Greenhouses and solar panels both need to be placed in areas with lots of sunlight - so why not combine the two? Semi-transparent solar cells could be integrated into the glass roof panels of greenhouses, capturing light at wavelengths that plants don't use anyway. Researchers from North Carolina State University developed a model of how it works, finding that in some climates the cells could produce enough solar energy to make the greenhouse completely self-sufficient.
Le solar cells organic (OSC) have some advantages over other projects. They harvest energy from sunlight, but can be made more flexible, transparent (or at least semi-transparent), and can be configured to absorb only certain wavelengths of light. This potentially makes them perfect for greenhouse roofs - they can let most of the light through for plants, while harvesting enough to offset some of the facility's energy needs.
"Plants use only a few wavelengths of light for photosynthesis, and the idea is to create greenhouses that make energy from that unused light while allowing the passage of most of the photosynthetic band of light"Says Brendan O'Connor, author of the study. "However, until now it was not clear how much energy a greenhouse could capture using these semi-transparent organic solar cells."
Semitransparent solar cells: the tests
To start answering this question, the researchers calculated how much energy would arrive on a greenhouse with OSC on the roof, compared to its energy consumption that it would normally consume. The idea was to find the point where the greenhouse becomes energy-neutral, i.e. it generates enough energy from the Sun to fully feed itself.
For this study, the greenhouses were modeled on the energy needed to grow tomatoes in three locations with different climates. The team found that the impact on the amount of light received by plants is minimal, but the benefits far outweigh it. In sunny places, for example, a greenhouse with semi-transparent solar cells could become energy-neutral, blocking only 10 percent of the light plants need. This shouldn't adversely affect the plants, the team says.
In colder places it would not be possible to achieve energy neutrality, but the semi-transparent panels would reduce the energy requirement of a greenhouse by half.