Electricity on Demand

t takes neither a science fiction fan nor a clairvoy- ant to launch the theory that electricity will be the Ideterminant energy form of the future. It is simply the most logical development. Electricity can be used safely and efficiently in all manner of applications, and – when generated from a renewable source – is also clean energy. But electricity does have one decisive disadvantage: it must be consumed immediately – storage has to date remained both complex and subject to expensive losses. The limited capacity of storage batteries, for example, is the chief obstacle to the widespread breakthrough of electric cars, a path of development with the potential to solve a massive share of the glo- bal CO2 problem. When oil tanks or coal bunkers are taken as the yardsticks for the energy density, cost ef- fectiveness and useful lifetime of electricity storage technologies, it becomes painfully evident: the storage problem is yet to be solved for electricity. This fact naturally has direct repercussions for the photovoltaics sector with its dependence on sun- light as a primary energy source. When the European PV industry claims that it is prepared to cover half of the continent’s power demand with solar electricity by 2050, then this must necessarily be described as ambitious. It will require not only reliable supplies of materials, sufficient investment capital and adequate manufacturing capacities, but also a solution to the storage problem – and that well before 2050. Many circumstances can be covered by the power supply systems in the industrialised countries, but one option is very definitely unacceptable, namely that half of the generating capacity simply goes off-grid when darkness falls. If electricity is to be generated from renewable sources on a larger scale, then it must also be possible to store it. Of the renewable energies currently under discussion, only biogas seems suitable as a baseload source. Wind and solar energy, by con- trast, are subject to marked fluctuation: you may get the full nominal output, or nothing at all – depending Decentralised and fluctuating power generation from the sun and wind is becoming on the momentary irradiation or wind intensity. more and more widespread. The expansion of power grids is thus important – but still not sufficient. Storage capacities are imperative. Photos (2): E.on Netz Diverse approaches

Various, in some cases quite exotic projects are aimed at overcoming today’s expensive and cumber- some battery concepts. In 2007, there were press re- Electricity on ports that Sony is working on a bio-battery which functions on the principle of photosynthesis. A year ago, news spread concerning experiments aimed at developing a bio-battery at the University of Colora- do. The idea: cells pump ions through a membrane demand and produce a potential difference which can be ex- ploited. It is similarly two years since the scientific There are certain technology challenges which have waited journal “Technology Review” reported on a battery prototype devised at the Japanese elite university in vain over several decades for a satisfactory solution. The Waseda. It is less than a millimetre thick, can be fully economical storage of electricity is one of them. But charged in just one minute and is said to handle 1,000 charging cycles. The positive electrode of the intensive work in the meantime is driving advances along battery is made not from a metallic compound, but in- stead from polymers. The cathode film forms only af- various avenues . ter the precursor material is subjected to UV radia-

