actively conducting R&D on CCHPs at the current time, and a publically available presentation some of this indicates that135: . One group is exploring a specially constructed two-stage compressor design that will allow the system to better optimize performance around several different operating points corresponding to different ambient temperatures. The simulations suggest that the system can achieve an (instantaneous) COP of around 4 at 32oF, and COPs greater than 2 all the way down to about -13oF. This would represent some increase in COP over existing higher end units. . Another Purdue project is exploring the use of compressors with multiple vapor injection ports, which the group claims may be able to obtain similar performance levels but be less expensive than two-stage compressor designs. This work suggests that this approach can achieve COPs of around 4 at 32oF, and as large as 3 all the way down to 0oF. This would represent a rather significant increase in COP. . Also encouraging is the fact that another group of researchers at Oak Ridge National Laboratory are developing a systematic design optimization procedure for CCHPs, and recently presented on their work at the ASHRAE 2012 Winter Conference Technical Program136.

135 http://www.ornl.gov/sci/ees/etsd/btric/usnt/11-8- 11Wkshp_presentations/IEA%20Cold%20Climate%20HP%20Pres%20Groll%202011-11-05.pdf 136 http://www.ashrae.org/File%20Library/docLib/Events/Chicago2012/ProgramBook-11-16.pdf

Solar Hot Water  Technology Description: o Solar hot water systems can be used for offsetting both domestic hot water and space heating costs, and integrate well with most existing domestic hot water and hydronic heating systems. Solar hot water collectors (flat plate collectors or evacuated tube collectors) are used to capture solar heat, which is usually stored in a “solar pre-heat tank”. The solar hot water can then be used for on-farm hot water needs or space heating needs. o Flat panel collectors are typically somewhat cheaper than evacuated tube collectors, but evacuated tube collectors can have higher efficiencies in cold weather and/or lower light conditions for the same water input temperature, and vice versa in warm and/or bright weather. Both types should therefore be considered, and both seem to function well in Vermont.

 Technology Special Benefits: o Solar hot water collectors are quite efficient, often exhibiting capture efficiencies in the neighborhood of 50%, even in winter (on clear days). They can thus provide large amounts of thermal energy and achieve substantial greenhouse gas reductions. o Solar hot water collectors in Vermont can provide close to 100% of domestic hot water needs for a home or farming operation in the summer, substantially less (~40%) during cloudy periods in the colder months, with an annual average of roughly 60%-70%. o Solar hot water technology is well developed and robust. o Solar hot water technology, if installed well, and affordably, can potentially save system owners substantial amounts of money over the long-run. Payback times of around 20 years are typical for many installations today in the US, but can likely be decreased to 10 years or less by reducing labor costs (see below).

 Overall Prospects for Successful Deployment: o Very good.

 Development Status: o Solar hot water systems are used on some farms today, and a growing number of Vermont homes and businesses.

 Barriers & Opportunities: o Recent Advances: The past decade has seen substantial advances in solar hot water system technology, including the widespread emergence of evacuated tube collectors, availability of pre-packaged and/improved balance of system components, and new, large capacity thermal storage options. o Cost Issues/Opportunities: The upfront cost of small solar hot water systems for homes has remained at prices that are perhaps unreasonably high (around $8000), due to a lack of competition and standardization. As installation costs represent up to 50% or more of the cost of many installations, a particular opportunity for farms in Vermont may simply be an increased level of self-installation of

systems, taking advantage of kits offered by company’s such as Vermont’s Radiantec137. Farm installations can often be ground mounted, which is less difficult that rooftop installation, and can often tie in easily with existing farm hot water systems. o Seasonal Heat Storage: Solar thermal collectors can be combined with ground source heat pumps to essentially create seasonal heat storage systems. See the section of Thermal Energy Storage Technologies for more information. o Freeze and Over-heating Protection Issues: Vermont is cold in the winter time, and so freeze protection for collectors is essential. Solar systems can also be damaged if allowed to overheat, for example, if no use of hot water occurs for a prolonged period, or if there is no circulation in the solar loop due to loss of electricity. . One system type are “pressurized glycol systems” which utilize a water-antifreeze mixture to prevent freezing. These types of systems can overheat if there is no use of hot water, or if a loss of electricity occurs, of if the pump fails. One strategy is to provide a “heat dump” for the extra solar heat, which involves diverting extra heat somewhere else. For example, some systems are configured to dump the extra heat into a hot tub, or to a heated slab or driveway, while others simply allow some of the hot water produced to drain (10-20 gallons/day, typically, when the system is not being used). A less sophisticated approach is to simply cover the collectors while the system is not in use. Many pressurized glycol systems today power the circulation pump for the solar loop with a small photovoltaic module. This way, the pump continues to operate even if the (grid) power goes down. . Another system type are the “drain-back systems”, which avoid problems with both freezing and over-heating by allowing the solar loop to fully drain and fill with air when a) there is no solar heat available, or b) when the water in the storage tank is hot enough, or c) when there is no electricity for pumping or if the pump should simply fail. These systems typically utilize a small secondary drain- back tank, called a “drain-back reservoir”, which allows the portion of the solar collection system which is located outside the thermal envelope of the building to fully drain of water. This type of system does not require the use of an anti-freeze. Drain-back systems are somewhat challenging to design and install, as small mistakes can lead to water failing to drain and freezing and damaging the system. The electrical power required to pump the water in the solar loop, which is unpressurized, can also be up to five times greater than in a pressurized glycol loop, although this load can be decreased significantly by placing the drain-back reservoir at a relatively high position, when this is possible. Despite the initial design and installation challenges, though, this type of system can work well and can operate for decades with little or no maintenance. o Thermal Storage Considerations: In some systems, the hot water tank to which the solar heat is delivered is the same tank from which the hot water is drawn. This makes it difficult, however, to simultaneously minimize use of back-up energy while maintaining a ready source of hot water. For example, after running showers in the morning, one would have to wait for the tank to heat up again, or run the back-up heat source right away, which would negate the usefulness of the solar system. . One way to deal with this issue is to design the installation so that the back-up heat is delivered only to the upper part of the hot water tank. For example, a tank can be outfitted with dual heat

137 http://www.radiantec.com

exchangers: One heat exchanger, which is fed by a boiler, is installed in the upper part of the tank, while the solar feeds a second heat exchanger in the bottom. Because water can support a fairly large temperature gradient (stratification), this can leave some cold water remaining in the bottom of the tank for the solar system to heat. . Alternatively, a separate “solar storage tank” can be installed to which the solar loop delivers its heat. The output of this tank is then fed into the hot water tank. In this way the solar system pre- heats water for the hot water tank. If there is not much sunlight, then, and only then, will the back- up heat be utilized. . It is possible to also utilize very large thermal energy storage systems, and even “seasonal” energy storage systems capable of storing energy for the better part of a year. This scale of storage is discussed further in the section on Thermal Energy Storage Technologies. . Systems designed primarily for only providing domestic hot water can often be configured so that any “extra” heat captured is utilized for space heating in a hydronic heating system, which improves the economics. o Special Applications for Farms: . Biodiesel Production: Solar hot water can be used heat vegetable oil for biodiesel production. Special attention must be paid to preventing overheating for obvious reasons, but otherwise there are no special hurdles. Large solar fractions can be achieved because the temperatures required are well matched to the output temperatures of solar hot water systems. An example of this application is a facility in Colorado that produces 50,000 gallons of biodiesel per year138. . Solar Dairies: Solar hot water production is finding increased use at dairies139. This application is straightforward. The Clark Crest Farm in PA is an example of a 600 cow operation with large (1000+ gallon storage thermal tank) solar hot water system140. . Crop Drying: Solar hot water production also provides ideal temperatures for crop drying systems. Callahan Engineering in Vermont assisted with the design of such as system at State Line Farm141. . Greenhouses: Solar hot water systems can be used to capture and store heat for greenhouses. For further information see the chapters on Thermal Energy Utilization and Thermal Storage Technologies. . Other potential uses: Animal Pen Heating, Equipment Sterilization, Cleaning, Vermiculture, Aquaculture, and Process Heat.

138 https://homepower.com/articles/solar-powered-biodiesel 139 See for example: http://newfarm.rodaleinstitute.org/features/2006/0306/solar/martin.shtml 140 http://www.earthenergyinnovations.com/solar-case-study/solar-hot-water-dairy-farm-applications 141 http://www.callahan.eng.pro/blog/index.php/2008/10/20/solar-hot-water-for-grain-drying/

Heating with Aerobic breakdown of Biomass  Technology Description: o Heating with the thermal energy produced directly from the aerobic breakdown of biomass either with compost, or in specially constructed aerobic digesters. Several organizations (including two in Vermont) have recently been pioneering systems that accomplish this either through the low-tech means or with more sophisticated systems.

 Technology Special Benefits: o A local source or renewable heat. o Compost is often already produced at farms. o Potentially very cost effective. o Manure is already collected at farms. o Aerobic digestion may be straightforward to scale down.

 Overall Prospects for Successful Deployment: o Although more rigorous validation work needs to be done, it appears that these systems may represent a viable option for farms for obtaining stable supplies of low-grade renewable heat for applications such as greenhouses, aquaculture, and animal pen heating. Some of the key questions that further R&D will need to answer are: . What are the optimal designs? In particular, will a low-tech design based on passive aeration suffice, or will aeration be needed? Or are both viable with proper design? . What are the optimal compost mixtures (recipes)? . What are the heat yields and economics of the optimal designs utilizing optimal compost mixtures?

 Development Status: o There exists an ancient history of this technology, for example placing animal pens beneath living spaces (e.g. in China), some history in the mid-nineteenth century (e.g. the work of Jean Pain – see below), and recently several organizations have been pioneering new technology.

 Barriers & Opportunities: o Some of the organizations pursuing capture of compost heat, and their particular approaches, include: . Compostpower: http://compostpower.org : This group (Director: Gaelen Brown) focuses on the development of low-tech residential scale systems, and is affiliated with Highfields Center for Composting in Hardwick, Vermont Compost in Montpelier and the University of Vermont. The group has been testing systems constructed primarily with wood chips and sawdust. Their systems consist of mounds of compost with a heat exchanger (gatherer) consisting of coiled plastic piping (A “Design Guide” on the group’s website describes one possible design in detail). The group traces their particular approach to the work of French farmer Jean Pain (1930 – 1981). They report that their initial systems have performed well, sans initial design errors, and that they are continuing to attempt to both optimize and measure the performance of the designs and compost mixes. Some of the key data reported by the group include:

 A 50/50 mix of sawdust and woodchips appears to be the most effective “fuel” tested to date142.  Mixes based on agriculture products, such as chopped grass mixed with manure, have not yet been tested, but the group things these have potential143.  “We believe a mound this size could produce between 20,000 and 40,000 btus per hour, enough to heat an average Vermont home. A mound made of shredded bark or bark + woodchips should produce heat for twelve to eighteen months.”  “A 30-40 yard mound with 900 feet of water line inside should be able convert 45-degree well- water to 110-140 degree water with a sustainable flow-rate between 1 and 4 liters per minute.”  “Most Compost Power systems can be built in a single day with the right materials and equipment. Three to five people should be able to construct a mound this size in an eight hour period with the use of a small tractor or excavator to dump mulch onto the mound as each layer is built.” . Agrilab Technologies, LLP: http://www.agrilabtech.com/Contact-Us.html : This company specializes in the development of heat capture and transfer technology for the capture of heat from compost. The company’s website describes its process as follows: “We capture the steam vapor generated during the composting process (125-165oF) and channel it through an insulated network. A very efficient electric fan on a timer controls the "pull" of the steam vapor. It is drawn into a controlled chamber which houses 6-12 IsoBar tubes. These IsoBar tubes are two phase super conductors which transfer the heat from the steam evenly across the entire surface of the IsoBars. A portion of the IsoBars are sealed into a water jacket referred to as a pre-heater. When the water temperature in the pre-heater reaches the desired temperature, it can then be directly circulated to where needed or transferred into larger hot water reservoirs for direct use as hot water, or circulated for specific heating needs.” “Heat capture and transfer is achieved through managing compost on a “negatively aerated” composting pad. Air channels built into the pad (insulated in colder regions) is drawn down through the composting feedstock versus pushing air in from below.” . Mother Nature’s Farms, Inc.: http://www.magicsoil.com/: This group has reported some fairly detailed R&D results which can be found at http://www.magicsoil.com/Research/index.htm. They claim to have a patent pending design for an approach involving what they call “compost silos”. Some of their findings and practices are:  Force aeration is essential to maintain adequate oxygen levels.  They utilize “Dynamic Bio-Filters” to prevent odor problems (they operate their systems indoors).  “We've captured heat at a rate of over 750 BTU's per hour, per cubic yard.”

142 Direct correspondence with Gaelen Brown, July 2012. 143 Direct correspondence with Gaelen Brown, July 2012.

Thermal Energy Storage Technologies  Technology Description: o Storage of thermal energy in various types of media, for use in conjunction with renewable heat sources such as solar hot water or heat pumps. Two broad categories are: . Sensible Heat Storage: Accomplished by simply changing the temperature of a substance without the occurrence of a change in phase or chemical reaction. . Phase Change Materials: Accomplished with the latent heat absorption and then release with a material undergoing a phase change. Storage may be implemented for periods ranging from several days up to several weeks or even many months (“seasonal thermal storage”). There are many different types of thermal storage technologies. These can be classified according to the following scheme: . Short Term/Small-Scale Thermal Energy Storage:  Short Term/Small-Scale Hot Water Thermal Energy Storage  Storage Heaters . Long Term/Large-Scale Thermal Energy Storage:  Long Term/Large-Scale Hot Water Thermal Energy Storage  Ice Storage Systems . Seasonal Thermal Energy Storage:  Seasonal - Hot Water Thermal Energy Storage (Seasonal SHWTES)  Aquifer Thermal Energy Storage (ATES),  Gravel-water thermal energy storage (GWTES)  Borehole thermal energy storage (BTES)  Cavern thermal energy storage (CTES) . Building Thermal Mass:  Sensible Building Thermal Mass  Seasonal Heat Storage with Phase Change Materials

 Technology Special Benefits: o Long-term thermal storage might greatly improve the ability of renewable heat sources for applications such as greenhouse heating. o Thermal storage materials are cheap, highly effective, and environmentally benign. o Well-constructed thermal storage units can last many decades with little maintenance. o It might be possible to construct large thermal storage units for farms in a very cost effective way, and affordable commercial units may be forthcoming.

 Overall Prospects for Successful Deployment: o Very good in general where the technology is well matched to the application. Prospects for much larger levels of storage, and for use of phase change materials, have improved due to recent R&D advances.

 Development Status: o Short term thermal storage is already widely implemented for solar hot water and heat pump systems. Interest in longer term thermal storage is gradually increasing. Large scale (seasonal) thermal storage is being rigorously developed in Europe. Phase change materials are now available.

 Barriers & Opportunities: o Water is Still Attractive for Many Sensible Heat Storage Applications: As mentioned above, this is accomplished by changing the temperature of a substance without the occurrence of a change in phase or chemical reaction. Water is still the sensible heat storage medium of choice for many applications: Water is readily available, non-toxic, easy to work with, and water handling equipment is also readily available. Water also has a very high heat capacity compared with most other materials, including so- called “thermally massive” building materials such as concrete. o Advantages of Solid Thermal Mass: Although water is attractive for many reasons, it also has some disadvantages, including the potential for leaks, expansion upon freezing, relatively low boiling point, and the fact that it cannot bear load. For these reasons heavy masonry materials such as cement are still often useful for “thermal mass” in buildings. And because these materials can be heated to very high temperatures they can actually store much more energy permit mass or volume for short term storage applications where high temperatures do not incur too large a heat loss penalty, such as with short term storage devices like “storage heaters”. o Small Storage Tanks: Many companies offer hot water tanks for solar hot water systems and other short term/small scale applications: Tanks with capacities of 40-120 gallons are typically available for insulated, pressurized residential applications such as domestic hot water and solar heating. A key distinction between these systems are whether or they use stainless steel or ceramic linings. The latter usually require an anode rod to avoid corrosion, but are less inexpensive. A typical example is the “thermomiser” tank for solar hot water systems144, which is included in some of the solar hot water system packages sold by the Vermont company Radiantec145. o Moderately Large Tanks (~1000 gallones): There are generally available in pressurized or unpressurized, insulated or uninsulated forms. Tanks with or without heat exchangers can be obtained. A crucial issue for any application is to avoid thermal bottlenecks by ensuring adequate heat exchanger size (surface area). A typical example of storage tanks in the 1000 gallon range are the custom tanks offered by SolarHot146. Some unpressurized hot water systems specifically designed for drainback solar hot water systems can also be found at Dr. Ben’s Blog147. o Temperature Stratification Issues: A key issue for hot water storage is achieving and exploiting temperature stratification. The advantage of stratification is that water much cooler than the delivered water temperature can be circulated through a solar hot water collector or heat pump to capture heat, which increases the efficiency of these devices. o Do-it-Yourself Systems: These are large hot water tanks can be constructed fairly straightforwardly by system owners at relatively low cost. An alternative to using a large tank is to daisy chain smaller tanks

144 http://www.altestore.com/mmsolar/others/Thermomiser_Tech_Sheet.pdf 145 http://www.radiantsolar.com 146 http://www.solarhotusa.com/products/large-solar-tank.html 147 http://www.solarhotwater-systems.com/fluid-handling-system/

together. This can be accomplished in such a way as to preserve strong temperature stratification by slowly transferring cooler fluid from the bottom each tank to the top of the next in the chain. Key issues for DIY systems are achieving adequate levels of insulation, especially in multiple tank systems. Some designers have worked out specific strategies and equipment to optimize DIY approaches, including incorporating water to air heat exchange directly into a large insulated box containing multiple storage tanks.148 o Storage Heaters: A storage heater is a type of electrical resistance heater which stores thermal energy in some kind of thermal mass, such as ceramic bricks or water, and releases the heat as required, sometimes with the assistance of a fan coil. These are most typically used to take advantage of low electricity rates at night, where such rates are offered, and are used widely in Europe. Some units incorporate heat pumps as well, or additional electric resistance air heating to boost output during the coldest periods of the year. One downside of these heaters is that it is usually difficult to completely shut down their release of heat, which can be problematic for their use in small spaces. They are also heavy, and can be expensive, especially given that they are not currently in wide use in the US. One possible (UK based) supplier is CNM149, which sells 1.7 kilowatt units for about $300. As sources of on- site generated renewable electricity become more affordable, however, these devices, especially if coupled with heat pumps to increase the efficiency of ambient heat capture, may well become useful for some space heating applications at farms in Vermont. o Long Term/Large-Scale Hot Water Thermal Energy Storage: Large systems for thermal storage on the order of several thousand gallons or larger can be constructed on-site, and there are now some companies that offer them. . Vermont has at least one such company today, Thermal Storage Solutions150, which is actively commercializing large thermal energy storage. The company, which is located in East Rygate Vermont, describes their storage units in the following way: “The storage module insulation is closed cell urethane foam that provides an R value of 80. A steel frame is embedded in the foam and this combination provides an extremely rigid structure. A completely waterproof coating on the inside of the store provides a barrier between the storage media and the insulation. The outside of the module also receives a waterproof coating for underground storage units.” These units are quite large, containing up to five thousands of gallons of water, and on the larger side are capable of storing at least several tens of therms of thermal energy (1 therm = 100,000 BTU). . Another example of a company pursuing development of this scale (in Ireland) is Scandavian Homes151. These units are large enough and insulated sufficiently to storage thermal energy for weeks or even several months. This can enable intermittent solar thermal collectors to provide a steady supply of heat in the winter time, and they provide some intrinsic efficiency advantages. For example, large amounts of storage helps to keep the storage temperature lower relative to what occurs using a smaller storage unit in the same application, which can lead to both lower losses and more efficient operation capture

148http://www.jc-solarhomes.com/multi_tank_heat_storage.htm. See also: http://www.youtube.com/watch?v=n90Y6Qwab_8&feature=related 149 http://www.cnmonline.co.uk/Storage-Heaters-c-109.html 150 See www.tss-ecx.com 151 http://www.scanhome.ie/research/solarseasonal.php

devices such as heat pumps and solar collectors (both of which become less efficient as storage temperatures rise). For home-scale applications, the use of one of these tanks (that is, one tank per home) is essentially a home-by-home form of seasonal thermal energy storage. It is important to distinguish this kind of approach from that discussed below, which are extremely large seasonal thermal energy storage systems that each serve tens of homes. The latter appear to be useful for carefully designed and regulated housing developments, or for very large consumers of thermal energy (including larger farms). The scale under consideration here is smaller, and is appropriate for single dwelling, or smaller operations such as a single greenhouse. There are several possibilities for how these storage units might be applied to greenhouse heating applications. Air source heat pumps might be used to capture thermal energy from the ambient (outside) air, or possibly even excess heat from the greenhouse during the day. Besides burning less fossil fuels for back up heat, the latter might have advantages such as being able to better maintain high levels of CO2 if CO2 enrichment is being used. Ground source heat might also be used, especially if the operation already has a suitable well. And solar hot water collectors might also be used. A large storage unit would assist all of these: For the heat pumps the advantage would mainly lie in efficiency gains. For the solar collector, the advantage would be both better efficiency but also the ability to store energy during the warm season for use later. If the tank is buried underground and the surface insulated, then the system would actually constitute a form of very large seasonal thermal storage, as the gradual heating of the surrounding soil would enable the tank to effective store more heat. When heat is required in the greenhouse, it could be delivered when needed to the greenhouse via fan coils. The use of fan-coils in a greenhouse system might strike some as likely not to be cost effective. But fan coil units have advanced substantially in recent years: A recent trade publication reports that many units today exhibit as much as a 90% reduction in energy consumption and states: “Today’s fan-coil units are very different from those of just three years ago — with major advances in their potential for energy-efficient air-conditioning and controllability, as our industry survey shows152.” o Ice Storage Systems: As mentioned above, an increasing number of utility companies in the US are promoting the installation of large chilled water storage systems for shifting air conditioning loads to off peak times153,154. Some companies offer highly optimized “ice slurry” making systems that can also be used for “cool storage”, that is, banks of ice for use in air conditioning during the day. They can also be used providing heat. For example, IDE Technologies155 offers a system that they say “can be utilized to provide environmentally clean and inexpensive heat for district heating. The application of the VIM as the first stage of the two-stage heat pump allows for extremely efficient fuel utilization of up to 220%. The VIM is capable of extracting heat at near freezing temperatures (0°C to 3°C) using virtually any naturally occurring water source.”

