THE HOPE OF STORAGE

The Challenge of Storing Energy on a Large Scale
Erica Gies, September 29, 2010 (NY Times)

"Renewable energy sources like solar power and wind have been in the spotlight lately, as have ways to improve control of the power distribution system through information technology…[Now] incentives from the Energy Department, increased interest from venture capitalists and policy shifts at the state level, where utilities are regulated, are laying the groundwork for bringing energy storage capability to the electricity grid… [G]rid-scale storage technologies…include pumped hydroelectric energy; air compression systems; flywheels; and even superlarge batteries…

"Grid operators must keep power flowing reliably to users, a task known as frequency regulation…[That is complicated by] solar and wind power…[which] can change output rapidly if external conditions shift: a cloud crossing the sun or a drop in the wind…Aside from these minute-to-minute changes…the sun does not shine at night, and in many places, wind is calm during the day…"

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"Utilities have generally used the more controllable output from fossil fuel power plants to compensate for intermittency. But if renewable sources are to contribute a greater share of the energy mix — California has a target of 33 percent by 2020 — the declining proportion of fossil fuel power available to smooth out the peaks and troughs of output will make storage technology essential… Recent research suggests that storage technology could respond faster to supply and demand shifts than fossil fuel plants…

"…Utilities must also build systems capable of meeting peak demand, which arises at different times of the day, week and year. For this purpose, utilities have traditionally relied on bringing additional fossil fuel generating plants into action…But fossil fuel plants run most efficiently at full power. And the marginal plants turned on to meet peak demand are often less efficient and more polluting than the power generators that run around the clock…Using stored energy to meet peak demand could eliminate the need to switch on dirtier, more expensive plants."

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"Depending on where storage is sited, it could also reduce the need for transmission lines…That would be a boon because utilities often struggle to get rights of way to build transmission lines. As a result, they usually overbuild after they get permission…Storage can also help utilities get the best price for the energy they generate, using a strategy called ‘time shifting.’ Energy managers can store lower-cost energy produced at night, then release it to the grid during peak demand when it is more valuable. With both traditional power plants and wind farms, much more energy is produced at night than can be used…

"The Energy Department is supporting a variety of storage projects…The venture capital world has taken note…The most common technology already in use for grid storage is pumped storage hydroelectricity, in which managers use electricity to pump water up into higher elevation reservoirs at night, then release it at times of peak demand…Another large storage option is compressed air…Electricity is used to force air under pressure into a cavern. To extract it, operators heat the compressed air with natural gas, then push it through turbines to generate electricity…Flywheel systems use electricity to drive a motor, which accelerates a massive disc, storing electricity in the increased momentum. When the stored power is needed, the flywheel is used to drive the motor in reverse…Batteries have not yet reached grid scale for the most part…Many experts think batteries hold the most promise because they are scalable and can be used anywhere…"