Currently most of the planet’s clean energy comes from the wind, sun and water. The pagans in the audience might have already noticed that one of the four classical elements is missing in that equation: the earth.

Solar power could one day be stored in the ground beneath our feet, if an “adventurous” new project to create a ‘soil battery’ succeeds.

UK Research and Innovation is investing €16.9 million in a soil solar power technology, along with 67 other projects that are high risk but have a the potential of a transformative impact. “The possible scale of that impact is really exciting,” says lead researcher Dr Michael Harbottle. “To see something that’s really quite novel, possibly having a big impact is what’s driving us.”

How does soil solar power works?

Throwing solar energy into the mix requires something more elaborate than “just putting soil into a jar, putting a couple of electrodes in and connecting them together” he says. The plan is to send electricity from solar panels to buried electrodes, thereby stimulating certain bacteria in the soil.

Healthy soils feed the entire food chain, from the food we eat to the water we drink and even the air we breathe. Conserving and restoring their natural balance requires urgent action for the survival of every living organism. The soil has the potential to sequester 2.04 gigatonnes of CO2 equivalents – or 34 per cent of global agricultural emissions. Put simply, soils have a massive potential to lock-up CO2, stopping it from being released into the atmosphere with harmful consequences. If soils are managed sustainably, the carbon they already store will be retained.

A bit like photosynthesis – whereby plants take in CO2 and transform it in their cells – but all happening below ground. Electric power, CO2, action: the “bugs”, as Harbottle calls them, get to work using the energy to reduce the carbon dioxide and make a more complex molecule called acetate.

This acetate, which Dr. Harbottle describes as being the same sort of molecule found in vinegar minus the acid, acts as a chemical store of energy. When needed, another circuit (known as a microbial fuel cell) is switched on, which activates a different set of bacteria to break down the acetate.

Soil could offer a subterranean alternative to lithium and in the long term, these batteries could be set up below fields of solar panels. But as the microbial fuel cells only supply low voltages for now, their use in relatively low power systems is more imminent.

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