Following the path of digitalization in Slovenia and Europe: Growing crops UNDER solar cells? The most efficient way to obtain solar energy

Agriculture is often the target of criticism related to high energy consumption. New ways of growing food, including placing solar cells directly above plants, could also bring this area closer to carbon neutrality.

Placing solar cells above plants is also called agrivoltaics, and it can be used to boost both yields and the efficiency of the solar cells. When planting a crop under a solar collector array, the plants grow better and need less watering, and the solar panels produce large amounts of electricity without interruption.

Of course, plants need sunlight, but too much sunlight can do more harm than good, as some plants get stressed when the sun is too intense. Furthermore, plants will require less water, which rapidly evaporates in an open field.

Plants also cool themselves in the process of “sweating”, more professionally called transpiration, in which water evaporates from leaves, stems, flowers and fruits. This process cools the panels above as well and consequently increases their efficiency.

A few years ago, a study was published in Nature Sustainability, in which experts examined all aspects of sunlight, air temperature and relative humidity. They concluded that croplands are currently the land “with greatest solar PV power potential“. Grasslands and wetlands also ranked in the top three land covers.

Researchers have successfully grown aloe vera, tomatoes, biogas maise, pasture grass, and lettuce in agrivoltaic experiments. The research abstract said that some varieties of lettuce produced greater yields in the shade than under full sunlight; other varieties produced essentially the same yield under an open sky versus under PV panels.

“Many of us want more renewable energy, but where do you put all those panels? As solar installations grow, they tend to be out on the edges of cities, and this is historically where we have already been growing our food,” said Greg Barron-Gafford, associate professor in the School of Geography and Development at the University of Arizona and lead author on the paper.

“So which land use do you prefer — food or energy production? This challenge strikes right at the intersection of human-environment connections, and that is where geographers shine!” he explained. “We started to ask, ‘Why not do produce both in the same place?’ And we have been growing crops like tomatoes, peppers, chard, kale, and herbs in the shade of solar panels ever since.”

A few months ago, Bloomberg wrote about Takeshi Magami’s farm in Japan, where the 2,826 solar panels are perched above the crops.

The panels, covering much of the one hectare of land east of Tokyo, serve a dual purpose. They supply nearly all the power needed to run the farm and are a source of extra income by selling surplus renewable energy to the grid.

For the owner, this means 24 million Japanese yen or 174,000 EUR of additional income per year, eight times more than the approximately 3 million yen generated from the crops. Magami benefits from tariffs that have been reduced, but this is nevertheless an indication of the value-added creation available to farms in Japan and around the world.

They are also interested in similar projects in Kenya, an African country, where they decided to place solar cells above crops in February, according to the Guardian.

Previously, experts from the University of Sheffield, World Agroforestry and the Kajiado-based Latia Agripreneurship Institute conducted year-long research in the semi-arid Kajiado county.

Cabbages grown under 180 345-watt solar panels have been a third bigger and healthier than those grown in control plots with the same amount of fertiliser and water. Other crops, such as aubergine and lettuce, have shown similar results. Maise grown under the panels was taller and healthier, according to Judy Wairimu, an agronomist at the Institute.

The solar panels can be placed three metres from the ground, providing ample room for a farmer to work below or higher in bigger systems to allow access to agricultural machinery.

The technology has been employed in other countries, including France, the US and Germany.

Fabian Karthaus in Germany grows berries under solar power systems. “I can’t feed a family with the earnings from growing 80 hectares of field beans, grain, rapeseed, and corn crops,” he explained to DW. “That’s how the idea of growing berries under a solar roof with translucent modules was born. We thought about which kind of berry goes with what sort of light and shade. Blueberries and raspberries are woodland plants, so that works really well,” he added.

Karthaus suspects the shade under the modules could increase yields. Sweltering summers are now an increasing problem for plants, even in Germany. And as already mentioned, roofs made of solar modules reduce evaporation. “The evaporation is about a quarter compared to plants in the open field,” he explained.

With 750 kilowatts of power, the system generates about 640,000 kilowatt hours (kWh) a year, equivalent to the electricity needs of 160 households. Karthaus receives a little less than 0.06 EUR per kWh for feeding it into the grid. He also plans to use part of the solar power to operate his refrigeration and lyophilisation (freeze-drying) systems. If he had to buy the electricity from the energy supplier, that would cost him around 0.25 EUR per kWh.

Author: Marko Želko

Keywords: solar energy, environment, agriculture, food.

Disclaimer:

This article is part of joint project of the Wilfried Martens Centre for European Studies and the Anton Korošec Institute (INAK) Following the path of digitalization in Slovenia and Europe. This project receives funding from the European Parliament. 

The information and views set out in this article are those of the author and do not necessarily reflect the official opinion of the European Union institutions/Wilfried Martens Centre for European Studies/ Anton Korošec Institute. Organizations mentioned above assume no responsibility for facts or opinions expressed in this article or any subsequent use of the information contained therein.