A team of material scientists at the UCLA Samueli School of Engineering in California designed a solar roof with semi-transparent solar cells for a miniature greenhouse prototype, producing sufficient energy from sunlight to grow plants or crops.

In the study published in the scientific journal Nature Sustainability, the experts incorporated a layer of naturally occurring chemical L-glutathione in the solar cells, which is generally sold as a dietary supplement.

They observed that the addition of the chemical extended the lifetime of solar cells and enhanced the efficiency while allowing sufficient transparency in the solar roof for the sunlight to reach the plants inside the miniature greenhouse which was the size of a dollhouse.

The scientists said that the focus of their work is agrivoltaics, which focuses on the simultaneous use of land for both solar power generation and agriculture.

Yepin Zhao, the lead author of the research, said, “We didn’t expect the organic solar cells to outperform a conventional glass-roof greenhouse. 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 scientists built the miniature to replace the glass panels in the greenhouse with solar panels. The solar cells developed by the UCLA team rely upon carbon-based materials, as opposed to the inorganic substances used in conventional devices.

Organic solar cells tend to degrade faster than their inorganic counterparts because sunlight can cause organic materials to oxidize and thus lose electrons.

The scientists discovered that the additional layer of L-glutathione prevented the other materials in the solar cell from oxidizing.

The solar roof achieved a power conversion efficiency of 13.5% and an average visible transmittance of 21.5%, with operational stability of 84.8% retention after being exposed to 1,008 hours of continuous illumination— as opposed to less than 20% without the added layer.

They observed the growth of common crops including wheat, mung beans, and broccoli in two separate experiments. One had a transparent glass roof with segments of inorganic solar cells, and the other had a roof made entirely from semi-transparent organic solar cells.

The crops in the greenhouse with the organic solar roof grew more than the crops in a regular greenhouse.

The scientists believe this is because the L-glutathione layer blocked ultraviolet rays, which can inhibit plant growth, and infrared rays, which can cause greenhouses to overheat and plants inside to require more water.

Experts from the U.S. National Renewable Energy Laboratory said in another study that distancing rows of solar panels apart could help maintain the module temperature, which usually increases when modules are exposed to sunlight for longer duration. They said that their research is particularly relevant to the growing field of agrivoltaics, wherein crops are placed adjacent to or below solar panels.