152http://www.modbs.co.uk/news/fullstory.php/aid/6443/__65279;State-of-the-art_fan- coil_units__tick_all_the_right_boxes.html 153http://www.austinenergy.com/energy%20efficiency/Programs/Rebates/Commercial/Commercial%20Energy/thermalE nergyStorage.htm 154 http://www.greentechmedia.com/articles/read/ice-energy-finds-profits-in-thermal-energy-storage/ 155 http://www.ide-thermalenergystorage.com/

o Seasonal Thermal Storage: Extensive R&D and large scale installation of Seasonal Thermal Storage (STS) has been taking place over the past few decades, primarily in Europe. Some useful resources describing these projects include a systematic review on the state-of-the-art by C. Sunliang156, along with the many references contained therein, and a website dedicated to “Solar District Heating157”, all of which will be drawn upon below. At least one company pursuing STS development can be found: ICAX158. This UK firm constructs “Interseasonal Heat Transfer” systems utilizing large inexpensive “asphalt solar collectors”, heat pumps, and underground “thermal banks” below buildings. The collectors charge the thermal bank during summer, and the heat pump transfers the heat to the building in winter. We will now discuss particular STS in some detail. These include: . Seasonal Hot Water Thermal Energy Storage (Seasonal SHWTES) . Aquifer Thermal Energy Storage (ATES) . Borehole thermal energy storage (BTES) . Gravel-water thermal energy storage (GWTES) . Cavern thermal energy storage (CTES) Two of these approaches are similar: The Aquifer Thermal Energy Storage (ATES) and Borehole thermal energy storage (BTES) both utilize the natural underground environment, and sometimes similar equipment such as heat pumps. They differ mainly in that ATES primarily involves (ground) water storage, while BTES primarily involves solids (rock, soil, etc). These differences might appear trivial, but in fact lead to strong performance and design distinctions. Gravel-water thermal energy storage (GWTES) also effectively combines both the sensible liquids and solids storage. It is therefore important to distinguish between these approaches. With the exception of Cavern Storage, all of these systems are actually being used by a number of communities in Europe presently. A list containing many of these can be found on the Solar District Heating Website159 (which also lists large solar district heating systems that do not utilize seasonal storage). The existence of these projects, and hence the experience gained, is largely attributable to the German Government program “Solarthermie – 2000 Part 3: Solar assisted district heating”. Overall, research on the performance of these systems has found that the systems performed as designed, except for certain fixable problems in the first generation systems, such as the occurrence of higher than optimal return temperatures from some of the heat delivery systems160. The cost of heat from these systems was still found to be fairly high relative to fossil fuels, at least for some of the approaches. That said, it is also clear that these technologies are not yet well refined, and efforts are underway to further lower costs. Moreover, at least one approach, the Gravel-water thermal energy storage (GWTES), appears to be intrinsically low cost, as it does not require drilling or a tank with

156 “STATE OF THE ART THERMAL ENERGY STORAGE SOLUTIONS FOR HIGH PERFORMANCE BUILDINGS,” C. Sunliang, Master’s Thesis, University of Jyväskylä, Department of Physics, Master’s Degree Programme in Renewable Energy, 2010: https://jyx.jyu.fi/dspace/bitstream/handle/123456789/24448/URN_NBN_fi_jyu-201006172096.pdf?sequence=5 157 http://www.solar-district-heating.eu/SDH.aspx 158 http://www.icax.co.uk/ 159 http://www.solar-district-heating.eu/SDH/LargeScaleSolarHeatingPlants.aspx 160 D. Bauer, R. Marx, J. Nußbicker-Lux, F. Ochs, W. Heidemann, H. Müller-Steinhagen, “German central solar heating plants with seasonal heat storage,” Solar Energy, Vol. 84, pp. 612-623, 2010: http://www.sciencedirect.com/science/article/pii/S0038092X09001224. Open version at: http://www.itw.uni-stuttgart.de/abteilungen/rationelleEnergie/englisch/pdfdateien/04-02%20.pdf

structural support. Each approach has its advantages and disadvantages, however, and it appears that all may eventually find applications. It should be stressed that these are very large storage systems – in the thousands or tens of thousands of cubic meters, and also that they have been built in conjunction with very well designed “district heating systems” that have very predictable and controllable loads. Nonetheless, these technologies may be applicable to farms in Vermont, especially greenhouse operations or others that require substantial heat (including process heat) for several reasons: . The number of apartments or houses served by these systems tended to be in the few tens, not hundreds or thousands. . The performance of devices such as heat pumps, heat exchangers, etc, has been steadily improving, and should help enable a wider range of viable system scales and designs. . Many farm operations do actually require a fairly predictable (if not constant) thermal energy supplies. It should also be noted that these systems involve many more components that are discussed here, including “buffer storage” (smaller hot water tanks), and a variety of heat delivery and capture systems. And finally, experience to date shows that careful design of these systems is essential to success, in large part because the efficiency of many components is temperature dependent. . Seasonal - Hot Water Thermal Energy Storage (Seasonal SHWTES): This approach uses large volumes of water (thousands of cubic meters) as the thermal storage material which are contained in a constructed tank, which can be above ground, buried, or partially buried. Thermal insulation is provided at least on the roof and the side walls. Steel liners (or possibly some other vapor barrier in the future) appear to be needed to avoid the heat losses due to the vapor diffusion through the walls. Some of these systems appear to have encountered some of the greatest problems with heat loss and overly high temperatures (issues that are linked to one another), and also high costs. The solution to these issues appears to be better design vis a vis the demand for heat, and lowering cost with new approaches to tank construction, for example avoiding large amounts of cement and steel. . Aquifer Thermal Energy Storage (ATES): This approach utilizes natural aquifer layers (if one is available with the right properties), which avoids the tank construction expenses of SHWTES. In this approach, groundwater is extracted from a well or set of wells and then heated or cooled within the buildings or with heat sources such as solar hot collectors or a CHP system before being reinjected back into another well group. The system is similar to a ground source heat pump, except that the aquifier can be “charged” with heat during the summer, or whenever extra heat is available. (In fact a heat pump is one means that can be utilized extract heat from the aquifer during winter). Charging of the aquifier (raising its temperature) helps to increase the coefficient of performance (COP), which reduces the amount of electricity used. SunLiang writes that “Many applications have proved that ATES performs quite good and viable”, and that another researcher (Anderson161) “showed that ATES can conserve 90-95% of energy in direct heating and cooling, 80-85% in heat pump assisted heating and cooling, 60-75% in heat pump assisted heating system, 90-95% in industrial process cooling, and 90-95% in district cooling.

161 O. Andersson, “ATES utilization in Sweden-An overview,” Proceedings of MEGASTOCK’97 7th International Conference on Thermal Energy Storage, Vol. 2, pp. 925-930, 1997.

. Gravel-water thermal energy storage (GWTES): In this approach a gravel filled pit is used to store heat. Usually the top is insulated, and possibly the sides. Little if any structural support is required. The cost of the pit is therefore reduced, but the pit must be approximately 50% larger than an SHWTES system of the same capacity to offset the lower heat capacity of the gravel relative to water. A heat transfer fluid (such as water or air) is circulated through those the loose granules to exchange thermal energy. Analysis shows that each square meter solar collector area requires 300 to 500 kilograms of rocks as the storage material. SunLiang concluded that “with a thorough life cycle and economical assessment, the packed bed storage solution can be considered as one of the choices for the thermal energy storage in high performance buildings.” . Borehole thermal energy storage (BTES): This approach utilizes solid earth (rock, sand, gravel, soil) to store thermal energy. Vertical bore holes are drilled, and “borehole heat exchangers” are inserted in the ground so that heat can be exchanged between the storage system and the ground. It appears that these systems are quite distinct from the others in that these require up to five years before the temperature of the storage increases sufficiently, and it may be necessary to utilize a heat pump, instead of simply radiators, to ensure that delivery temperatures are sufficient, especially during the first years. . Cavern thermal energy storage (CTES): This approach requires the construction of large underground water reservoirs, such as steel lined chambers in bedrock, to serve as the thermal energy system. One advantage of this approach is that if the reservoir is located in solid rock, the walls provide very good structural support, even if the water is superheated, therefore allowing very high thermal capacities for high temperature systems. Such storage could also be located very deep (~400 meters), and can therefore be extremely large. The costs of constructing cavern storage have apparently prevented it from being utilized. A thesis by A.R. Tanner in 2003 however concluded that this approach could be cost effective for use in conjunction with large Concentrating Solar Power Plants162. o Building Thermal Mass: Thermal mass in buildings, that is, the incorporation of materials that have the ability to rapidly absorb large amounts of heat from the surroundings with little change in temperature, can be very helpful for absorbing excess heat during the day, and releasing it at night when needed. Incorporating adequate amounts of thermal mass, including achieving adequate surface area, thickness, and placement, is already a widely used part of Passive Solar Design, and could be very helpful in the efficient utilization of emerging heat sources such as heat from CHP systems. The placement of thermal mass in greenhouses is also a useful and widely practiced technique. We next look at the use of both sensible thermal mass and phase change materials. The former are already commonly used, but design rules for optimizing the use of sensible thermal mass are not that well understood even today by many building designers in the US. The use of phase change materials involves many of the same ideas, but can potentially greatly reduce the amount of thermal mass material needed, and also enable existing buildings to be more easily retrofit with additional thermal mass.

162 “Application of Underground Thermal Energy Storage for Solar Thermal Power Generation in New South Wales.” A. R. Tanner, School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, November 2003.

. Sensible Building Thermal Mass: Extensive research took place in the US during the late 70’s and early 80’s on Passive Solar Design (PSD) principles in both the private sector and at National Laboratories. Out of this research came insight and rules of thumb about thermal mass sizing and placement in passive solar buildings, and in buildings in general. A few of these are summarized next. A more complete summary, along with other PSD guidelines, can be found online163.  For a thermal mass surface that is exposed only on one side, only the first four inches are active on a diurnal (daily) basis. Increasing the thickness beyond 4 inches might still be helpful for adding thermal storage that contributes on longer time scales, but will not improve diurnal dynamics greatly. It may therefore be more cost effective to increase the area of thermal mass as opposed to increasing the thickness beyond 4 inches.  For a passive solar dwelling a south-facing window area approaching 12% of the floor area (full passive solar), the thermal mass needs to have a surface area between 6-9 times the area of the south-facing windows. This can be a difficult level of surface area to achieve while maintaining sufficient thickness as well (and is one of the reasons phase change materials are so attractive).  Thermal mass is most effective if it is placed in locations where it will receive direct sunlight at times, or in line-of-sight of other directly lit mass. Thermal mass placed elsewhere will be less effective. This is due to the fact that up to 2/3 or heat transfer in a passive solar structure is via infrared radiation. . Beyond these simple rules, there exist more advanced techniques that can be utilized by designers. For example, a dated but still useful guide by the New Mexico Solar Energy Association describes the design of “Thermal Storage Walls.164” . Diurnal Heat Capacity (DHC): This powerful but not well known technique was developed by Los Alamos National Laboratory scientists in the 1980s165. In this approach, instead of looking at the heat capacity of the material in bulk, these researchers calculated what the effective heat capacity of different materials would be in the context of the 24 hour daily heating and cooling cycle, and as a function of surface area. In other words, they looked at the dynamic response of the thermal mass. This allowed the true effective heat capacity of different materials in buildings to be determined, leading to better prediction of and control of temperature swings. (This research is where the 4 inch rule above derives from.) The researcher also provided formulas which can be used to calculate the

total DHC of a building, the estimated temperature swing given a certain amount of solar heat QS entering the structure, and a recommended minimum DHC for a structure. . Phase Change Materials (PCMs): As seen above, large volumes of sensible thermal mass (to achieve adequate thickness and area) are needed for effective passive solar design, or simply to create a building capable of acting more as a “thermal battery.” And as also mentioned, thermal mass can be

163 http://www.nmsea.org/Education/Homeowners/Detailed_Passive_Solar_Guidelines.php 164 http://www.scribd.com/doc/47200868/THERMAL-STORAGE-WALL-DESIGN-MANUAL 165 This and other work by Balcomb et al. can be found in the book “Passive Solar Buildings”, by D. Balcomb, ISBN 0-262- 02341-5, 1992. This can also be accessed online at: http://books.google.com/books/about/Passive_Solar_Buildings.html?id=L8uAq-7YJooC

69 useful for storing heat for a number of applications, such as in greenhouses, or in large or seasonal thermal energy storage systems. The difficulties of achieving optimal thermal mass in buildings has led many researchers over the years to consider the use of PCMs, which can utilize the latent heat associated with a material’s phase change to absorb or release much larger amounts of heat compared with sensible thermal mass materials. Today, a number of commercial PCM products are finally available, mostly in Europe, either in the form of phase change materials directly, or the form of PCM integrated products (such as PCM integrated gypsum board, concrete, plasters, etc). These are little known or used in the US but nonetheless have promise as a means for improving (stabilizing) the thermal performance of buildings, and also for achieving large heat storage capacities in smaller spaces and at lower temperatures. Their applications can in fact cover almost every part of a building’s construction, including walls, floors, ceilings, roof, windows and even special sunshading systems. The next paragraphs discuss some of the background on PCMs, followed by a list is given of some available PCM products. One of the distinction that is useful to make when discussing PCMs is macro-encapsulation versus micro-encapsulation: Early attempts at macro-encapsulation, that is, placing a PCM in large volume containments largely failed for various reasons, for example, low thermal conductivity. Today, most PCMs are micro-encapsulated, and can be incorporated into construction materials. Theoretically, a PCM has a particular phase change temperature, but in practice the phase change process happens over a certain temperature range. For example, the PCM in Dupont‘s product “Energain” is paraffin wax that is micro-encapsulated within a copolymer. According to SunLiang, as the temperature of this PCM is raised, it begins melting at about 56oF. But when fully melted, if the temperature is now lowered, it will begin solidifying (freezing) at about 74oF. The temperature which is generally identified as the phase transition temperature is the point where the melting process is maximum, which is about 72oF in this case. There are many requirements that potential PCM products have to satisfy in real applications, which according to SunLiang are:  Thermal requirements:  Proper phase change temperature  High latent heat storage capacity during phase change process  Desirable heat transfer characteristics (eg. good thermal conductivity)  Physical requirements:  Small volume change during phase change process  Low vapor pressure  Kinetic requirements:  No or limited super-cooling  Sufficient crystallization rate  Chemical requirements:  Long term chemical stability  Compatible with the storage container or integrated thermal mass  No/low toxicity

 No/low fire risk  Economical requirements:  Plenty of resource  Available for application  Cost effective for large production PCMs can be classified into solid-liquid, liquid-gas and solid-solid. Among these types, solid-solid and liquid-gas PCMs are not generally suitable for thermal storage in buildings for various reasons, leaving only solid-liquid PCMs. According to SunLiang, there are three primary types of solid-liquid PCMs with promising characteristics. These are: Organic-PCMs: These have many good characteristics except are flammable, have low thermal conductivity, and can be expensive. Encapsulation helps solve these problems.  Paraffins  Non-Paraffins: Fatty acids, glycols, esters Inorganic-PCMs:  Salt Hydrates: These also have good characteristics, and potential separation issues can be solved with encapsulation, and interruption issues by adding small amount of solvent.  Metallics: Generally too expensive. Eutectic-PCMs: These are mixtures of chemical compounds or elements in particular ratios that solidify at a lower temperature than any other ratio of the same ingredients. Some examples are (omitting the exact ratios): Capric-lauric acid, Mistiric acid + Capric acid, and CaCl ⋅6H O+ MgCl ⋅6H O. These can also be classified as organic-organic, inorganic-inorganic, and inorganic-organic Micro-encapsulating PCMs inside polymers or membranes effectively mitigates many potential problems, and so most products on the market today take this approach. Once encapsulated properly PCM products may be “immersed” into building materials, or supplied in products that are meant to be “attached.” For example, the Micronal PCM product mentioned below can be conveniently immersed with concrete, plaster or other building structure materials, whereas Dupont‘s “Energain” is an attached product. For economic reasons, the “attachment” approach is presently more widely utilized than the “immersion” approach. Suppliers: The following is a list of PCM Suppliers (updated from SunLiang)  DuPont - Energain: www.energain.dupont.com  Entropy Solutions, Inc.- PureTemp: http://www.puretemp.com/  Climator Sweden AB – ClimSel: www.climator.com  PCM Energy P. Ltd- PCM Latest: www.pcmenergy.com  PCM Products Ltd – PlusICE PCM: http://www.pcmproducts.net  Rubitherm Technologies GmbH - RUBITHERM: http://www.rubitherm.com/english/index.htm  BASF SE – Micronal: www.micronal.de  Dörken GmbH & Co. KG - DELTA : http://www.doerken.de/bvf-en/produkte/pcm/index.php Seasonal Heat Storage with Phase Change Materials: Some of the problems described by SunLiang and others with the German sensible seasonal storage systems to date include incorrect estimation of heat loads which resulted in undesirably high return temperatures to and then of the storage medium, poor insulation of the storage envelopes, inconsistencies between heat sources and the

71 storage system, and size problems with the storage volumes. The use of PCMs for seasonal storage may mitigate some of these problems by enabling a reduction of storage size and/or reducing and stabilizing storage temperatures and desirable heat. Very little R&D has focused on this idea yet, however, so it remains untested. But it seems reasonable, for example, that the use of “gravel” material of some kind that incorporates encapsulated PCMs might function well, especially if the PCMs are tuned to the proper temperature. Such tuning is possible, for example, by varying the length of carbon chains in paraffin waxes. In any case, the success of PCMs to date suggests that the potential uses for PCMs in other applications is great.

