Energy Storage: Changing the rules of the game

The rising importance of renewable energy is placing increasing emphasis on the need for utility-scale energy storage systems. In this article, IFandP takes a look at the current status of the various technologies on offer.

One of the issues that the power utilities of the future will have to deal with is an ever increasing contribution of intermittent renewable energy sources to the grid. While substantially more than the current level of solar and wind power can be accommodated with few repercussions, once the percentage of generating capacity they represent increases above 30 per cent there will be a clear need for advances in super grids and energy storage. The former is to allow electricity to be brought in from regions that are producing a surplus of power during times when local generation fails to match demand. At the same time, energy storage effectively smoothes out the peak and troughs experienced locally. Both technologies are of prime interest, as their progress has the potential to reduce, or perhaps one day entirely eliminate the need for expensive fossil-fuel (typically natural gas)-fired back-up capacity. In this article, I will summarise the latest developments in the Energy Storage field.

Much of the recent excitement in the field has been generated by an increase in the funding of energy storage research by the US Department of Energy. In November 2009, it announced US$185m in grants for 16 utility energy storage projects, of which compressed air energy storage (CAES) accounted for nearly US$60m. The Department’s Energy Storage Systems Research Program is also collaborating with over 20 projects, including nearly US$10m of grants with the California Energy Commission and almost US$6m for six projects with the New York State Energy Research and Development Authority. The DoE is also providing US$2-5m a year to six Frontier Research Centres for the purposes of developing energy storage technologies.

The growth of this sector is expected to be significant. According to a report by GTM Research, the current amount of energy storage for the purposes of mitigating short-term supply disruptions is just 49MW, of which the vast majority is in the form of pumped hydropower. However, GTM expects this to rise to 479MW by 2015 and could peak at 7,317MW in the US and 37,828MW worldwide. More significantly, energy storage for the purpose of balancing daily demand and supply could rise to 1321MW by 2015, representing a cumulative investment of nearly US$2bn. GTM estimates that a mature market for this suite of technologies could be 450GW worldwide and 85GW in the US.

A key driver is the rapid expansion of the wind industry. According to current DoE data, every new 1GW of wind capacity requires an additional 17MW of spinning reserves to compensate for the increased variability in supply. While the most efficient method of tackling this problem is probably the construction of supergrids, to allow local fluctuations in output to be countered by sourcing electricity from other regions experiencing a power surplus, energy storage devices have the advantage of being a much smaller undertaking and as a result can be more rapidly deployed.

There are currently three main avenues that are being pursued by companies in the Energy storage field: compressed air, which stores energy in the form of air kept at high pressure and releases it through a turbine to produce electricity, batteries which store electricity in the form of chemical energy and flywheels which can quickly convert electricity to kinetic energy and back again at high efficiency.

Compressed air

Californian power utility PG&E is working on a compressed air project in Kern County, which once complete will be capable of storing 300MW for 10 hours. It is looking to store energy at off-peak times before releasing it back onto the grid during periods of peak demand. It considers the technology as a vital tool in its goal of attaining compliance with California’s renewable portfolio standard, which requires that 20 per cent of a utility’s electricity needs to be sourced from renewables in 2010.

CAES hit the headlines late last year with the announcement that FirstEnergy Generation Corp had acquired from the Haddington-owned CAES Development Company, LLC, the rights to the Norton Energy Storage project in Ohio. All the permits needed to develop the 2000MW+ storage facility, which is being converted from a 2200ft deep disused mine have already been acquired and the engineering and equipment design, together with project cost estimates, have been completed for the first 268MW of generation and 200MW of storage capacity.

Meanwhile, General Compression (see our “Reliable wind power” article) has secured US$17m in commitments for its Series A funding round, with which the company is hoping to install its first full scale 2MW CAES unit later this year. It is also looking to have a commercial project up and running in 2011, in partnership with its new investorss, USRG and Duke Energy. General Compression has opted for a modular approach, allowing facilities to easily be scaled according to a client’s requirements.

