The power industry works in cycles. Technical developments wax and wane over periods of several years. We have had boom years for the construction of CCGT plant, which is now followed by an emphasis on low carbon generation. Wind power continues to dominate the renewable energy sector. A few years ago, the talk in the energy storage community was one of hope and anticipation that the cycle of technical development would be replaced by a cycle of commercial demonstration. It was possible ten years ago to produce a list of large scale battery systems with a reasonable certainty that it would be complete. There were relatively few manufacturers of energy storage systems and developers would announce large scale battery projects in advance of construction. But times have changed. The enthusiasm for energy storage has swept through the power industry at least in North America, and repowered the drive to use energy storage as a means of improving the power system and making money as well.

An indirect measure of the interest in energy storage is given by the number of conferences and events on energy storage – there now seems to be one every month. More striking is the attendance figures for the major events on the subject. The Electricity Storage Association meeting in Washington DC in 2009 had 300 delegates, many more than in 2008. News was abundant, with many manufacturers announcing work in progress, not just work about to begin. And it is no longer possible to think of storage as just being one or two types of battery, as there are now ranges of battery technologies as well as ranges of other devices capable of providing useful storage to the power system.

In September, the US Department of Energy, together with Sandia National Laboratories and ESA, hosted the bi-annual Storage Applications and Technologies Conference (EESAT), which was looking forward to announcements of active support for storage technology under the American Recovery and Re-investment Act, ARRA, signed into law in February. Compressed air energy storage is always one of the contenders because of its potential for scaling up to plants of the 100 MW class, and most energy storage meetings contain at least one reference to compressed air systems, despite the fact that there have been no successful plants of any size built since the early 1990’s. The flow of money from the Recovery Fund, mainly through stimulus funding announced in November, will inject $60 million across three projects with a total project value of $429 million. The large scale projects will be developed by Pacific Gas and Electric in Kern County, California, New York State Electric and Gas Corporation in Binghampton NY, while SustainX will receive $5M to develop a 1 MW, 4 hour system using above-ground industrial pressure vessel facilities.

$28 million has been allocated to two flywheel projects. Beacon Power, already in receipt of a $43 million loan guarantee from the Department of Energy for its 20 MW flywheel energy storage project in Stephentown, New York, has also received $24 million for the development of a second 20 MW project for frequency regulation in Chicago. This will finance the lion’s share of its Stephentown project, of which 3MW has been installed and which is already providing frequency regulation for the NYISO, ensuring cycle by cycle stability for the grid. Beacon Power is taking the role of manufacturer, project developer, owner and operator for the flywheel system. Amber Kinetics receives $4 million for development of a smaller flywheel system in distributed applications.

Batteries are high on the agenda – several flow battery projects across a range of technologies are being supported as well as three lithium battery projects of sizes ranging from 8 MW to community energy storage systems of 25 kW each.

Future for storage

The message is clear that storage is one of the technologies of the future. But future technologies are not always economic, so what are the arguments? At its simplest, energy storage offers the opportunity to balance energy variable costs of energy production against time. Storing energy at time of low cost and releasing it at times of high cost is similar to the trading strategies for almost any commodity. The difference lies in the very different method of delivery. Speed of response is vital, and if storage can be used to replace fast acting reserve plant it can have high value. The importance of this will become most apparent when the proportion of electricity produced from renewable sources increases substantially, probably above the 20% mark.

Leading the race

The sodium sulphur battery developed by NGK Insulators Ltd continues to hold the yellow jersey in the race to commercialise large scale batteries. NGK installed a 34 MW, 220 MWh battery system at Rokkasho in Northern Japan during the summer of 2008 and it has been operating since then to smooth the output from the adjacent wind farm. In terms of energy, this must be the largest battery in the world, although its peak power rating is below that set by SAFT’s 40 MW (~5 MWh) battery at Golden Valley in Alaska. NGK continues to dominate the distributed storage market as well, supplying American Electric Power (AEP), with another three 2.4 MW battery systems for deployment at substations throughout its area.

AEP is taking a very enlightened view of energy storage. It is developing a community energy storage program using small batteries deployed into the distribution network in order to provide improved network stability for their customers. One concern is that plug-in hybrid electric vehicles (PHEV) will change the way that local clusters of customers demand power and it will be necessary to manage load fluctuations on a localised basis. AEP has published an open source specification for energy storage in order to open the market to as many suppliers as possible.

Long term assessment

Many years ago, a 1 MW VTLA battery was installed at Metlakatla, an island on the Alaskan coastline. The battery was replaced in September 2008, after just over 10 years of operation and this provided Exide, part of GNB Industrial power, with the opportunity to make an assessment of the costs and benefits of the project. The battery was used to modulate the output from a hydro plant, so avoiding the use of a standby diesel with its high fuel and maintenance costs. George Hunt, who was project manager for GNB at the time of the installation, was also managing the repowering of the system. The batteries would have been capable of a further 3 years life, giving a 15 year life. Even the humble lead acid battery has its part to play.

Lithium battery projects

Lithium batteries come in many flavours, from many different suppliers. Altairnano, a manufacturer of lithium titanate batteries is working with AES on the deployment of MW size batteries to provide frequency regulation in the PJM market. The batteries are mounted in trailers, and can be moved to a suitable substation for connection to the network. They are shortly to deploy 2 MW of batteries to California to demonstrate frequency regulation in its ISO.

