Agro-photovoltaics: how to generate energy and food simultaneously in the field

ANDIn 1981, an article by scientists Adolf Götzberger and Armin Zastrow appeared in the journal “Sonnenenergie”. It was called “Potatoes Under the Collector.” The authors suggested using the fields in such a way that two things were collected there: potatoes and solar energy. Because the potato gets a shade of photovoltaic (PV) modules better than the sun at its zenith.

The idea for “Agri-PV” was born. It took over 40 years for politicians to become enthusiastic about it. In early July, the Bundestag passed an amendment to the Act on Renewable Energy Sources (EEG). It states that Agri-PV is now also allowed on grassland. And the Federal Ministry of Agriculture has announced that EU area bonuses, which are essential to farmers, will continue to be paid for a combination of harvesting and potatoes or grassland. This means: Agri-PV should also be considered agriculture from a legal point of view, not the construction of a power plant. Two important parameters have been changed to speed up the expansion.

The Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg has been working on this topic for some time. Max Trommsdorff is in charge of Agri-PV research there. In his eyes, their time had come “faster than expected.”

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Trommsdorff sees Agri-PV as “a technology that can reduce water consumption and make land use much more efficient.” A lot is happening in material research: for example, there is a growing interest in organic PV films or thin-film PV that accurately transmits the light spectra required by individual plants. “There is also a trend towards so-called bifacial photovoltaic systems, the back of which is also electrically active,” says Trommsdorff. This results in a higher electricity yield per square meter of module surface.

In practice, however, its enforcement is determined not only by good scientific arguments, but most of all by business management. Farmers are clear now: an EU agricultural subsidy still exists if there is ‘primary agricultural use’, ie no more than 15 percent of the usual crop is lost to solar systems. However, there are still no clear criteria for animal husbandry.

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The first scientific test facility in Germany was built in 2015 in Heggelbach on Lake Constance, supervised, among others, by by ISE. In Heggelbach, six-meter-long solar modules cover the fields of celery, potatoes, clover and wheat. A lot of light passes through them, and the first research results were already promising.

The agrophotovoltaic system in the farming community of Heggelbach The first grain harvest is brought under the APV system.

The first cereal harvest is imported using the APV system at the Heggelbach test center.

Source: © Hofgemeinschaft Heggelbach

The harvest fell as a result of shading – about 18 percent. for potatoes and wheat, but the electricity yield improves the overall balance. The land was used by 60 percent. more efficiently than in the case of purely field agriculture. I’m special In the hot summer of 2018, the harvest of cereals in the photovoltaic shade was even slightly higher than in the open comparison fields. The fruit was protected.

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The more and more sunny summers encourage the idea of ​​additional shading of photovoltaic roofs in other areas. In viticulture, heat and drought cause the grapes to ripen earlier, often too early, and the roof can have a particularly positive effect here, say researchers at Geisenheim University with its famous vineyard school in the Hessian Rheingau.

Source: WORLD Infographics

Ideally, the grapes should be harvested under the roofs of Agri-PV next year in Fuchsberg Geisenheim. The solar roofs are covered with young vines three meters high. The area is small: half a hectare. This is not about market maturity – but, as the research application says, about opening up new ways of adapting to climate change and gaining “public participation in designing the energy transition by a practical example”. The yield effects are documented. Another question in Geisenheim is what can be achieved by integrating so-called biodiversity islands – flowering and nesting areas in the middle of roofs.

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What are the farmers saying? They have reason to think about Agri-PV: the drought is urgent, the shadow suppliers are essential to survival. The floors are dusty again in the Bavarian Rhön. How will such a desert land feed us in the future?

Farmer Mathias Klöffel and his son cultivate 180 hectares of land in Großbardorf. Wheat, corn and others ripen here. He has already done a lot to adapt agriculture to the new climatic conditions. Away from maize, towards crop rotation with triticale, deeply rooted alfalfa, pods, sage. Most of it goes to biogas plants.

Klöffel would be an ideal prospect for Agri-PV. The panels can protect its fields from drying out quickly. Klöffel, also managing director of the Agrokraft energy co-operative, thinks above all about the additional expenditure and uses his company example to calculate it: one hectare of wheat land puts 300 euros in his company’s cash register, which is not quite a lot. Work must be uncomplicated. “If there are five PV systems in between, the working time for mowing becomes too long.”

He doesn’t think about it. His own path to solar energy was less complicated: 20 years ago, Klöffel covered his barn roofs with photovoltaic modules. And the cooperative operates with a classical solar system that consumes space.

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But agri-PV technology is evolving. Large tractors and harvesters could pass through the rows – the height of the photovoltaic roofs is 6 meters, the distance between the rows of panels is 18 meters.

Markus Haastert wants to allay fears. An entrepreneur from Berlin advises farmers with his AgroSolar Europe GmbH and reports a sharp increase in interest after the parliamentary decision in July. There are questions from all over the country: it is about the best shade for fruit in the Old Country, blueberries in Brandenburg, potatoes and beetroot in the Rhineland. But also, says Haastert, about more natural systems. “We don’t want to pour concrete onto the field, we want to put the systems on filigree steel anchors made like tree roots.”

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There are still many unanswered questions: How to arrange the panels so that they protect against hail in spring and improve the microclimate in summer? How to integrate irrigation systems? Will it affect biodiversity or will birds be blinded?

In agricultural sciences, meaningful answers are often given only for very specific applications. Every fruit, every soil, every climatic region has its own needs. You know which fields of application make sense from an agricultural point of view: permanent grassland or cereals tolerate morning and evening shading. For example, the southern German energy supplier Lechwerke has been experimenting with this in the Allgäu for a good year. These panels allow sheep, goats or chickens to graze.

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Fruit crops such as pears and apples or potatoes that require protection from the midday sun are more likely to be connected to roof-mounted PV modules on stilts. So far, there have been only a few pilot plants in Germany – for example, one at Lake Constance and one in Rhineland-Palatinate, where the fruit in apple orchards is effectively protected against sunburn.

How much more expensive is an elevated PV system like the one used in Heggelbach? The Competence Center for Renewable Resources in Straubing, Bavaria, has data on this: investment costs are € 1,234 per peak kilowatt hour – maximum power under standard conditions – the electricity yield for these systems is only € 572 compared to common terrestrial systems. As management is possible under a more expensive solar roof, there is a sale of grain or fruit, as well as an EU area premium of around € 300. Agri-PV will be profitable initially on very fertile soils.

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There is a

There are several options for so-called integrated photovoltaics such as Agri-PV, wherever solar panels are installed in existing infrastructure, on house facades, on railroad tracks, on car roofs, to quarry ponds on which systems float. Researcher Trommsdorff and his colleagues calculated that the development potential of agriculture-PV is particularly large.

To this end, he compared Agri-PV’s electricity yield with other areas: they had a peak of 1,700 gigawatts, which is much more than solar expansion for buildings, roads and railways, water surfaces, noise protection walls or similar use of car areas. And it would be many times more than it would be necessary for climate neutrality in the energy sector according to CEI calculations.

Source: WORLD Infographics

The agro-PV expansion cannot be done with a crowbar, and there are also concerns among the population. The ISE in Freiburg is also examining the acceptance of agro-PV. First results: The combination of agriculture and photovoltaics is perceived by people as less worrying than purely photovoltaic areas on the ground or, above all, as wind farms.

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