Newcastle University connects first grid-scale pumped heat energy storage system

Pumped heat energy storage (PHES) shuffles heat between two tanks containing mineral gravel by means of a working gas, generally an inert gas such as argon. In storage mode, the argon is pressurised to around 12 bar, which heats it up to 500°C. The hot gas enters the top of one of the tanks (designated hot), and flows down slowly at about 3m/s, heating the particulate in the tank and itself cooling down. At the bottom of the tank, the gas is still at 12 bar but now at ambient temperature. At this point, it is expanded back to ambient pressure which cools it to -106°C. It then enters the second tank, cooling the particulate and itself warming up, exiting the tank at the top at ambient temperature and pressure.

To recover energy, the process is reversed with ambient argon entering the cold tank, being cooled and becoming pressurised. It then enters the hot tank, where it is warmed to 500°C but remains at the same pressure. It returns to ambient pressure in the expander, which drives a generator. The round-trip AC-to-AC efficiency is claimed to be 75 to 80 per cent, with the energy to be stored driving the compressor in the charging phase.