The new hotness in energy storage: gravel

Can a humble system of gravel and a heat pump provide a breakthrough for utility-scale energy storage? British startupIsentropic thinks so, and this week announced that they’ve raised $22 million in project funding and an equity investment from the Energy Technologies Institute (ETI), a collaboration between the U.K. government and companies in the energy industry.

I covered Isentropic back in 2009, and back then the company was looking for a $5 million Series B round. The five-year-old company, previously raised a Series A round from Credit Suisse Securities Europe and won a £250,000 ($380,112) research grant from The Carbon Trust.

The innovation behind Isentropic’s idea is an advanced heat pump connected to a super simple, low cost energy storage design. Heat pumps are basically engines that can work in reverse and Isentropic’s device can store and release energy when needed. Founders and engineers Jon Howes and James Macnaghten developed the design of the heat pump a decade ago, and then brought on Mark Wagner as chairman to help with business direction.

An isentropic process (hence the name) is a thermodynamic process that can be reversed. Chairman Mark Wagner told me back in 2009 that the key to the company’s heat pump is that it can be reversed extremely efficiently, and has an isentropic efficiency (reversible efficiency) of 99 percent. More