Thermal Energy Utilization  Technology Description: o A variety of renewable energy technologies discussed in this report produce thermal energy, either as a primary output, or in addition to electricity or fuel production. This section discusses possibilities for the utilization of that energy, including general issues around heat recovery and use, various types of engines, absorption chillers, and greenhouse heating strategies. Possible sources of thermal energy at farms include: . Recovered heat from pyrolysis reactors used for bio-oil and biochar production. . Combustion of vapors, biochar, bio-oil, or biogas from pyrolysis reactors. . Combustion of syngas from gasification reactors. . Combustion of grass pellets, briquettes, or bales. . Combustion of biogas from anaerobic digesters. . Air source heat pumps. . Ground source heat pumps (geothermal heat pumps). . Solar hot water collectors. . Thermal energy from compost (aerobic digestion). . Thermal energy recovered with Refrigeration Heat Recovery units (RHRs). Each of these many sources is unique in terms of cost, availability, temperature, and delivery form (via combustion of fuel, hot air, or hot water). Each type of end use, such as use for space heating, process heat, etc, is also different in terms of when and how much heat is needed and at what temperature, and in what form it is needed. The key to effective usage is to match up the sources and end uses, that is, to seek “synergies” between the sources and uses. The following is a general list of possible thermal energy uses for farms, including some less commonly utilized options: . Space heating . Domestic hot water . Process heat: Drying crops, food, firewood . Cultivation of algae . Anaerobic digestion (Mesophilic) . Aquaculture . Heating greenhouses . Mushroom cultivation . Animal pen heating . Soil and mulch sterilization . Composting . Dehumidification . Refrigeration (absorption chillers) . Cooling . Pellet manufacturing . Ice melting . Electricity generation

 Technology Special Benefits: o Effective use of “waste heat” can improve the overall economics of renewable energy technologies, reduce costs and emissions, and reduce the exposure of farms to energy price volatility. o Local production of food in winter using renewable heat could greatly reduce the embodied energy and greenhouse gas emissions of Vermont’s food supply.

 Overall Prospects for Successful Deployment: o Prospects are good but very source and application dependent.

 Development Status: o Some effective use of waste heat from anaerobic digesters is occurring. Heating with anaerobic decomposition of compost is just beginning in Vermont. Heating of greenhouses with biomass is moderately well developed already. Use of solar hot water for greenhouses is undergoing initial trials. Little use of heat pumps is presently occurring in Vermont. Little or no use of other new heat driven technologies (absorption chillers, other engines) is occurring.

 Barriers & Opportunities: o Technology Matching Considerations: A key consideration in matching thermal energy sources and uses is the method by which the heat will be delivered. There are several basic categories of methods: . Direct delivery of combustion heat by radiation and conduction by placing a combustion device in a structure. . Indirect delivery of heated air by forced air convection. . Indirect delivery of heated water by hydronic heat (fan coils, radiators, base board, radiant flooring). . Immediate co-location of hot air producing sources with uses (e.g. compost in a greenhouse). . Heat Recovery Systems (air-to-water heat exchangers) + indirect delivery of hot water.

Some general technical issues with heat recovery and delivery are: . Surface Area: Delivery of low-grade (< 200oF) hot water is generally do-able, but requires adequate surface area. For example, base board radiators may be insufficient, necessitating the use of devices such as fan-coils or other air handlers. . Recovery of Low-Grade Heat: It will often not be economical to utilize a heat recovery system based on air-to-water heat exchangers for recovery of low-grade hot air sources (< 200oF), due to the cost of such equipment and operating costs relative to the amount of heat captured. In these cases the best option is often to co-locate the use with the source (e.g. locating hot refrigeration coils inside the structure to be heated, composting facilities inside a greenhouse, etc). . Recovery of High-Grade Heat: For high-grade hot air sources (> 200oF), such as the hot flue gasses of a generator, the use of heat recovery systems based on air-to-water heat exchangers often does make sense, and these systems can also be easily coupled with thermal energy storage units. Here careful attention must be paid not to extract too much heat so as to cause problems with exhaust systems and back pressure on the source. . Temperature Differences of Sources: Not all biogas-fueled electricity generation methods are equivalent in terms of the temperatures they provide waste heat at.

. Design Requirements: In general, heat recovery systems used in conjunction with a given installation need to specifically designed for that installation to both protect the generator as well as to minimize heat loss. More specifically, the design should ensure that the engine will not overheat when the heat load (say a hot water tank) cannot absorb any more heat. This usually requires that the engine have some kind of radiator system (efficient heat dump) to dump the extra heat. Careful design should be employed to minimize the amount of heat that needs to be dumped, or to possibly utilize this heat in some way (if economical). o Summary of Opportunities: Each of these is discussed in more detail below. . Co-location Synergies: Heating structures with extra thermal energy from anaerobic digestion is already successful, and could be used to increase overall agricultural production through integration of operations, such as co-location of greenhouses with such facilities. . Adsorption chillers: These are devices that utilize a heat source to achieve cooling for refrigeration or air conditioning. These chillers may be economical for farms depending on the cost of the biomass heat in a given situation. An intriguing possibility for adsorption chillers is the potential for dual use of the heat. . Desiccant dehumidifiers: These utilize thermal sources to achieve dehumidification, and can achieve very low humidity levels, and also can operate well at fairly low temperatures. . Thermally Driven Engines: Steam engines, stirling engines, and hot air engines, all may offer new and useful ways to generate mechanical and/or electricity in the future from heat. . Greenhouse Heating Strategies: Operating greenhouses in winter time can be very fossil fuel intensive, but heating with biomass energy is viable, and large thermal energy storage offers new possibilities for utilizing solar hot water collectors or heat pumps as a means for reducing or replacing fossil fuels in greenhouse heating. These renewable heat greenhouse heating approaches can also be combined with the low energy growing techniques, such as the use of row covers inside a greenhouses (as championed by grower Eliot Coleman). . Thermal Energy from Aerobic Digestion of Compost: Heating buildings with aerobic digestion (e.g. compost) is relatively new in Vermont, but initial experiments such prospects are good. See the Chapter on Heating with Compost for more information on this topic. . Heating with Biogas/Bio-oil/Syngas: Heating with these fuels is promising. See chapter on Utilization of Biochar/Biogas/Bio-oil/Syngas for more information. . Aquaponics: This approach now offers a means to grow both plants and fish in the same space previously required for just the plants, and the fish tanks provide thermal mass and a heat storage medium ideally suited to low temperature heat sources such as solar hot water collectors and heat pumps. o Thermally Driven Systems: There are a number of thermally driven systems, applicable to farms today or possibly in the future, for applications including generating electricity, cooling water, heating, and dehumidifying air. These sources include heat obtained from heat recovery from other systems and/or from combustion of biomass, where the latter includes the combustion of raw biomass, densified biomass such as pellets, biochar, biogas, bio-oil, or syngas. The thermally driven systems include: . Absorption Chillers . Desiccant Dehumidifiers . Steam or Hot Water Heating Loops

. Steam Turbines & Engines . Stirling Engines . Hot Air Turbines Combinations are possible: For example, absorption chillers and desiccant dehumidifiers have been implemented successfully in conjunction with CHP systems, and can function effectively together166: The dehumidifier action reduces the latent heat load on absorption chiller. o Thermally Driven Systems in Detail: . Absorption Chillers: These are devices that utilize a specially designed refrigerant cycle involving the dissolving of a refrigerant in another fluid to achieve cooling for refrigeration or air conditioning. These chillers, which include commonly used propane fueled refrigerators, are widely used in applications where electricity supplies are inadequate to power compressor based refrigeration systems, although they are not generally used elsewhere for cost reasons. Adsorption chillers can be driven by biomass combustion heat, however, and can be economical for farms depending on the cost of the biomass heat in a given situation.  When considering these chillers, however, careful attention must be paid to the temperature limits and heat rate capabilities of these chillers relative to the application. For example, one source states167:”Absorption chillers based on lithium bromide and water achieve cold water temperatures of 3°C [37oF] while the minimum temperature of the heat source needs to be 80°C [176 oF]. In order to achieve lower temperatures with absorption chillers the application of ammonia as refrigerant and water as solvent and higher temperatures of the heat source are required. Other technologies such as adsorption chillers or diffusion chillers are also suitable for cooling based on heat.”  A temperature of 37oF would be just marginally low enough for milk chilling, and possibly not in practice, depending on the heat rates required and the economics of achieving those rates.  An intriguing possibility for adsorption chillers is the potential for dual use of the heat. The Sourcebook entitled “Biomethane from Dairy Waste: A Sourcebook for the Production and Use of Renewable Natural Gas in California168” states that “Double-effect chillers, producing hot and cold water simultaneously, are available for applications over 30 tons and could be coupled with a heated digester (1 ton cooling = 12,000 Btu/h). Corrosion-resistant models are not available; therefore, biogas must be treated for water and H S removal before it can be used to fuel 2 absorption or adsorption chillers.”  Companies offering Absorption Chillers include: www.yazakienergy.com, www.broadusa.com, www.commercial.carrier.com, www.dunham-bush.com, www.robur.com, www.trane.com. . Desiccant Dehumidifiers: These devices use an absorbing material to absorb water from an incoming air stream. The absorbing material is then physically moved into a separate exhaust stream where heat is then utilized to re-evaporate the water. These dehumidifiers are commonly used in industry, can achieve very low humidity levels, and can operate well are fairly low temperatures (where other types of dehumidifiers are often less effective).

166 http://www.southeastcleanenergy.org/resources/reports/DDAC%20Final%20Report.pdf 167 http://www.bios-bioenergy.at/en/cooling-technologies-supply.html 168 http://www.suscon.org/cowpower/biomethanesourcebook/chapter_5.pdf

 Companies offering Desiccant include: www.bry-air.com, www.munters.us, http://ats.stulz.com, www.kathabar.com . Steam or Hot Water Heating Loops: Hydronic (radiant) heating systems using underfloor PEX tubing is a well-developed technology that is extremely compatible with many potential sources of both low-grade and high-grade heat. Radiant floors, as they are called, can be used for heating greenhouses, drying crops, and heating homes and barns. These systems provide good control, and deliver heat where it is really needed.  One key attribute of insulated radiant floors that utilize large amounts of thermal mass (via large amounts of masonry material, such as cement or even earth), is that they can store large amounts of thermal energy with little change in temperature. Related to this is the fact that the stored thermal energy only conducts and radiates slowly out of the thermal mass. For these reasons, radiant floors make an ideal thermal storage medium to store large amounts of heat, and heat that may not be delivered very steadily. They are also ideal for storing heat from a variety of different sources. For example, a large radiant floor system might utilize a combination of waste heat from a generator, heat from a biomass boiler, and solar heat, all at once. . Steam Turbines & Engines: Steam engines saw extensive use around 1900, but then largely fell out of use for a number of reasons, including excessive pollution, maintenance costs, labor intensive operation, low power/weight ratio, and low overall thermal efficiency169. Today, a movement exists to revive use of steam engines, and various companies are selling or trying to commercialize steam engines today, some with direct interest in utilizing biomass heat. Some of these groups and companies are:  Energiprojekt: Sells 1 megawatt scale steam power plants: http://www.energiprojekt.com/?home  Reliable Steam: Sells small steam engines: http://www.reliablesteam.com/RSE/RSEboilers.html  Green Steam Engines: Sells small steam engines: http://www.greensteamengine.com/  A group attempting to develop an engine with biomass (and other) heat sources in mind: http://opensourceecology.org/wiki/Steam_engine  Cyclone Power: Offers a “Waste Heat Engine” that would be compatible with biomass combustion heat and grid-tied power generation170. . Stirling Engines: Cornell University’s Jerry Cherney has suggested that pellet fueled “stirling engines” (which he sometimes spells as “sterling” here – both terms appear in the literature) were about to emerge, which he described as follows 171: “Combined heat and power (CHP) in the near future? Robert Stirling, a Scottish priest who came up with the idea, patented the Sterling engine in 1816 and developed various uses of the idea together with his brother James Stirling, who was an engineer. It is run by a heat differential instead of an explosion (as in an internal combustion engine), and can be used to generate electricity. After its invention it was shortly made almost obsolete by the combustion engine, the Sterling engine was a nightmare to put into commercial production. Space-

169 http://en.wikipedia.org/wiki/Advanced_steam_technology 170 http://cyclonepower.com/works.html 171 http://www.extension.umn.edu/forages/pdfs/grass_for_bioheat_on_farms_21309.pdf

age materials and technology have allowed the Sterling engine to resurface. Companies around the world are developing Sterling engines (which only work on a small scale) for potential use with heat generating devices. They are capable of generating enough electricity to power an average residential household, and basically generate the electricity for free. Austria is currently field testing Sterling engines attached to one of their wood pellet boilers, which may be available commercially in 2009. This technology should eventually enable most pellet burning appliances to have the ability to generate enough electricity to run an average home.” A review of what can be found on Stirling Engines in 2012 seems to indicate a mixed outlook:  Stirling engines have not yet been commercialized, unfortunately, and:  The “Biomethane from Dairy Waste: A Sourcebook for the Production and Use of Renewable Natural Gas in California172” states that “Modern Stirling engines produce high power and efficiency levels by using high pressure helium or hydrogen as the working gas. However, these engines have not achieved widespread use because of their heavy weight and high production costs.”  On the other hand, there are active development activities occurring, including specifically for use of biomass (specifically, pellets): . A pellet fueled stirling engine CHP system is still in under active development in Austria by the company okoFEN173. . An Italian group, Fondazione Bruno Kessler (FBK), is also pursuing a pellet based system, and in 2011 published a detailed scientific paper analyzing their design174. Some additional information is provided on their site175. With respect to the status of this, the paper states “The full system is actually under integration for the test phase and not yet tested. The first tests on the single components have confirmed preliminary results on the Stirling engine with respect to the tolerances, pressurization, and proper integration of the electrical generator- driven control system. The pellet boiler has been tested separately, confirming an overall thermal efficiency of 90%.” . At least one fairly carefully done trial of a 3 kw biomass-fired stirling engine, and a test of 50 kw engine, along with some cost analysis, was conducted in the late 1990s through 2004 at Joanneum Research in Austria by E. Podesser et. al.176,177. This work seems to suggest that reasonable electricity production costs can be achievable if the stirling engine power is sized to about 5% of the furnaces thermal power. . Very recently, Farm Show Magazine has reported the development of “a revolutionary new "external combustion" Stirling engine that gets 30 to 50% better fuel efficiency than similar

172 http://www.suscon.org/cowpower/biomethanesourcebook/chapter_5.pdf 173 http://www.okofen-e.com/en/okofen-e.html 174 Development of a pellet boiler with Stirling engine for m-CHP domestic application, Luigi Crema, Fabrizio Alberti, Alberto Bertaso and Alessandro Bozzoli, Crema et al. Energy, Sustainability and Society 2011: http://www.energsustainsoc.com/content/pdf/2192-0567-1-5.pdf 175 http://reet.fbk.eu/en/node/156 176 http://bpc.fe.uni-lj.si/BPC_old_06/bpc2005/images/CD/Paper/RES/Podesser_BPC2005_PPT.pdf 177 http://wbc-inco.net/attach/VBPC-RES.D.4.pdf

sized conventional "internal combustion" engines. 178“ The magazine also reports that the John Deere and another agricultural equipment manufacturer, Valmont Industries, are both interested in the design. Stirling engines are an old, well understood and potentially practical technology. For example, they have been successfully tested in solar energy applications, in fossil fuel and biomass fired applications, and even in submarines179. For reasons that have to do with the physics of these devices, they are also intrinsically suited to smaller applications (farm-scale, as opposed to large power plant scale). The feasibility issues therefore hinge primarily on coupling issues between the heat source and the stirling engine, and overall cost effectiveness of the system. Despite the activity mentioned above, there has been little work on stirling engines probably because as generators, stirling engines are not ultra-efficient unless the temperature difference driving them is extremely high, and the complete dominance of internal combustion engines in small-scale liquid fueled generators today would appear to confirm that stirling engines are not competitive with ICEs for fossil fueled generators. The potential advantage of stirling engines lies instead in being able to provide mechanical drive to a generator from simply a heat source, that is, without explosions, and without bringing the fuel into the engine. The latter is not a great advantage when utilizing higher refined and clean fossil fuels. But not having to bring the fuel in contact with engine parts might be a strong advantage when it comes to using biomass fuels. Stirling engines may also have advantages in terms of operating and maintenance costs unrelated to fuel quality. . Hot Air Turbines: This is a new kind of thermally driven electricity generation approach that can utilize heat from biogas combustion to generate electricity without the use of either a reciprocating engine or a steam cycle. More specifically, it is a turbine similar to a gas-fired turbine, but driven instead by hot air. This turbine appears to be possible, but it is not clear if it is actually commercially available.  One of the first AGT, a 500 kw generator, was installed by Heat Transfer International in 2009 at Sietsema Farm Feeds180. HTI partnered with Michigan-based turbine manufacturer Williams International to develop the turbine181. . Aquaponics: This is a relatively new approach to combining aquaculture (fish cultivation) with hydroponic plant cultivation has emerged recently: The approach involves placing plant cultivation directly over fish tanks with the plant roots submerged into the tanks. The approach seems to work well, and offers a unique opportunity to save energy (as well as improve the cultivation of both fish and plants):  The fish tanks contribute large amounts of thermal energy storage to the greenhouses in which the systems are housed. Low temperature heat sources such as heat pumps and solar hot water systems can be applied very effectively to the fish tanks.

