29.03.22 Apples underneath electricity Author: Jost Burger • Reading time: 5 min.

Summary

On top solar panels and underneath plants: agrivoltaics combines agriculture and electricity production. It has significant potential in Germany and the government is already showing interest.

For anyone who regularly travels by train or on the autobahn through Germany, it is a familiar sight: photovoltaic (PV) systems covering large areas of what was previously arable land or pasture. We could soon be seeing even more of them, because a large number of photovoltaic crops of this kind are needed for the planned expansion of renewable energy generation.

But at the same time, land is still required for agriculture. In addition, the agricultural industry is one of the largest producers of greenhouse gases, with responsibility for around 8.2 percent of German emissions in 2020, according to the German Environment Agency. At first glance, it would appear that the agricultural industry, the “climate offender,” is standing in the way of the “clean” solar sector.

Solar modules protect plants

A relatively new technology – agrivoltaics – should now help to resolve this conflict. It involves using land under cultivation – from berries through to pasture – as a location for photovoltaic systems at the same time. This would not only help to resolve the problem of the shortage of land, but could even have a positive impact on the crops, because climate change is causing difficulties for farmers in Germany and throughout Europe. Heat, droughts, and soil erosion are all increasing in many areas. Agrivoltaics could enable farmers to counteract these problems more effectively in some circumstances.

Several projects in Germany and elsewhere in Europe over recent years have demonstrated how this could work. For example, in March 2021, BayWa r.e., a subsidiary of BayWa and a project developer for renewable energy generation, installed an agrivoltaic system on the fields of farmer Rini Kusters in Wadenoijen in the Netherlands. On the land where 4,500 blackcurrant bushes are growing, 4,500 solar modules will generate up to 1.2 megawatts of electricity, supplying 400 households.

The solar farm consists of horizontal PV modules fitted onto aluminum frames that are three meters high. The semi-transparent panels allow enough sunlight to reach the plants to enable them to thrive. Rainwater is collected in gutters in the modules and supplied to the plants via an irrigation system.

But the PV modules not only generate energy, they also protect the plants from excessive sunlight, hail, and heavy rain. This means that there is no need to install new polytunnels over them every few years. “Extreme weather events are becoming increasingly common and they cause damage to the plants. For example, a problem that is occurring more and more often is the growth of mold on the fruits because the weather is too wet,” says Kusters and goes on to explain: “On the hottest day in 2020, it was ten degrees cooler under the PV modules than in the full sun. On the wettest day, the plants stayed dry. Agricultural photovoltaics is a technology that I really have faith in.”

Letting some light through

There are several types of agrivoltaic system that can be adapted to the conditions in each location. For example, the challenges include ensuring that the plants are not deprived of light as a result of the inevitable shade cast by the panels. Alongside the use of semi-transparent modules, another option is alternating solar panels with translucent glass or plastic panels. Movable, adjustable modules that are sensor-controlled can adapt their angle to the direction of the light. This increases the amount of electricity generated and, at the same time, ensures that more light reaches the plants because of the changing angle of the shadows. Another solution is bifacial PV modules, which have solar cells that can generate electricity on both sides.

However, agrivoltaics not only has to supply electricity and leave enough light for the plants. The machinery used by the farmer also has to be taken into consideration. Harvesters, for potatoes for example, need space to be able to drive under and between the PV modules. For pasture or fodder crops, the solar modules can be installed vertically so that there is enough room for the animals and the tractor that cuts the hay.

The Fraunhofer Institute for Solar Energy Systems (ISE) investigated the balancing act between energy generation and crop cultivation in a pilot project with the Heggelbach farming cooperative in southern Germany. In potato fields on the farm, which is not far from Lake Constance, angled, bifacial solar modules facing south-west were installed on frames five meters high.

The results of the project are encouraging. For example, in the hot summer of 2018, the electricity output from the potato fields with PV modules was only 83 percent of the output from an equivalent field with no crops, because the panels in the potato fields had to be positioned further apart. However, the partial shade from the PV system protected the potatoes from the sun, which resulted in a three percent higher yield than from a field without protection.

Since spring 2021, BayWa r.e. has been working with the Fraunhofer ISE on the Nachtwey organic fruit farm in Germany’s Rhineland-Palatinate region to discover whether the same type of system can be used with apples and espalier fruit. A solar farm with a maximum output of 285 kilowatts has been set up over an area of 9,100 square meters. The partners in the project intend to find out to what extent PV modules can protect plants and fruit from harmful environmental influences, such as hail, heavy rain, sunburn, and frost. The electricity that is generated will be used among other things to power an electric tractor and the irrigation system, which also helps to reduce the farm’s CO2 emissions.

Funding for agrivoltaics under the Renewable Energy Act

According to calculations by the Fraunhofer ISE, only four percent of German arable land would be needed to “meet the entire existing demand for electricity (final energy) in Germany in financial terms (around 500 GWP of installed output)” using agrivoltaics. The German government has also recognized the potential of agrivoltaics. In February 2022, the German Ministries for Economic Affairs, Food and Agriculture, and the Environment issued a joint statement saying that in the future agrivoltaic systems would be subsidized on all arable land via the Renewable Energy Act.

The German Farmers’ Association (DBV) takes a largely positive view of this move, but also has concerns: “The planned expansion of agrivoltaics allows for the effective dual use of land for both agriculture and energy generation,” says Bernhard Krüsken, Secretary General of the DBV. “However, it should not be restricted to arable land. It should also be extended to areas that are difficult or impossible to use for agricultural purposes. The new solar farms should also be constructed on brownfield sites that have been converted to new uses, military training areas, nature reserves, and extensively farmed grassland.”

Marcus Vagt, agricultural energy specialist at the German Agricultural Society (DLG), takes a different view. For him it depends on what is being grown: “Specialized crops, vines, fruit, and vegetables that often need greater protection from rain, hail, wind, or other environmental influences offer excellent opportunities.” However, in the case of the large-scale cultivation of wheat, the situation is different. “If you install solar modules in a field where wheat is being grown, the combine harvesters still need to be able to pass through it and turn at the end.” In practice, this is difficult to achieve and the result is an area where less PV electricity is generated than is possible, accompanied by falling yields from the food crops. “This is where the food or fuel or, in this case, the food or electricity debate in connection with biofuels raises its ugly head.”

The German Nature and Biodiversity Conservation Union (Nabu) welcomes the subsidies for agrivoltaics. “We see agrivoltaics as one way of moving closer to our climate and conservation goals,” says Sebastian Scholz, climate expert at Nabu. “Agrivoltaics can be a means of making better use of land, which is a resource in short supply. Ultimately that is good for biodiversity because it reduces the pressure on biotopes and other important conservation areas.”

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