Renewable energy sources like wind and solar have a problem: When the wind stops or it is night, they stop generating power. That drawback has focused minds on the question of how to store electricity generated by intermittent sources...

...In an ideal storage system, all the energy put in can be extracted later. When air is compressed, however, the work that goes into compression produces heat as a side effect. In early compression storage systems — technically known as diabatic — this heat has been lost into their surroundings, making them less efficient.

Current experimental systems aim to be more efficient by retaining or recovering the heat. Some, known as isothermal, use a coolant to absorb it, keeping the air at a near constant temperature. The coolant, stored separately, is tapped later to give back the energy through a heat exchange system. Others, known as adiabatic, allow the temperature of the compressed air to rise and fall, using the air, when hot, to warm heat storage units that retain energy within the system.

SustainX, [founded in 2007 by Professor Charles Hutchinson and engineering students Dax Kepshire Th'06, '09, Ben Bollinger '04 Th'04, '08, and Troy McBride Th'01] based in Seabrook, New Hampshire, is set to build a pilot isothermal plant capable of storing and releasing up to two megawatts of power, making it the largest demonstration of the technology to date.