108 Sun & Wind Energy 4/2009 tion. According to “Technology Review”, the perfor The first commercial availability is expected for 2009, mance data of the battery are satisfactory: 0.84 volts but there are only two manufacturers worldwide. and a specific capacity of 106 mAh. The journal has also described a flexible battery in connection with Vanadium redox flow battery: This battery type func- the European solar polymer battery project: this bat- tions with salts dissolved in a liquid electrolyte. The tery comprises further-developed lithium ion batte electrolyte is held in separate tanks and is only ries which are charged via an integrated dye solar pumped to the electrodes and the membrane in the cell. The battery is extremely thin and light, and with- central reaction cell when necessary. The vanadium stands also high temperatures. But several more redox flow battery is just one of a number of material years can be expected to pass before these new con- variants, but “is still the only one which functions”, cepts are ready for practical applications. says Dirk Uwe Sauer, Professor and storage expert at the RWTH University in Aachen, Germany. This points Common battery concepts to interesting cost-reducing potential, because vanadium, after all, is expensive. The batteries impress by For the time being, we must continue to make do with way of a long lifetime and their insensitivity to deep the familiar electrochemical storage media which discharging. There are presently three commercial function according to the principle: Electrode materi- suppliers, one of whom – VRB Power, headquartered al reacts with electrolyte. The lithium battery is the in Richmond, Canada – covers the wider spectrum only chemistry-free alternative: The ions are here from 5 to 10,000 kW. European Sales Manager Hugh pumped from one electrode to the other. Sharman estimates the 2008 turnover to have been Only a few of the battery concepts can be deemed one million dollars and sees an annual “doubling, if promising, as an overview reveals: not more”. According to Sharman, the concept has already begun to steal business from the lead battery Lead battery: This is still the workhorse option. The in the field of telecommunications. lead battery is an inexpensive, technically mature system with a high level of efficiency, but also one Sodium-nickel chloride battery: This “high-tempera- significant drawback: the limited lifetime. The high ture” battery – also known as the “ZEBRA battery” – weight is generally not a problem for fixed-location requires an operating temperature of around 350°C applications. Lead batteries are thus the measure for to be maintained, though this can be guaranteed any new storage technology. It is difficult to imagine through its own heat generation while kept on charge. any kind of further “research breakthrough” for this The lifetime of the sodium-nickel chloride battery fur- battery type. The massive demand for standardised ther exceeds that of the vanadium redox flow battery, batteries for fixed installations, however, could force its efficiency ratio is better, and it is also a little the price down still further: whereas the cheapest cheaper in daily operation. Vital development re- The tasks for grid control lead batteries with slow discharge rates for non- search is still ongoing, as there are safety issues con- centres – like that of the E.on mobile use are priced at around 100 €/kWh, car start- cerning the molten sodium, which causes sealing Netz in Lehrte/Germany – er batteries cost barely 25 €/kWh. problems. The battery is currently undergoing testing would be made much simpler in electric vehicles. The only two fixed installations to in future if solar electricity Zinc-bromine battery: This type of battery is in the date are to be found in Canada and Great Britain. could be stored at the place of meantime no more expensive than a lead battery, but generation. achieves twice the lifetime. Even so, it has so far not Sodium-sulphur battery: This battery has a lot in advanced beyond demonstration projects with stor- common with the sodium-nickel chloride battery, in- age capacities of up to 500 kWh in the USA and Japan. cluding the high temperature, and is already in quite

Sun & Wind Energy 4/2009 109 Photovoltaics energy storage

widespread use in Japan – albeit for grid stabilisation water which is required for an open lead battery. This rather than for off-grid energy storage. Again as with is no doubt in part why nickel-cadmium batteries are the sodium-nickel chloride battery, there is only one still the only non-lead systems in use for 840 instal- manufacturer of such batteries. lations with off-grid photovoltaic generation in China, for example. One important disadvantage is the re- Lithium-ion battery: The market share of this battery duced capacity after a partial discharge. Moreover, type is increasing constantly. To date, however, the the batteries contain more than 0.002 % of the high- extremely high efficiency and low weight – a decisive ly toxic heavy metal cadmium, which means that they factor for laptops, mobile phones and vehicles – have been banned in the EU since 2008 – with the ex- must be traded off again high costs and inferior safe- ception of batteries for cordless electric tools. ty. Dirk Uwe Sauer nevertheless expects “a significant reduction in the costs to around 300 €/kWh for Nickel-metal hydride battery: These batteries incor- non-mobile batteries without peripherals in the com- porate a cathode with nickel hydroxide and an anode ing years”, and believes that the technology could of a metal hydride – a metal alloy capable of revers play “a key role in many areas of electrical energy ible hydrogen storage. The electrolyte is an alkali of storage” in the medium term. This assessment is potassium. Nickel-metal hydride batteries have es- backed by the fact that there are many manufactur- sentially replaced their NiCd counterparts. The ener- ers and variants of the technology. On the other gy density is twice that of a nickel-cadmium battery, hand, the availability of lithium is as limited as that but they react sensitively to overcharging and over- of many other resources. heating. At around 20 ¤-ct/Wh, nickel-metal hydride batteries represent the second-most economical Nickel–cadmium battery: Apart from a long lifetime technology for energy storage in batteries after the In the SOLION house, a and operation at temperatures down to -40°C, the lead battery. lithium-ion battery serves as performance characteristics of this battery technolo- intermediate storage for the gy are rather average. Even so, the batteries have Research continues on all of these concepts – with electricity from the photovol- been sold by numerous manufacturers for many the exception of the lead battery. The problem, how- taic installation. years, and can furthermore do without the distilled ever, is reconciliation of the many different demands. Graphic: Saft Copyright