178 http://www.farmshow.com/view_articles.php?a_id=1094 179 http://www.kockums.se/en/products-services/submarines/stirling-aip-system/ 180 http://biomassmagazine.com/articles/3024/hti-installs-biomass-powered-turbine-at-michigan-feed-mill/ 181 http://biomassmagazine.com/articles/3450/gasification-guru/

 The square footage that must be heated to support the cultivation is greatly reduced (~50%) compared to cultivating plants and fish separately. The heat supplied to the fish tanks also directly provides “root heat” to the plants. o Renewable Heating Strategies for Greenhouses: A wide range of new technologies and approaches are emerging that should enable much greater energy efficiency and use of renewable energy in greenhouse operation. Greenhouses are an effective way to produce warmer and better protected environments for growing, but by their very nature they must be designed to allow the majority of incident solar energy to pass inside, which usually enables heat to escape easily. This can be mitigated to some extent using coverings with higher R-values, but with diminishing cost returns. Greenhouses must also well ventilated or dehumidified to prevent the buildup of moisture. This places severe constraints on how well insulated greenhouses can be, especially when economics are factored in. For this reasons, greenhouses have been traditionally utilized mostly from late spring to early fall, that is, for season extension, with little or no supplemental heat. Today, however, interest in and demand for locally grown produce is increasing rapidly, and many greenhouses are now operated substantially during colder weather, and even all year long. For example, a survey of 51 Vermont greenhouse growers by the UVM Agricultural Extension found that 16% are heated all year round, while many others start early and end late in the year182. The same study found that the use of fossil fuels for this greenhouse heating was high: “We have calculated that the state uses 296,000 gallons of propane and 59,000 gallons of fuel oil each year to heat greenhouses. This equates to a cost of $768,000/yr and 2,458 tons CO2/yr - roughly equivalent to 6.2 million automobile miles.”All of this suggests that greenhouse heating should be a major focus of efforts to reduce energy consumption and/or use of renewable energy. . Low Energy Growing Techniques: Grower Eliot Coleman has pioneered the use of “row covers183” inside greenhouses, along with careful planting strategies (timings). These are described in Coleman’s 2009 book “The Winter Harvest Handbook: Year Round Vegetable Production Using Deep Organic Techniques and Unheated Greenhouses”, ISBN-10: 1603580816 (available in electronic form as well as hard copy).  According to Coleman, the row cover approach he (re)pioneered was first proposed in the US by University of Kentucky Horticulturist E.M. Emmert in the 1950s. Today, these covers usually consistent of a protective, translucent layer over plants during the coldest months, ideally at least 85% translucent, that is also permeable to air and moisture. These are suspended just over the plants a few inches. Coleman suspends these covers with wire wickets, spacing them about every 4 foot along the long length of the rows.  In essence, the row covers provide a warmer microclimate that enables plants to make much better use of available sunlight, the latter being more abundant at Maine’s (and Vermont’s) latitude than many growers might otherwise assume based on the slow rate of plant growth that occurs without row covers. The techniques also enable a greenhouse to function as a cold

182 BIOMASS FURNACES FOR GREENHOUSE VEGETABLE GROWERS. Report to the High Meadows Fund. May 31, 2010. Submitted by: Chris Callahan, Callahan Engineering and Vern Grubinger, University of Vermont Extension: http://www.uvm.edu/vtvegandberry/Pubs/Greenhouse_Furnace_Project_Report.pdf 183 Translucent coverings about 1 foot above the soil, supported by wire wickets.

storage unit, making fresh produce available throughout more or all of the year. As Coleman puts it, the harvest season is shifted as well as the growing season.  These techniques are now being increasingly used in Vermont. One prominent grower, Pete Johnson of Pete’s Greens, has stated that “yes we use them, they are a key part of unheated winter production in this climate. They are standard fare in greenhouse and outdoor production these days.184”  Vermont is generally regarded by many as a cold state where the growing season is short, and it is only in recent years that a significant number of growers have begun growing vegetable crops all year round. But, as Eliot Coleman likes to stress for Maine as well, while Vermont certainly does have long cold winters (as the average minimum temperatures and HDD above attest) Vermont lies mainly between the 43rd and 45th parallels, the same as southern France, where vegetables have been grow year round for centuries. Thus, while Vermont is colder, Vermont and Southern France share the same day lengths, that is, the same available sunlight for photosynthesis aside from cloud cover considerations. Coleman reports that the sunlight available in these months in Maine is more than adequate for maintaining plants that are already at or approaching maturity, that is, that have well developed root systems, and of producing significant additional growth if adequate temperatures are maintained around the plants. And he also finds that these temperatures can be surprising low for many plants (a list appears below).  The fact that the plants need to be at or approaching maturity means that they need to be planted at the right time. In particular, winter crops need to roughly reach maturity by the time the length of the day decreases to 10 hours. Coleman stresses this and provides detailed information on planting times in his book for his location. To meet this criterion, some winter harvest crops need to be started as early as August 1, with planting times in general stretching into October, depending both on harvest times and crop type.  As Coleman describes it, the effect of adding row covering over plants effectively shifts the location of growing 500 miles to the south. In particular, a single-ply covered greenhouse with an additional row covering above the plants effectively shifts the greenhouse 1000 miles, or three USDA growing zones, south.  Coleman defines two types of greenhouses (which he notes differ from similar terms used in English gardening). We now define these again for our purposes with the number of covering layers included: . Cool greenhouse: Minimum temp is kept just above freezing. Greenhouse covering is inflated double-ply. . Cold greenhouse: No supplementary heat at all. Greenhouse covering is single ply.  Even though Coleman’s techniques can allow some produce to be grown with no supplemental heat, there can still be significant advantages to using at least some supplemental heat, even for cold-hardy plants, especially in colder parts of Vermont. Even with row covers, plants do not grow as quickly at lower temperatures. Supplemental heat can result in more crops grown – roughly twice as much in the winter – and also more types of crops. Coleman writes “During the

184 Direct communication with P. Johnson, Spring, 2012.

years when we experimented with adding minimal heat to our largest greenhouses we were able to keep producing a far wider variety of crops than just those available from cold [unheated] houses during the first two months of the new solar year that begins after winter solstice.” He also writes “The eventual solution for an ideal winter-production system may come either through finding better inner- and outer-layer materials or though managing some greenhouses with minimal heat.”  Coleman also gives some idea of the effect of row covers in terms of temperatures. He states that they enable the temperature in the immediate vicinity of plants to remain at no lower than about 15oF on an -15oF night, which he finds is enough to preserve certain cold-hardy plants. Recall that -15oF, which is about right for typical midwinter temperatures for the Zone 5 location of Coleman’s Four Season Farm (the minimum average of being about -20oF), is a bit warmer than what is typically found in the Zone 3 and 4 regions of Northern Vermont, which can get down to -35oF or so in some places. This clearly suggests that some supplemental heat may still be needed in the colder parts of Vermont, just to keep plants alive.  The plants that Coleman finds he can grow with his row covering approach in a cold or cool greenhouses at his site in Maine include Arugula, beet greens, broccoli raab, carrots, chard, chicory, claytonia, collards, dandelion, endive, escarole, garlic greens, kale, kohlrabi, leeks, lettuce, mache, minutina, mizuna, mustard greens, pak choi, parsley, radicchio, radish, scallions, sorrel, spinach, tatsoi, turnips, and watercress. Coleman notes that spinach in particular has worked out well for his farm in cold houses because it produces new leaves all winter, unlike, for example, kale.  As a general rule of thumb, Coleman finds that the time from planting to maturity for a given crop roughly doubles as compared with summertime for a February harvest in a cool house, and triples for a cold house. He also finds that an average of 5-6 crops per year can be produced in a cool house compared with 3-4 in a cold house at his site. This indicates that fairly minimal supplementary heat (enough to prevent temperatures below freezing) can lead to a significant increase in annual productivity, and of course help keep production up during midwinter. It can also allow a wider variety of crops, such as baby turnips and crisp radishes to remain available, that might otherwise not grow adequately due to freezing.  It is of interest to inquire as to whether the shorter growing period and higher productively will more than offset the additional cost of fuel or whatever other means is used to provide supplementary heat (such as a solar + water storage system). Coleman states that he found that when propane prices were relatively low in the past, a single extra crop made up for the fuel cost.  Besides row covers, Coleman also makes extensive use of moveable greenhouses. These are useful, for example, for providing protection for heat-loving crops such as tomatoes during the summer, and when they are not needed during the first phase of the winter crop’s growth. Then in the fall they are moved over the winter crops. Exposing the soil to the sun, rain, wind, and snow can be good for eliminating pests, diseases, and the buildup of excess nutrients. . Supplemental Heating Strategies for Greenhouses: With some background on low energy growing techniques and terminology established, we now examine opportunities for supplying supplemental heat with renewable energy sources, including biomass, compost, solar, and air/ground source heat

pumps. To be clear, however, we are not suggesting that supplemental heat is absolutely required for some level of cultivation of certain crops in Vermont: Coleman allows that his cold-hardy plants experience temperatures below freezing, and even down to 10oF on occasion185, as long as plants are not exposed to additional stresses of outdoor conditions such as desiccating winds. . General Conclusions:  The economics of maintaining a warm greenhouse all winter long are challenging with any type of system yet, due either to the cost of fuel and/or the capital cost of systems required to do this. For this reason the low energy techniques of Coleman, and any other means of reducing the thermal load, remain important.  Significant expertise with the use of biomass heating systems in Vermont has developed and is available.  Providing the necessary minimal heat with compost, solar thermal, or ground source heat pumps, and possibly the use of air source heat pumps in certain ways, is promising.  Finally, we note that Eliot Coleman has explored the use of renewable solutions to some extent, for example, in using a wood furnace in one of his cool houses, and looking into other methods to some extent, but to our knowledge has not systematically explored the approaches we consider here. He does remark though that “soil heat has much to recommend it”, and the systems we consider here are ideal for doing that, which is hence another reason why looking at solar thermal and geothermal may be worthwhile. . Specific Strategies:  Heating Greenhouses with Compost: The section of this report on Heating with Aerobic breakdown of Biomass reviews recent progress capturing heat from compost. This approach appears to be promising, although further work is needed on system design, compost mixtures, and economics. Application of compost heat, if it is economical at all, is likely to be economical for greenhouses. Many, perhaps most, greenhouse operations already involve composting, and likely to already have most of the equipment required for creating and moving compost around. They are also potentially able to benefit from an increased production of compost. Moreover, many greenhouses already employ radiant-heat tubes in seedbeds and/or hydroponics and/or use of fan-coils which are well suited to delivering heat captured from compost.  Heating Greenhouses with Biomass: A 2010 UVM Agricultural Extension study on biomass fired186 found that wood heat was a minority source of greenhouse heat in VT: “Fuel used to heat greenhouses is predominantly propane (47%), with secondary fuels being wood (14%) and fuel oil (14%). The remainder use vegetable oil, biodiesel, corn or other fuels (e.g. kerosene or natural gas.” The researchers went on to study the efficiency with which these different fuels were being utilized, and found that many of the existing wood heating practices were quite inefficient, with average energy use rates of 97 kBTU/ft2/year, compared with the average for all the fuels of 51 kBTU/ft2/year. They then assisted 14 growers in choosing, purchasing, and utilizing new biomass

185 Coleman mentions “10oC” in his book, but it appears he means 10oF based on his other content. 186 BIOMASS FURNACES FOR GREENHOUSE VEGETABLE GROWERS. Report to the High Meadows Fund. May 31, 2010. Submitted by: Chris Callahan, Callahan Engineering and Vern Grubinger, University of Vermont Extension: http://www.uvm.edu/vtvegandberry/Pubs/Greenhouse_Furnace_Project_Report.pdf

systems, which performed significantly better both in terms of energy (46 kBTU/ft2/year), and also emissions (e.g. less particulates). Based on this experience, then they developed advice on use of biomass systems for greenhouses. This study should be consulted carefully if biomass heating of greenhouses is considered, and biomass does appear to be an attractive way to reduce fossil fuel usage by heated greenhouses. In general, then, it appears that the practical aspects of heating greenhouses with biomass fuels are well under control, as one might expect. Key related resources in Vermont on greenhouse energy consumption and advice are: . The UVM Extensions Resource Collection: http://www.extension.org/pages/Introduction_to_Greenhouse_Efficiency_and_Energy_Con servation . UVM Professor Verne Grubinger’s Resource Collections: http://www.uvm.edu/vtvegandberry/index.html http://www.uvm.edu/vtvegandberry/energylinks.html . In particular, the UVM extension offers items such as greenhouse efficiency checklist, while Verne Grubinger’s site has indepth studies such as those cited above and elsewhere in this report. . Heating Greenhouses in Vermont with Solar Hot Water and Heat Pump Systems: Although biomass can be used effectively to heat greenhouses, and possibly compost, it is also of interest to explore whether other renewable energy sources might be useful. This may become increasingly relevant as biomass sources become more attractive for production of transportation and heating fuels for society in general, and as local food production expands. Possible alternatives to biomass include solar hot water collectors, ground source heat pumps (geothermal), and advanced air source heat pumps. All of these may also require or at least benefit from substantial amounts of thermal energy storage as well. All of these technologies, including storage, have been discussed elsewhere in this report, so only their use in the context of greenhouse heating will be discussed here.  Active Solar Heating of Greenhouses in Vermont: Vermont possesses a fairly good solar energy resource in the wintertime (especiallyh after December). In general, it appears from several feasibility studies that active solar collection can be cost effective or at least marginally cost effect in cases where the solar energy is well utilized and utilized effectively. In practice this means that the output of the solar collection needs to be utilized during a significant fraction of the cold season, and that the thermal energy needs to be stored so that output needs to be delivered when the greenhouse requires it. Conversely, installing a system that is only used for a month or two and/or for which much of the thermal energy is delivered at times when the direct solar gain into the greenhouse is more or less adequate, will not be cost effective. . One recent feasibility study of the use of a solar hot water heating system for supplemental greenhouse heating in Putney, VT was carried out by grower Michael Collins and Callahan Engineering, PLLC187. This study predicted that a particular solar hot water system should be able to “provide nearly 83% of the heat needed for a 24’x60’greenhouse in Vermont for at

187 “Feasibility and Cost/Benefit Study of Solar Hot Water Greenhouse Heating System”, Prepared by Christopher W. Callahan, PE for Michael Collins, Old Athens Farms, Putney, VT: http://www.uvm.edu/vtvegandberry/Pubs/Solar_Hot_Water_for_Greenhouse_Heat.pdf

least two of the main growing months (May and June)” and “between 10% and 20% in the early growing months of March and April.” In terms of economic results, the study found payback times before incentives of roughly two decades if propane and heating oil were assumed to be $4/gal and $5/gal, respectively. . Two other studies (carried out by the author of this report and students) found the following 188,189 sets of results : The first study looked at the viability of simply delivering solar thermal heat directly to the floor of the greenhouse with a radiant floor, that is, without, thermal storage. This study concluded that this (non-storage) approach could be marginally cost effective in warm greenhouses operated all winter long, although the solar fractions were quite small. The second study examined using solar thermal heating for an Eliot Coleman style “Cool House”, that is, a greenhouse kept at 32oF or higher, and in conjunction with large amounts of thermal storage. Specifically, the study looked at what would be required to provide almost all (90%+) of the supplemental heating needs of a Cool House, where the storage is allowed to fully charge up before the heating season begins. This study found that solar fractions of 90%+ are achievable in Vermont’s climate with this approach, although the economics could be challenging unless the cost of the storage can be well controlled.  Geothermal Heating of Greenhouses in Vermont: This study mentioned in the previous paragraph also examined prospects for achieving the 90%+ target for a Cool House with a ground source (geothermal) heat pump system. The results were positive, and the cost effectiveness in this case was found to depend mainly on the installation and operating costs of the geothermal system. In general, geothermal systems are cost effective if the system is well designed and certain installation costs, such as well drilling costs, do not prove to be excessive (see the chapter of geothermal heat pumps for more information).  Air Source Heat Pumps: As described in the section on Advanced Air Source Heat Pumps, significant improvements in these devices has occurred, and further improvement may occur. Today’s air source heat pumps will likely be cost effective for at least modest season extension greenhouse applications if they are operated when ambient temperatures are not too low (say, greater than 25oF). This follows from their low capital costs and ability to attain Coefficients of Performance (COPs), of well over 2 in this range. It may also prove beneficial to utilize high end air source heat pumps as heat recovery units, for example, to remove excess heat from a greenhouse and store that heat for later. This potentially makes sense because the temperature difference between the greenhouse and the energy storage during sunny hours would not be excessively large.

188 “Feasibility of Providing Supplemental Heating to Greenhouses in Vermont with Direct Delivery of Externally Collected Solar Thermal Energy,” Ryan Cloutier and Ben Luce, for the Vermont Agency of Agriculture, VTREAP Grant number 10006, 2010. 189 “Providing Supplemental Renewable Heating for Eliot Coleman Style Greenhouses”, Samantha Wolf, Danielle Jepson, and Ben Luce, for the Vermont Agency of Agriculture, VTREAP Grant number 10009, 2011.

Micro-hydropower  Technology Description: o The production of electricity via small turbines such as “pelton wheels” in “run of the river” installations. Although definitions vary somewhat around the world, micro-hydro generation in the US is usually defined as hydropower generation systems under 100 kilowatts190. The basic components of a system include: . Water intake: This is placed upstream and channels some of the stream’s flow (ideally less than 50%) into a pipe. Self-cleaning intakes have recently been developed for micro-hydro systems. See below for more information about these. . Penstock (pipeline): A pipe to carry the diverted water down to the turbine. This can be buried or on the surface, although it is advisable to bury these in Vermont. . Generator Station:  Housing structure  Turbine . Tailrace: Piping to return water to the stream. . Energy Storage, Diversion & Power Conditioning:  A battery bank: Required for all off-grid systems and most smaller grid-tied systems. Stores energy for later use in off-grid systems, and in grid-tied applications ensures a steady supply of electrical power to the inverter.  Charge Controller/Diversion Controller: A device which prevents battery overcharging, and also diverts power to “diversion loads” once the batteries are charged, or if the grid goes down for grid-tied systems.  Inverter: A device to convert the DC power into AC Power. o Micro-hydro systems are considered to be ‘run-of-river’ systems, meaning that the water passing through them is directed back into the stream with relatively little impact on the surrounding ecology. o Turbine Types: There are different types of micro-hydropower turbines which are appropriate for different situations. All designs involve a turbine wheel also known as a “runner.” To catch the water, some runners have “blades”, others have “buckets.” The common types of turbines can be classified as shown below. Note: For various reasons different sources of information on turbines give somewhat different numbers on what ranges of hydraulic heads and flow rates are appropriate for different turbine types. The particular numbers quoted below are from the website of the micro-hydro turbine company St. Onge Environmental Engineering (S.E.E.), PLLC191. Anyone considering a particular turbine product for a particular site, however, should check with the manufacturer directly as to the turbine’s intended and optimal operating conditions. . Reaction Turbines: Water pressure, as opposed to water impulse, drives the runner blades. The pressure decreases as the water moves through the runner, which is enclosed in a strong encasement to maintain pressure. Generally more efficient than impulse turbines in low head applications.

190 http://www.microhydropower.net/size.php 191 http://www.hydro-turbines.com/id74.html

 Francis Turbines: Medium head sites: 30’ – 375’. Up to 90% efficiency. Can be set in an open flume or attached to a penstock.  Kaplan and Propeller Turbines: Low head sites: 6’-125’. This is an evolution of the Francis Turbine optimized for low head applications through the use of adjustable (“regulated”) vanes. Unregulated propeller turbines are common in constant flow applications. . Impulse Turbines: Potential energy of the water is first converted to kinetic energy in the form of a water jet, which then exert impulses (transfers of momentum) to the buckets located on the periphery of the turbine. Pressure remains constant and an encasement is not needed. Efficient in high head applications.  Pelton Wheels: High head sites: 150’-5000’. High efficiency at high head over a wide range of flow rates. The jet is in the plane of the runner. The buckets move at about half the speed of the jet. Runner sometimes has two rows of buckets to split off-flow to balance side-load forces.  Turgo Turbines: Medium head sites: 50’-175’. The jet enters the plane of the runner at about 20o, causing less interference of water leaving buckets with other buckets, enabling higher runner speed and efficiency, at least at the design flow.  Cross Flow (Banki-Michell, Ossberger) Turbine: Wide head range 9’-750’. Lower efficiency than other low head turbines at design flow, but operates with a flat (and reasonably good) efficiency over a wide range of discharges between 20 liter/sec and 10 cubic meters/sec and heads of 1-200 meters, so is well suited for unattended generation. A graphic that can be found online from the St. Onge E.E. site192 nicely summarizes the operating ranges as a function of both head and flow rates. (Note that the horizontal axis is mislabeled – the company confirms is should read m3/sec). It can be seen that the ranges overlap, and that the limits for a given turbine also strongly depend on flow rates. As noted above, both the pelton wheel and Cross Flow (Banki-Michell, Ossberger) turbines maintain good efficiencies over a wide range of flow rates. This provides design flexibility and design robustness, which is especially helpful for small installations where there are more uncertainties and less funding available for design services. o Vermont Scale Systems: Most applications at Vermont farms are likely to have relatively low flow rates, on the order of or less than a cubic meter per second. Nevertheless, it is conceivable that any of the five turbines listed above might be applicable, depending on the details. o Electrical Classifications/Battery Issues: According to Home Power Magazine193, the turbine generators divide into two classes depending on capacity and application: Higher power AC turbines (for high flow rates) and low-power DC or AC/DC turbines (for low flow rates). Higher power turbines can be directly interconnected with the grid (if desired) with an AC inverter without battery banks. Lower power systems, including grid-tied system, have usually charged a battery bank to provide storage or at least ensure proper invertor functioning, although some low-power systems are now directly grid-tied without batteries (e.g. induction generators).