A company called SustainX Energy Storage Solutions is currently working on a CAES system with a radically different approach from many of its peers. It is aiming to store compressed air in off-the-shelf tanks and has set itself the goal of fitting 4MWh of stored energy in a 40ft long container, capable of delivering 1MW. As a means to achieving this goal, SustainX is building a 100kWh pilot project, which will be used to test the technology. Instead of letting the compressed air escape through a turbine, the company’s system will use a hydraulic piston to convert the high pressure back into electricity.

Dax Kepshire, president of SustainX, expects the initial efficiency of the system to be around 50 per cent, before rising to roughly 70 per cent in the fully developed system. The use of near isothermal gas cycling as opposed to adiabatic compression, in which the temperature increase associated with increased pressure is retained within the gas, is a key feature of the system and allows it to make use of cogeneration and waste heat from nearby industrial processes.

Batteries

Battery technology is perhaps one of the most established energy storage technologies used today. One of the issues with traditional lead-acid batteries is their environmental footprint, primarily in terms of their disposal. In comparison, lithium-ion batteries are rapidly gaining favour among utilities. Their chemistry allows for very high energy densities and results in a very low rate of self-discharge. The worldwide market for lithium-ion batteries was thought to be worth an impressive US$8bn in 2008 and expected to regularly record double digit figures for growth, given the pace set by related renewable energy and electric vehicle markets. Pike Research believes that it will become the energy storage technology of choice for electric vehicles and it expects that “improved storage capacity and economics will lead the utility sector to adopt Li-ion [lithium-ion] as well…” The analyst group also predicts that Lithium-ion batteries will represent 26 per cent of what will be a US$4.1bn stationary energy storage industry by 2018. Recently, Southern Californian Edison Co has applied for a US$25m stimulus grant for what could be the world’s largest lithium-ion battery, which would be built and developed by A123 Systems Inc.

Sodium Sulphur batteries have been extensively developed by NGK Insulators Ltd and Tokyo Electric Power Co (Tepco), to the point where Tepco believes they may one day replace central pumped hydro as the principal means of energy storage in Japan. The main reason for their initial decision to develop the technology was that all of the raw materials could be sourced within Japan. American Electric Power Co is working on a “bus-sized” 7MW sodium sulphur battery string to help address the issue of congestion on transmission lines and initially trialled NGK and Tepco’s technology back in 2001 at the Dolan Technology Centre. More recently, NGK Insulators has formed a consortium along with EDF Energy, MEIDEN and JWD, to develop the “large scale sodium sulphur NAS battery assets to provide ancillary services in the UK.”

GE Energy is focusing its research efforts on improving its sodium metal halide batteries. In addition to the more obvious applications, GE is also looking to use them as a key-enabler of electric trains and in various stationary roles.

In Chile, AES Energy Storage and A123 systems teamed up to develop and successfully commission a 12MW frequency regulation and spinning reserve project at AES Gener’s Los Andes substation in the Atacama Desert, Chile. The system uses A123 System’s Hybrid Ancillary Power Units, a lithium-ion battery system.

Boston-Power Inc, a leading provider of lithium-ion batteries has chosen to team up with AV Concept Holdings Limited with the goal of breaking into the lucrative Korean and Chinese markets. Its technology is based “on flat, oval-shaped prismatic cell design with external dimensions equivalent to two conventional 18650 lithium-ion cells. The design includes an aluminium can, supporting high energy density, dependable cycle-life, and multiple independent safety features.” For utilities, it offers the Swing 4400, which features a 20-50 per cent space saving compare to “existing solutions”.

Despite all these efforts, the story is by no means over for lead batteries. Axion Power International is currently developing its Axion PowerCube ™, an advanced 500kW lead-carbon battery and received nearly a quarter of a million dollars from the Pennsylvania Energy Development Agency to help commercialise the system. Axion has won the Frost & Sullivan Technology award for North America in the field of lead-acid batteries as its approach has “the potential to revitalise the lead-acid battery industry by breathing new life into an established technology that is not well suited to the requirements of important new applications like hybrid electric vehicles and renewable power.”

