What is energy storage?
Energy storage secures and stabilises energy supply, and services and cross-links the electricity, gas, industrial and transport sectors. It works on and off the grid, in passenger and freight transportation, and in homes as ‘behind the meter’ batteries and thermal stores or heat pump systems. Energy storage in the form of heat can also help to reduce the costs and emissions from industry.
Energy can be stored as:
- electrical energy as electromagnetic fields in capacitors and induction coils, as electrochemical charge transfer in batteries, or via conversion to and from mechanical potential as in pumped hydro
- chemical energy in the chemical bonds of molecules such as methane or hydrogen in gas and liquid fuels, and in fossil fuels
- thermal energy in heat that can be conserved, stored and recycled instead of being wasted, or cooled using natural assets such as underground aquifers when it is not required.
Energy storage in Australia
In Australia, we are increasing our capacity for pumped hydro with Snowy 2.0 and the mapping and development of new sites like the Kidston pumped hydro project under construction at an old gold mine in central Queensland.
We are building utility-scale batteries in South Australia and Victoria. But batteries at large utility or small ‘behind the meter’ scales are not enough to keep our energy system reliable and lowest cost.
They will not enable decarbonisation of the hard-to-abate sectors, like metals, liquid natural gas and chemicals. These sectors may require extremely high-temperature processes or high-density fossil fuels as a feedstock.
At CSIRO, we are developing new chemical energy technologies and uses, such power-to-gas, converting surplus renewable energy into hydrogen or methane for storage, and then using it for industry feedstock or converting it back to electricity for the grid or high-grade heat for industry, or many other end uses.
Why is energy storage important?
If we are to keep warming at close to 1.5 degrees C, we need to phase out carbon-intensive energy sources and replace them with low or zero-emissions alternatives.
Currently we are electrifying our households, businesses and transport — using renewable energy sources directly — but we are still using vast amounts of fossil-derived energy for industrial processes, for example. This must be replaced by alternatives that have equivalent energy-dense properties to fossil fuels.
We also need a mixture of energy storage that is very-short-term (milliseconds to seconds) to stabilise the electricity grid and control voltage and phase, short-term (hours) to stabilise electrical energy systems and provide uninterruptible power supply, and long-term (days to years) to resupply the energy system.
In this way, energy storage can act as an enabler to reduce emissions while fossil fuels are replaced in the transition towards net zero emissions.
Storing energy underground
At CSIRO, we are interested in energy storage research on firming renewable energy technologies.
Energy supplied by renewable energy technologies, like solar and wind, are variable — supply occurs when the sun is shining and the wind is blowing. At night or when the weather is not favourable, stored energy can be used to ‘firm’ supply. This means a more reliable and constant supply of energy on and off-grid.
Currently storage of electrical energy in Australia consists of a small number of pumped hydroelectric facilities and grid-scale batteries, and a diversity of battery storage systems at small scale, used mainly for backup. To balance energy use across the Australian economy, heat and fuel (chemical energy) storage are also required.
Underground storage of compressed hydrogen or compressed air can deliver backup and firming supply, account for seasonal changes in load and provide strategic reserves of energy to call on if there is a risk of system outage.
Compressed hydrogen has very high energy density. This makes it a great long-term and high-capacity energy storage option. Compressed air can be stored for a long time in shallow, medium and deep storage, and even under water. It is likely to be cheaper than pumped hydro and battery technology for medium storage.