192 http://www.hydro-turbines.com/id73.html 193 “The Electric Side of Hydro Power,” https://homepower.com/articles/electric-side-hydro-power/page/0/1?v=print

Micro-hydro systems must remain electrically loaded at all times (except when the water flow is stopped) to keep the turbine’s rpm and peak output voltage for becoming too high. All systems are therefore equipped with “diversion loads” of some kind, including a back-up load in case the primary diversion load fails. In grid-tied systems the grid itself can function as the primary diversion load. Other common diversion loads include water heating elements and (air) resistance heaters, and electronic devices called “diversion loads” are also available that are specifically designed to work with a diversion controller.

 Technology Special Benefits: o Micro-hydro generation can be a cost effective of renewable electricity for sites possessing a hydro resource with sufficient hydraulic head and flow rate. o Stream flow tends to be well anti-correlated with solar energy, such that micro-hydro generation can provide a very useful complement to solar energy generation. o Micro-hydro systems are quiet, and have low environmental impact.

 Overall Prospects for Successful Deployment: o Very good. Although not widely deployed, this technology has been shown to function well in Vermont and elsewhere, and has good technical prospects at sites possessing a stream with adequate flow and/or vertical drop. o Environmental permitting issues have sharply limited prospects in the past, but new law in Vermont should help remove this barrier (see below).

 Development Status: o A small number of (mostly off-grid) micro-hydro systems already exist in Vermont at present, and various renewable energy companies offer to install them.

 Barriers & Opportunities: o Summary of Opportunities: Regulatory barriers have been decreased recently. Turbines covering a wide range of hydraulic heads and flow rates exist, extending by new models. Self-cleaning screens have greatly improved the environmental performance of water intakes for micro-hydro systems. o Regulatory Issues: It is possible to interconnect micro-hydro generation with the grid, as either net- metered systems or as independent power producers, depending on the peak power capacity and other factors. Until recently, however, interconnection with the grid required system owners to obtain a permit or an exemption from the Federal Energy Regulatory Commission (FERC), and the cost of either route has usually been prohibitive for micro-hydro systems. In 2012, the Vermont Legislature adopted a new law which should enable the state to seek approval of pre-screened projects from FERC, and to generally streamline the application process. An official summary of this legislation can be found online194. o Commercial Availability Has Improved: Many retailers now offer micro-hydro turbines and associated components, and these can be located easily online via search engines. Some of the turbine

194 http://www.leg.state.vt.us/docs/2012/Acts/ACT165sum.htm

manufacturers, many of whom also offer system design help, are listed below. These manufacturers offer a wide range of turbine types, power capacities, and voltages. The data on the first two turbines is quoted from GreenWired195. . Harris Hydroelectric Permanent Magnet Turbine: http://www.lopowerengineering.com  Widely used pelton wheel turbine in the 1 kw range  Head Range: 20 – 600 feet  Flow Range: 4 – 250 gpm  Maximum 12-volt power: 700 watts  Maximum 24-volt power: 1400 watts . HI-Power low-voltage hydroelectric generator: www.hipowerhydro.com  Newer pelton wheel turbine in the 1 kw range  Head Range: 40 – 400 feet  Flow Range: 5 – 100 gpm  Maximum Power: 1500 Watts  Battery Voltage Options: 12V, 24V, 48V, 120VDC . Alternative Power & Machine Pelton Turbines: http://www.apmhydro.com/  Pelton wheel turbines from 1-4 kw . Canyon Hydro Turbines: www.canyonhydro.com  “Broad selection” of micro-hydro turbines up to 100 kw . Energy Systems & Design: www.microhydropower.com  Pelton wheel turbines from very small (200 W) units and larger, and very low head (2 ft) axial flow propeller turbines. . St. Onge Environmental Engineering (S.E.E.), PLLC: http://www.hydro-turbines.com/  Wide range of turbines from 200 W to 30 kw. . Toshiba: http://www.tic.toshiba.com.au/product_brochures_and_reference_lists/ekids.pdf  Propeller Turbines from 5 to 200 kw o Charge/Diversion Controller Manufacturers: . Morningstar Inc.: www.morningstarcorp.com . Xantrex: www.xantrex.com o Self-Cleaning Intake Screens (SCSs) are based on the Coanda Effect, which is the tendency of a fluid jet to be attracted to a nearby surface196. SCSs for micro-hydro applications can be obtained from HydroScreen LLC197 (and possibly others). US Government researchers have in fact studied SCSs for a number of reasons, and developed detailed models which successfully predict the behavior of SCSs. This work strongly supports the assertion that SCSs perform as advertise198: o Economic Considerations: Many publications and websites state that micro-hydro systems are or can be cost effective. This is somewhat difficult to verify only because the costs of constructing components

195 http://www.greenwired.net/micro-hydropower/ 196 http://en.wikipedia.org/wiki/Coand%C4%83_effect 197 http://www.hydroscreen.com/products/hydro_turbine_diversion/index.html 198 “Laboratory Testing and Numerical Modeling of Coanda-Effect Screens.” Tony L. Wahl and Robert F. Einhellig, 2000 Joint Conference on Water Resources Engineering and Water Resources Planning & Management, July 30 - August 2, 2000 — Minneapolis, Minnesota: http://www.usbr.gov/pmts/hydraulics_lab/pubs/PAP/PAP-0841.pdf

such as the penstock and the turbine housing are very site and design dependent. Nonetheless, it appears to be true, due to 24/7 nature of this type of generation and relatively low cost of the turbines, piping, and other equipment. The addition of some “sweat equity” for these installations can also help substantially. Systems costing up to about $10,000/kw are typically cost effective. A study which looked at micro- hydro generation internationally showed that costs typically fall well below this level, and can often be reduced further “by using indigenous expertise and technology.199” To gain deeper insight into costs, installation costs can be broken down into turbine related component costs, intake and penstock related costs, housing structure costs, and installation costs. Turbines costs range from approximately $1000 to $3000/kw. Inverters and battery packs appear to each cost around $1000/watt. Controllers, diversion (resistive) loads, and other components cost significantly less. Overall, the entire set of turbine related components appears to range from $4000-$6000/watt. This estimate and the $10,000/kw threshold adopted above suggest that the sum total of the intake and penstock related costs, housing structure costs, and installation costs, need to total less than about $4000-$6000/kw for cost effectiveness. The piping used for penstocks is often steel piping, 4” PVC pipe, or 1.5-2” polyethylene pipe. The website Microhydropower.net discusses some of the cost tradeoffs involved in designing and installing the penstock (pipeline) thusly: “The penstock often constitutes a major expense in the total micro hydro budget, as much as 40 % is not uncommon in high head installations, and it is therefore worthwhile optimising the design. The trade-off is between head loss and capital cost. Head loss due to friction in the pipe decrease dramatically with increasing pipe diameter. Conversely, pipe costs increase steeply with diameter. Therefore a compromise between cost and performance is required200”. The same website notes:“Penstock pipelines can either be surface mounted or buried underground. The decision will depend on the pipe material, the nature of the terrain and environmental considerations. Buried pipelines should be ideally be at least 750 mm below ground level, specially when heavy vehicle are likely to cross it. Burying a pipe line removes the biggest eyesore of a hydro scheme and greatly reduces its visual impact. However, it is vital to ensure a buried penstock is properly and meticulously installed because any subsequent problems such as leaks are much harder to detect and rectify. Where the nature of the ground renders burying the penstock impossible there is sometimes no option but to run the line above the ground, in which case piers, anchors and thrust blocks will be needed to counteract the forces which can cause undesired pipeline movement…The size and cost of support structures for a given penstock are minimised by: keeping the penstock closer to the ground, avoiding tight joints, avoiding soft and unstable ground.” Another site states201: “If you live in a cold climate you will probably need to bury the piping below the frost line to keep it from freezing. Burying the pipe is usually a good idea in any event since exposed pipe on the surface can easily be damaged by human traffic or by events such as a falling tree. Also, PVC pipe tends to deteriorate when exposed to sunlight so burying the pipe protects it from sun exposure as well.”

199 http://josiah.berkeley.edu/2007Fall/ER200N/Readings/Paish_2002.pdf 200 http://www.microhydropower.net/basics/components.php 201 http://www.energybible.com/water_energy/piping.html

From these and similar discussions it appears overall that cost effective micro-hydro systems are possible, but that penstock material and installation costs can be substantial, especially if buried, and need to be carefully controlled to ensure cost effectiveness. o Resource Considerations: As a rule of thumb, the power generation potential for micro-hydro resource, where the hydraulic head is specified in feet (ft) and the flow rate in gallons per minute (gpm), is (realistically) given by: . Power (watts) = Flow rate (gpm) x head (ft) /10. This can be used to assist in the design of a system. For example, a resource with a “design flow” of 20 gallons per minute and 200 feet of head will have a design power capacity of: . P=20 x 200/10 = 400 watts An important issue for small micro-hydro generators in Vermont is the highly seasonal nature of precipitation, which bears strongly on the design flow rate. Flow rates in Vermont are generally much greater during the spring (days 90-140), moderate in fall and winter, and quite low in mid-summer (around day 250). For small run-of-river (damless) systems with design flows that are a significant portion of a stream’s average flow, it may be necessary to curtail production during summer. Fortunately, this is the best time for solar production, so it may be advantageous to combine photovoltaics and micro-hydro generation, where possible.

Photovoltaics  Technology Description: o Photovoltaics, or “PV” for short, literally means “electricity from light”, and is a class of solid-state technologies that instantly convert the energy of sunlight into electrical power using the unique properties of semiconducting materials. Materials used today for PV panels, or “modules” as they are called in the industry, include silicon, copper-indium-gallium-selenide (CIGs), cadmium-tellurium (Cad- Tel), and others. There are several major categories of PV technologies: . (Mono and Poly) Crystalline Silicon PV, which have efficiencies between. . Thin-film PV, including silicon, amorphous silicon, CIGs, Cad-Tel, and others. . Multi-junction and/or high temperature PV for Concentrating PV (CPV) applications. The DC power may be stored in batteries for later usage (off-grid systems), or converted immediately to grid-synchronized AC power and fed directly into the grid.

 Technology Special Benefits: o Good Conversion Efficiency: PV modules convert sunlight to electricity at a rate which is one to two orders of magnitude than plants (up to about 20% for flat plate collectors). Greater efficiencies will likely be available soon. o Good Cost Outlook: Reasonable costs today, and promising cost trend (and associated technological drivers). o Unlimited Resource: The solar energy resource is essentially unlimited relative to electricity demand. . A recent NREL study found that solar is the most abundant source of all the renewables, and estimated that the technical potential of utility-scale photovoltaic (PV), that is, larger systems, is a full 80,000 gigawatts (total US demand is 470 gigawatts on average), and that rooftop PV potential alone (under very conservative assumptions) weighs in at 700 gigawatts202,203. . PV could supply Vermont’s 2010 electrical energy demand in principal (aside from storage issues) with a total solar collector area of slightly under 10,000 acres worth of total collector area204, assuming 15% PV modules, and an average production of 3 kWh/day per kilowatt of PV capacity. o Essentially unlimited potential for mass production and material: That is, at least for some forms of PV (e.g. silicon is one of the most common elements in the Earth’s Crust). o Extremely Useful Product: Electricity is a high quality form of energy that can be utilized for (increasingly) many applications, including powering farm machinery, and can be effectively multiplied for thermal applications with devices such as heat pumps. o Good R&D Potential: Strong potential for further innovation and much higher efficiencies. o Low Emissions: . Zero emissions at the point of generation. . Low life-cycle emissions: Reasonable energy pack periods (3-8 years). o Low Impact: PV systems are silent, are benign to wildlife, and require very little site preparation.

202 http://www.nrel.gov/analysis/re_futures/ 203 http://www.greentechmedia.com/articles/read/stat-of-the-day-80-percent-renewables-at-mid-century/ 204 By “total collector area” it is meant not counting spacing between individual collectors. This is the appropriate measure to evaluate the scale of the resource because spacing requirements vary with installation type. For example, there are none for contiguous roof-top systems.

o Good Longevity: Modules can/do last many decades. Systems are robust (no moving parts), and require little maintenance. o Widely Applicable: . Very good scalability, ranging from microsystems (e.g. powering a calculator) up to city scale. . Very good siting flexibility. . Farms are often ideal sites for PV generation due to open space, south-facing barns and other structures, good access, good separation from neighbors, etc. A single acre can support up to about 100 kw of PV generation.

 Overall Prospects for Successful Deployment: o Cost Trend Up to the Present: PV is an extremely promising source of electric power for a variety of reasons, and has undergone a historic drop in price recently: The price of PV modules has fallen from $10 per watt in 1980 ($23/watt in 2010 dollars) to roughly $1 per watt in 2012205,206. The reaching of $1/watt is a major milestone for the industry, and explains the predictions for the continued rapid growth of PV. The price trend suggests PV is on track to reach “grid parity” with retail electricity prices in many US states, including Vermont, by as soon as 2015207. Prospects are good both for production of on-farm electricity and also for production of large amounts of solar electricity for Vermont as a whole via “solar orchards” located on farms. o Future Cost Outlook: Even further reduction in the price of silicon PV can be expected, as manufacturing scales up further and innovations continue. As just one example of the ongoing evolution of this trend, a new U.S. PV company, Twin Creeks Technologies, claims it has a new production system that can produce thin-film silicon PV cells for less than $0.40/watt208 using a new technique called Proton Induced Exfoliation (PIE)209. The company also states this technology can be used for other types of PV cells as well. o Intermittency Issues: PV’s primary disadvantage today as an energy source is the intermittent nature of its production. Prospects for resolving this barrier will ultimately hinge on whether and when inexpensive electrical energy storage becomes available. This topic is discussed further in the (next) section on Electrical Energy Storage. o Aesthetic Impact Issues: Concerns also sometimes arise over aesthetic impacts. This issue is discussed further below. o Manufacturing Impact Issues: There can also be issues related to impacts of PV manufacturing, especially where release of toxics is concerned. It appears overall that PV manufacturing can have minimal impacts if carried out with proper safeguards and re-use, post-processing, and disposal of

205 http://www.nrel.gov/docs/fy12osti/51847.pdf 206 http://www.pv-tech.org/guest_blog/pv_module_costs_and_prices_what_is_really_happening_now_5478 207 See: http://www.nrel.gov/docs/fy10osti/46909.pdf. Statement also factors in the large recent cost decreases referenced later in this report, which support the likelihood that PV systems are already approaching $6/watt and may achieve even much lower costs by that time. 208 http://www.pv-magazine.com/news/details/beitrag/40c-w-silicon-solar-cells_100006097/#axzz20MXq5TyP 209 http://www.twincreekstechnologies.com/technology/

chemicals, but potentially problematic if not carried out properly210. Similar comments apply to installation practices, in terms of impacts to soils, aesthetics, etc.

 Development Status: o Exponential Growth: The global PV industry has been growing exponentially at over 20% per year on average for the past two decades211, and it is expected that 27 gigawatts (27,000 megawatts) of PV will be installed worldwide in 2012 alone, surpassing even large concentrating solar power plant construction212. (A gigawatt of PV is enough to power approximately 200,000 homes on average.) . Vermont is now seeing hundreds of PV systems installed each year, including at some farms. . The International Energy Agency recently forecasted that total grid-connected PV capacity will grow from 91 GW in 2012, to as high as 230 GW in 2017213. o Widespread Net-Metering in the US: As of this writing, 43 US states including Vermont and also DC and Puerto Rico have net-metering laws and/or utility programs214. o Industry Consolidation Trend: Due to the economic downturn, massive investments by China in its solar industry, and various technological factors such as steep reductions in the price of polysilicon (the primary precursor material for silicon PV cells), the PV industry is presently in a period of what some characterize as “consolidation” and others “turmoil,” meaning that many weaker manufacturers have and will likely continue to fail, while other larger or otherwise stronger firms will thrive. But despite this, and even despite the recent imposition of tariffs on Chinese PV modules in the US, the industry continues to thrive, including both the Chinese the US manufacturing and installation industries215. Despite the loss of some US companies, the “consolidation” currently occurring may actually be a positive development overall. o Status of Thin-film PV: It has been widely predicted that thin-film PV would eventually overtake conventional crystalline PV technologies. Some thin-film PV companies using non-silicon technologies, particularly Cad-Tel, had been making significant inroads into the PV market up until 2009, but are currently facing difficulties. Cad-Tel PV is less efficient than silicon PV, but was cheaper to manufacture than silicon PV on a per watt basis for nearly a decade. It had captured nearly 20% of the market by 2009, but began to lose its edge after that. Over the past year extremely stiff competition from a recent price drop in polysilicon prices has now caused several thin-film companies (as well as less competitive crystalline PV companies) to fail. This also led GE to pause a major 400 MW Cad-Tel PV facility it was constructing, and thin-film industry leader First Solar to close a facility in Germany216,217.