110 Sun & Wind Energy 4/2009 sessments, such as those of the Swiss bank Sarasin & Cie AG, support this assumption. How ever, if the production costs for solar electricity fall to the same level or even less than the average price for electricity from the grid, the operators of photovoltaic installations will use the electricity they generate themselves, and will feed only the excess into the grid. Furthermore, a steep increase in demand can be expect- Lighting the Way. ed in this case. The public grid, on the other hand, would then be affected to a much greater extent by the dis- AS Control PV tributed and fluctuating power Our manufacturer inde- generation. Answers to this chal- pendent, modular lenge are intelligent grid man- system can be used for agement, more accurate fore- monitoring any kind of PV-Central PV installation. It offers casting of the yields of solar gen- a large graphical touch erators, reserve capacity, and screen with easy, last but not least the facility to intuitive navigation and store excess electricity. It can al- wireless GSM trans- mission capabilities. so be excluded that even the best Inform yourself about management strategies could the many advantages render storage superfluous. on our website Alongside the positive effects for PV-Link www.as-portal.com Storage technologies such as this lithium-ion batte- grid stability, storage systems ry (10 kWh, 240 V) could buffer the PV electricity for would also offer additional bene- a domestic household. Photo: Saft Copyright fit to the PV operators – especial- Flat plate collector ly where the costs for their own The unique assembly design provides a An increase in lifetime, for example, is production lie below the price for power costefficient solution achieved only at the expense of energy or from the public grid. Local storage facili- allowing for quicker power density. ties would extend the effectively useful pe- installation times while riod by several hours, and thus into the maintaining reduced labour. Industry looking to night – and are thus also attractive from AS-FK photovoltaics an economic viewpoint. Industrial developments are first and fore- French-German project EVK tube collector most addressing a trend to increased over- The EVK offers a all battery system capacity. At the recent This opinion is shared by French manufac- top-performance due to 3rd International Conference on the Inte- turer Saft S.A. – one of the world’s fore- extensive fabrication gration of Distributed Energy Resources in most suppliers of high-tech batteries for experience and high-tech manufacturing with Nice (France) for example, Katsuya industrial use. Batteries from Saft serve as first-class materials and Ishikawa, senior development engineer energy buffers in high-performance appli- optional absorbers turned with the Japanese Kawasaki group, pre- cations, and the company is a world lead- by 30°. sented a so-called “GigaCell” – a nickel- er in the production of nickel-cadmium AS-EVK metal hydride battery with a capacity of and lithium batteries. In the meantime, 2,000 Ah. “We have two fields of applica- Saft is also looking out beyond its tradi- tion in mind”, said Ishikawa. “Firstly in tional fields of business and has discov- AS Solar GmbH www.as-solar.com Am Tönniesberg 4A Tel.: +49 511 475578 - 0 conjunction with the new Swimo light-rail ered photovoltaics. Together with the D - 30453 Hannover Fax: +49 511 475578 - 11 system, and secondly as a buffer for large- German and French system integrators AS Solar Benelux BVBA www.as-benelux.com scale solar installations and wind farms.” Conergy and Tenesol, the latter a joint ven- Nijverheidsstraat 10 Tel.: +32 51 4052 - 22 The strategic alignment towards pho- ture of the utility company EDF and oil B - 8760 Meulebeke Fax: +32 51 4058 - 22 tovoltaics is quite understandable. So- multinational Total, Saft last year founded AS Solar Ibérica de S.E.A. S.L. www.as-iberica.com C/La Resina 37, Nave 12 Tel.: +34 91 531855 - 4 called grid parity is to become reality in the project SOLION. “The objective of the ES - 28021 Madrid Fax: +34 91 531654 - 0 Central Europe around 2015, at least ac- SOLION partnership”, says company AS Solar France SAS www.as-france.com cording to the convictions of the European spokesperson Jill Ledger, “is to develop an 205-207 Avenue F. Roosevelt Tel.: +33 472 3714 - 33 Photovoltaic Industry Association (EPIA) integrated energy kit able to be produced F - 69150 Decines Charpieu Fax: +33 472 3716 - 61 and others. Even more conservative as- on an industrial scale for decentralised

