The panels are mounted vertically, even on grassland. When envisioning manoeuvring through the area with a mower or tillage equipment, the mirrored glass surfaces may appear somewhat delicate. “You just need to get the hang of it,” chuckles Rainer Hall, co-owner of this land close to Donaueschingen in the South West of Germany, where the system designed by the company Next2Sun has been in place since 2020. Spanning 14ha, it stands as one of the largest agrivoltaics installations in Europe today.
The concept of dual land use was initially introduced in Germany in 1981, but stayed in the experimental phase for a considerable period. With backing from renewable energy specialists, the agrivoltaics sector has become more established in recent years. Alongside concerns regarding potential impacts on land values and lease agreements, a crucial question revolves around the extent to which the shade cast by solar panels affects crop development.
Protecting the Grass
In Donaueschingen, the installation spans a hillside, featuring 10m-wide grass strips alternating with rows of solar modules. At 3m in height and oriented north-south, these modules decrease available sunlight by 15 %, casting a shadow that serves to safeguard the grass during critical stages. Next2Sun reports an 88 % yield for 22 and 23 compared to the 100 % control area, mostly due to the 10 % reduction in surface area for growth due to the solar modules. Rainer cautiously but optimistically notes: “I observe growth similar to that on my own farm, potentially even more during dry periods.” Besides providing shade, the windbreak effect also helps to maintain lower temperatures.
Grass management does not present particular difficulties.
Rainer Hall
The reduction in production per hectare, primarily due to the loss of cropping area, can be offset by gains from electricity generation, especially in extremely hot years. From an economic perspective, this plot remains viable even without factoring in the energy generated: Hay, which is sold to neighbouring Swiss farmers, proves to be a profitable crop in the region. To address the situation for farmers who previously rented the land, an agreement was reached: They now receive a payment tied to the hay sales from a farming collective which owns machines and provides services where Rainer is employed. The energy output amounts to approximately 4,850MWh per year. “With the solar panels facing east-west, power peaks align with times of higher network demand, allowing us to achieve optimal prices on the electricity market.”
No significant adjustments have been required for the farm machinery. “The process is rather straightforward as we don’t need to plough or spray in this area. While the tedder spreader may occasionally throw up stones, it’s not common for us to damage modules each time we pass through. The main challenge is making U-turns with the 9m-wide butterfly mower, as the parcel is entirely enclosed by mandatory fencing,” says Rainer.
Field Crop Trials
In Donaueschingen, a trial was conducted in 2022-2023 to assess how field crops perform under shade. Three strips of peas and wheat were planted, overseen by Martin Müller, a farmer and agricultural engineer. “We decided against plowing and instead used a cultivator,” he explains. “We applied fertiliser using a pneumatic fertilizer spreader; a centrifugal fertiliser spreader is not suitable.” Manoeuvring a partially folded 24m sprayer is feasible, but the spray boom’s oscillations on the sloped terrain demand heigh attention during operations: The RTK guidance system has proved to be “very useful, even essential”.
The results: The shade had a negative impact on pea yield, while wheat showed improved germination in the autumn compared to the control plot. “It’s feasible but not ideal,” notes Rainer. For field crops, such a system is best suited for flat terrain. Additional trials are currently in progress.
Next2Sun reports promising yield results at various locations: +1 to +19 % for wheat and +17 % for lentils in Channay, France; and a 10 % increase for barley in Guntramsdorf, Austria. These percentages are based on the cultivated area, excluding the 10 % left uncultivated. Notably, these findings are specific to the 2022 season, a year where the shade effect may have benefited the crops.
Raised Panels
Another significant system category includes solar modules installed at height above the crop. Sylvain Raison adopted this arrangement on his farm in 2022. Operating on 850 ha in Amance, Haute-Saône, he grows wheat, barley, rapeseed, maize, soyabeans, and forage rye using conservation farming practices. The solar panels, positioned 6m above ground, are owned by the energy company TSE, which leases the aerial space above a 3 ha plot from Sylvain. A sophisticated system of cables and weather sensors enables the panels to track the sun, providing a power output of 900 kW/ha.“The yield per hectare is remarkable,” says Sylvain, who also has a 500 kW biogas plant.
Following six months of construction, soyabeans were planted in June 2022. One of the tested crop varieties showed no significant difference in yield under the shade, and the protein content was 3 % higher compared to the control plot. For the subsequent season, wheat was sown, but the wetter conditions led to poorer outcomes. “The downside, as there are with any method, is that it maintains high soil moisture levels during the winter months,” notes Sylvain. On this waterlogged soil, the construction works undeniably had a detrimental impact on the wheat crop that year due to soil compaction.
