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.
The Newcastle team has assembled and commissioned the system at the Sir Joseph Swan Centre for Energy Research. It is rated at 150kW and is capable of storing up to 600kWh of electricity.
Originally developed as part of a distribution scale energy storage project funded by the Energy Technologies Institute, which aims to test and de-risk new energy-related technology, the system is designed to store energy generated by renewable sources to buffer their inherent intermittency. The team at the Swan Centre has operated the system in both expansion and compression modes and claims it can switch between discharge and charge in a few milliseconds, according to Andrew Smallbone, co-director of the National Facility for PHES, who led the project.
"Pumped Heat Energy Storage or Pumped Thermal Energy Storage is cheap and is compatible with the technical and scale-up challenges of grid-scale energy storage," said Prof Tony Rosskilly, director of the Swan Centre. “Given the thermal power cycle’s enormous potential, there has been a tremendous amount of research and commercial interest in PHES technology over the last ten years, however until now nobody has managed to get as far as to demonstrate a real-world working system. What is exciting is that the UK is the first to do it and as such, is now leading the world in what looks like a highly disruptive and cost-effective technology which can balance renewable energy supply and demand.”
Smallbone’s team has not yet achieved the full potential efficiency of the system, but he said that the 60- 65 per cent efficiency it has obtained is consistent with the original target design specification and is high enough to place the technology as the lowest-cost and most flexible grid-scale energy storage technology currently available.
"Additionally, these tests also indicated there is significant opportunity for further improvements through design enhancements and operational optimisation. This will now continue over the next few months," he said.