What a massive thermal battery means for energy storage

Thermal batteries could help clean up difficult-to-decarbonize sectors like manufacturing and heavy industrial processes like cement and steel production. With Rondo’s latest announcement, the industry has reached a major milestone in its effort to prove that thermal energy storage can work in the real world. Let’s dig into this announcement, what it means to have oil and gas involved, and what comes next.

The concept behind a thermal battery is overwhelmingly simple: Use electricity to heat up some cheap, sturdy material (like bricks) and keep it hot until you want to use that heat later, either directly in an industrial process or to produce electricity.

Rondo’s new system has been operating for 10 weeks and achieved all the relevant efficiency and reliability benchmarks, according to the company. The bricks reach temperatures over 1,000 °C (about 1,800 °F), and over 97% of the energy put into the system is returned as heat.

This is a big step from the 2 MWh pilot system that Rondo started up in 2023, and it’s the first of the mass-produced, full-size heat batteries that the company hopes to put in the hands of customers.

Thermal batteries could be a major tool in cutting emissions: 20% of total energy demand today is used to provide heat for industrial processes, and most of that is generated by burning fossil fuels. So this project’s success is significant for climate action.

There’s one major detail here, though, that dulls some of that promise: This battery is being used for enhanced oil recovery, a process where steam is injected down into wells to get stubborn oil out of the ground.

It can be tricky for a climate technology to show its merit by helping harvest fossil fuels. Some critics argue that these sorts of techniques keep that polluting infrastructure running longer.

When I spoke to Rondo founder and chief innovation officer John O’Donnell about the new system, he defended the choice to work with oil and gas.