A technology invented to use chilled air as a power source for engines has been put forward by Britain’s Institution of Mechanical Engineers as a possible solution for storing electricity generated by renewables, such as solar and wind power.
One of the main criticisms levelled against renewable energy sources is their inability to provide “baseload” generation, as they are dependent on inputs that regularly fluctuate in intensity or availability. Storing energy from renewable sources and then releasing it at useful times is one option, but of course batteries are sub-optimal for that task.
Hence IMechE's interest in a process developed by Peter Dearman (and working towards commercialisation over at the Dearman Engine Company) in which energy is used to super-cool stored air. When the air is released, the process of warming produces a rapid expansion that can power a generator.
As described at the BBC, the process has five steps: water and CO2 are removed from the air so they don’t freeze; the remaining air is cooled to -190°C, at which point it liquefies for storage; upon release, it returns to a gaseous state, expanding to power a turbine.
At the moment, the process has very low efficiency – about 25 percent – but IMechE has a few ideas about how that can be improved.
The company that took the proposal to IMechE, Highview Power Storage, says scale is the key. A large cryo-generator could be co-located with a large-scale conventional industrial plant or power station, to harvest waste head otherwise released to the atmosphere. This heat could be used to speed up the warming of the stored air, boosting the power output.
Also, when the cooling process has been completed, excess low-temperature air could be passed through gravel-filled tanks, to help prime the cooling process on the next cycle.
This, the company says, could yield efficiency of as much as 70 percent (if its calculations are accurate). This still falls below the efficiency of batteries, but IMechE’s head of energy Dr Tim Fox told the BBC the cryo-generator has other advantages: it could “last for decades and it can be fixed with a spanner”.
And with any luck, Earth won't run out of air anytime soon. ®