SustainX eyes compressed-air energy storage at megawatt-scale

A company developing compressed-air energy storage technology has earned a seventh US patent for an innovation it says will make its offering even more promising for large-scale storage systems.

According to New Hampshire-based SustainX, the latest patent will enable additional ways to use its compressed-air system with either hydraulics or a mechanical crankshaft. The company says the crankshaft design offers low frictional losses for better efficiency, and can also transfer large amounts of power, which will support the construction of megawatt-scale storage systems.

“The patent award is an important milestone for SustainX because it combines the mature, reliable technology of crankshafts with our patented heat-exchange methods and allows us to design energy-storage systems that are more powerful, compact and efficient than ever,” said Dax Kepshire, vice president and co-founder of the company. “This patent (No. 12/879,595) expands the types of systems that SustainX can develop, providing more market options.”

One of the problems with compressed-air energy storage (CAES) is heat: when air is compressed to store energy, it heats up, and dissipated heat that’s not recaptured means wasted energy and a loss of efficiency. SustainX claims its technology keeps air temperatures nearly constant (isothermal) during both compression and expansion, making it more efficient that other systems.

The company also stores air in standard, off-the-shelf industrial gas cylinders above ground instead of in underground salt domes, as do the world’s two existing CAES operations. That allows its system to be both scalable and transportable to wherever energy storage is needed, according to SustainX.

The market for energy storage has been growing rapidly as more renewable energy comes online. That’s because renewable energy is often intermittent, meaning it isn’t always available when demand is highest. Meeting peak demand has typically required the use of expensive and polluting “peaker” plants that burn natural gas or other fossil fuels. Energy storage technologies make it possible to instead store wind or solar energy for later use when demand is high.

SustainX’ isothermal system removes heat from air being compressed for storage and adds heat to air being expanded to generate electricity. This prevents the temperature extremes that can occur with high-pressure compression and expansion of air.

The company is currently on track to demonstrate its first megawatt-scale, grid-connected system in collaboration with AES Energy Storage under an award from the Energy Storage Program at the US Department of Energy.