Cost-effective and efficient medium-duration energy storage
The Australian electricity sector is transitioning to use a larger proportion of renewable energy generation, like solar and wind. But these sources vary with the weather, throughout the day and over seasons.
To support variable renewable energy sources, we need to be able to store energy when there is more than enough supply, say on sunny, windy autumn days. Then we can draw on this energy when needed.
We need to be able to store energy safely for different lengths of time. Storage needs to be cost effective, and it needs to be efficient, that is, we need to get a high proportion of the energy we put into storage back out again.
Compressed air energy storage feasibility study
Compressed air energy storage (CAES) is a promising, cost-effective technology to complement battery and pumped hydro storage by providing storage over a medium duration of 4 to 12 hours.
CSIRO and MAN Energy Solutions Australia conducted a feasibility study on adiabatic-CAES (A-CAES), storing compressed air in porous media. As A-CAES compresses the air, the heat that is generated by the compression is preserved by extracting it through heat exchange and storing it separately (thermal energy storage).
The thermal energy can then be used to heat up the compressed air before it is expanded to run a turbine and generate electricity. By recovering this energy and using it, A-CAES can have a higher ‘round-trip’ efficiency than other systems. This means more of the stored energy is recovered.
Cost-effective storage with excellent round-trip efficiency
The study was conducted in a depleted gas porous rock reservoir, around 1500 metres deep, using three separate modelling methods, which showed results in close agreement of a round-trip efficiency of around 65 per cent.
We then calculated the levelised cost of storage for comparison with other storage technologies and concluded that A-CAES would be a zero emission and cost-effective storage technology to complement short-duration, fast-response batteries, and long-duration pumped hydro.
Future research will be conducted at shallower reservoirs, around 400 metres deep, to see whether round-trip efficiency can be improved to more than 75 per cent. We will also be looking at different locations to determine cost competitiveness and the management of risk.