There is “green energy” and then there is truly GREEN energy. A colorful colony of photosynthetic cyanobacteria, known as blue-green algae, has successfully powered a microprocessor for more than six months, according to a study published Thursday in the journal Energy & Environmental Science.

The small alternative to bio-based batteries could be used to power small electronic devices without rare earth elements and lithium, materials that are scarce and in growing demand, according to the study’s researchers. The system could also help bridge the electricity gap, providing another source of power for people in rural areas or low-income countries, study lead author Chris Howe, a biochemist at the University of Cambridge, said in a news release.

During the pandemic lockdown, the algae-based computer system was placed in the window of the home of another Cambridge biochemist, Paolo Bombelli. It was there from February to August 2021, and the entire time it was running, according to a report by New Scientist. In the six months after the official test, the algae-based device and computer continued to work.

Although the microprocessor has since been turned off, the cyanobacteria device continues to produce current. “It is still working and I hope it will work for a long time. Given the right light, temperature, and water conditions, I can’t predict when it will stop,” Bombelli said in an email to Gizmodo. To which Gizmodo replies: Well done, microbes!

Cyanobacteria harvest energy from sunlight and convert it into food for themselves. For this study, the researchers placed the energy-providing microorganisms (specifically, Synechocystis sp. ) in a plastic and steel container, about the size of an AA battery, along with an aluminum anode.

During the experiment, the microprocessor was programmed to do a bunch of calculations and then check its work. He did this continuously in 45-minute increments, followed by 15-minute waits, for months with the cyanobacteria unit as the only power source.

The researchers offered two hypotheses about how their system created current. In the so-called “electrochemical” model, the microbes simply produced the right conditions for the aluminum anode to oxidize or release electrons, which then create an electrical output. In the “bioelectrochemical” model, the cyanobacteria themselves generated electrons that were transferred through the bacterial membranes to the aluminum anode, generating a current. Since the aluminum anode did not appear to degrade much over time, the scientists believe the latter explanation is more likely than the former.

Even though the algae depend on a light source for food, the biosystem continued to produce enough power to run the microprocessor in the dark. Scientists attributed this phenomenon to leftovers. When it was light, the cyanobacteria cooked an overabundance of food, and when it got dark, the microorganisms continued to eat the leftovers.

The computer, an Arm Cortex-M0+ microprocessor, drew an average of 1.05 microwatts and 1.4 microamps of electrical current at a voltage of 0.72 V from the cyan cube throughout the experiment. By comparison, a standard AA battery starts life at 1.5V and decreases with use.

Although the results of the experiment are promising, it is important to note that the processor in the tested computer uses very little power, requiring only 0.3 microwatts to run. In context, even an energy-efficient LED light bulb uses around 10 watts. More research is needed to know exactly how much the tiny AA battery-sized device could scale, Howe told New Scientist. “Putting one on your roof will not provide the power supply for your house for now .”