Sun & Wind Energy 4/2009 Photovoltaics energy storage

on-grid, residential PV systems.” The French storage battery with ABB’s SVCLight technology. SVC stands specialists from Saft are responsible for the battery for “Static Var Compensator” and is a facility to com- station, which comprises a bank of series-connected pensate reactive power in distribution networks. It lithium-ion modules, each of which incorporates an permits fast and dynamic response to load fluctua- electronic board for the monitoring of voltage and tions, and thus dampens the variation which can lead temperature. The interface for system management is to grid failures. It can be imagined as a technology to to be a joint development of the two PV system inte- juggle with inductivities and capacities – hence the grators Conergy and Tenesol. It remains unclear to use of a lithium-ion battery. Per Eckermark, head of date, however, how and whether the system can be the FACTS system group at ABB, summed up the in- optimised to the point where the storage losses no tentions in Paris at the end of November 2008: “The longer devour the whole economic benefit of the sys- key aim of this project is to demonstrate the feasibil- tem. To be able to test this under real-world condi- ity and added value of incorporating Li-ion energy tions, Conergy and Tenesol are planning to install a storage within a FACTS system.” The integration of total of 75 systems – 50 in France, 25 in Germany. the two technologies is of particular significance for German and French institutes are accompanying the worldwide triumph of renewable energies, as these field trials. The first systems are still to be in- Eckermark underlined: “It could play a vital role in en- stalled, as the actual product development is not yet suring the stability of utility grids as the penetration completed. If the technology achieves a break- of wind power increases.” The fact that photovoltaics through, then the storage specialists at Saft forecast remained unmentioned at this point can be attribut- an enormous socio-economic impact: “Energy stored to the lesser role which solar generation currently age could offer a number of benefits. Mainly, it will plays in the energy mix. But that is a situation which help to stimulate the continuous growth of PV as an will change relatively quickly. element of the overall energy mix. At the same time, it will also help to reduce grid losses and encourage Hydrogen and the fuel cell reduced consumption in PV households.” It is beyond doubt that the new battery technologies Focus on grid stability have achieved decisive improvements, but they nevertheless remain tied to fundamental limitations: The stability of the distribution grids also stands at they are based on a chemical reaction, which places Pumped storage power plants the focus of another Saft undertaking. Four months a cap on their potential useful lifetime. Furthermore, like this one in Germany convert ago, Saft and the Swiss technology group ABB an- they are restricted to a particular temperature range. electrical into potential energy. nounced the provisional conclusion of a joint devel- All these factors add to the operating costs. Even Photo: dpa opment project. The new system combines a 5.2 kV though storage experts such as RWTH Professor Dirk

112 Sun & Wind Energy 4/2009 Sun and Wind Energy Half Page_4-09_Come to America.pdf 3/16/2009 4:12:29 PM

Uwe Sauer venture the prediction that electrochemical storage will still prevail in 2050, there are perhaps also promising alternatives: hydrogen and the fuel cell. This system comprises an electrolyser, a hydrogen tank and the fuel cell itself. Commercial systems are not available to date, al- though Austrian manufacturer Fronius has plans to add solar modules and an electrolyser to a fuel cell system which already exists as a prototype and is to be brought to the market at the end of 2009. The complete system is scheduled for a market launch from 2012. Test installations set up in cooperation with the HTL-Steyr technical college and the Upper Austrian utility company Energie AG are already in operation. Fronius representative Michael Schubert even prophe- sies that the hydrogen will still be delivered from the fuel cell (PEM) at a pressure of more than 150 bar without an exter- nal compressor. That would save the energy otherwise required for compression and thus improve the overall system efficiency. Schubert declines to reveal details on how that is achieved. There is also no word yet on the price – but the system is promised to be “economically attractive for autonomous applications with no connection to the public electricity grid.” The system is to be designed for an average output of 4 kW and will cover peaks with an additional battery. The electrolyser, hydrogen tank and fuel cell are to be ac- commodated in a housing similar to those of today (without electrolyser).

