Compressed-Air System Could Aid Wind Power  

Technology Review has a look at a new approach to CAES energy storage - Compressed-Air System Could Aid Wind Power.

SustainX, a startup in West Lebanon, New Hampshire, has received $20 million in venture capital to test its compressed-air energy storage technology on a large scale.

The technology could allow for a wider use of compressed-air storage, which in turn could make renewable energy more attractive, since it would allow wind power generated at night to be stored until daylight hours, when demand is higher. If it's successful, the technology could decrease the need to build natural gas plants to supply peak power demand.

The need for storage is increasing as governments mandate the use of more renewable energy. SustainX has demonstrated a 40-kilowatt prototype and is now completing a one-megawatt system, slated to be deployed next year with the power company AES.

In conventional compressed-air storage, electricity is used to compress air, which is stored in underground caverns or aquifers. That air is then released to drive a turbine-generator to produce electricity when needed. Such storage costs roughly a tenth of what battery storage costs, but it isn't used much because in large part because it requires a location with underground storage space. SustainX's system eliminates this problem because it can efficiently use above-ground storage tanks rather than caverns.
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Storing compressed air in tanks aboveground is impractical with a conventional turbine-based system because of the large size and cost of the tanks. SustainX's technology reduces the cost of the tanks and other capital costs. "We do aboveground compressed-air energy storage at belowground prices," says cofounder and vice president Dax Kepshire.

The company reduces costs by using pistons, rather than turbines, to generate electricity. Gas turbines can only generate electricity from a narrow range of air pressures. The pistons can operate at a larger range—and because air can be compressed more, the system can store more energy. What's more, the pistons operate well after the pressure in the tank has fallen too low to drive a turbine.