The man-made structure that is most easily distinguished in Spain from space (see NASA photos for example), and much more so in plane flights, are the large greenhouses of El Ejido (Almería). Some sources indicate that these plastic-covered fields add up to a surface area of just over 13,000 hectares (130 million square meters).
Could this type of greenhouse become, in addition to cultivation areas, large plants for the production of electricity? In other words, could the plastic roof of these facilities be replaced by roofs made of photovoltaic panels?
Until now, the main impediment to this type of solution is that the most common solar panels are opaque, that is, they prevent the passage of light and, therefore, do not allow the usual agricultural crops.
There are some types of transparent solar panels, one of them developed in Catalonia by ICFO experts, but it seems that all the requirements have not yet been met for them to be immediately viable alternatives in facilities such as agricultural greenhouses.
The team led by Yang Yang, an expert in new materials from the Samueli School of Engineering at the University of California in Los Angeles (UCLA), has now designed a new type of semi-transparent photovoltaic panels that can solve the problem, according to a study whose Results have been published in the scientific journal Nature Sustainability (March 6).
The authors present a new type of semitransparent organic solar cells -the main component of photovoltaic panels) with great efficiency in the production of electricity and provide data from pilot installations that indicate that greenhouses with this type of panels on their roofs can improve performance. of agricultural crops with great insolation and high temperatures such as California.
"These cells are based on carbon-based materials, unlike the inorganic substances in conventional devices," explains UCLA in a disclosure note on the work of its experts.
The researchers layered a natural chemical called L-glutathione, which is sold over the counter as an antioxidant dietary supplement, and found that the addition extended the lifespan of solar cells, improved their efficiency, and still allowed sunlight to shine through. adequate.
"Organic materials are exceptionally suitable for agricultural solar energy due to their selectivity of light absorption," says Professor Yang.
“The main drawback that has prevented its widespread use so far is its lack of stability,” the UCLA note states. Organic solar cells tend to degrade more quickly than their inorganic counterparts because sunlight can cause organic materials to oxidize and therefore lose electrons. Professor Yang's team found that the extra layer of L-glutathione prevents the other materials in the solar cell from oxidizing; which resulted in the organic cells maintaining an efficiency of more than 80% after 1,000 hours of continuous use, as opposed to less than 20% without the added layer.
The research team also tracked the growth of common crops such as wheat, green soybeans (mung beans) and broccoli in two separate field trials, and compared the results to conventional greenhouses. One of the greenhouse crops had a transparent glass roof with segments of inorganic solar cells and the other had a roof made entirely of semitransparent organic solar cells.
Crops in the organic sunroof greenhouse grew more than crops in a normal greenhouse. The scientists believe this is because the L-glutathione coating blocked ultraviolet rays, which can inhibit plant growth, and infrared rays, which can cause greenhouses to overheat and indoor plants to require more water.
"We didn't expect organic solar cells to outperform a conventional glass-roofed greenhouse," said Yepin Zhao, a co-author on the research and a UCLA postdoctoral fellow in Professor Yang's lab. “But we repeated the experiments several times with the same results and after further investigation and analysis, we found that the plants do not 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 where sunlight is more abundant."
On the heels of these findings, the team has established a startup at UCLA that aims to increase the production of organic solar cells for industrial use. The researchers said they hope to make green greenhouses incorporating commercially available organic solar cells in the future.