Solar pumped storage – M a realistic alternative? Y

CM Pumped storage power plants are today accepted as stand- ard installations to permit the use of wind energy – but there MY is no reason why that should remain their sole domain. The CY principle of pumped storage is very simple: the power to be CMY stored drives pumps to lift water from a river or reservoir in- K to a second basin at a higher level. When electricity is need- ed, the water flows back down via turbines and generates power. It is thus a reversal-mode system, which converts electrical energy into potential energy. Basically, pumped- storage plants could also be used to store solar electricity. Dirk Uwe Sauer agrees: “As far as the pumps are concerned, the source of the drive power is irrelevant.” The cycle times of several hours are similarly appropriate for the active pro- files of solar power generation – the downtimes in photovoltaics vary between 9 and 14 hours over the course of the year. All such plans are thwarted, however, by the power losses which are incurred with each conversion. A pumped- storage plant always consumes more energy to pump the water to the upper basin than it can later regain from the turbines. The losses still lie between 20 and 25 %, even for modern plants – much too high when operating with relatively expensive solar electricity. On top of this, pumped-storage plants are large-scale facilities and are thus hardly an ideal solution for the expected decentralisation of power generation with small and medium solar installations. The nominal outputs of pumped-storage plants lie between 5 and 1,000 MW. For residential PV applications, that is generally far too high and would mean providing appropriate area col- lection and transport facilities, which would reduce the efficiency still further. The situation could be more conducive, on the other hand, in the immediate vicinity of multi-megawatt solar installations.

Sun & Wind Energy 4/2009 113 Photovoltaics energy storage

creases with the square of its angular velocity. Only high-quality materials and special coatings are used to manufacture the flywheels, as practically loss- and wear-free rotation must be achieved at running speeds of several tens of thousands of rpm. Penta- dyne has developed the technology into a complete system which is suitable for purposes of grid stabilisation. Flywheels can be used where electricity is to be stored and reactivated within short periods. Sub- ject to appropriate modifications, therefore, the technology could also be employed to stabilise power grids with large numbers of fluctuating consumers. Pentadyne explains the benefits as follows: “Com- pared to batteries, the flywheel system has higher re- liability, vastly lower cost of ownership, near-zero maintenance, 99.998 % uptime availability and much longer useful life.” Another form of short-term storage for grid stabilisation is the ultracapacitor, or ultracap for short. Such capacitors possess an enormous power density and permit very short cycle times. They are based on a relatively new double-layer technology and comprise two metal or carbon electrodes in an electrolyte solution. When a voltage is applied, ions of the opposite polari- ty gather at the two electrodes, forming zones of im- mobile charge carriers. Charging and discharging is achieved by moving the ions within the electrolyte. The Through the rotation of a useful life of an ultracapacitor stretches to several flywheel, kinetic energy Flywheels and ultracaps hundred thousand charge/discharge cycles. They can be converted back into could be used as short-time storage to stabilise the electricity. Photo: Pentadyne A survey of the technologies for the intermediate stor- low-voltage grid of a solar neighbourhood. age of electric current would be incomplete without at least brief mention of two possibilities for electro- Texan super battery? physical storage. The US company Pentadyne is world market leader in kinetic energy storage by way of a But back one last time to the subject of batteries – flywheel. “A flywheel power system is a mechanical and to a concept which, despite appearing rather far- battery”, is the way the company describes its tech- fetched at first, could indeed prove to be a revolution- nology. Through the rotation, the temporarily stored ary approach. If the announcements from Texas can kinetic energy can be converted back into electricity. be believed, a solution to the storage problem is just It is most effective, however, to expand the energy around the corner. The American company EEStor storage capacity via faster rotation rather than great- claims to have developed a “super battery” with ten er masses, because the energy of a rotating disc in- times the storage capacity of a lead battery. And as if that were not enough: the weight is said to be only one-tenth of that of its lead counterpart, and the su- A brief history of energy storage per battery also costs only a fraction of the price of the already relatively inexpensive lead battery. The Around 1745, two scientists working independently of each other, namely Pieter van extremely short charging times and a practically un- Musschenbroek and Ewald von Kleist, developed the first capacitor. Their Leiden jar limited lifetime are similarly unsurpassed. To illus- was coated with tin on the outside and with gold on the inside. trate the dimensions of this invention: if an EEStor su- In 1796, the Italian count Alessandro Conte di Volta built the first actually func- per battery were to be made as heavy as a lead bat- tional electric cell, which delivered a voltage of 25 volts. He used various pairs of cop- tery, it would store one hundred times the amount of per, brass, silver and zinc electrodes, separated by pieces of cloth soaked in brine. energy, i.e. around 3 kWh/kg – and thus also 30 In 1802, German physicist Johann Ritter developed the so-called “Ritter pile” – a times more than the Li-ion battery which is currently stack of copper and brine-soaked cardboard discs. This device could be charged by considered the state of the art. applying a current and is considered the first accumulator. Only few details of the technology are known. In 1859, the French physicist Gaston Planté invented the rechargeable lead bat- One key step in the development at EEStor was an au- tery, which acquired its still characteristic box-like form in 1881. tomated production line for ultrapure barium tita Around 1899, Thomas Edison (USA) and Waldemar Jungner (Sweden) developed nate, which is subsequently sintered. This material the nickel-cadmium cell. belongs to the class of electroceramic materials and In 1935, a gas-tight nickel-cadmium cell was patented. is used, among other things, as a dielectric, i.e. as an 1990 saw the market launch of the nickel-metal hydride cell. electrical insulator with a high dielectric strength and thus as a central element in capacitors. The EEStor

