RheEnergise has successfully demonstrated its dense-fluid pumped hydro technology at a site in Cornwood, Devon. The system features upper and lower reservoirs, pumps, pipes, and generating equipment. It uses a proprietary fluid roughly 2.5 times as dense as water to generate electricity.
The demonstrator achieved its design power of 500 kW, though it provided only 15 minutes of storage instead of the planned four hours. This discrepancy resulted from challenges in producing sufficient quantities of the specialized high-density fluid. The system recorded a round-trip efficiency of 59%.
Scaling the technology presents significant economic and material challenges. For a 600 MW system operating for 18 hours, the required volume of barite-rich fluid would reach approximately 8.8 million tonnes, a quantity comparable to current annual global mine production.
The company is exploring the use of local mine waste or quarry materials to mitigate supply chain constraints. However, this approach limits potential project sites to locations with specific geological and mineral resources, creating a new set of siting requirements.
The technology faces a competitive squeeze. At shorter durations of four to eight hours, it competes with lithium-ion batteries, which saw prices drop to about $70 per kWh in 2025. At longer durations, it struggles against conventional pumped hydro, which uses water as a free medium.
