Solar power from the vineyard aims to combine climate and vine protection. Prof. Manfred Stoll from Geisenheim University leads the research project Vitivoltaic. He spoke with Alexander Lupersböck about the management of the future.
Rotatable and foldable solar modules above the vines offer many advantages.
HS Geisenheim Philipp StieffenhofferWhat is the Vitivoltaic project about?
Stoll: Below are vines, above one installs a photovoltaic (PV) system. I like to call it "Back to the Future". The "back" comes from the shading of the vines: it becomes cooler again in the vineyard, and the future arises from the ever-increasing energy demand. Power above, vines below, thus double land use. Additionally, electrically operated tools can be charged directly in the vineyard – that is the concept of Vitivoltaic.
What are the concrete advantages for winemakers?
Stoll: A vineyard is the predestined agricultural area for Agri-PV. There is already support material like posts and wires. And the vines are increasingly suffering from heat, drought, and late frosts. The PV modules above can help against all of this.
How exactly?
Stoll: PV modules can be installed rotatable and foldable on a supporting structure above an existing vine installation. When the sun shines directly on them, the modules are unfolded, generating power and shading the leaves and grapes. This can be done either energy-optimizing, where the modules follow the sun, or using an algorithm optimized for the location. This allows the modules to be briefly folded away during heat and high humidity, effectively ventilating. Once the humidity is back in the desired range, the modules unfold again and generate power.
How do solar cells help against drought?
Stoll: During drought, the modules can reduce evaporation and increase soil moisture. During rainfall, they lead water from a larger area over a drip edge and thus increase the penetration depth of the water into the soil. Since the modules rotate, they do not always have the same drip edge. Ideally, they direct the water through a gutter into a cistern. We use this for irrigation. We are currently installing a system in Geisenheim.
How can Agri-PV help with late frosts?
Stoll: At the end of April 2024, shortly after bud burst, we had frost. Our PV system has heating wires built in. During the day, power was generated and stored in batteries. This allowed us to heat the heating wires and the immediate surroundings of the fruit canes. Additionally, there is physical protection from the system itself. Just as it is cooler under the panels during the day, it is up to one degree Celsius warmer at night. We fold them up to keep the warmed air below. This saved us this year. However, this only works up to certain negative temperatures.
How much effort is required for winemakers?
Stoll: The structural effort is high. One needs good statics to withstand wind and snow loads. The elevation must be high enough to allow a tractor to pass through. The maximum height of our system is 5.50 meters. But since the panels are movable, the passage height is reduced to 3.50 meters. However, it gives us all possibilities for decentralized energy supply and can be optimally controlled. There is also a simpler option.
What does it look like?
Stoll: These are mobile systems. They can be easily mounted on existing posts. The PV modules can be retracted at night or in strong winds like an accordion. This is especially interesting for young installations. With less structural effort, one can investigate how the system affects the young vines. After two to three years, it can be dismantled and set up again in another location. This can provide important protection for new installations.
The smaller mobile system VitiCULT-PVmobil protects young installations.
Manfred StollWhat are your experiences with it?
Stoll: During the heat waves of 2024, it became apparent that it was three to four degrees Celsius cooler under the PV. It prevents direct sunlight, which affects grape development and berry contents. The storage of sugar proceeds more slowly. In 2024, we experienced a ripening delay of one to two weeks. At the same time, we achieve a higher acid concentration. Thus, we can harvest the wine with lower sugar and higher acid values. This is particularly beneficial for aromatic varieties like Riesling. And the grapes do not get sunburned and remain healthy longer. In the control area, which is right next to it – with the same planting material, the same treatment, and the same age – we see damage instead.
Is there a difference in yields?
Stoll: We cannot quantify that at the moment; the trial is still too young. But: The grapes hanging underneath are loose-berried and healthy. There is a difference compared to the comparison areas.
Are there already wineries using Viti-PV?
Stoll: There are three systems in Germany. One at the Wine Institute in Freiburg, one in Ihringen at Blankenhornsberg, and one in Geisenheim. Ours is the oldest. We have also already produced the first wine in small quantities from this system.
Can you provide information on costs?
Stoll: This cannot be answered so easily. Our system is designed for various research questions. We are also testing emission-free autonomous vehicles in the vineyard that charge themselves. We are investigating how plant protection changes and many other aspects. Our system is equipped with sensors; it is so to speak the Rolls-Royce among Viti-PV systems because it must be able to do almost everything. A winemaker does not need to cover so many areas with their system; it can certainly be cheaper. And: Every vineyard needs an individual solution. But the smaller mobile system VitiCULT-PVmobil also offers possibilities.
Regarding landscape appearance: Have there been any complaints?
Stoll: One cannot think of the construction height as separate from the landscape. From a distance, such a system looks like a closed building. The closer you get, the more airy and light it actually is. Our scarcest resource is acceptance itself. No one wants to have it in their front yard, but we need new solutions for an energy transition and must find compromises. I do not think that large investors will extensively expand Agri-PV in viticulture. Because viticulture here is too fragmented due to its operational size and structure. Almost every plot has a different row spacing, different grape varieties. These are variations that require individual solutions. Each variety has different requirements. Therefore, these are island solutions. But: They bring the power where we would need it if we had new forms of management.
How should this management look?
Stoll: Certain monotonous tasks like plant protection or mowing can be done by autonomous, electrically operated vehicles that charge themselves in the vineyard. This gives the winemaker more time to focus on really important details. They can observe the vines more closely. This has been somewhat neglected due to the efficiency increase and mechanization, which always required human control. In a tractor cabin, one does not hear the birds chirping, nor the wire getting caught, nor see small differences in health status. The driverless vehicles are three to four times lighter than conventional tractors despite the batteries. Occupational safety is also a topic; think of pesticides. And the winemaker can interact more with the vineyard, microclimate, and vine again.
Are there also negative aspects?
Stoll: The devil is in the details. The glass modules above the foliage absorb radiation in the shortwave range. Radiation of 300-450 nanometers hardly passes through anymore. However, this is important for leaves to form their protective pigments and berries to produce phenols. This does not have much influence on Riesling, but for other varieties like Pinot Noir, it could have an effect that we would need to react to. We need to take a closer look at this.
Can the Geisenheim project be visited?
Stoll: Of course. The message to practice is: Come, see it, and tell us your thoughts! My co-project leader Prof. Claudia Kammann, doctoral candidate Lucia Garstka, and I look forward to visits. The more we exchange ideas, the more information we can gather and develop the project further. One can calculate a lot in theory, but only when one has installed such a system does one see how it really works, how it affects, and what the acceptance for landscape protection looks like. Only when you work under it in summer do you realize how pleasant it is.