The U.S. Department of Energy (DOE) announced last week that it had given a $3-million grant to develop a low-cost, long-duration electrical energy storage system that uses a CO2 heat pump.

This was one of 10 projects selected for funding as part of a new Advanced Research Projects Agency-Energy (ARPA-E) program called ‘Duration Addition to electricitY Storage,’ or DAYS.

Each program aims to develop energy storage systems to provide reliable, affordable power to the electric grid for up to 100 hours, enhancing grid resilience and performance.

In the Echogen Power Systems project, an energy storage system uses a CO2 heat pump cycle

to convert electrical energy to thermal energy by heating a “reservoir” of low-cost materials such as sand or concrete, according to the DOE.  The reservoir’s heat is stored so it and converted back into electricity upon demand. 

When the electricity is needed, liquid CO2 is pumped through the heated reservoir until the CO2 reaches a supercritical state. The CO2 is then expanded through a turbine to generate electricity from the stored heat. 

“The Department of Energy is committed to researching innovative energy technologies and discovering opportunities to make America’s energy infrastructure more competitive and more secure,” said Paul Dabbar, Under Secretary for Science at the DOE. “The DAYS awardees will take a good look at what tomorrow’s grid-scale storage could be, and work to develop the technologies that get us there.”

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