Other companies active in the lead-carbon battery field include Furukawa Battery Company and Exide technologies, which has recently teamed up with Axion to develop a range of products based on Axion’s technology. Products such as the Ultrabattery suggest that Lead-carbon batteries may be able to out-compete lithium-ion batteries on economic grounds, as far as electric vehicle applications are concerned. This suggests that the same could be true for stationary applications, particularly as weight is less of an issue (lead-carbon batteries typically weigh more than their lithium-ion counterparts).

Xtreme Power is taking a different approach. It is working to commercialise a fibre-glass dry-cell battery which, thanks to being composed of solid materials, is able to deliver high efficiency power coupled with high levels of reliability, to the point where the company claims its device can still function after being riddled with bullets. It is seeking to raise up to US$475m to help fund the retooling of a closed Ford Motor factory in Michigan, as part of a joint venture with Clairvoyant Energy with the aim of producing 2000MW of batteries a year. Xtreme Power has stated that the batteries would cost about one-tenth of comparable lithium-ion systems and their modular set-up allows individual installations to scale up to 100MW.

Flywheels

Beacon Power Corp’s Smart Energy 25 Flywheel can be used both for frequency modulation and to boost the effectiveness of wind farms

One of the major advantages that flywheel have over other forms of energy storage, is the rate at which they can respond to sudden changes in demand, making them particularly suited for frequency modulation. According to a study by Pacific Northwest National Laboratory carried out in 2008, 1MW of fast responding flywheels provides the same response as double the capacity of conventional slow-responding regulation, such as hydropower.

Beacon Power Corp has started construction of a 20MW US$69m energy storage facility in southeastern New York. The project is expected to be completed in 2011 and has obtained a conditional US$43m federal loan guarantee from the DoE. Beacon has also received a US$24m stimulus grant for use in the construction of its second 20MW energy storage plant to serve the Chicago, Illinois area, which will help the PJM interconnection manage its grid. It also announced that it has recently shipped, installed and connected a flywheel system to a wind farm in Tehachapi, California, as part of a wind power/flywheel demonstration project being carried out for the California Energy Commission. According to a report from the California ISO, up to 4200MW of wind power could be installed in the area over the coming years. It will feature “intelligence agent” controls designed to unlock the full potential of flywheels as a means of boosting the amount of electricity that can be delivered from the wind farm without overloading the locally constrained transmission system.

Pentadyne Power Corp (which we featured in our “Flywheels: reducing energy risk” article) has also been busy with the recent launch of the GTX, which offers 25 per cent more energy storage, than its previous flywheels. According to the company’s CTO, Claude Kalev, it operates without bearings and without the need for a vacuum pump, making it highly reliable “and virtually maintenance free.”

Supercapacitors

Another approach that may make its presence felt a number of years down the line is the use supercapacitors as a means of energy storage. This is currently being developed by Battelle, South Korea’s Nesscap, EESTOR Batteries, Graphene Energy, EnerG2 and Ioxus, which have been attracted by the fact that such devices may be able to offer over 10 times the energy density of present-day capacitors and a cycling lifetime 10 times that of present lithium-ion batteries, once the full potential of nanotechnology is realised. At present, super- or ultra-capacitors can discharge their power 10 times faster than batteries, but are far less energy dense, needing 16 times as much area to store the same amount of energy. Researchers such as Joel Schindall, a professor of electrical engineering and computer science at MIT, believe that nanotechonlogy may be able to drop this figure down to four, but this is still far from ideal and suggests that it will be a long time before such devices become viable for utility-scale applications.

Heat Engines

One of the more innovative approaches to hit the headlines in recent months was the public unveiling of UK company Isentropic’s reversible heat engine, which can pump heat from one container of thermal storage material (such as gravel) to another, and then subsequently use the temperature gradient to generate electricity. Approximately 75 per cent of the energy stored by the device can be recovered, putting it in the same ballpark as pumped hydro power, but with the added advantage of being independent of geography and with a footprint 300 times smaller. It also boasts an isentropic efficiency of 99 per cent and can be used to produce electricity from solar thermal systems.

