Grid-scale Electricity Storage

 

Electricity cannot be directly stored, so electrical grid managers must constantly ensure that overall demand from consumers is exactly matched by an equal amount of power fed into the grid by generating stations. Because the chemical energy in coal and gas can be stored in relatively large quantities, conventional fossil-fuelled power stations offer dispatchable energy available on demand, making grid management a relatively simple task. However, fossil fuels also release greenhouse gases, causing climate change – and many countries now aim to replace carbon-based generators with a clean energy mix of renewable, nuclear or other non-fossil sources.
Clean energy sources, in particular wind and solar, can be highly intermittent; instead of producing electricity when consumers and grid managers want it, they generate uncontrollable quantities only when favourable weather conditions allow. A scaled-up nuclear sector might also present challenges due to its preferred operation as always-on baseload. Hence, the development of grid-scale electricity storage options has long been a “holy grail” for clean energy systems. To date, only pumped storage hydropower can claim a significant role, but it is expensive, environmentally challenging and totally dependent on favourable geography.
There are signs that a range of new technologies is getting closer to cracking this challenge. Some, such as flow batteries may, in the future, be able to store liquid chemical energy in large quantities analogous to the storage of coal and gas. Various solid battery options are also competing to store electricity in sufficiently energy-dense and cheaply available materials. Newly invented graphene supercapacitors offer the possibility of extremely rapid charging and discharging over many tens of thousands of cycles. Other options use kinetic potential energy such as large flywheels or the underground storage of compressed air.
A more novel option being explored at medium scale in Germany is CO₂ methanation via hydrogen electrolysis, where surplus electricity is used to split water into hydrogen and oxygen, with the hydrogen later being reacted with waste carbon dioxide to form methane for later combustion – if necessary, to generate electricity. While the round-trip efficiency of this and other options may be relatively low, clearly storage potential will have high economic value in the future. It is too early to pick a winner, but it appears that the pace of technological development in this field is moving more rapidly than ever, in our assessment, bringing a fundamental breakthrough more likely in the near term.