Scientists Develop Semi-Transparent Solar-Powered Roof for Greenhouses

Scientists have created solar roofs for greenhouses, but these aren’t just any solar panels. A team from UCLA developed semi-transparent organic photovoltaics with added stability, so plants within the greenhouse can still receive sunlight while the solar panels harvest energy to power other components of the greenhouse.

In a greenhouse setting, solar panels could help control operational elements, like irrigation systems or lighting. But when installed on a roof, solar panels typically would shade everything below the glass roof, meaning the plants would need to rely on grow lights rather than sunlight.

Semi-transparent organic photovoltaics could provide a solution, but organic photovoltaics typically lack stability, making them less reliable to give ongoing power to the greenhouse.

So a team of scientists introduced an interlayer of L-glutathione, a naturally occurring antioxidant, for more stable organic photovoltaics. 

“The interlayer effectively suppresses the generation of radicals from the electron transport layer under sunlight and prevents the structural decomposition of the organic photoactive layer during operation,” the scientists explained in the study of their findings, published in the journal Nature Sustainability. “The defects that serve as the charge carrier recombination sites are nullified by the electron-donating functional groups of the reduced molecules, which improves photovoltaic performance.”

The resulting semi-transparent organic photovoltaics proved to have solar cells with longer lifespans and better efficiency without blocking sunlight to the plants within the greenhouse prototype.

Organic photovoltaics tend to have shorter lifespans than inorganic photovoltaics, because the organic solar cells can oxidize when exposed to sunlight. But the L-glutathione layer helped prevent the oxidization. Operational stability had 84.8% retention after over 1,000 hours, a feat the study authors noted as “remarkable.” Without the interlayer of L-glutathione, organic photovoltaics would comparatively have less than 20% retention after 1,000 hours.

“Organic materials are uniquely suitable for agrivoltaics because of their light-absorption selectivity,” Yang Yang, materials scientists at UCLA and study author, said in a statement. “The main drawback that has prevented their widespread use up to now is their lack of stability.”

The solar cells also improved crop growth. The scientists grew crops, including mung beans, broccoli and wheat, in two greenhouses: one transparent greenhouse with segments of inorganic photovoltaics on the roof, and one greenhouse with the organic photovoltaics that had the L-glutathione layer added.

In addition to preventing oxidization, the L-glutathione also blocked UV rays and infrared rays. As such, the plants in the greenhouse with organic photovoltaics had better growth.

“We didn’t expect the organic solar cells to outperform a conventional glass-roof greenhouse,” said lead author Yepin Zhao, as reported by Electrek. “But we repeated the experiments multiple times with the same results and after further research and analysis, we discovered that plants don’t need as much sunlight to grow as we’d originally thought. In fact, too much sun exposure can do more harm than good, especially in climates such as California’s, where sunlight is more abundant.”

The study shows opportunity and promise for incorporating semi-transparent organic photovoltaics into agricultural uses. Rather than installing large solar panels on land, farmers could incorporate these solar panels onto greenhouses and harvest energy for the greenhouses and other agricultural operations.

The study authors have now collaborated in creating a startup company, hoping to eventually develop these organic solar cells for industrial use and even sell greenhouses with the incorporated stable, semi-transparent organic photovoltaics on the roofs.