Scientists figure out how to turn rocks into batteries

Granite and soapstone offer low cost and environmentally friendly method of storing solar energy

Granite (left) and soapstone samples could help store heat from the Sun and convert it into electricity (American Chemical Society)

Scientists have discovered a way to store the Sun’s energy in rocks and convert the heat into electricity.

Using an approach called concentrated solar power, a team of researchers from Tanzania found that certain granite and soapstones could store solar heat at a sufficiently high density to serve as a primitive form of battery.

Thermal energy storage has been touted as a low-cost way of storing and harvesting energy from the Sun, even when it’s no longer shining.

Last year, scientists from Sweden and China came up with a way to store solar energy for nearly two decades using an ultra-thin chip, which serves as a thermoelectric generator.

The innovative system could technically be integrated into electronics, however it remains too costly to implement at scale.

By contrast, the granite and soapstone samples offer a low cost and readily available method of storing solar energy, the researchers said.

“Using rocks as a storage medium offers the potential of affordability due to the abundance and low cost of rocks,” the researchers noted in a paper outlining their findings.

“An air-rock bed has low investment cost, high reliability and efficiency, is environmentally friendly, and does not require the use of heat exchangers.”

The rock bed captures and collects solar thermal energy up to 600 °C, which is then used to boil liquid into steam that powers a generator turbine to produce electricity.

The results were detailed in a study, titled ‘Experimental Investigation of Soapstone and Granite Rocks as Energy-Storage Materials for Concentrated Solar Power Generation and Solar Drying Technology’, published by the American Chemical Society.

Other thermal energy storage systems have focussed on salt and water, with researchers at Eindhoven University of Technology unveiling a heat battery last year that they claim could work at scale.

Rather than capturing heat from the Sun, the system instead collects industrial residual heat.

“While the potential is great, we have also seen many great potential technologies that have not made it,” the scientists said at the time. “So we’re going to keep our feet on the ground and take this one step at a time.”

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