Agrivoltaics – Dual land use
By constructing an in-field photovoltaic system, farmers can create a second source of income and consequently increase the degree of land use significantly. The planning of such a system should be aligned with agricultural requirements.
It is a bumpy ride past gigantic excavators that strip the ground layer by layer. They are still mining lignite in the Garzweiler open-cast mine near Bedburg, Germany, extracting it from Rhineland soil to be burned in nearby power plants to generate electricity. Yet at the edge of the pit, the future of energy supply becomes visible — a future that has already begun even for energy giants such as RWE.
On the area between the lignite mine and the A44 motorway, RWE has installed an extensive photovoltaic system. But these are not conventional installations. Here, agriculture is combined with electricity generation. Three different systems demonstrate the currently established technologies used for such applications: a tracker system that follows the path of the sun, a system with vertically mounted modules, and a solar canopy covering a berry plantation.
Agriculture remains the priority
So-called agrivoltaic systems, using photovoltaics on arable land, offer clear advantages. The German Environment Agency (UBA) considers the combination of photovoltaics and agriculture to be the appropriate approach for implementing the planned expansion of ground-mounted solar capacity. After all, it helps to ease land-use conflicts and increase acceptance.
More and more farmers are now recognizing that agrivoltaics can provide them with a second source of income. The aim is to produce food and electricity on the same land — almost without restrictions. The prerequisite is that the photovoltaic (PV) system is compatible with agricultural use. Agriculture must remain the primary activity. Electricity generation is merely an additional benefit that increases land-use efficiency.
Maintaining sufficient spacing
For this reason, several aspects must be considered when planning an agrivoltaic system. Tracker systems and vertically mounted modules are suitable when land continues to be used as either arable land or grassland. In such cases, the distance between the module rows must be at least as wide as the largest machine used by the farmer to cultivate the land. This spacing is mandatory for vertically mounted modules anyway to prevent mutual shading. With tracker systems, solar planners generally have greater flexibility, but the system must still be adapted to agricultural requirements. This must be taken into account early in the planning phase.
If the land is used as pasture, agrivoltaic offers double benefits. In this case, the modules not only generate electricity but also provide shelter for animals. Cattle find shaded areas beneath tracker rows, and even vertically mounted systems provide shade. Poultry are afforded more protection from predators under a roof of solar modules. Vertically mounted systems can also function as fencing for grazing areas.
Suitable for livestock husbandry
Wildlife protection is particularly important in such applications. Animals must not be injured by sharp edges on the substructure or module frames. Cables must also be properly protected to prevent damage from biting. This is not only about protecting the energy yields of the photovoltaic system in the event of cable damage, but also about ensuring that wildlife is not harmed by electric shock.
If crops are cultivated on the land, the technology must likewise match the intended agricultural use. Solar modules cast shade over the fields, reducing light availability. Crop selection must therefore be adapted accordingly. Several studies now indicate that combining photovoltaics with C3 crops is particularly advantageous. C4 crops react more sensitively to shading, whereas C3 crops are not only more tolerant but even appear to thrive better under partial shading than under direct, intense sunlight.
Cultivating shade-tolerant crops
This observation is also supported by plant physiology. In C3 plants, photosynthesis performance declines during hot and dry conditions, while C4 plants are better adapted to arid environments. This was demonstrated by a study conducted in Austria, where winter wheat and millet were grown between tracker-mounted solar module rows with different spacing. Plant morphology and canopy height were compared with those on a reference area without solar modules.
The results showed that millet, as a C4 plant, reacted more strongly to shading than winter wheat. Winter wheat, a C3 plant, actually performed better as the spacing between module rows decreased. In contrast, millet performed best without solar modules. The denser the shading, the slower and lower the plants grew — although differences in morphological development largely evened out across the field by the end of the growing period.
Cereals thrive well
RWE observed similar results in Bedburg, Germany. During the first year of operation, winter wheat was grown between the rows of solar modules. Here too, yields under and between the modules were comparable to those on the reference area without a solar installation. In fact, the harvest under and between the modules showed slightly better quality, particularly with regard to protein content. The quality was high enough for processing into flour for baked goods or use in breweries, rather than being used solely as animal feed.
Improved temperature and water distribution also contributed to these good harvest results. Especially in the context of climate change, crops such as wheat benefit when temperatures do not rise excessively. In fact, temperatures within the module field under the trackers are around one degree Celsius lower than on the reference area. On very hot days, the difference can reach up to three degrees Celsius.
Improved water management
Photovoltaics also help improve water balance. Trackers in particular offer advantages here. In Bedburg, precipitation levels were measured beneath the trackers and at reference points. It was found that, at times, more water accumulated beneath the safety strips than in the reference zone. Rainwater flows off the modules and collects on the ground beneath the lower edge of the panels.
This might suggest better water distribution on the reference area — but the opposite was true. In some periods, even more water was present under the trackers than on the reference plot. A key advantage is the significantly reduced evaporation beneath the modules. As a result, the soil within the solar installation remains moist even after prolonged dry periods, whereas the soil on the reference area became noticeably dry after six weeks without rainfall.
Modules replace plastic covers
Even more advantages arise when agricultural land is directly covered with solar modules. For arable farming, this is generally too complex and therefore only economically viable in exceptional cases, as the structures must be mounted very high to allow farmers to operate tall machinery. In fruit, berry and wine cultivation, however, conditions are different. Machinery is smaller, and modules do not need to be mounted as high.
The benefit here is clear: the solar canopy protects sensitive crops from extreme weather events such as hail or heavy rainfall. Until now, such protection has typically been provided by plastic coverings. These plastic films are simply replaced by solar modules, allowing existing structures to be reused. Compared to plastic covers, solar modules not only generate additional electricity but are also far more durable. While plastic sheets must be inspected after every storm and are often replaced, these maintenance efforts are eliminated when using solid solar modules.
Protection against late frost
Here too, the installation must match the crops grown underneath. When semi-transparent modules are used that allow some sunlight to reach the plants below, a degree of shading remains. Some fruit and berry crops benefit from this, while others are more sensitive.
Solar modules also offer improved protection against late spring frosts and help normalize vegetation periods, which are becoming longer due to climate change. This is increasingly relevant in viticulture. Earlier onset of spring accelerates grape ripening, increasing must weight and sugar content more quickly. This reduces residual acidity, which is important for producing wine styles typical of Germany. Solar modules counteract this effect by delaying grape ripening by several days.
This demonstrates that agrivoltaic systems must be carefully planned and adapted to their specific agricultural application. It is crucial that agriculture remains the primary land use. With proper planning, farmers can make ideal dual use of their land through additional photovoltaics and establish a reliable second source of income.
More details on the dual use of land through agrivoltaics can be found in the joint special publication by DLG and photovoltaik, in German (English: “Solar Technology for Farmers – Pathways to a Dual Harvest”=, which is available for free download.
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