"VitiVoltaic" projects aim to make viticulture fit for climate change. The term is a portmanteau of the Latin genus name for the grapevine, vitis vinifera, and the word for solar power generation, photovoltaics. This new technology makes it possible to harvest two very different things on two levels: Electricity above and wine grapes below. Pilot projects are underway to test which technology works where — and at what price.

In Germany's southwestern Rheingau region, known for its picturesque vineyards, the Hochschule Geisenheim University (HGU) specializes in all aspects of the wine industry. Here, researchers have created a test facility to determine how the region's beloved white Riesling might sustainably thrive with the help of photovoltaic (PV) modules despite changes to the climate.

The modules are mounted high up to allow space for the vines and agricultural machinery below. The structure provides the delicate vines with support and protection from hail, heavy rain and strong sun. When the sun shines, the semi-transparent solar modules create a checkerboard pattern on the ground. A tracking system automatically aligns the modules so that they capture every ray of light.

Riesling at risk

"In viticulture, we have not yet seen protected cultivation," said Manfred Stoll, who leads the university's Department of General and Organic Viticulture. Grapes do not ripen in greenhouses or under plastic sheeting, and the idea of using PV modules to provide passive protection against hail and heavy rain is quite novel, he added.

But climate change means that Riesling, Germany's most popular wine variety, could use some help. The vines now shoot earlier and are highly vulnerable to late frosts. The grapes are also exposed to more sun, and therefore have more sugar and less acidity, which changes the alcohol content and taste. There are now two vintages of the university's "Watt wine," a Riesling that is lighter and fruitier — just like it used to be.

Using heating wires to ward off frost

Through the project, the HGU has also gained a wealth of experience in the field of microclimates. The €350,000 ($400,000) experimental facility — financed by the European Union and state funds — uses numerous sensors to measure soil moisture, temperature and light. There was no damage from solar damage or heavy rain under the panels, while the adjacent reference area was severely affected.

Heating wires and drip irrigation hoses snake along the vine rows. The former proved their worth during a three-night frost in late April 2024. The acutely endangered shoots, already 10 cm (3.9 inches) long, were warmed by the wires powered with stored green electricity. Traditionally, winegrowers burn enormous wax candles during such late frosts, said Stoll, but the practice is arduous and results in heavy smoke that pollutes the environment.

The HGU also uses the electricity it produces to control the facility and charge agricultural vehicles, cars and e-bikes, as well as operating pumps and an autonomous caterpillar, a robot which mulches, cultivates the soil, works the undergrowth and applies plant protection products.

"A winery needs energy all year round for production, storage and logistics," said Stoll.

VitiVoltaic technology is attracting attention as the wine industry struggles with multiple challenges: Harvests in some regions have been poor, and changing consumer habits, tariffs and oversupply have stressed the world market. There is a lack of money for investment, even though generating electricity could be a second source of income for wineries.

Last year, another, much smaller mobile system made of PV modules was installed in Geisenheim. Attached to existing vineyard posts like an awning, the modules automatically fold up with the help of a small motor in the event of a storm or hail.

The structure is much more affordable, but the protection and electricity yield are lower. Still, the HGU continues to test for optimal solutions because, as Stoll said: "We definitely don't have time to wait any longer."

Abandoned vineyards

Engineer and hobby winegrower Christoph Vollmer is also working with photovoltaics. Cultivation of his small vineyard in Oberkirch, southwest of Stuttgart, with agricultural machinery is difficult due to its steep slope with a gradient of over 30%, partly laid out in terraces.

Vollmer is the managing director of Intech Clean Energy GmbH, a family business specializing in agrivoltaics that has developed a design for such steep slopes, whereby some of the glass modules are suspended from steel cables. Vollmer is now installing these in his own vineyard.

The young winemaker wants to plant 2 hectares under solar panels with robust new fungus-resistant grape varieties and generate around 1.5 megawatt hours per year. He is currently negotiating a contract with municipal utility providers for the electricity. He also wants to charge an autonomous caterpillar tractor to relieve him of tedious work on the slopes.

Photovoltaics are significantly more difficult to install at steep angles, but present an exciting challenge from an engineer's point of view. It is also a necessary undertaking, Vollmer said. While the sun-drenched hills were once a sought-after location for viticulture, global warming means that it can also be practiced successfully in the less arduous German lowlands.

"Many vineyards have already been abandoned because no one wants to cultivate them anymore," he said, adding that more will follow if the minimum wage for staff reduces winegrowers' returns. But, he added, the vine-covered slopes are part of the cultural landscape, a tourist attraction and important for species protection.

Inadequate grid, slow bureaucracy

"With VitiVoltaic, we offer farmers the opportunity to reduce manual labor, harvest healthier grapes and become profitable. Electricity always has value, especially when PV is coupled with storage," said Vollmer. "Winegrowers are aware that they need to take action. We receive a lot of inquiries. But often a lack of grid connections dampens the enthusiasm."

The length of power lines that need to be laid, along with the options for using the electricity produced or selling it directly to local consumers, are decisive for economic efficiency. But the approval process can be protracted because energy production changes land use. Only PV systems located a short distance from the farm can be built without a permit. "This severely restricts the market," said Vollmer.

VitiVoltaic in Oberkirch is co-financed by the state of Baden-Württemberg's research program "Weinbau 4.0" (Viticulture 4.0). Whether such a system costing several hundred thousand euros is worthwhile even without subsidies is a question of grid connection and wine marketing, said Vollmer. In his view, it would be most practical for local businesses to join forces because individual plots in viticulture are typically small.

This article was originally written in German.