Algae are probably one of the most attractive directions of scientific development when it comes to finding new green energy sources. They are cheap. They can be used either as a direct source of oil to make biofuel from, as Exxon is doing or, as a team of Cambridge chemists did, used in a fuel cell to make electricity.
This is not the first fuel cell powered by what is called biophotovoltaics. A biophotovoltaic, or BPV, is a solar cell that uses microorganisms to turn solar energy into an electric current. Algae are particularly suitable for these cells, since they grow quickly and, again, are cheap to produce. These, however, were also genetically modified to convert solar energy into electrons more efficiently by minimizing the loss of electrons during the conversion.
What makes this team’s cell different is that unlike most, it is divided into two chambers: one for the conversion of solar energy into electrons through photosynthesis and one for the conversion of these electrons into an electric current.
One of the researchers working on the project, chemistry postgrad Kadi Liis Saari, said, “Charging and power delivery often have conflicting requirements. For example, the charging unit needs to be exposed to sunlight to allow efficient charging, whereas the power delivery part does not require exposure to light but should be effective at converting the electrons to current with minimal losses.”
This division allowed the researchers to make power delivery more efficient, but the fact that the cell was miniature helped, too. “At miniature scales, fluids behave very differently, enabling us to design cells that are more efficient, with lower internal resistance and decreased electrical losses,” explains Professor Tuomas Knowles, another team member.
But that’s not all. The division of the cell also made it possible to store the energy produced by the algae. That’s not something that was possible with the single-chamber cells: the electricity they produced was to be used immediately. Now that energy storage has become no less of a buzzword than “digital disruption” or “operational efficiency”, anything that has storage in its name is bound to draw a lot of attention. But this cell’s attention is well deserved. It combines low cost, low energy investment, and high efficiency.
The miniaturization aspect could hamper the commercial prospects of the new solar cell for the moment, but it is nevertheless a significant invention at a time when everyone is looking for cheaper and more efficient alternatives to existing technologies for extracting energy from renewable sources.
Their power density is minuscule, at 0.5W per sq m, but that’s already five times more than a previous algae-powered fuel cell design made by the team. It is also a tenth of the power density of silicon solar cells. If we consider all factors, including the energy intensity of producing a silicon solar cell as compared to the algae-powered one, a tenth might not be so bad.
Algae grow naturally. You don’t need to use a lot of energy to make them grow, and that’s one very big difference with silicon-based PV systems. What’s more, they don’t need a factory to grow in, so algae-powered fuel cells can be produced where they are needed. This, according to the researchers, could make these cells especially well-suited for places where there is no electricity transmission and distribution infrastructure.