However, last April, at the time of the interview, the barley was growing well. “The most impressive part is seeing the growth restarting in the spring. It is a microclimate that also protects against the cold.” The temperature records from TSE have shown up to 5.6° C lower temperature under the panels in warm weather and +1.3° C higher temperature at the beginning of spring. In addition, the panels serve as protection against hail and automatically adjust their tilt to the weather: When there is heavy rain, their orientation is altered to 75 ° to avoid a gulley effect.
Parameters to be adjusted
In France, the Agri PV programme allows for a minimum yield threshold of 90 % compared to a reference surface, averaged over five growing seasons. Xavier Guillot, R&D manager at TSE, believes this target is entirely attainable and supports ongoing field trials planned for nine years on pilot farms. However, he acknowledges the need for more agronomic benchmarks to unlock the full capabilities of Agri PV.
In France, the shifting climate trends are leaning towards more hot and dry years. “During these challenging conditions, these systems will demonstrate their full potential by providing protection during crucial growth stages, thereby reducing losses and potentially boosting yields in specific scenarios,” says Xavier.
At several TSE sites, data indicates that the decrease in temperature had a beneficial effect on the flowering stage and kernel development. Additionally, the soil keeps a higher water reserve. Nevertheless, the persistent lack of light poses limitations for cereal crops, resulting in apical elongation and ear loss which may not be offset by subsequent benefits from the shade.
“This constraint needs to be addressed,” acknowledges Xavier. “We have undertaken substantial efforts to identify the most appropriate crop varieties.” The organisation intends to experiment with several approaches, like growth regulators, to channel the plant’s energy towards tiller production, or towards pods in the case of legumes.
Agri-PV systems will add protection at key stages for cereals.
Xavier Guillot
Research is also looking into the effect of varietal type on early plant development, given that the reduced thermal intensity impacts the average temperature, which delays wheat maturity by about 12 days in Amance. Here, different varieties or earlier spring sowing could spread growth over the whole acreage to smooth the organisation of fieldwork. Another point to be studied is the risk of fungal disease. “Along with light, this is one of the risk factors identified because the humidity is slightly higher under the panels.”
A new Tool
Sylvain has not encountered any significant challenges with field operations. The support pillars are spaced 27 m apart and he sprays with the boom folded to one side, while using a sowing width of 12 m. Sylvain avoids applying solid fertiliser under the canopy to prevent metal oxidation. There have been instances of interference with the tractor’s RTK signal, which might require the installation of additional repeater stations. The combine can easily harvest with an open grain tank without encountering any issues.
In financial terms, there is a plan for a 40-year lease, with a three-way agreement in place in case the field is used by a tenant farmer. Addressing concerns about rising land values, Sylvain remarks, “I believe the added income could serve as a financial leverage for young farmers”. Furthermore, this approach could safeguard future agriculture from climate uncertainties by spreading risk. “It’s a new tool that we should adopt,” he concludes pragmatically.
Improving Grape Quality
In Spain, the Daramezas domain has conducted a two-year trial of a “vitivoltaic“ system under their Winesolar project. Miguel Tejerina, agricultural engineer and regional technical director, notes the increasing summer temperatures and prolonged drought periods observed in recent years. “We have been studying the possibility of protecting our vines to have slower maturation for quite some time,” he says.
A sophisticated solar tracking system has been implemented in a small section of the vineyard, adjusting shade levels with variable tilt to optimise sunlight exposure during the flowering period, to support grape development. Comprehensive monitoring is conducted both underneath the panels and in control areas, collecting meteorological, soil, and physiological data, water consumption metrics, and analyses of grape sugar content and pH throughout the season.
The Airen grape variety, predominant in Spain and covering 99 % of the domain, is primarily intended for spirit production due to its tolerance for wide temperature fluctuations. Located at an altitude of 640m, the site experiences temperatures exceeding 42ºC during July and August, with an annual rainfall of about 400mm. “During the hottest times of the day, the temperature in the shade is 3 to 4° C lower,” says Miguel. First observations reveal that a higher acidity and a more balanced ripeness are to be expected, with a slower accumulation of sugars. Notably, there has been no significant impact on pest or disease incidence to date.
Adjustments have been made to the vineyard machines’ working hours to align with the panels’ orientation in the agrivoltaic area for efficient operation. According to Francisco J. Navarro, the vineyard manager, “the benefits provided to the crop and the reduction in energy costs fully justify these adjustments”. The installation currently covers 10-15 % of the vineyard’s energy consumption, particularly for the drip irrigation pump. The next phase involves expanding the coverage to meet 100 % of energy requirements.
The temperature in the shade is 3 to 4° C lower.
Miguel Tejerina
Miguel highlights a key advantage in terms of water conservation, reducing evapotranspiration and extending soil moisture retention. Given the declining water availability for irrigation in many Spanish regions, Miguel foresees wider adoption of such installations in the Iberian Peninsula, following the success of the Winesolar project.