Scientists have created a bio-photovoltaic energy harvester system using a species of photosynthetic blue-green algae called Synechocystis on an aluminum anode that can power an Arm Cortex M0+, a microprocessor widely used in Internet of Things applications.

This system, containing Synechocystis blue-green algae, powered a microprocessor continuously for a year using nothing but ambient light and water. Image credit: Paolo Bombelli.

Sustainable, affordable and decentralized sources of electrical energy are required to power the network of electronic devices known as the Internet of Things.

Power consumption for a single Internet of Things device is modest, but the number of Internet of Things devices has already reached many billions and is expected to grow to one trillion by 2035, requiring a vast number of portable energy sources.

Batteries rely largely on expensive and unsustainable materials (e.g., rare earth elements) and their charge eventually runs out.

Existing energy harvesters (e.g., solar, temperature, vibration) are longer lasting but may have adverse effects on the environment.

“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, a researcher in the Department of Biochemistry at the University of Cambridge.

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

In the experiments, the team’s device was used to power an Arm Cortex M0+, which is a microprocessor used widely in Internet of Things devices.

It operated in a domestic environment and semi-outdoor conditions under natural light and associated temperature fluctuations, and after six months of continuous power production the results were submitted for publication.

“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, also from the Department of Biochemistry at the University of Cambridge.

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.

“This is because the algae processes some of its food when there’s no light, and this continues to generate an electrical current,” the researchers said.

The team’s work was published in the journal Energy & Environmental Science.

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P. Bombelli et al. Powering a microprocessor by photosynthesis. Energy Environ. Sci, published online May 12, 2022; doi: 10.1039/D2EE00233G

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