Another lithium ion battery manufacturer, A123, is also demonstrating progress in commercialisation and deployment. 2 MW and 500 kWh of batteries are installed in a shipping container, to provide ancillary services to the network. Valence Technology produces lithium cells, initially for the electric vehicle market, but also looks towards the stationary storage market as an extension of their business. BYD Company, developers of the lithium iron cobalt phosphate battery is also on a similar track, developing battery systems for small scale and large scale applications. Their stationary system would be rated at 1 MW and 4 MWh. Their demonstration 1 MW project is due to start operation in Shenzen, China, to be followed by a 2 MW demonstration project in the USA.

Driving force

The driving forces for this acceleration in US development come from a number of different sources. First, the Department of Energy has run an energy storage programme for many years. Much of their money has been spent on relatively small, but high profile demonstrations followed by enthusiastic promotion of the results and benefits. Secondly, the drive towards increasing the use of renewables has placed increased pressure on distribution and transmission network owners to install enough capacity to move the electricity to where it is needed. Thirdly, the entrepreneurial spirit of a number of developers has refused to be swayed by those who claim that there is no economic benefit in storage, instead relying on the fact that the system must change, smart grids will arrive, and they want to be part of it. Obstacles such as regulation of utilities are only a minor hindrance to the development. Finally, all this happens at the crucial time in the economic cycles when there is money available under ARRA to support good quality demonstration projects. Dr Imre Gyuk, head of the Department of Energy’s Energy Storage Programme, has been resolute in promoting demonstration projects of size and quality, not just in batteries but also in flywheels, compressed air, supercapacitors and many others.

Other developments

There is still ongoing interest in pumped hydro technology. A project is under construction in San Diego, due for completion in 2010. Scottish and Southern have announced plans for new pumped hydro in Scotland and Japanese companies are looking at using variable speed pumped hydro for frequency regulation whilst in the pumping mode.

Around the corner are several interesting developments. Thermodynamics always plays an important part in considering the operation of energy storage systems. There are several interesting thermodynamic cycles which are being considered in developments. Mark Wagner of Isentropic (a British company) working with Jaques Ruer of the French company Saipem have brought forward a novel storage cycle based on the temperature difference between two large tanks of gravel, one heated and one cooled. A Siemens engine between the two tanks can be used to store energy as heat or recover the energy when required. After laboratory testing Isentropic is now looking to its full scale demonstration hoping to build a 4 MW, 40 MWh system. Other thermal storage systems are at various stages of development, such as a 1 MW system currently being installed by Highview Power Storage on the Slough Estates network. This system uses a working fluid of liquefied gas to drive a turbine or expansion engine to power an alternator.

Model system

The German renewable energy systems company Younicos has installed a 1 MW NAS battery on its own site at Adlershof, Berlin. The battery is part of a demonstration of an island renewable hybrid system that almost completely eliminates the use of fossil fuel. Younicos has modelled the island of Graciosa in the Azores, taking a real time input for the solar PV and wind production and the total island demand and sending the data to Berlin. There, a simulator feeds inputs into the MW scale demonstration system, supplying a local load to mimic the requirements of the island, and using the battery for storing excess energy or providing a supply at times of low renewable production. There is a diesel generator on site, which would come into production if needed, but Younicos confidently expects there to be almost no production from fossil fuel because of the capability of the hybrid battery system. This demonstration uses the high power, high energy NAS battery developed by NGK and is one of two batteries supplied to German companies during the past year.

Energy storage in the UK

There is a wide range of energy storage activities taking place in the UK. Scottish and Southern announced at the end of June 2009 that it was looking to build between 300 and 60 MW of pumped storage in the Great Glen of Scotland as well as adding 60 MW of pumped storage to its existing Sloy hydro-electric power station. In their press release, Ian Marchant, chief executive of SSE, said: “Our goal is to maintain a diversified portfolio of power stations, with the flexibility to respond to customer demand for electricity, while achieving a 50% reduction in the carbon dioxide intensity of electricity produced. Pumped storage can help us achieve this goal and, after 30 years, I believe is a technology whose time can come again.” Scottish and Southern is not shy to look at a range of options, for it has also purchased a demonstration zinc-bromine battery from Premium Power of Massachusetts, which will be tested at its Nairn substation later this year.

Meanwhile EDF Energy Networks is attending to the final details on their energy storage demonstration at Martham substation in the East of England. This project comprises a lithium battery supplied by SAFT with power electronics supplied by ABB to provide 600 kVA automatic voltage control in an area with a high penetration of wind energy.

At the research level, Nottingham University is looking at novel forms of storage using bags of compressed air under the sea, while other British universities are concentrating on more conventional forms of battery storage.

Energy storage in Ireland

Dundalk Institute of Technology has received a 500 kW zinc bromine battery from ZBB. The battery, shipped in July 2009 sits alongside a 850 kW wind turbine in order to maximise the onsite value of the wind resource, allowing the institute to take more than half of its energy requirements from renewable resources. The installation will demonstrate the operation of the battery in conjunction with a wind turbine, an application that is frequently considered by wind power developers but rarely employed, except on islanded sites.