114 Sun & Wind Energy 4/2009 development probably involves some form of ultracapacitor, but that in a kind of ultracap-battery hybrid rather than a pure capacitor technology. Storage experts remain sceptical. Their doubts are nour- ished by the company’s extremely secretive manner. No website exists, and no-one has yet actually seen the product. Normally, the whole story could be dismissed as a fig- ment of the imagination – if it were not for the press reports on possible cooperation partners which keep the old ru- mours burning: no smoke without fire. Two names have been mentioned repeatedly in the past: the Canadian auto- mobile manufacturer Zenn Cars is allegedly equipping its electric cars with the EEStor super battery – confirmation, however, is yet to be given. The second name: Lockheed Martin, the largest arms contractor in the USA. There seems to be no end to the reports on cooperation between the two companies. Only recently, on December 29, 2008, the re- spectable and serious “New York Times” wrote about the planned integration of battery units incorporating the EEStor technology into body armour and utility garments for US sol- diers. This would permit a significantly longer autonomous use of radios, night-vision devices, communication systems and GPS navigation, for example. If a super battery with the described attributes really exists, then in principle it would also be suitable for use in photovoltaic systems. From the little which is known about the technology, it seems that it could at least be beneficial for residential PV applications. It is hardly a good sign, however, that the military is apparent- ly involved. Many a past technical innovation, after all, has then been kept under wraps for years or even decades. As was said at the beginning: the economical storage of electricity is one of the greatest technical challenges since the invention of the dynamo. And it is common knowledge that the military usually demands first refusal wherever the “philosopher’s stone” is involved. Jörn Iken, Alexander Morhart

Thin films and batteries – related technologies

Microbatteries are a very promising line of development. Various function principles are found – on the basis of so- called MEMS: Micro-Electro-Mechanical Systems. They once used exclusively semiconductors, but plastics and even biological components are becoming more and more common. MEMS are not a single technology, but a whole family of different approaches, such as polymer- metal thin-film composites, for example. The future im- portance of this technology can be derived from the fact that Japan launched a ten-year research programme for more than 20 institutes in 2001. The applications for microbatteries are seen in intelligent plasters with medical sensors, paper toys or mul- tifunctional smartcards rather than large-scale PV systems. But that, of course, does not exclude future uses for microbatteries in smaller solar applications. Another interesting side aspect: the manufacturing processes for ultraflat microbatteries are quite similar to those used in thin-film photovoltaics. There is thus potential for valu able synergy effects in this field – both for the production and in applications.

Sun & Wind Energy 4/2009 115