Blue-green algae, a type of cyanobacteria, set in a container on a windowsill powered a computer continuously for six months using photosynthesis
12 May 2022
Blue-green algae sealed within a small container have powered a computer for six months. Similar photosynthetic power generators could run a range of small devices cheaply in the coming years, without the need for the rare and unsustainable materials used in batteries.
Christopher Howe at the University of Cambridge and his colleagues built a small enclosure about the size of an AA battery out of aluminium and clear plastic. Inside, they placed a colony of a type of cyanobacteria called Synechocystis sp. PCC 6803 – commonly known as “blue-green algae” – which produce oxygen through photosynthesis when exposed to sunlight.
The device was placed on a windowsill at the home of team member Paolo Bombelli during a covid-19 lockdown in 2021, and stayed there from February to August. It provided a continuous current across its anode and cathode that ran an Arm microprocessor.
The computer ran in cycles of 45 minutes of calculating sums of consecutive integers to simulate a computational workload, which required 0.3 microwatts of power, and 15 minutes of standby, which required 0.24 microwatts. The computer itself measured the current output from the device and this data was stored in the cloud for researchers to analyse.
There were no power interruptions during the six months of the experiment, and in the six months since it ended the cyanobacteria have continued to produce power.
Howe says that there are two potential ideas for the source of the power. Either the cyanobacteria themselves produce electrons, which creates a current, or they create conditions in which the aluminium anode in the container is corroded in a chemical reaction that produces electrons. Because the experiment ran without any significant degrading of the anode the researchers believe that the cyanobacteria are producing the bulk of the current.
The approach could be scaled up, says Howe, but further research is needed to know how far. “It’s not entirely straightforward,” he says. “So putting one on your roof isn’t going to provide the power supply for your house at this stage. There’s quite a bit more to do on that front. But [it could work] in rural areas of low and middle income countries, for example, in applications where a small amount of power might be very useful, such as environmental sensors or charging a mobile phone.”
The cyanobacteria create their own food during photosynthesis and the device can even continue producing power during periods of darkness, which the researchers believe is possible because the cyanobacteria continue to process surplus food.
The researchers have experimented with creating a similar enclosure from empty plastic bottles and believe that effective devices could be produced very cheaply, with commercial application possible within five years. They have also found species of algae that create higher currents.
Journal reference: Energy & Environmental Science, DOI: 10.1039/D2EE00233G
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