Microprocessor powered for six months with algae battery

The University of Cambridge researchers behind the project believe their invention could be used as a reliable and renewable way to power small devices in the future.

The whole system is comparable in size to an AA battery and contains a type of non-toxic algae called Synechocystis that naturally harvests energy from the sun through photosynthesis.

The tiny electrical current this generates then interacts with an aluminium electrode and is used to power a microprocessor.

The system is made of common, inexpensive and largely recyclable materials, meaning it could easily be replicated hundreds of thousands of times to power large numbers of small devices as part of the Internet of Things (IoT).

The researchers believe it is likely to be most useful in off-grid situations or remote locations, where small amounts of power can be very beneficial.

“The growing Internet of Things needs an increasing amount of power, and we think this will have to come from systems that can generate energy, rather than simply store it like batteries,” said professor Christopher Howe, joint senior author of the paper.

“Our photosynthetic device doesn’t run down the way a battery does because it’s continually using light as the energy source.”

In the experiment, the device was used to power an Arm Cortex M0+, which is a microprocessor used widely in IoT devices. It operated in a domestic environment and semi-outdoor conditions under natural light and associated temperature fluctuations, and managed six months of continuous power production.

“We were impressed by how consistently the system worked over a long period of time – we thought it might stop after a few weeks but it just kept going,” said Dr Paolo Bombelli, first author of the paper.

The algae does not need feeding, because it creates its own food as it photosynthesises. And despite the fact that photosynthesis requires light, the device can even continue producing power during periods of darkness. The researchers think this is because the algae processes some of its food when there’s no light, and this continues to generate an electrical current.

There are currently billions of IoT devices, from smartwatches to temperature sensors, that make use of low-power chips and only require small amounts of energy run. This figure is expected to grow to one trillion devices by 2035, requiring a vast number of portable energy sources.

The researchers say that powering trillions of IoT devices using lithium-ion batteries would be impractical: it would need three times more lithium than is produced across the world annually. Traditional photovoltaic devices are made using hazardous materials that have adverse environmental effects.