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As the food versus fuel debate around solar farms in Ireland heats up, a new report from a team of researchers at Cornell University, USA, has found that co-locating commercial crops under solar panels can improve solar panel performance and longevity.
The findings, published in the journal Applied Energy, show that solar panels mounted over soya beans have lower surface temperatures compared with panels placed over bare ground.
Solar panels placed four metres above the soya bean crop demonstrated temperature reductions of up to 10°C compared with those mounted half a metre above bare soil.
Model
The team developed a numerical model to investigate the micro-climate under a solar farm, measuring the influence of evapotranspiration, panel height and light reflection on the crops and the solar panels.
The results indicate that the cooling effect created by the crops increases solar panel efficiency.
“As you decrease the solar panel operating temperature, you can increase efficiency and improve the longevity of your solar modules,” said co-author of the report Henry Williams.
Crop yield
While co-locating solar panels above commercial crops provides benefits for performance and longevity of the panels, the report fell short on detailing the impact on crop yield. It stands to reason that shading crops would have an impact on yield.
However, work is currently ongoing to test this concept. TSE Energy, a French power company, conducted the trial on a farm in the northeast of France, focusing on soya bean crops.
The aim was to determine if solar energy could be generated without affecting the crop’s yield.
The study used a wire grid, strung between pylons, to mount 5,000 solar panels which produced 2.5MW of electricity.
The panels were placed at a height that allowed combines and other machinery to pass underneath them. The wire mounting grid was connected to motors that tracked the sun and adjusted the panels accordingly.
The panels could also be raised to a vertical position to allow rain or sunlight to penetrate and ensure that crops grow.
Findings
Researchers found that an added benefit of the trial was providing cover from extreme weather conditions during key points of the year.
Head of agronomy research at TSE Xavier Guillot stated that the panels can be positioned horizontally to provide cover against hail, heavy rain or direct sunlight to preserve soil moisture.
He also explained that the panels acted as a roof to trap warmth in colder conditions, providing a degree of temperature control.
The study suggested that it is possible to meet France's renewable energy needs without sacrificing prime agricultural land.
The panels will be connected to France's power grid, generating enough energy to power 1,500 homes.
However, at a height of over four meters, the visual impact of this system would likely prove to be a challenge when applying for planning permission here in Ireland.
Last week, planning permission for a 300ac solar farm by Obton Limited in Co Meath was refused.
Meath County Council cited that the development would “result in an incongruous feature in the landscape, would be out of character and if permitted would serve to set an undesirable precedent for similar proposals into the future”.
German study
Another agrivoltaics project which gained global attention was the pilot project led by German-based Fraunhofer ISE. This project demonstrated the viability of using agricultural land for both food and electricity production.
The project, which used bifacial solar modules to limit the shading impact on crop growth, tested winter wheat, potatoes, celeriac and clover grass.
The results were promising, with only a 5.3% reduction in crop yield for clover grass and slightly higher yield losses for potatoes, wheat and celeriac. However, the commercial crops could still be grown and harvested as normal.
The power production from the 194kW PV system matched the daily farm load, with surplus electricity fed into the grid.
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