Fuel Cells

ZBB’s Zinc Energy Storage System (ZEES) utilises fuel cell technology to deliver 2-3 times the energy density of lead-acid batteries

More commonly thought of as lying in the realm of distributed generation (as recently publicised with the launch of “the Bloom Box”) or as an alternative to the internal combustion engine, ZBB Energy Corporation has been pioneering fuel cells as a means of energy storage. Its current Zinc Energy Storage System (ZEES) uses zinc and bromide electrodes separated by a microporous separator, which are suspended in an aqueous zinc/bromide solution. A key difference in this approach from conventional batteries is that the electrodes act only as substrates for the reactions, meaning that electrode degradation via repeated cycling does not occur. ZBB claims that the ZEES offers 2-3 times the energy density of conventional lead/acid batteries. Its ZESS 50 system, which weighs in at a dainty 30,000lb, can store 50kWh and can deliver 250kW for two hours, together with 200 per cent peaking capacity.

Pumped storage

Whilst not at the cutting edge of R&D, pumped hydro storage systems in terms of capacity account for around 99 per cent of all large-scale electricity storage systems. In fact there is over 127GW of pumped storage worldwide. Given that it is still the most cost-effective utility-scale form of energy storage, it will be with us for a long time to come. It is also seeing healthy levels of investment. For example., Ukraine has been building what will be Europe’s largest pumped storage plant since 1983. The first generating unit was launched in December 2009 and another six will soon follow. Japan’s Itochu Corporation has expressed an interest in assisting in the completion of the project. The design capacity of the plant is an impressive 2268MW for turbine operation and 3010MW for pumping.

Meanwhile, Alstom Hydro, which has a 47 per cent market share in the pumped hydro equipment market, was awarded a EUR178m contract in October 2009 to supply four 250MW variable speed pump turbine and motor generator units for a 1000MW pumped storage facility in Switzerland. It also received a EUR125m contract back in May 2009, to equip the Swiss 628MW Nant de France facility with reversible turbines and other related equipment. In Hungary, power utility Matrai Eromu, which is majority owned by German’s RWE is planning to build a 600MW pumped hydro facility at a cost of HUF140-150bn (US$735-788m) and expects to launch the permitting process in the second half of 2010. It would be Hungary’s first such plant and is sorely needed, given that the country’s wind turbine fleet is expected to expand significantly in the coming years. Israel is also looking to pumped storage and its public utilities authority has set up a supporting tariff scheme for 450MW of storage capacity. Two projects have already been approved for construction in the north of the country and the development is expected to result in substantial savings.

No clear winner?

The large differences between the various energy storage technologies described above, makes it clear that as with solar power, no one solution is likely to prevail. Instead, as is currently the case, it will be a case of selecting the right tool for the job in hand: compressed air or pumped hydro for large scale storage, advanced batteries for small-scale wind projects and flywheels for frequency modulation and applications where rapid response is paramount. However, it is entirely possible that future breakthroughs may generate a clear winner in the current tussle between advanced supercapacitors, lithium-ion and lead-carbon batteries.

There is another element to energy storage in that it is a key enabler in terms of the electric vehicle, which is expected to achieve significant market penetration in the medium-term. The wider implications of this shift in technology are immense. A recent report from Deutsche Bank makes the case that hybrid and electric vehicles will boost the global average efficiency of new light vehicles by over 50 per cent by 2030 and will cause a peak in global crude demand in 2016, while US gasoline consumption is forecasted to drop by 46 per cent by 2030. This will have dramatic consequences for the power sector, which will have to expand significantly in order to meet the additional demand for electricity, although clever demand management may substantially alleviate the need for additional capacity. A similar trend is expected to occur worldwide, with developing nations such as China and India largely skipping the internal combustion engine, in as much as they have land-based phone lines.

There are clear signs that many companies are already looking to capitalise on these opportunities. GE has already invested over US$150m in battery R&D and its transport division received a US$25.5m tax credit in January to help build a manufacturing facility in Schenectady, NY, to produce the next generation of energy storage systems. The facility is expected to be commissioned in mid-2011 and will employ 350 full-time workers. At full capacity, it could potentially build as much as 10m cells capable of generating 900MWh per year.

look out for our article in September, which will go into much further detail regarding the current state of the electrical vehicle and its impact on power utilities.