Researchers have demonstrated that the use of tinted, translucent solar panels can simultaneously generate electricity and produce nutritious crops, leading to higher income prospects for farmers and maximizing agricultural land use.
By allowing farmers to diversify their investment portfolios, this novel system could provide financial protection from fluctuations in market prices or changes in demand, and mitigate risks associated with climate unreliability. On a larger scale it can greatly increase the solar power supply capacity to generate electricity without affecting agricultural production.
This isn't the first time that semi-transparent solar panels have been used to produce crops and electricity at the same time, a technique known as agrophotovoltaics. But in a novel adaptation, the researchers used orange-tinted panels to make the most of the wavelengths (or colors) of light that might pass through them.
Tinted solar panels absorb blue and green wavelengths to generate electricity. Orange and red wavelengths pass through, allowing the plants below to grow. While crops grown in standard farming systems receive less than half of their total light, the colors that pass through the panels are the ones best suited to their growth.
“For a high-value crop like basil, the value of electricity generation simply makes up for the loss of biomass production from tinted solar panels. However, when crops such as spinach are of lower value, this has significant financial advantages. This Lead researcher Dr Paolo Bombelli of the University of Cambridge's Department of Biochemistry said.
Under normal growing conditions, the combined value of spinach and electricity produced using a tinted agricultural PV system is 35% higher than growing spinach alone. By comparison, the total financial gain for basil grown this way is only 2.5%. The calculation uses current market prices: Basil sells for about five times as much as spinach. The value of the electricity produced is calculated assuming that it will be sold to the Italian National Grid, which conducted the study.
"Our calculations are a fairly conservative estimate of the overall financial value of the system. In fact, if farmers bought electricity from the national grid to run their houses, the benefits would be greater," said Professor Christopher Howe, University of California, USA. The University of Cambridge's Department of Biochemistry also participated in the research.
The study found that basil grown under tinted solar panels had a 15 percent lower marketable yield and spinach about 26 percent lower than normal growing conditions. However, spinach roots grow far less than stems and leaves: less light is available, and the plant puts energy into growing "bio-solar panels" to capture the light.
Laboratory analysis of spinach and basil leaves grown under the plates showed that both had higher protein concentrations. The researchers believe that plants may produce additional proteins to enhance their ability to photosynthesize under reduced light conditions. To accommodate the reduced light, spinach produces longer stems that make harvesting easier by lifting the leaves from the soil.
“From a farmer’s point of view, it is beneficial if your leafy greens have larger leaves, the edible part of the plant that can be sold. As the global demand for protein continues to grow, it is possible to increase protein in plant crops Content technology would also be very beneficial.”
The study's lead author, Dr Eleanor Thompson from the University of Greenwich, said: "With so many crops currently growing under some kind of transparent cover, there is no land loss for additional energy production using coloured solar panels. "
All green plants convert light from the sun into chemical energy that fuels their growth through photosynthesis. The experiments were carried out in Italy using two test crops. Spinach (Spinacia oleracea) represents a winter crop: it grows with less sunlight and tolerates cold weather. Basil (Ocimum basilicum) represents a summer crop that requires a lot of light and higher temperatures.
The researchers are currently discussing further trials of the system to see how well the system works on other crops, and how growing under mainly red and orange light affects crops at the molecular level.