Thayer engineers create energy storage system

| 11/30/09 11:00pm

SustainX, a startup founded by engineers associated with the Thayer School of Engineering, has received a $5.39-million grant to develop an energy storage system designed to make the use of renewable energy sources more efficient. The grant, from the U.S. Department of Energy, will support further research and development in anticipation of a demonstration of how the technology can be used on a large scale.

SustainX's technology relies on compressed air to store energy, which can be used as needed when the air is expanded. Although compressed air has been used in the past to store energy, SustainX's technology has several new design features that its creators hope will improve efficiency and make the system easier to use on a mass scale, the company's president and co-founder Dax Kepshire Th '06 said in an interview with The Dartmouth.

Energy storage technologies like the system developed by SustainX are particularly important to facilitate the use of energy from renewable sources, including wind and solar power, which are not always readily available, according to SustainX co-founder Charles Hutchinson, a Thayer School professor and former Thayer School dean.

"The wind doesn't always blow when you need the electricity," Hutchinson said.

Unlike other storage systems, SustainX technology uses isothermal cycling, which keeps the air at a constant temperature, Kepshire said. In classic compressed air storage systems, the air is heated as it is compressed and rapidly cools down when it is expanded. The classic system is less efficient because it must use an external energy source, usually natural gas, to heat the air once it is expanded, SustainX co-founder Troy McBride Th '01, said.

"By keeping it at a constant temperature, we are able to operate at a very high round-trip efficiency," McBride said.

SustainX's technology also allows for a different storage mechanism. Traditionally, the compressed air is stored in large underground caverns, McBride said, explaining that because the number of caverns is limited, it is difficult to obtain permission to use them.

SustainX's technology allows air to be stored above ground in cylinders, rather than in caverns, because they store air at higher pressures, allowing more energy to be stored in a given volume, McBride said.

The SustainX technology also features staged hydraulic conversion, which uses a hydraulic pump to compress and expand the gas. The pump can carefully control air expansion, allowing heat transfer to occur and increasing efficiency. Classic compressed air storage systems are generally turbine-based, which causes rapid compression and expansion that does not allow time for heat transfer, McBride said.

Other mass-scale energy storage technologies in development use lead-acid batteries, flow-batteries, lithium-ion batteries and sodium sulfur batteries, Kepshire said. These designs are not only more expensive, Kepshire said, but also harm the environment.

"The other approaches are short lifetime, very expensive and toxic," Kepshire said.

SustainX plans to complete a 50-kilowatt pilot system before the end of next year, according to McBride. The demonstration system will be built in 2011 and deployed in 2012.

SustainX was also co-founded by Ben Bollinger Th '04.

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