Low-head micro-hydroelectric demonstration project at a former grist mill site Stevens River, West Barnet, Vermont
Objective: Design and build a small “run-of-the-stream” turbine for a former mill brook to: • Generate individual household power with a clean, sustainable, and locally available resource as a demonstration project for the community • Research and document power usage and storage requirements
Goals: 1. Generate approximately 100W power 2. Installation must be environmentally friendly 3. Installation should be aesthetically acceptable 4. Setup should continue to operate winter and summer 5. Low maintenance, withstand occasional floating branches, etc.
Deliverables: Build and install full-size working prototype of turbine and generator. If necessary, full-size model could be appropriate.
Background: New England is endowed with abundant streams, rivers, and lakes, which create many hydropower opportunities. In the eighteenth and nineteenth centuries, New England was home to numerous water-powered mills of all types, from huge factories to small local grist-mills and saw mills. Some of these sites, especially the largest, are now used for electrical power generation, but many of them were abandoned or dismantled. Numerous small dams which created head for these sites have been removed to address environmental concerns or because they are in danger of failing. There is presently a lively renewed interest in sustainable, non-polluting power generation. Small-scale installation of solar panels and wind turbines is encouraged with tax incentives to improve our supply of clean power and diversify the grid. Until recently, small hydropower has not received the same attention as wind and solar, largely due to constraints on site availability and environmental issues, but it appears that this is beginning to change. For instance, Renewable Energy Vermont (www.revermont.org) is sponsoring a drive for a Town Meeting referendum encouraging small-scale, environmentally-friendly hydro-electric projects (brochure attached).
History and description of the site: The site is a former gristmill, now a seasonal residence, on the bank of the Stevens River in the small farming village of West Barnet, Vermont. The Stevens River is a fairly fast-running mill brook and trout stream. It is shallow, about 20 feet wide, and flows year-round without freezing near our site. The river has its source in nearby Harvey’s Lake, a glacial kettle some 400 acres in size and over 50 feet deep, and it empties into the Connecticut River 6 miles downstream in Barnet Village. The first gristmill on the site was built by Walter Brock, who settled in West Barnet in 1776. It was water-powered by means of a flume which ran to a dam at the outlet of Harvey’s Lake, about a thousand feet upstream (see attached aerial photograph). A sawmill next to the dam shared the water power. By 1900, this gristmill is said to have done twenty thousand dollars of business annually. The original mill burned down, and a second mill was erected in 1906 on the same site, using a existing building moved from nearby South Peacham. This new gristmill is said to have had a “modern” mechanical turbine similar to the one still present at Ben Thresher’s Mill, two miles downstream. Ben’s Mill continued to operate by water-power until the early 1980’s. It was the subject of a 1981 PBS documentary, and is now being restored as a working mill and historic site. The turbine at Ben’s Mill is large enough for a man to climb inside; it generates 30 horsepower on about 10 feet of head. The gristmill property was purchased by the E.T. & H.K. Ide Company in 1930 for use as a feed store. It continued in this use until 1970, at which time the right to run a flume to the Harvey’s Lake dam was surrendered. The present dam, owned by the town of Barnet, is a concrete structure dating to 1975, and is said to be in good condition. In the early 1980’s the former gristmill was converted to a residence. Only a few traces of the mill works remain visible below the building, the floor of which stands some 12-15 feet above the stream at the very edge of the water. A ditch (the former tailrace) exits from below the foundation and rejoins the river about 50 feet downstream; it is pretty well silted up at present. The property, which includes the riverbed and land on both banks, apparently retains the remains of the old mill privilege -- that is, hydropower rights to the Stevens River from the end of the tailrace up to a point 100 feet below the Harvey’s Lake dam.
Problem Statement: Because the dam is no longer included in this property, very little head will be available for this project. (Lots of kinetic energy, very little potential energy.) Some turbine possibilities might be: • a submerged open-stream turbine (propeller, helical, or other design) • a traditional waterwheel (such as a Poncelet or other undershot wheel) • a very low-head reaction turbine (such as Kaplan or Francis) In addition to the selection and design of an appropriate turbine, there are some practical issues to address. • How would the turbine’s mechanical power be transferred to a generator? • How would the turbine and generator be mounted in or near the stream? • How would the turbine be protected from water turbulence and stream debris?
Commercially available micro-scale low-head turbines: There is a commercially available run-of-the-stream propeller-style turbine and generator, the Aquair UW, that can generate up to 100 watts (8 Amps) from a stream flowing at 15 kph. Minor modification of the stream bed (moving a few rocks around) would probably be necessary to create an installation site with sufficiently fast and deep flow for this turbine. It is available from several online sources for about $1300, brochure attached. It might be possible to collect water by means of a small open flume or irrigation pipe and discharge it several hundred feet downstream, thereby gaining a few feet of head (probably less than 5 feet). However, construction and maintenance of the flume would present a number of problems (esthetics, preventing ice formation, keeping out debris, etc.) The LH1000 low-head turbine produced by Energy Systems & Design could produce between 100 and 1000 watts on 2 to 10 feet of head with such a setup, see the attached brochure. It costs about $2400, including the generator and tailwater draft tube but not the required penstock/flume.
Attachments, References and Links:
1. Attachment: Aerial photograph of 307 West Main St., Barnet VT, obtained from http://terraserver.microsoft.com 2. Attachment: Photograph of the Stevens River behind the former mill building 3. Attachment: brochure from Renewable Energy Vermont: http://www.revermont.org 4. Link: Ben Thresher’s Mill, http://www.bensmill.com 5. Attachment: Aquair UW Turbine color brochure, http://www.boost- energy.com/ampair/products_product5.asp 6. Attachments (2): Energy Systems and Design LH1000 turbine, color brochure and owner’s manual, http://www.microhydropower.com 7. Attachment: “The Poncelet Design”, online historic article, The Waterwheel Factory, http://www.waterwheel.com 8. Attachment: “The Darrieus turbine, Turbine Construction”, Alternative Hydro Solutions Ltd., http://althydrosolutions.com/ 9. Attachment: “Micro Hydro Power”, online article on modern low-head water wheel design, The Sustainable Energy Research Group at the University of Southampton, UK, http://www.energy.soton.ac.uk/research/microhydro.html 10. Attachment: “Microhydro-Electric Systems Simplified,” by Paul Cunningham and Ian Woofenden, Home Power Magazine vol. 117, pp 40-45, http://www.homepower.com/files/featured/HP117_pp40-45_Cunningham.pdf 11. Attachment: “Homebrew Hydro Electric: Hydro Electric experiment with direct drive PM Alternator”, online article with photos, http://www.otherpower.com/scotthydro1.html
Attachment 1. Aerial photo of site in West Barnet, VT. Obtained from http://terraserver.microsoft.com Harvey’s Lake is below the lower boundary of the picture.
Photograph of the Stevens River, looking upstream, with the back of the former mill on the right.
This picture was taken in February, 2006, and shows the extent of winter ice formation in this part of the river.