Solar farms and conventional agriculture are competing for land, and this conflict will likely only get worse as our need for both grows. UCLA scientists have now tested a way to combine the two by placing semi-transparent solar cells on the glass roofs of greenhouses, finding that they can actually improve plant growth inside.
Greenhouses and solar power both need lots of sunlight, so it’s no surprise that engineers have been experimenting with integrating them into the same structures. Experiments have shown that this is essentially a win-win situation – semi-transparent solar panels can produce a decent amount of electricityall in do not starve the plants of their vital sun. In some cases, the the plants even thrived below there.
For the new study, the UCLA team investigated a few tweaks to an existing recipe. They started with organic solar cells, which are made from carbonaceous materials and can be made into transparent and flexible solar cells. This seems perfect for greenhouse use, but the downside is that these organics degrade quickly in the sun.
So the team added a new ingredient – a layer of a chemical called L-glutathione, to keep the organics from oxidizing and breaking down. In tests, organic solar cells with and without this protective layer were placed under solar irradiation for 1,000 hours of continuous use. And sure enough, those with the extra layer retained over 84% of their original efficiency, while those without dropped to less than 20% during that time.
Next, the researchers put the solar cells to work in model greenhouses, growing wheat, mung beans and broccoli. Each crop was grown in one of two greenhouses – one with a transparent glass roof dotted with segments of inorganic solar cells, and the other with a roof made entirely of semi-transparent organic solar cells.
The organic cells demonstrated a power conversion efficiency of 13.5% and passed 21.5% of visible light. But that was enough, it seems – the plants inside these greenhouses grew, surprisingly, even better than those in traditional greenhouses. The team suggests this is because the L-glutathione layer has blocked ultraviolet rays, which can damage plants, and infrared rays, which can overheat a greenhouse.
“We did not expect the organic solar cells to perform better than a conventional glass-roofed greenhouse,” said Yepin Zhao, lead author of the study. “But we repeated the experiments several times with the same results and after further research and analysis, we found that plants don’t need as much sunlight to grow as we had originally thought. In fact, too much sun exposure can do more harm than good, especially in climates like California’s where sunlight is more plentiful.
The team has now created a startup to commercially scale up production of these organic solar cells.
The research was published in the journal Natural durability.