210 “Progress in Photovoltaics: Research and Applications,”: Prog. Photovolt. Res. Appl. 8, 27±38 (2000): http://www.calepa.ca.gov/cepc/2010/AsltonBird/AppAEx7.pdf. See also: http://www.oregon.gov/ODOT/HWY/OIPP/docs/life-cyclehealthandsafetyconcerns.pdf?ga=t 211 http://www.solarbuzz.com/facts-and-figures/markets-growth/market-growth 212 http://www.forbes.com/sites/tomkonrad/2012/06/26/the-next-trend-integrating-pv-with-solar-thermal/ 213 http://www.pv-magazine.com/news/details/beitrag/global-installed-pv-capacity-to-hit-230-gw-consolidation-will- continue_100007658/#axzz20MFTrNSs 214 See the net-metering summary map at www.dsireusa.org. 215 http://www.forbes.com/sites/toddwoody/2012/06/13/u-s-solar-industry-booming-despite-china-trade-war/ 216 http://www.pv-magazine.com/news/details/beitrag/mid-year-pv-review_100007695/#axzz20MXq5TyP 217 http://www.greentechmedia.com/articles/read/thin-film-manufacturing-prospects-in-the-sub-dollar-per-watt- market/

In the short-term, the prospects for thin-film are difficult to predict, but there are bright spots: The new production technology by Twin Creeks Technologies mentioned above, for one, may invigorate silicon thin-film solar and other technologies. Another Cad-Tel company Calyxo GmbH believes it can remain competitive and is ramping up production218. And in 2010 the company Oerlikon Solar announced that its new thin-film (amorphous silicon) PV fabrication line is capable of manufacturing costs as low as $.64/Watt219. Careful analysis of the cost structures of crystalline and thin-film PV manufacturing reveals that because their costs of material are already only a small fraction of costs, one of the primary ways for thin-film to regain competitive status is to increase efficiency (without significantly increasing cost unit area)220. And thin-film companies are in fact showing steady progress at increasing efficiency221, which would appear to bode well for the long-term. o Industry Information Sources: A few of the many publicly available sources of information about the growth trends and other data about the PV industry are: . National Renewable Energy Laboratory Photovoltaics Research Program222 . “2010 Solar Technologies Market Report.223” (for data through 2010) . PV Magazine224 . PV Tech225 . Green Tech Media226

 Barriers & Opportunities: o New Financing Routes: A number of Vermont companies, such as SunCommon227 and AllEarthRenewables228 have introduced new approaches to financing PV Systems, enabling customers to essentially purchase the energy with relatively little investment upfront. o Reduced Installation Costs: AllEarthRenewables has also introduced a tracking system that enables pole-mounted systems to be rapidly and more cheaply installed without cement foundations (these tracker levels out during windy periods to reduce wind loading). o Aesthetic/Land Impact Issues: A possible barrier to PV development may prove to be public opposition to larger PV projects. Vocal opposition to some PV projects and/or complaints about the existing siting process have arisen already229,230, and in at least one case has led to a proposal to adopt new town

218 http://www.pv-magazine.com/news/details/beitrag/calyxo-ramps-up-thin-film-capacity-in- germany_100007318/#axzz20MXq5TyP 219 http://www.pv-tech.org/news/_a/eu_pvsec_oerlilon_solar_launches_upgraded_si_thin-film_production_line_hits/. 220 http://www.greentechmedia.com/articles/read/thin-film-manufacturing-in-a-sub-dollar-the-watt-market-ii/ 221 http://www.greentechmedia.com/articles/read/Stion-Ups-Efficiency-for-CIGS-Solar-Panels-Plus-Recent-PV- Performance-Reco/ 222 http://www.nrel.gov/pv/ 223 http://www.nrel.gov/docs/fy12osti/51847.pdf 224 http://www.pv-magazine.com 225 http://www.pv-tech.org/ 226 http://www.greentechmedia.com 227 http://suncommon.com/ 228 http://www.allearthrenewables.com/ 229 http://www.samessenger.com/node/3271 230 http://www.7dvt.com/2012solar-flare-six-charlotte-fight-power

regulations governing solar development. The draft town plan in this case presently states231 :“The siting of some existing solar installations, particularly along Route 100 (the federally designated Mad River Byway) has raised concerns about the impacts that such facilities can have on the town’s scenic, historic and agricultural resources. As a result, the Planning Commission has developed community siting standards…” In another case, a project has specifically sought to shield itself from view (although the outcome for this project is not yet known)232. Although the adoption of solar siting standards might ultimately actually benefit solar development, development might proceed more smoothly and effectively if proactive planning for solar development occurs widely first, such as through the widespread adoption of a model set of town rules governing solar development. Such rules might include language about aesthetics, minimizing stormwater runoff, preservation of soils, etc. o Enhanced and More Reliable Electronics: . Enhanced Inverters: In the early days of off-grid PV development, inverters, which convert DC solar power to AC, were often prone to failure, and the “charge controllers” that regulate charging of batteries were not sophisticated. Today, much more highly developed and reliable controllers and inverters are available, with both functions often combined in a single unit. Companies including Morningstar Corp233, SMA America234, and Outback Power235, have revolutionized the industry, and costs have been decreasing with production scale and competition, such that the electrical conversion needed for PV systems is no longer considered a significant barrier. Long term warranties are now available on inverter equipment. . The shift to high voltage: Early PV systems always operated at 12 or 24 volts, for battery charging related reasons. This necessitated high currents and hence large diameter wiring. Today’s grid-tied PV arrays operate with output voltages of several hundred volts or higher, mean lower currents and much smaller wire diameters. “Plug and play” wiring systems have developed along with this shift and are also now common place, further reducing installation costs. . Micro-inverters: Until recently, PV system buyers needed to purchase inverters that would convert the power from many different modules. This imposed minimum power capacities (usually a kilowatt or more) and significant inflexibility on system sizing. Over the past four new companies such as Enphase236 have introduced “micro-inverters” that convert the power from a single module. This enables purchasers to install one module at a time, if need be, and provides more flexibility even if they purchase more. It also enables the conversion to be optimized for each module individually, which better takes into account variations from module to module due to manufacturing, shading, dust build-up, etc. This increases the amount of useful power produced by a given module, and hence leads to lower levelized costs of power, all else being the same. o Building Integrated Photovoltaics (BIPV): BIPV systems combine PV directly with roofing and/or window systems to achieve overall cost reductions. Although BIPV installations only represent 1% of the

231 http://www.waitsfieldvt.us/townplan/waitsfield_town_plan_2012-06-05_draft_ch9_energy.pdf 232 http://www.samessenger.com/node/3258 233 http://www.morningstarcorp.com 234 http://www.sma-america.com/en_US.html 235 http://www.outbackpower.com/ 236 http://enphase.com/

PV market237, and generally cost more, this development helps pave the way for better integration of PV into the general infrastructure, and may eventually lead to lower costs. o Novel Manufacturing Techniques: There are many new developments in PV manufacturing techniques. One especially novel one is represented by, Nanosolar Inc, a CIGs PV company, that has been developing a novel ink-based manufacturing process (that does not require vacuum deposition) and a robotically advanced assembly facility. An overview of the technology can be found on YouTube238. Nansolar’s production has been slow to ramp up thus far, but the company continues to attract strong investment and is thought by some investors to be a potential major contributor in the future, especially if it can increase its efficiency somewhat239. o Emergence of Stable Thin-film PV: First Solar Inc. was the first company to successfully commercial Cad- Tel PV, becoming the first to produce over a gigawatt in 2009240. Crucial in this development was proving the longevity of their technology, which overcame a long-standing reputation for rapid degradation with thin-film PV (a problem that plagued the industry in the early 1990s). o Significantly more efficient crystalline silicon PV: SunPower241 developed a new architecture for crystalline-silicon PV generation that increased the efficiency of this type of PV technology from about 15% to over 20% - a very substantial increase242, while decreasing the amount of silicon required at the same time. Suntech243, a Chinese company that is currently the largest PV manufacturer in the world, achieved major progress in increasing efficiency by developing a new chemical based approach to reducing the size and distance between the tiny wires in the surface of crystalline-silicon PV cells that collect electrons244. o Future Innovation in PV: The prospects for future innovation in PV are very good, and much R&D is presently occurring, much of which is not publicly visible. Many announcements of PV “breakthroughs” have also been announced publicly, some of which may prove to be significant. Some possible current candidates are: . A new approach on optimizing the collection of solar cells by MIT by arranging the cells in a special way245. . The company Semprius is developing promising looking concentrating PV technology that utilizes extremely tiny, printed high-efficiency PV cells246. . The company Solar3D247 is developing a “3D” technology that minimizes loss of light that occurs in conventional cells.

237 http://www.renewableenergyworld.com/rea/news/article/2012/05/the-challenges-building-integrated-photovoltaics 238 http://www.youtube.com/watch?v=FTiSIZIA3YA 239 http://www.greentechmedia.com/articles/read/Nanosolar-Scores-70M-to-Keep-Its-CIGS-PV-Dream-Alive/ 240 http://www.123jump.com/market-update/First-Solar,-Inc-Q4-Earnings-Call-Transcript/36717/ 241 http://us.sunpowercorp.com/ 242 http://us.sunpowercorp.com/homes/sunpower-advantage/more-electricity/ 243 http://am.suntech-power.com/ 244 “Solar’s Great Leap Forward”, Kevin Bullis, MIT Technology Review, July/August 2010, p. 52: http://www.technologyreview.com/featured-story/419453/solars-great-leap-forward/ 245 http://web.mit.edu/newsoffice/2012/three-dimensional-solar-energy-0327.html 246 http://www.smartplanet.com/blog/intelligent-energy/printed-solar-cells-the-size-of-a-ballpoint-pen-tip-are-tiny-but- mighty/11347?tag=search-river 247 http://www.solar3d.com/

. Incremental Efficiency Improvements: In general, there is great potential for increase in the efficiency and cost reduction for virtually all existing PV technologies. Most PV modules on the market today that are marketed for terrestrial applications (as opposed to space applications) having efficiencies ranging from about 10% (the lower end of the thin-film technologies) to a little over 20% (for the higher of the crystalline silicon PV cells). For a long time most thin-film PV technologies lagged far behind crystalline PV, but these are now gaining rapidly248. The situation with conversion efficiency is complex:  All technologies with efficiencies of at least about 5% are potentially useful. For example, a very cheap organic “PV paint” would potentially be useful, even if it was only 5% efficient. The really crucial factor is the levelized cost-per-kilowatt-hour, which depends on the initial cost per watt and also longevity (more specifically, the rate of degradation with time).  All other factors being the same, though, higher efficiencies can translate into lower costs, and so much R&D is focused on increasing efficiencies. Higher efficiencies can also be helpful because it decreases the size of systems (for a given capacity), which in turn reduces installation costs. Higher efficiencies are also important for applications such as PV embedded on vehicles, or for commercial or industrial applications where the power utilized per square foot of a facility is relatively high. And higher efficiencies are also important for thin-film PV in particular, due to the cost structure of thin-film production.  Specialized “multi-junction concentrator” research cells have achieved efficiencies of twice the current commercial range – a little over 40%. These systems use mirrors or lenses to concentrate sunlight. These high efficiencies may mean that concentrator systems will eventually become useful even in Vermont, even though a significant amount of Vermont’s insolation is diffuse.  So-called “organic” PV cells are steadily gaining in efficiency, with some test cells now hovering around the 11% mark. This is notable because organic cells will likely be extremely inexpensive, although good longevity under real world conditions will also need to be demonstrated before cost competitiveness can be claimed. . Potential for Large Increase in Efficiency: Despite the innovations and efficiency advances described above, however, these still represent mainly incremental advances. A promising fundamental breakthrough in the physics of PV materials now suggests that the basic physical limit on conventional PV cell efficiency itself may be is surmountable, and possibly soon:  The key factor that limits the efficiency of conventional PV technologies is the fact that in bulk semiconductor materials such as silicon only a single electron can be utilized to capture a photon’s energy (a photon is an energy packet of light), coupled with the fact that it’s impossible to capture all the energy of a photon with a single electron. The latter limitation springs from the fixed “energy band gap” of the semiconductor material used: If a photon has greater energy than the band gap energy, only the portion equal to the band gap energy can be captured – the rest is lost to heat. To make matters worse, photons with energies less than the band gap energy can’t be captured at all. These two loss mechanisms together theoretically

248 http://www.greentechmedia.com/articles/read/Stion-Ups-Efficiency-for-CIGS-Solar-Panels-Plus-Recent-PV- Performance-Reco/

limit the efficiency of PV cells, for example, to about 29% for silicon, and to less than about 31% for all semiconductor materials.  Up till now the only way to surmount this was to layer different semiconductors together to create “multiple junction cells.” This has worked, but only for concentrating PV technology. All of this may be about to change: It now appears to be physically possible for the energy of a photon to be captured with multiple electrons in “nanocrystals”, that is, small crystals consisting of just a few hundred thousand atoms apiece. This appears possible because the tightly constrained geometry of these crystals forces electrons to interact more strongly, enabling an electron that captures a photon to immediately excite and hence share the energy it captured with its neighbors, instead of simply losing the extra energy to heat. This effect is called the Multiple Carrier Effect, and also the Multiple Exiton Generation (MEG) effect. The term “exiton” used here, refer to electrons inside nanocrystals. These electrons are also called “quantum dots.”  Interest in the possible application of the MEG effect to PV cells began with work by PV scientist Art Nozik at the National Renewable Energy Laboratory (NREL) in the late 1990s249. It had also been previously pointed out by Duggan and Barnham that the band gaps of quantum dots should be tunable, and that this should enable solar cells which are better optimize to the solar spectrum (even in the absence of the MEG effect)250. The full range of emerging possibilities presented by nanocrystals is now often called “quantum dot solar,” and classified as “Third Generation Solar.”  A few years after Nozik predicted the MEG effect, researchers led by physicist Victor Klimov at Los Alamos National Laboratory verified the effect in lead-sulfide nanocrystals, and carried out calculations estimating that MEG could theoretically support efficiencies as high as 44% without concentration, and as high as 80% with concentration251. NREL then verified these findings, and also found that the MEG effect can also occur in silicon252. Progress was subsequently made on working out how to extract the stored energy from the excited electrons in the nanocrystals253, and in 2011 NREL researchers created an actual solar cell that exhibited the “overcurrents” predicted to result from the MEG effect254.  Quantum dot test cells are now being tested, and their efficiency is gradually ramping up. Only 5% efficiency has been demonstrated so far, but the technology is still in its infancy. Its significance lies in overcoming the fundamental limit to PV efficiency. It is also likely the case that some of the new manufacturing techniques under development by companies such as Nanosolar may be able to bring quantum dot solar to mass production very rapidly if and when the technology is ready.

249 http://www.nrel.gov/news/press/2005/350.html 250 Barnham, K. W. J.; Duggan, G. (1990). "A new approach to high-efficiency multi-band-gap solar cells". Journal of Applied Physics 67: 3490: http://adsabs.harvard.edu/abs/1990JAP....67.3490B 251 “Solar Energy: Can the Upstarts Top Silicon?”, R. Service, Science, Vol. 319. no. 5864, pp. 718 – 720, 2008: http://www.sciencemag.org/content/319/5864/718.summary 252 http://www.understandingnano.com/solar-cell-efficiency-quantum-dot.html 253 “Multiple Exciton Collection in a Sensitized Photovoltaic System”, Justin B. Sambur, Thomas Novet, B. A. Parkinson. Science 1 October 2010, Vol. 330. no. 6000, pp. 63 – 66: http://www.sciencemag.org/content/330/6000/63.abstract 254 http://www.nrel.gov/news/press/2011/1667.html

Electrical Energy Storage  Technology Description: o A full transition to renewable sources of electricity will ultimately require the successful deployment of affordable electrical energy storage. Technologies which are presently the focus of most electrical energy storage R&D are: . Pumped Storage Hydropower . Advanced Lead Acid Batteries . Lithium-Ion Batteries . Sodium-Sulfur Batteries . Other Innovative Battery Technologies including:  Flow Batteries  Zinc-Air  Aqueous Hybrid Ion (AHI) . Hydrogen Fuel Cells . Supercapacitors . Compressed Air Energy Storage . Thermal Storage Approaches:  Pumped Heat Electricity Storage  Molten Salt . Magnetic Energy Storage

 Technology Special Benefits: o Affordable electrical energy storage would enable the intermittency of renewable electricity sources such a solar and wind to be overcome, allowing much larger amounts of renewable energy generation, including generation sited at farms. o The availability of “dispatchable” renewable electricity would also enable, for example, heat pump systems to be achieve much greater greenhouse gas reductions (roughly 50% more as compared to running such systems on electricity purchased from the New England grid). o Affordable electrical energy storage would enable a significant amount of farm machinery to eventually be powered with on-farm generated renewable electricity.

 Overall Prospects for Successful Deployment: o Although still uncertain, there are many promising emerging electrical storage technologies. : Successful deployment of affordable electrical energy storage could have a very large effect of Vermont farm energy practices. A couple of examples can be given to convey a sense of the extremely high level of interest and activity in this area, and the issues driving this interest: . The “Intersolar Europe 2012 Conference”, one of the largest solar energy related conferences in the world, saw a strong focus on electrical energy storage this years: “In the field of electricity storage alone, more than 140 international exhibitors this year presented the latest products and solutions

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ranging from small battery storage systems through combinations of different storage systems with fuel cells to large storage solutions for industry and commerce.255” . The US Department of Energy (DOE) recently provided $185 million in funding for storage projects, which in turn attracted $585 million in industry cost-share256.( A presentation by Imre Gyuk, DOE Program Manager for Energy Storage Research, is available online257.) . It is reported that “New energy storage deployment totaled 121 megawatts globally in 2011 and a forecast from Pike Research sees 2,353 megawatts in 2021. Worldwide energy storage deployed as of May 2011 was 370 megawatts, which grew to 590 megawatts by April of 2012258.” . The electrical storage industry is already a $50 -$60 billion a year and is projected by one group to grow another $113.5 billion a year by 2017259. . Solar generation in Italy has now reached the point that backflow problems at substations are occurring, and vigorous discussion is occurring in many countries on how to meet the growing need for electrical storage260. The Italian situation – megawatt scale development overwhelming a rural grid - appears to be similar to what could occur relatively soon in Vermont.

 Development Status: o Vermont Deployment: New electrical storage technologies have not yet made significant inroads in Vermont. o Cost Outlook: The Department of Energy published a study in 2011 of the “10 Year Present Worth Cost” of electrical storage technologies, providing estimates of the cost per kilowatt of storage power capacity taking into account factors such as cycle life, efficiency, and operating costs. . It was found that storage for short duration/infrequent discharge usage patterns, which correspond to applications such as short-term grid backup that need to store/deliver energy for less than an hour, and only deliver about 20 times a year, yielded the lowest costs, mostly about at or under $1000/kw. . It was also found that long duration/frequent discharge usage patterns, which means applications such as smoothing out solar project output, that need to store/deliver for 4-8 hours, and need to do so every day, yielded the highest costs, ranging as high as about $3400/kw. These are pretty high costs, so these latter most clearly show the challenge of achieving electrical storage for renewable energy applications. One of the crucial cost questions for the coming decade will be the cost trend of Lithium-ion (LI), which are the battery of primary focus for electric vehicles presently. LI batteries are available for applications such as computer laptops for about $250 per kilowatt-hour, which is a much lower cost than a decade

255 http://www.solarserver.com/solar-magazine/solar-news/current/2012/kw25/worlds-largest-exhibition-for-the-solar- industry-packs-a-punch-with-topics-grid-integration-and-electricity-storage-intersolar-europe-2012-closed-on-friday- june-15.html 256 http://www.greentechmedia.com/articles/read/Slideshow-DOE-Energy-Storage-Project-Portfolio-Funded-by-ARRA/ 257http://www.electricitystorage.org/events/annual_meetings/2012/2012_annual_meeting_agenda/session_c/presentat ion_c10/ 258 http://www.greentechmedia.com/articles/read/Slideshow-DOE-Energy-Storage-Project-Portfolio-Funded-by-ARRA/ 259 http://seekingalpha.com/article/479251-grid-scale-energy-storage-lux-predicts-113-5b-global-demand-by-2017 260 http://www.eco-business.com/press-releases/new-energy-storage-projects-examined/

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prior261, but creating batteries for electric vehicles (EVs) and grid-scale applications is significantly more challenging, and hence costly, for a number of reasons. Obtaining good information on lithium-ion battery cost is also difficult, due to the highly proprietary nature of most of the R&D. A recent comment by a Ford executive, however, revealed that the current cost of lithium-ion batteries, for at least that particular company, is between $522 and $650/kWh implying that the cost of the 23 kw battery along for the Ford Focus is $12,000 - $15,000 262. This is clearly too high for that application, and accordingly, the U.S. Department of Energy has set a goal of lowering the cost of lithium-ion batteries to $300 a kilowatt-hour by 2013 (which would still be high, but might allow the EVs and lithium-ion battery industries to survive).

 Barriers & Opportunities: o Small-Scale Distributed Storage is Attractive: These systems tend to have less stringent requirements than grid-scale systems, and can often be housed in existing buildings, lowering overhead costs. Extensive deployment of small-scale storage may also be easier to justify public investment in due to the lowering of demand and also services such as the voltage support that these systems can provide on distribution grids. The main barrier to cost effective storage for small-scale systems is therefore the cost of the storage media itself, and perhaps a latent under-valuing of the potential benefits of distributed storage by regulatory agencies. o Vermont Possesses AC-DC Rectification Expertise: If a battery system is to be used for grid-storage applications, then it must also possess “rectifiers” and “inverters”, which convert AC power to DC, and vice versa, respectively. These components can be a significant part of the cost of a storage system, so there exists intense R&D and a number of companies devoted to just these components. An example of such a company is Vermont’s own Dynapower263. o Summary of Emerging Storage Technologies: There are presently many emerging electrical storage technologies that have promise. These are described in more detail below: . Pumped Storage Hydropower: Companies are pioneering new version utilizing two water-filled shafts as deep as 6000 feet that might find use in the Northeast. . Advanced Lead Acid Batteries: New versions, including “lead-carbon” batteries that have added carbon to reduce sulfation of the electrodes, appear to have much longer cycle lives. . Lithium-Ion Batteries: These offer very high energy densities, and may come down in price with economies of scale and further technical advances, such as the addition of graphene. . Sodium-Sulfur Batteries: Already used for large grid-scale applications, there is some possibility for improvement of these batteries. . Flow Batteries: Essentially a type of fuel cell storage, some industry watchers predict that much of the energy storage market will soon be dominated by this technology. . Zinc-Air: Some companies claim they have surmounted previous problems with these batteries and that they will become competitive with lithium-ion batteries.

