Another Cheap Way to Store Solar and Wind Power

May 4th, 2011 by Susan Kraemer

UK startup Isentropic Energy has proposed the simplest of thermal energy storage systems, according to Powermag. Two large containers of gas and gravel, one hot (500C) and one cold (–160C) provide the temperature difference to operate a heat pump. Off-peak surplus wind power or solar energy is used to heat up the contents of the hot tank and to retain that temperature.

No refrigerants, chemicals or water are used, and it has no particular geographic requirement, unlike several energy storage ideas currently in pilot testing. It could be cheap at utility-scale – as little as $10/kWh (one time, to build it), according to the company’s chief technology officer, Jonathan Howes, and the overall operating efficiency of the energy storage process is claimed to be 72% to 80%.

For this much energy storage, each tank of gas and gravel is the size of a small building, a little over 20 feet in height and in width, and the heat differential between the two containers (this size) operates a 6 MW heat pump. Scalability is possible. The company says that it could be scaled up: so larger containers could store more energy, and run a larger heat pump for longer.

According to Howes, it will cost about $16 million, and take up to two and a half years, to test the prototype’s ability to store and release 16 megawatt hours of power at a rate of 2 MW for 8 hours.

California is looking for energy storage now that 33% of our electricity is to come from renewable sources by 2020, ideally very fast releasing storage – in 1,000 MW units.

More energy storage is needed to even out the intermittency of renewables. To ensure a good match between the rise in renewables and storage – rather than haphazard storage development that might not be sufficient – a rising percentage of storage on the grid is mandated.

To keep the grid stable, storage that can release stored power within seconds are the most valuable to the renewable powered grid, as we see in the change in incentives now offered under new FERC director Jon Wellinghoff. It is also why General Compression’s Renewable Energy Storage that Ramps Up in Under 30 Seconds was selected by ARPA-E for funding.

FERC wants to offer higher payments to suppliers of fast storage, (FERC Wants Smaller, Faster, Distributed Storage to Speed Renewables) or at least to incentivize utilities to offer breaks to customers who conserve: Equal Pay for Negawatts and Megawatts Thanks to FERC.

Although Californian utilities do offer these “negawatts” incentives to large commercial users, some electric utilities in the South, typically coal-powered, currently actually offer these customers a break for wasting more energy. So the waste of fossil powered energy there has an impact on climate change globally, which is currently being felt in the South with extreme weather. FERC has national jurisdiction, so the rule could impact greenhouse gases nationally.

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