"Our system is a highly reversible, gas cycle machine that works as both an engine and a heat pump. It is the first time that a reversible system has been developed both to store and recover electricity using a thermodynamic approach.
"The received wisdom is that thermodynamic devices are not very reversible, but that certain thermodynamic processes in isolation can be highly reversible. This led to the direct incorporation of heat exchange to a storage medium within the gas circuit of our heat engine. The key innovation is the reduction to four highly reversible processes within the cycle with integrated heat exchange to the storage medium."