261 http://gigaom.com/cleantech/xtreme-power-a-super-battery-for-hawaiian-wind-farms/ 262 http://online.wsj.com/article/SB10001424052702304432704577350052534072994.html 263 http://www.dynapower.com/

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. Aqueous Hybrid Ion (AHI): A very promising new type of battery that may be particularly useful for grid-scale storage. . Hydrogen Fuel Cells: Although there has been less focus on these in recent years, advances are continuing, and this may still become a viable technology. . Supercapacitors: These have been exhibiting one of the fastest growth trends of any electrical storage technology, and recent advances suggest they may attain energy densities comparable with lithium ion batteries soon. . Compressed Air Energy Storage: Recent advances by a Northeast company suggests that above ground and scalable CAES without the need for natural gas use may become cost competitive. . Pumped Heat Electricity Storage: This new and promising form of electrical energy storage uses heat pumps operating between two thermal storage containers. . Molten Salt: This high temperature thermal storage technology appears to work well for large concentrating solar power plants and may have other applications, such as storage of high temperature thermal energy for process heat. . Magnetic Energy Storage: Although still expensive, some companies are claiming progress in improving this technology. o Pumped Storage Hydropower: Pumped Storage Hydropower (PSH), or just “Pumped Storage”, involves pumping water from one reservoir to another at higher elevation when electricity demand is low, and then releasing that water to generate hydropower when the demand is low. Hydropower is very cost effective where available, and presently accounts for more than 99% of the “bulk storage” capacity worldwide: Around 127,000 MW (which represents a substantial fraction of US generation potential)264. . Developing additional PSH, however, is challenging. The overall potential for conventional PSH relative to US electrical demand appears to be very limited, simply due to the fact that there are few places in which pairs of large reservoirs at different elevations exist or can be developed. Vermont may be able to sustainably develop more than 93 MW of additional hydropower265, for example, but much of this would be “run of the river”, that is, very seasonal and not associated with large reservoirs of water, and the ability of dam operators in Vermont to vary water levels in existing ponds and lakes associated with hydropower generation is likely quite limited. . Some companies, however, are attempting to develop new forms of PSH that might be applicable to the Northeast. One promising looking approach is being pursued by Gravity Power266, which is attempting to commercialize a system utilizing two water-filled shafts, one with much greater diameter than the other, which are connected at both ends. The shafts would be as deep as 6000 feet. To store energy, water is pumped down through the smaller shaft to raise a heavy piston in the larger shaft. To generate power, the piston is allowed to sink back down the main shaft, forcing water up through the smaller shaft and back through a turbine to create electricity. The system has extremely small footprint and no emission issues, and so should be relatively easy to permit. . A critical question for this technology will be how much the excavation costs impact the cost. The company has been partnering with another that has special technology for this, and states that they

264 http://www.economist.com/node/21548495 265 http://www.communityhydro.biz/documents/ANR-Conference-April2007.pdf 266 http://www.gravitypower.net/

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believe they will be able to achieve costs as low as $1000/kw. For a technology that has potentially low operating costs, good efficiency, and very long cycle life, this cost would in fact be a major breakthrough if realized. o Advanced Lead Acid Batteries: Lead-acid batteries still comprise the vast majority of starting batteries in automobiles and storage batteries for off-grid solar power systems. They are still the focus of R&D as well, and makers continue to hope that they will find new applications in electric vehicles and general electrical storage markets. An international consortium called The Advanced Lead Acid Battery Consortium (ALABC) is promoting a number of advanced lead-acid battery approaches: . “Lead-Carbon Battery” lead acid batteries that have some added carbon to block harmful sulfaction effects on the electrodes. . The “Ultra battery”: This is a conventional lead-oxide plate and negative electrode comprised of a “sponge lead active material” and a “special capacitor electrode” containing a mixture of carbon black and activated carbon. Here, the capacitor electrode acts as a buffer to share the discharge and charge currents with the lead–acid negative plate and protect it from being discharged and charged at high rates. . Some of the companies that appear to be leading the effort to commercialize these approaches include:  East Penn (Deka Batteries)267: This company is commercializing Lead-Carbon batteries, and has already installed a successful large scale facility with Public Service Company of New Mexico.  Xtreme Power268 : This company is attempting to commercialize an ultra battery with a "chemical capacitor", as they call it, that they believe can match lithium-ion battery performance269.” Some of the claimed characteristics of this battery are: Room temperature operation, 90% or better “efficiency270, and very fast recharge. . Lead-acid batteries can generally be made with widely available materials (even the advanced versions, it appears), and these examples would appear to suggest that lead-acid technology may yet wind up being competitive with other technologies, especially for grid-storage applications. The 2011 DOE cost estimates discussed above already reflect this. o Lithium-ion Batteries: As mentioned above, these batteries are still the primary focus for EVs, many companies are pursuing them271, and vigorous R&D is ongoing as there is still great room for improvement in terms of cost reduction and other aspects. There are also many different types of LI chemistries, and each chemistry has its own characteristics in terms of cost, energy density, cycle life, etc. . One of the areas of possible improvement is energy density. A Chinese maker’s website states “The specific energy density can range from 100 wh/kg to 125 wh/kg, and volumetric energy density from 240 wh/L to 300 wh/L (double of the Ni/Cd, 1.5 times of Ni/MH) , which has not reached the maximum energy density in theory of 150 wh/kg or 400 wh/L272”.

267 http://www.dekabatteries.com/ 268 http://www.xtremepower.com/xp-technology/powercells.php 269 http://www.greentechmedia.com/articles/read/xtreme-power-to-build-3mw-battery-on-kodiak-island/ 270 http://gigaom.com/cleantech/xtreme-power-a-super-battery-for-hawaiian-wind-farms/ 271 http://gigaom.com/cleantech/20-battery-startups-hitting-the-road-with-lithium-ion/#more-49111 272 http://bydit.com/doce/products/Li-EnergyProducts/

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. Research at Northwestern University has also suggested that the addition of graphene to LI batteries might increase their energy density and charging rate by as much as factor of ten273. Many other interesting findings and proposals along these lines exists in the R&D literature. . One of the long-standing issues with lithium-ion batteries is that they are prone to thermal runaway274, which has its roots in the fact that lithium reacts violently with water. The batteries can ignite, for example, if they become too hot. This has particular implications for large scale storage. As one commentator put it, “a megawatt-sized lithium-ion battery is a much greater challenge when it comes to one of the main drawbacks to that chemistry, its potential for thermal runaway”275. Battery manufacturers use a variety of ways to handle this, including special “fail-safe” circuits, cooling strategies, chemistry, etc. The issue at this present time does not appear to be a major issue for EV applications, but is problematic for grid-storage applications and is still of general concern. . All in all, despite the strong focus on these batteries, large cost reductions may need to occur quickly in order for the LI industry to survive. o Sodium-Sulfur Batteries: These batteries are a type of molten-metal battery constructed from sodium and sulfur. They have a high energy density per unit mass – on the order of what LI batteries can achieve at best (~150 Wh/kg), high efficiency (~90%), long cycle life, and are fabricated from inexpensive materials. As such they are ideally suited for large, grid-storage applications, and in fact are already widely deployed for such. A Texas town even operates a 4 megawatt unit large enough to power the town in case the sole power line to the town should fail276. . Sodium-sulfur batteries operate at high temperatures (~ 325 °C), however, and the highly corrosive nature of the sodium leads to higher costs and has also limited them largely to grid-storage applications, at least up until recently (although there are non-rechargeable “sodium batteries” for small applications). . The DOE cost estimates discussed above also place these batteries at about $2500/kw, at least as of 2011, which is not very promising for the long term. . Nevertheless, sodium ions are an intrinsically attractive charge carrier for batteries, and some research has already suggested that new sodium based batteries that avoid some of the disadvantages of the current sodium-sulfur batteries are possible277. o Flow Batteries: Flow batteries are essentially fuel cells, that it devices which chemically react a fuel to produce electricity. A Sandia researcher describes the principle behind a “flow battery” thusly: “A flow battery pumps a solution of free-floating charged metal ions, dissolved in an electrolyte — substance with free-floating ions that conducts electricity — from an external tank through an electrochemical cell to convert chemical energy into electricity.278” . There are many different types of flow batteries that use different metals. These include vanadium redox, polysulfide bromide, zinc-bromine, zinc-cerium, and lead-acid types.

273 http://www.northwestern.edu/newscenter/stories/2011/11/batteries-energy-kung.html 274 http://energy.sandia.gov/?page_id=9638 275 http://gigaom.com/cleantech/xtreme-power-a-super-battery-for-hawaiian-wind-farms/ 276 http://news.nationalgeographic.com/news/2010/03/100325-presidio-texas-battery/ 277 http://www.sciencedaily.com/releases/2011/06/110607121139.htm 278 http://cleantechnica.com/2012/02/18/new-flow-battery-does-that-cheap-energy-storage-thing/

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. One DOE supported company currently developing zinc-flow batteries for grid-storage applications is Primus Power279 , which claims a 70% efficiency.280 . There appears to be very strong optimism about the prospects for flow batteries in general. The Lux Research quote above, for example, predicted that much of the energy storage market will soon be dominated by this technology. o Zinc-Air Batteries: These batteries are zinc–air fuel cells that oxidize zinc with oxygen from the ambient atmosphere to produce electricity. The battery is recharged later by reversing the process and returning the oxygen to the atmosphere. . This battery type has some fundamental advantages over other technologies: Zinc is widely available (estimated zinc reserves are extremely large), and zinc is non-toxic. Zinc batteries can also achieve high energy density, in part because they utilize ambient air. . In the past there have been problems with efficiency and cycle life. Companies such as Eos Energy281 and ReVolt282 , however, claim to recently have surmounted these issues and claim they will soon be offering batteries competitive with lithium-ion283. o Aqueous Hybrid Ion (AHI) Battery: The company Aquion Energy284 is attempting to commercialize a new battery type they call the “Aqueous Hybrid Ion (AHI) Battery” based on research by Carnegie Mellon University Professor Jay Whitacre. . A presentation on their website by Whitacre et. al. describes how the group first noted that:  Cheaper battery costs might be achieved with thicker electrodes and cheaper solvents.  Aqueous electrolytes have much higher ionic mobility than organic solvents, although have limited potential (voltage) ranges.  Sodium (Na) has a significantly better ionic conductivity in aqueous solution than lithium.

. It was then discovered by Whitacre et. al that the compound Na4Mn9O18 in particular appears to have excellent microscopic morphology (shape) for a potential cathode material. The group then developed the AHI battery around these observations, and found it seemed to perform well over 5000+ cycles with ”no fade in delivered capacity,” and have achieved “stable performance for over a year of continuous deep cycle use.” DOE reports it has over an “85% roundtrip efficiency.285” . The company has been able to attract strong support for its R&D and further scale-up from DOE and the private sector, and is building a commercial scale production facility in Pittsburgh286. . The company states that this battery can achieve a volumetric energy density of “over 30 Wh/L”. This would seem to suggest that its volumetric energy density is nearly an order of magnitude lower than lithium-ion batteries, so this battery might not be viable battery for some EV applications, but

279 http://www.primuspower.com 280 http://www.primuspower.com/products/ 281 http://www.eosenergystorage.com/ 282 http://www.revolttechnology.com/ 283 http://www.technologyreview.com/news/426535/startup-promises-a-revolutionary-grid-battery/ 284 http://www.aquionenergy.com/technology/ 285http://www.electricitystorage.org/events/annual_meetings/2012/2012_annual_meeting_agenda/session_c/presentat ion_c10/ 286 http://www.businesswire.com/news/home/20120221005737/en/Aquion-Energy-Selects-Pennsylvania-Large-Scale- Manufacturing-Facility

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it’s potentially low cost, long cycle life, and high efficiency would seem to make it attractive for grid applications. o Hydrogen Fuel Cells: Hydrogen fuel cell (HFC) energy storage systems have been the focus of intense R&D over the past two decades. These systems would utilize a fuel cell running in reverse to electrolyze (split) water into hydrogen and oxygen, store the hydrogen, and then later use the hydrogen to produce electricity from the fuel cell. . There are many types of fuel cells, but the focus of most of the R&D for storage applications and fuel cells for vehicles has been on the Proton Exchange Membrane (PEM) type. A number of companies have developed fuel cell vehicles (e.g. GM), and interest is ongoing287. . The potential advantage of hydrogen is the possibility of a clean, renewable energy based fuel with high energy density to allow vehicles to achieve ranges of several hundred miles. The long range in particular is a major reason for continued interest in HFC. . The major barriers to HFC storage has been the cost of PEM fuel cells and the cost of hydrogen storage. PEM fuel cells have been expensive due in part due to their use of platinum, while hydrogen storage is expensive because extremely high pressures or low temperatures are required to achieve sufficient energy density. . It appears that although HFCs have not been in the news as frequently as a few years ago, that R&D is still progressing, significant progress has been made. For example, the DOE reports that it “has reduced the cost of automotive fuel cells from $275/kW in 2002 to $49/kW in 2011 and is targeting a cost of $30/kW by 2017.288” This would be a competitive level with respect to conventional engines289. They also report advances in producing and storing hydrogen, and in field testing of HFC vehicles. Various reports of R&D advances can be found, for example, in finding potential alternatives to platinum290,291. . Automakers also appear to maintaining near term targets for HFC vehicles, and some have been leasing HFC vehicles for over 4 years already292. . Finally, it is worth noting that one of the older hydrogen storage and HFC manufacturers, Plug Power293, has survived, and is one of a number of companies offering fuel cell systems as substitutes for batteries. Overall, it would appear that significant barriers to HFC systems remain, so it is unclear whether HFC energy storage systems will become competitive soon, although there is a possibility that new advances might enable this. o Supercapacitors: Capacitors are devices that store energy in the electric field created by parallel sheets of positive and negative charges. Capacitors have the ability to charge and discharge extremely quickly, and to withstand hundreds of thousands of cycles without degrading. Conventional or “electrolytic” capactors are widely used in electronic circuits, but can only store a small amount of charge and energy.

287 http://www.bloomberg.com/news/2012-06-27/bmw-ends-talks-with-gm-on-fuel-cell-research-cooperation.html 288 http://www1.eere.energy.gov/hydrogenandfuelcells/accomplishments.html 289 http://oilprice.com/Alternative-Energy/Fuel-Cells/Hydrogen-Fuel-Cells-Not-Long-to-Wait-Now.html 290 http://www.sciencedaily.com/releases/2012/03/120315110407.htm 291 http://fuelcellsworks.com/news/2012/03/29/runcorn-energy-firm-acal-unveils-new-fuel-cell-design-in-tokyo/ 292 http://www.whec2012.com/uncategorized/news-release-june-6-2012/ 293 http://www.plugpower.com/

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Their capacitance is only measured in millionths of a “Farad” (1 Farad equals one coulomb of charge per volt). To obtain even these small capacitances, a material called a dielectric is usually inserted between the plates to increase the capacitance. The charge polarization of the dielectric effectively partially cancels out the electric field, leading to a device that holds more charge and energy for a given voltage. . It was found over the decades that creating a special double layered dielectric consisting of two layers of porous carbon separated by a charge barrier would enhance this effect294 and increase the capacitance by more than a millionfold. These capacitors are called “supercapacitors”. It is now possible to obtain supercapacitors with many thousands of Farads of capacitance. . A graph tracing the progress of supercapacitors through 2008 in relation to various types of batteries can be found in technology trend research at MIT295. This data reveals that although supercapacitors (which are labeled simply “Capacitors” in the key for this graph) had energy densities far below those of batteries, the growth rate of their energy density has been far faster. Moreover, the graph is plotted on a log-linear scale, so the apparently nearly linear trend for supercapacitors it reveals actually represents exponential growth in energy density. Finally, it follows from extrapolation of this graph that supercapacitors will overtake batteries if this trend continues. . Recent research appears to confirm that this trend is continuing, and in fact may be accelerating. In 2010 a group of researchers announced that using specially prepared graphene can achieve energy densities of 85.6 Wh/kg at room temperature, which is comparable with nickel-metal-hydride batteries, and up to 136 Wh/kg at 80 °C296, which falls in the Lithium-ion range. Graphene consists of a single layer of carbon atoms, and is one of the most conductive materials known to exist. . In 2012, another group announced that it succeeded in using an inexpensive “LightScribe DVD burner” to create graphene supercapacitors with energy densities comparable to LI batteries and three order of magnitude faster charging/discharging rates297. o Compressed Air Energy Storage: Compressed Air Energy Storage (CAES) involves using excess electrical energy to compress air, and then later allowing the pressurized air to flow back through and power a turbine. In conventional approaches, this occurs with the combustion of some natural gas in the turbine to achieve the proper operating conditions. . Traditionally, CAES facilities (the few that exist) utilize large-scale underground caverns. These can actually be created quite easily by either solution-mining salt domes or utilizing aquifer structures in regions with the correct geological conditions. The approach has been successfully generated in the US and Germany at two facilities for load shifting applications (shifting night time generated power to peak times) for several decades. . One problem with CAES up to this point, however, has been the fact that the compression process also heats the air, which leads to a rather low overall efficiency of about 42%. This has led a number

294 http://www.nrel.gov/vehiclesandfuels/energystorage/ultracapacitors.html 295 “A functional approach for studying technological progress: Extension to energy technology,” Heebyung Koh, Christopher L. Magee, Technological Forecasting & Social Change 75 (2008) 735–758. 296 http://physicsworld.com/cws/article/news/2010/nov/26/graphene-supercapacitor-breaks-storage-record 297 http://www.extremetech.com/extreme/122763-graphene-supercapacitors-are-20-times-as-powerful-can-be-made- with-a-dvd-burner

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of companies to seek a method to store and then recapture the heat298. Three of these companies and their approaches are:  RWE299 and GE: These partners are attempting to use ceramics to store the heat. The technical feasibility has been, but R&D is still in process.  SustainX300: This company, a Dartmouth spinoff, is attempting to commercialize “isothermal CAES”, wherein the extra heat is stored temporarily by injecting water vapour. The water absorbs the heat and is then stored and reapplied to the air during the expansion process. The company also uses steel pipes to store the compressed air, allowing its systems to be installed anywhere. A 40 kw system exists, and a larger project is in process. Their design also does not require natural gas.  General Compression301: This company has also developed an isothermal CAES system, but unlike SustainX is planning on using underground caverns. Vermont likely lacks the kind of geologic conditions required for cost effective CAES facilities. In principle, a hardrock underground cavern could actually provide very good CAES storage, but would likely be prohibitively expensive to excavate. Because their systems do not require underground caverns, and are scalable, and do not require nature gas, it would appear that the SustainX approach may be best suited for Vermont. o Pumped Heat Electricity Storage: This is (apparently) a new form of electrical energy storage under development by the company Isentropic. An article describes Isentropic’s approach as using “argon gas to transfer heat between two vast tanks filled with gravel. Incoming energy drives a heat pump, compressing and heating the argon and creating a temperature differential between the two tanks, with one at 500°C and the other at -160°C. During periods of high demand, the heat pump runs in reverse as a heat engine, expanding and cooling the argon and generating electricity. Isentropic says its system has an efficiency of 72-80%, depending on size302”. Another article notes that the approach is specifically based on the “First Ericsson cycle303”. . The company’s current goal is to deploy a 1.5-megawatt, 6-megawatt-hour storage unit on a U.K. primary substation. o Molten Salt Thermal Energy Storage: Although a thermal energy technology, this was specifically developed by the DOE and its private sector partners for large concentrating solar power (CSP) plants, and for “power tower” type CSP plants. These plants produce extremely high temperature heat, and it was desirable to identify a working fluid that could be used both to collect solar heat at the central receiver and to store it. . The researchers involved found that various mixtures of sodium nitrate and potassium nitrate salts (common fertilizer ingredients), provide a very suitable working fluid for this purpose. The approach

298 http://www.economist.com/node/21548495 299 http://www.rwe.com/web/cms/de/183748/rwe/innovation/projekte-technologien/energiespeicher/ 300 http://www.sustainx.com/ 301 http://www.generalcompression.com/ 302 http://www.economist.com/node/21548495 303 http://www.greentechmedia.com/articles/read/22M-for-Potential-Breakthrough-in-Energy-Storage-Isentropic- Energy/

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was thoroughly and successfully tested (including using the molten salt for thermal storage) at the Solar III power tower test station near Barstow, CA. . The advantages of using nitrate salts are they are liquid at high temperatures at atmospheric pressure (unlike water), and are environmentally friendly, durable, have fairly good heat capacity, are inexpensive, and are widely available . This technology survives today with several CSP companies, including BrightSource Energy’s SolarPLUS System304. It is not clear that this storage approach will have any relevance to Vermont. On one hand, Vermont lacks the levels of direct normal insolation required for CSP plants. On the other hand, if there was some reason to store thermal energy at high temperatures, say in conjunction with a gasification process or some other heat source, molten salt technology might be useful. o Magnetic Energy Storage: Also known as “Superconducting Magnetic Energy Storage (SMES)”, this type of energy storage involves storing energy by creating a magnetic field with a doughnut shaped coil of superconducting wire. These storage systems are generally designed for short term storage, and are potentially useful for certain grid applications due to their high efficiency and short charging and discharging types, which are analogous to supercapacitors. . Due to their reliance on superconducting material, however, these systems have tended to be expensive, and to have relatively low capacities. . The company ABB, however, claims to be developing “superconducting magnets that could store significantly more energy than today’s best magnetic storage technologies at a fraction of the cost.305”

304 http://www.brightsourceenergy.com/brightsource-energy-launches-solarplus%E2%84%A2---high-efficiency-soar- thermal-power-plants-with-storage 305 http://arpa-e.energy.gov/ProgramsProjects/GRIDS/SuperconductingMagnetEnergyStorageSystemwith.aspx

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Wind Power (Placeholder only, section to be Finished by VAAFM staff)  Technology Description: o A wind turbine, consisting of a spinning set of blades (rotors) attached to a horizontal shaft which turns a generator (often via a gearbox), generates electricity from the kinetic energy of the wind.

