Basic overview of how the SustainX system uses hydraulics to create, store, and release compressed air for making electricity.

SustainX announced today it's received $14.4 million in funding from GE subsidiary GE Energy Financial Services, Cadent Energy Partners, Polaris Ventures, and Rockport Capital.

The New Hampshire-based company is a start-up that grew out of the Thayer School of Engineering at Dartmouth College in 2007, and has been developing a compressed-air energy storage unit intended for integration with smart grids.

Simply put, its innovative storage unit uses compressed air to store, then generate electricity. But unlike other compressed-air storage units, which use a compressor to store air underground, SustainX stores the air in a standard tank located above ground and uses a hydraulic piston system and hydraulic motor.

Electricity initially runs the hydraulic piston system to create and store high-pressure air in the tanks. Then, when electricity is needed, that high-pressure air is channeled to drive a hydraulic motor that powers an electric generator. The system uses isothermal compression and expansion to keep the air at a consistent temperature to maximize efficiency.

"SustainX technology keeps air at a nearly constant temperature during compression and expansion' this significantly improves efficiency and reduces the cost of compressed-air energy storage below that of other above-ground energy storage options," the company said in a statement.

GE wind turbines at an offshore wind farm.

The grid storage unit is intended for use in place of today's current "peaker plants," or auxiliary go-to plants for when electric grids reach peak demand and need an extra source of electricity to draw from.

The investment is part of GE's Ecomagination program in which the company said it plans to invest $10 billion in green-focused research and development between 2010 and 2015. SustainX's compressed-air grid storage system falls under the Ecomagination "Powering the Grid" program.

SustainX had previously been developing the tech with about $5.4 million it had garnered from a combination of public grants from the National Science Foundation and the U.S. Department of Energy, as well as previous private funding from Cadent Energy Partners, Polaris Ventures, and Rockport Capital. With the new round of funding available, the company says it will soon be showcasing a more scalable prototype that it's developing with AES Energy Storage. That prototype will be capable of storing and dispensing enough energy to power the equivalent of 1,000 U.S. homes.

GE's interest in a system like the one SustainX is attempting to develop makes sense given GE's huge wind turbine manufacturing business expanding in Europe and winning over wind farms in the U.S. Because of their intermittent nature, wind and solar are less reliable than other energy sources. Energy storage units, like the one being developed by SustainX, would change that because they would allow wind and solar energy excesses to be easily and cheaply stored and retrieved as needed, making their variable natures less problematic.