How Isentropic PHES Works
The cycle uses a proprietary reciprocating heat pump/engine developed in-house by Isentropic Ltd, powered by electricity from the grid, to charge Isentropic Thermal Stores.
The heat pump compresses argon gas up to 12 bar and 500°C. The gas then passes through crushed rock in a pressure vessel, the “hot store”. This crushed rock is an inexpensive, abundant and safe medium of energy storage.
The argon gas, now at near-ambient temperature, exits the hot store and enters a second heat pump cylinder. In that cylinder, it is expanded down to around 1 bar, which cools it to -160°C. This cold gas enters a second thermal store, the “cold store”, cooling its contents.
The argon gas is now at ambient pressure and ambient temperature, and the cycle recommences.
The cycle stores electrical energy as a temperature difference. When the electricity is needed again, the temperature difference is used to drive the heat pump as a heat engine, driving a generator and producing electricity.
Isentropic Ltd has designed a number of key features in the heat pump/engine and thermal stores that will enable a round-trip efficiency of 70-75% (ac to ac).
The use of natural materials allows for a projected ex-factory cost of $140/kWh.
The components are engineered to give each installation a life of 25 years with no limitation on number of cycles or depth of discharge.
PHES combines the three essential features required of an electricity storage technology: high efficiency, low capital cost and long life.