Claims of up to 70% efficiency have been made for converting ‘wrong time’ electricity produced by intermittent generators such as wind turbines to ‘right time’ electricity supplied onto the grid. The proposed storage medium is liquid air (with co2 and water vapour first removed. This -190C medium is used to drive a piston engine without combustion, and waste heat is re-used.
The BBC’s Roger Harrabin mis-reports this engine as a ‘turbine’ in this report:
Turning air into liquid may offer a solution to one of the great challenges in engineering – how to store energy.
The Institution of Mechanical Engineers says liquid air can compete with batteries and hydrogen to store excess energy generated from renewables.
IMechE says “wrong-time” electricity generated by wind farms at night can be used to chill air to a cryogenic state at a distant location.
When demand increases, the liquid air can be warmed to drive a turbine.
Engineers say the process to produce “right-time” electricity can achieve an efficiency of up to 70%.
The process follows a number of stages:
- “Wrong-time electricity” is used to take in air, remove the CO2 and water vapour, which would otherwise freeze solid
- the remaining air, mostly nitrogen, is chilled to -190C (-310F) and turns to liquid – this provides a compact storage medium that can later draw energy in the form of heat from the environment
- the liquid air is held in a giant vacuum flask until it is needed
- when demand for power rises, the liquid is warmed to ambient temperature. As it vapourises, the expanding gas drives a turbine to produce electricity – no combustion is involved
IMechE says this process is only 25% efficient but it is massively improved by co-siting the cryo-generator next to an industrial plant or power station producing low-grade heat that is currently vented and being released into the atmosphere.
Dearman’s website page concerning the engine is here.
I wonder how much more efficient this engine is than a stirling engine using liquid air to create the heat differential.