28 March 2017
By Barney Slater AMRSB, BBSRC PhD student at University of Cambridge and policy intern at the Royal Society of Biology, talks about renewable energy from photosynthesis.
The need for renewable energy will only increase as our global supplies of fossil fuels begin to run dry. One of the most famous examples of renewable energy is solar power. Solar panels typically use expensive light-sensitive semiconducting materials like silicon to convert sunlight into electricity. However, biologists teaming up with engineers have been working on an equivalent solar semiconductor system, one already utilised by living things: photosynthesis.
Researchers are currently investigating photo-bioelectrochemical systems (photo-BES, often known as Plant-BES), which use photosynthesis to convert sunlight into electricity. One method, called the plant microbial fuel cell (PMFC) uses a symbiotic relationship between plants and microbes to produce power. The plants convert sunlight into energy-rich compounds, which can be passed to soil bacteria. The bacteria consume these compounds to release electrical charge which passes into a circuit through an electrode, forming an electrical current. Another form of photo-BES, called biophotovoltaics, uses photosynthetic microorganisms such as algae, to convert sunlight into electrical charge. This cuts out the middleman by removing the need for soil bacteria, thus making the connection between solar energy and the creation of electricity more direct.
Schematic cartoon for a plant-BES system. Photo: Dr Paolo Bombelli (source)
But these systems provide more than just a fun science project. Already, as a demonstrative example, moss-BES has been used to power a radio. Prototype ‘green walls’ that use PMFCs are being tested, so that the plants covering a building could help to power it. This means you could combine solar panels, insulation and aesthetics to make the ultimate green home! ‘Crop-BESs’ are also being investigated, opening new opportunities in combining agriculture and renewable energy. Biophotovoltaics could also provide solar power on a smaller scale, and researchers are currently looking into algae-watch batteries.
Advantages of photo-bioelectrochemical systems
So what would the benefits of these plant solar panels be? Firstly, photo-BESs are created in smaller facilities, and therefore require much less infrastructure to set up than current solar panels, and are much easier to fix, since whole organisms can reproduce and repair themselves when damaged. Therefore, photo-BESs have great potential for delivering electricity to areas off the national grid. Also, the organisms involved in these systems are specialists at storing solar power from the sun for a supply of energy at night. Therefore the photo-BESs have potential to generate electricity in the dark, something unheard-of in current solar panels. Finally, as photosynthesis removes carbon dioxide from the air, the use of photosynthesis in solar cells has the potential to be carbon neutral.
The future of solar bioelectrochemical systems
A major goal for renewable energy is to achieve ‘grid parity’: the ability to provide the same amount of power as the current electricity grid at the same or lower cost. In order for photo-BES to reach this goal, it needs to be more efficient. The organisms involved in these systems still use some of the electrical energy produced from photosynthesis to survive and grow, so the energy output for other uses is reduced. Therefore, scientists and engineers are looking into modifications to increase this output and reach grid parity. For PMFCs, researchers are optimising the soil conditions for energy transfer and healthy plant growth, whilst utilising genetic technologies to derive better electrical output from soil microbes. For biophotovoltaics, work has started on increasing the ‘wiring’ of the organism into the circuit, for example by directly attaching the cells to the electrode. If successful, these steps could make photo-BESs a viable competitor to conventional solar panels.
This combination of biological research and electrical engineering has the potential to grant us a win-win in renewable energy: all the benefits of a beautiful garden, which, as it happens, also provides the power for your home.
For more information, please see Cambridge BPV website