Unlikely Alliance:Energy Storage & Gravel

British startup Isentropic has raised $22 million in project funding and an equity investment from the Energy Technologies Institute (ETI) to develop a system consisting of gravel and a heat pump, a potential breakthrough for utility-scale energy storage.

The innovation behind Isentropic’s idea is an advanced heat pump connected to a simple, low cost energy storage design. Key to the company’s heat pump is that it can be reversed extremely efficiently, allowing the device to store and release energy on demand. Moreover, the device possesses an isentropic efficiency (reversible efficiency) of 99 percent.

Isentropic’s device consists of a heat pump connected to an energy storage system using two silos filled with gravel (or any cheap mineral or particle that can retain heat and cold well). Using the heat pump, the system compresses argon gas to produce a temperature differential and deposits heat and cold into the two separate large silos of gravel. Energy is stored in the gravel and when the process is reversed, it can be released.

The benefits of such a system include cost-effectiveness, system efficiency and ease of system installation, enabling the system to be installed in a variety of locations. Utilities are looking to add more forms of energy storage to the power grid, to store energy when it’s not being used immediately, but many energy storage options are expensive and can only be built in certain locations (in elevations or underground reservoirs). Batteries are among the most expensive options, and the most location-specific choices are technologies like pumped hydro and compressed air energy storage (CAES).

Isentropic will use part of the funds raised to build a demonstration project — sized at 1.5 MW — of its energy storage system at a primary substation owned by U.K. power company Western Power Distribution. Isentropic’s ideas and technology are still in its infancy stage and only time will tell if Isentropic’s system will work on a large scale, however, with the support of a viable vision and substantial funding, Isentropic’s device just might play a role in the building of a sustainable future.

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