Bacteria that can convert electricity into methane could help solve one of the biggest problems with renewable energy – its unreliability compared to the steady output of polluting fossil-fuel power stations.
Wind power is capricious, while solar cell output drops off at night or on cloudy days. That fluctuating output poses big problems for electricity grids that rely on steady levels throughout the day. Proposals to deal with the ups and downs of green power supply have included better batteries or redesigning the electricity grid.
An intriguing new idea involves "feeding" surplus power to bacteria instead, which combine it with carbon dioxide to create methane. That could then be stored and burned when needed. The method is sustainable too, as the carbon is taken from the atmosphere, not released from long-term storage in oil or coal.
The new method relies on a bacterium discovered by Bruce Logan's team at Pennsylvania State University in University Park. When living on the cathode of an electrolytic cell, the organism can take in electrons and use their energy to convert carbon dioxide into methane.
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Of the energy put into the system as electricity, 80% was eventually recovered when the methane was burned – a fairly high efficiency. "You don't get all the energy back, but that's a problem with any form of energy storage," says Curtis.
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Logan is optimistic about the method's potential: "Commercial applications could be just a few years down the road," he says.
Curtis is also impressed. "If you have a windmill, say, you need a relatively simple way to store the energy. What I like about this method is it's simple, it's replicable and it's scalable."
Several similar techniques use bacteria to produce hydrogen fuel rather than methane. But the hydrogen economy is not here yet, Logan points out. "These methods are great, but hydrogen doesn't fit into our existing infrastructure. Methane does."
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