In the race to ramp up renewables, we can't ignore heat storage

It is by now well established that to mitigate the worst effects of climate change, we need to reach net-zero carbon emissions as fast as possible. That means getting more of our energy from renewable sources and finding ways to store it for long periods to overcome the intermittency of wind and solar.

Huge battery installations and green hydrogen – where excess renewable energy is used to split water – are often touted as the most promising storage solutions, and clever new ways to hoard excess power are popping up all the time (see “Giant dome filled with CO2 could store excess power from renewables”). However, the possibilities for storing renewable energy as heat are often overlooked.

When we think about renewables, we tend to think about electricity. But heat itself is also a valuable commodity. About half of the world’s total energy demand is for heat, whether for warming homes or to power the industrial production of food, medicines, materials and more. Besides, stored heat can also be used to generate electricity when the sun stops shining and the wind dies down.

The good news, as we discover in our feature “How incredibly simple tech can supercharge the race to net zero”, is that a whole range of heat storage technologies are emerging. Known collectively as Thermal Energy Storage (TES), many of these innovations are disarmingly simple – from toasted bricks to molten salt. Crucially, they should also be affordable. Early estimates suggest that these technologies could be as little as a fifth of the cost, per kilowatt-hour, of energy storage using green hydrogen. In a recent report, the International Renewable Energy Agency said TES offers “unique benefits”.

The problem is that there is relatively little awareness of TES, and even less investment. Private backers are beginning to put serious money into pilot projects in the US and Europe. But governments everywhere need to step up if we are to make good on TES’s promise as a relatively easy way to make a hefty dint in renewable energy’s intermittency problem. If the prices are as good as they look, we can’t afford not to.