 Technology Special Benefits: o At good wind sites, wind turbines can produce substantial amounts of electricity. o The Bergey 10 kw (the most common turbine in Vermont) has a good track record relative to other small wind turbines.

 Overall Prospects for Successful Deployment: o Good at farms possessing a good wind resource. Possibly small (due to resource scarcity).

 Development Status: o A little over 100 grid-connected small wind turbines exist in Vermont, many of which are on farms. (Overall performance of these is unknown)

 Barriers & Opportunities: o Small wind turbine technology has advanced significantly, and certain brands have more or less emerged as standards. o Thorough evaluation of a potential site’s wind resource is an essential first step, but can be fairly cost and time intensive. Computer evaluation tools appear to have improved, however, and some relatively cost effective anemometer systems are now available. o Wind turbines require fairly regular maintenance, and have visual, aesthetic, environmental, and auditory impacts, which must be considered carefully, and which can bear significantly on the practical viability of a proposed project. Smaller turbines (e.g. 10 kw – 120 kw) are perhaps more likely to be acceptable to neighbors. o Tilt-up towers can help make maintenance more manageable and less costly o The actual performance of wind turbines at farms in Vermont should be assessed and used to validate and improve site assessment methodologies.

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Solar/Battery Powered Farm Equipment  Technology Description: o Electric tractors, utility/cargo vehicles, cultivators, harvesting equipment, and other equipment that utilize batteries and electric motors, such that they can be “fueled” with renewable electricity sources.

 Technology Special Benefits: o High Power: The high torque at low rpm of electric motors is ideally suited to farm machinery. o Weight: The extra weight of the batteries can actually be an asset to equipment such as tractors. o Shade: For some equipment, PV modules can be mounted over the operator to provide both shade and additional charging, and will generally have good sun exposure all day long. o Low Impact Operation: Electric equipment is generally much quieter, and has no point-source emissions. o Low RPM: Very low rpm operation can be easily achieved, which is useful for certain applications such as harvesting equipment.

 Overall Prospects for Successful Deployment: o Prospects for Smaller Equipment (under 100 horsepower) are Good: . Battery power-density and weight calculations (performed for this report) suggest that battery packs for smaller equipment will not be too large or heavy for smaller equipment. . GE recently announced a joint project to develop such equipment with a Chinese company306. . As described below, small electric tractors have been successfully marketed in the past, and are still maintained and used by some, and some individuals have retrofit larger equipment successfully. The increasing activity in this community suggests there is an increasing level of interest in electric farm equipment in general. Some small-scale commercial and pre-commercial activity around smaller equipment also already exists. . The decreasing cost of solar power coupled with the high efficiency of electric motors may enable solar electric farm equipment in general to become directly competitive. . In addition to being able to power electric farm equipment with renewable electricity, electrical equipment can also be much quieter, more reliable, and creates no harmful point-source emissions. . Unlike electric cars and trucks, the extra weight of batteries can be an asset for tractors. . Electric motors have high torque at low rpm (which is useful at least for drive systems). . PV arrays are relatively light, and can be used to provide needed shade as well as power, and in the future may be significantly more efficient (more powerful per unit area). . Electric drive technology (motors, gearing, etc), has advanced substantially over the past decade due to general interest in electric vehicles, including some R&D specifically on electric farm equipment307. . Some significant advances in battery technology have occurred over the past decade, for example the development of advanced lead-acid batteries (e.g. “lead-carbon” batteries) and lithium ion batteries, and further advances can be expected.

306 http://news.xinhuanet.com/english/china/2012-05/18/c_131597112.htm 307 http://farmindustrynews.com/electric-tractors

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. Unlike electric cars and trucks, farm equipment does not require a massive network of re-charging or hydrogen re-fueling stations. . The current trend in tractors appears to be providing electric power generators on tractors for accessories, which may help pave the way for fully electric tractors (but also has a disadvantage, in that tractor electric loads may increase substantially). o Prospects for the commercial availability of large electric farm equipment (>100 hp) are mixed. . Very high energy/power density storage will be needed, such as hydrogen fuel cell storage, and although advances have occurred, such storage is not yet commercially viable. . The company New Holland has in fact already developed a large fuel-cell powered electric tractor, but is also on record predicting it will take another decade for electric tractors to appear308, and there is little indication that other major manufacturers are actively pursuing large electric tractors (although it appears that John Deere has actively sought to explore advanced motor technology and could likely easily pursue R&D on this due to relationships it has established).

 Development Status: o Interest in electric farm machinery appears to be rising. o A vibrant community of people, including some in Vermont, maintain older electric tractors. o Various individuals and small companies are developing small electric tractors and other electric farm equipment. o GE recently began partnering with a Chinese company to manufacture lighter duty electric tractors.

 Barriers & Opportunities: o New Industry Opportunity: The technical prospects and potential benefits for smaller equipment are such that a near term opportunity for Vermont may be encouraging the development of a new local industry that provides conversions and/or manufactures innovative new equipment. Such an industry would be analogous in many ways to the Vermont woodstove industry. It should also be noted that the use of smaller electric farm equipment may be especially well suited to the scale and nature of farms in Vermont, and more so than, say, the more industrial scale of farms in the Midwest. o Lead-Carbon Batteries: The recent emergence of lead-carbon batteries may offer a near-term opportunity to develop cost effective electric farm equipment. See the section on Electrical Storage Technologies for more information. o Survey of Existing Electric Tractors: . A company called The Electric Tractor Store in Virginia309 has provided parts to owners of older electric tractors since 2007, and has recently expanded its operations. . The Elec-Traks Owners Club310 actively facilities communication between dedicated owners of the GE Elec-Trak, an electric tractor manufactured by GE in the 60s and 70s, and related models by the companies Redhorse and New Idea. A collector has posted detailed descriptions and documents

308 http://farmindustrynews.com/row-crop-tractors/new-holland-hydrogen-fuel-cell-tractor 309 http://electrictractorstore.com/ 310 http://www.elec-trak.org/

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pertaining to many of these models311 (which he powers with solar power), and a listing of electric tractor sites (including all three models) can also be found312. . The Sunhorse 4812 All Electric Tractor by FreePower Systems is a new tractor design with an on- board PV array313: The company plans to market this tractor starting in 2013. The Sunhorse features an 8 HP motor, a category one three point hitch with power-take-off (PTO), and a 200 watt PV panel. . The Electric Ox by the Canadian company Electric Tractor Corp314 is a small electric tractor that has already been marketed recently (the company states that it is presently in the midst of a product “re-launch.”) In the past the Electric Ox has sold for about $8,000, and the multi-purpose version marketed previously could be fitted with a 44-inch mower deck, sweeper blade/brush, and 48-inch dozer blade. . PV installer Steve Heckeroth, apparently in a collaboration with Professor John Fabel at Hampshire College and “several major manufacturers315”, has created a prototype "Solar Tractor" has developed a prototype electric tractor with an on-board PV array. This tractor utilizes two 10 hp motors to drive the rear wheels, powered with a 5 kWh battery316. The tractor has a PTO driven by separate motors, which the website states can run any category I implements. Predicted cost is $15,000 - $25,000, although no production is apparently planned. The website mentions two possible size options for the on-board PV capacity (300 W and 1 kw), and the option of adding auxiliary battery packs for extending use or power. . PV installer Steve Heckeroth has also converted a Yanmar tractor with a front loader that falls in this “utility tractor” range317: He utilized 12 Interstate 125 batteries. . Many Allis Chalmers "G" Cultivating and Seeding tractors have apparently been converted, and complete instructions can be found online318. These tractors, which can still be found for sale, were built in the late 1940's and 50's and lack a 3 point hitch system and have a non-standard PTO. They are therefore not usually used to plow or disk fields, but they useful for seeding and cultivating. Conversion costs appear to be $3000+, but are said to be straightforward due to the manner of mounting of the original engine. Users report several hours of use per charge319. An Allis Chalmers tractor was historically the first fuel cell powered vehicle. . The Italian company Bagioni Alfiero offers some harvesters especially designed for asparagus and other crops320, which sells for about $5000. . An individual with the moniker “PD-Riverman” has constructed a solar powered machine for planting, picking, and pulling, named the “P-Machine”321: This drive system for this hand-welded machine is from an electric wheel chair.

311 http://www.myelec-traks.com 312 http://www.econogics.com/ev/etsites.htm 313 http://www.freepowersys.com 314 http://www.electrictractor.com/etc_about.asp 315 http://www.eeevee.com/tractors/TNF_article.html 316 http://www.renewables.com/Permaculture/ETractorSpecs.htm 317 http://www.evalbum.com/216.html 318 http://www.flyingbeet.com/electricg/ 319 http://www.youngfarmers.org/farm-hack/2010/12/05/farmhack-tools-electric-g-tractor-conversion/ 320 http://www.asparagus.it/ 321 http://www.builditsolar.com/Projects/Vehicles/GardenHelper/GardenHelper.htm

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. The John Deere company offers small electric utility vehicles, such as the TE 4X2 Electric322. This vehicle costs about $10,500. . GE recently announced a joint project to develop energy-efficient and environmentally friendly electric tractors” that they hope “ will be able to mow lawns, maintain domestic gardens and undertake light agricultural operations” with a Chinese YTO Group Corporation323. . As of 2012, the company Valtra is developing a special modular tractor technology with units that have power capacities of 100 and 200 kw324. Referring to the power sources for this, an article states it “is powered by electricity produced in various ways, including batteries, fuel cells and turbo generators, or through a highly efficient internal combustion engine that can exploit biogas or bio diesel produced on farms325.” . In October 2010 New Holland displayed a hydrogen fuel cell powered tractor, the NH2, that they stated had been developed two years previously. The company also stated that it would probably be another decade before viable alternatives to diesel fueled tractors would be available326. In March 2012 indicates that New Holland is still working with the NH2 and described it as having a 104 HP fuel cell (which would be equivalent to about 80 kw)327.

322http://www.deere.com/wps/dcom/en_US/products/equipment/gator_utility_vehicles/traditional_utility_vehicles/t_se ries/te4x2electric/te4x2electric.page 323 http://news.xinhuanet.com/english/china/2012-05/18/c_131597112.htm 324 http://www.valtra.com/news/4767.asp 325 http://www.assemblymag.com/articles/89880-green-tractors-on-the-horizon- 326 http://farmindustrynews.com/row-crop-tractors/new-holland-hydrogen-fuel-cell-tractor 327 http://www.assemblymag.com/articles/89880-green-tractors-on-the-horizon-

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Energy Efficiency  Technology Description: o There are many opportunities for efficiency improvements on farms, which roughly divide into opportunities for improved retention of thermal energy (e.g. building thermal envelopes), heat recovery opportunities, electrical efficiency opportunities, and fuel efficiency opportunities. These are interrelated in some cases, for example, where heat recovery can be used to decrease the electrical consumption of a hot water heater. The following lists some of the specific energy efficiencies measures that can be implemented at farms today. Efficiency Vermont already supports all of these as possible measures, subject to cost effectiveness requirements: . Lighting: Incandescent bulbs should be replaced with Energy Star certified compact fluorescent lamps (CFLs), or LED lighting (in the case of outdoor lighting). CFLs use 75% less energy and have a life span of 6,000-10,000 hours (LEDs have even better numbers). Cold cathode fluorescent lamps (CCFLs) are also an option in cases where either a dimmable light is necessary or where an extremely long life lamp life is important (rated for 25,000 hours).  Screw-in CFLs are appropriate and convenient in many applications as a replacement for incandescent bulbs.  For low bay lighting (< 12 ft) in particular, such as in a dairy, an effective measure is to install a sealed and gasketed EV qualified HPT8 lighting system.  In areas where increased light levels are needed (e.g. the center alley of a tie stall), T5 high output (T5HO bulbs) are a good choice.  In high bay lighting (>12 ft), the commonly found “probe start” 400 watt metal halide lamps can be replaced with “pulse start” 320 watt metal halide lamps, which will provide more light, better starting, and 25% less electricity consumption. Or 3 to 6 lamp EV qualified HPT8 fixtures can be utilized instead. . Milk Cooling: Dairies should consider installing either a plate cooler or a refrigeration heat recovery unit (RHRs), or both (both especially for larger dairies). High efficiency compressors should also be used when cost effective. . Plate coolers are plate metal heat exchangers that enable milk to be cooled with well water. The warmed water can also be stored and used for washing, or for watering cows. Warmed water is less stressful metabolically on cows, and research shows that cows will drink more of it. A variable speed milk pump (VSMP) can be used to slow down the flow of milk achieve greater cooling and lower the amount of water needed. . Refrigeration heat recovery units (RHRs) consist of a hot water storage tank with a built-in heat exchanger through which the output of the milk cooling’s system compressor is circulated. . High efficiency scroll compressors are 15-20% more efficient than the older hermetic reciprocating compressors, and should be installed when economical (for example when a compressor needs to be replaced). . Ventilation: For example, high volume, low speed (HVLS) Fans. HVLS fans are overhead fans with large diameter paddle fans (ranging from 8’-24’ diameters) that operate at slower speeds (rpms). o References: . Efficiency Vermont: http://www.efficiencyvermont.com

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. Massachusetts Farm Energy Program Guide: http://www.berkshirepioneerrcd.org/i/publications_26_1559619182.pdf

 Technology Special Benefits: o Energy efficiency measures are often both cost effective and environmental beneficial. o Reducing electrical energy consumption reduces the need for infrastructure investments.

 Overall Prospects for Successful Deployment: Very good.

 Development Status: o Vermont is fortunate to already enjoy the services of Efficiency Vermont (EV), the first statewide energy efficiency utility in the nation. EV provides technical assistance and financial incentives to help Vermont households and businesses reduce their energy costs with energy-efficient equipment and lighting. Efficiency Vermont also provides energy-efficient approaches to construction and renovation . EV began providing efficiency services to Vermonters in 2000, and in 2007 succeeded in assisting Vermont to become the first state in the nation to have negative electrical load growth. More recently, the utility helped Vermont achieve a 1.91% reduction in electricity use in just 2011 alone. . EV is operated by a private nonprofit organization, the Vermont Energy Investment Corporation, under a competitively awarded appointment administered by the Vermont Public Service Board. VEIC was founded in 1986 by Beth Sachs and Blair Hamilton with a goal to reduce energy costs for consumers by promoting energy efficiency and encouraging the conservation of natural resources . EV has an Agricultural Services Program, which among other things “provides standard rebates to Vermont agricultural facilities for installing Heat Recovery Units, Plate Coolers, Variable Speed Milk Transfer Systems (VSMT), and Variable Frequency Drive Controllers (VFD) on Milk Vacuum Pumps and Maple Sap Vacuum Pumps.” . During the period 2009-2011, EV reports that is has worked with 701 distinct farms, assisting each operation with one to several individual projects. The majority (95%) of these were dairies. EV estimates they have worked with 60-70% of VT dairies to date, and due to their success are presently finding fewer and fewer short-term payback measures to do at dairies. . EV has identified that upgrades to refrigeration at farms in VT in general is still a major need. The utility also has some depth of insight on this. For example, their analysis to date suggests that walk- in coolers are probably not cost effective for most farms, although larger commercial refrigerators may be.

 Barriers & Opportunities: o Although LED lighting is significant more efficient that fluorescent lighting, EV does not recommend using LEDs inside farming facilities, at least at this time, although outdoor applications are encouraged where cost effective: EV finds that LED fixtures are still too expensive (roughly $500-$600 per fixture, which is several hundred more than fluorescent fixtures), and the utility has concerns about the fins clogging up leading to premature burn-out. EV also says manufacturers have not actually tested LEDs inside farming facilities. Given the high efficiency of LED lighting, however, the cost and technical

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feasibility of using LEDs for farms should be monitored, and EV may do a pilot project in the future depending on current conditions. o EV finds that for milk cooling operations it is often not cost effective to upgrade to a more efficient compressor until the existing compressor fails. o EV finds that it is now commonly assisting the replacement of older plate and refrigeration heat recovery units. o EV is witnessing that the rate of farm energy audits has been decreasing, but that much or most of the information for achieving improvements can be communicated by email and phone. o In the past, EV rebates covered 60-80% of project costs, but is now covering roughly 20-30%. The rebates are now also based on flat rates for each measure. For example, the rebate for a plate cooler is now fixed at $1500, which works out to be 20-30% of the average cost. EV confirms that some fraction of projects are not going forward due to a combination of lower rebates, low milk prices, high feed prices, etc. EV also finds that many farmers are currently focusing more on repairs instead of upgrades. o EV has done one solar hot water project for a dairy farm (replacing an electric hot water), a project which did pass the cost-benefit test. EV is not promoting this measure yet in general because they are not sure it will prove widely cost effective, and no one has been approaching EV for solar hot water for dairies either. See the section of this analysis on solar hot water for more information about how the costs of solar hot water for farms might be decreased. o EV has not worked extensively on greenhouse heating, or maple production (reverse osmosis) or other fossil fuel heating related applications. This is mainly due to insufficient funding. o EV’s mandate has been expanded to thermal energy, but the funded for this is very small. More specifically, funding for thermal is based on the forward-capacity market in the NE-ISO (New England Integrated System Operator – the organization the operates the New England grid). EV bids into the “forward-capacity market” with efficiency reductions. This provides EV with certain funds in return that are currently dedicated to thermal applications. This budget is much less than the electricity funding: Only $20,000 for the AG program in 2012. EV would like to see this increase. o EV has done a few “cheese cave” projects. EV might be interested in increased use of root cellars, and would be open to exploring the economics of this option.

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