Since 2022, a farmer in Kressbronn, near Lake Constance in southern Germany, has been growing part of his apple crop beneath solar modules of varying transparency. A reference area is covered with the protective film that is becoming increasingly common for fruit growing in the region.
The installation and the film together cover 0.4 hectares, with Gala Red apples grown on M9 rootstock beneath them. In 2023 and 2024, researchers at the Fraunhofer Institute for Solar Energy Systems (ISE) documented every application of water, fungicides and other pesticides, both under the solar installation and on the reference area. They also recorded how much time each task took.
The researchers based the cost of machinery use on the billing rates of the regional machinery cooperative and then scaled the figures up to one hectare, giving comparable values that can also be applied to other farms. They excluded any effects that could not be clearly attributed to the agri-PV installation.
Fewer fungicides, faster work by hand
Earlier calculations, based solely on expert interviews, had put the savings at 8.2 percent, so the measured figure is more than two and a half times higher than expected. Most of the savings come from crop protection and labour-intensive tasks such as removing leaves and thinning fruit by hand, both of which were quicker under the modules. “From my point of view, one of the biggest gains is that significantly fewer fungicides are needed,” says study author Oliver Hörnle of Fraunhofer ISE.
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As a result, apples grown under the solar modules cost around 10 cents per kilogram less to produce than those under the film cover, Hörnle explains. And that is only on the farming side, before any income from the solar installation. How much can actually be saved depends heavily on the weather. In 2023, the farmer needed only half as much water under the solar modules as on the reference area, while in the rainy year of 2024 he needed slightly more. “The difference between individual years is at times greater than that between the agrivoltaic and the reference area,” says Hörnle.
Slightly lower yields, but more economical
Yields, however, were around 7 percent lower under the solar modules than on the reference area. One reason was that in 2024, a duller year, the farmer had to thin the fruit a second time because the apples were growing too close together. Even so, the cost savings mean that growing apples under the agri-PV system still pays off.
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Then there is the income from the solar installation. Although the modules face east and west, they delivered more than 1,200 kWh per kW of installed capacity every year. The system also costs less to run than a conventional ground-mounted installation, as the farmer maintains the module area as part of his regular work. The combination even brings savings on insurance. “The farmer takes out hail insurance for both the PV installation and the apple crop under the film. Comparing the two premiums, the farmer also saves on insurance thanks to the solar installation,” Hörnle explains. (su)
