Shared Ground | Renewables and Farming on Limited Land

The shift towards renewables requires space to build windmills and solar parks. Land is scarce and under pressure from agriculture, housing and industry. But can the production of energy be successfully combined with agriculture?

Under the banner of Agrivoltaics, a term referring to the coexistence of solar and agriculture on the same land area, I spoke with a few pioneers in Belgium and The Netherlands to find out how scientists and farmers are looking for ways to combine solar and food production.¹

A gentle marriage between food and energy

Renewables are adding to the pressure on overused land. Large solar parks built on former fields swallow up more and more agricultural land because of extensive technologies.^² Subsidies and high energy prices make it interesting for farmers to transform farmland into solar installations, especially in countries with poor zoning laws. A problem, because land for solar is lost to food production. However, scientists are looking for ways to co-use renewable energy sources with food production activities on the same piece of land in order to reconcile the demands on land from both energy and food. Ideally, this would also provide farmers an additional source of income. Having solar panels and crops in the same field could combine energy and food production. However, the interaction between panels and crops is complex, and solutions need to be tailored to local conditions.

Outside a rural village in the south of the Netherlands, near Oude-Tonge, a moon-like lander machine slowly moves over the fields of the agricultural company V.O.F Dogterom. The futuristic colossus consists of a sturdy surface 6 metres wide and 50 metres long, covered with solar panels and mounted on wheels. It's not meant for space exploration but the first experiment with mobile solar panels. Snail-like in mobility, it has a top speed of five kilometres per hour, explains Jacob Jan Dogterom, one of the brothers running the family farm. By crawling between the rows at a slow pace, the shade is evenly distributed between the crops.

A mobile agrivoltaic machine, produced by h2arvester. (Photo by h2arvester)

“It moves as slow as possible, otherwise, you lose too much energy. On the field, sugar beets are growing, and by the end of the season, we will be able to check whether the mobile panel has impacted the harvest. That's what matters the most, after all. There's an irrigation system linked to the machine, a nice perk. It's a bit like a cloud passing by. Moreover, in winter, when there are no crops on the field, the panel does not have to drive at all.”

“The mobile solar panel is the first experiment of its kind,” says Jacob Jan Dogterom. “The panels are the same as those used on roofs, so the potential yield is easy to predict. It is more important to check how the crops react to it. We are farmers in the end. We hope to find a compromise between cultivation and energy to generate electricity without giving up valuable agricultural land.”

Double use

Dogterom touches on an important point. Energy generation requires land, land that is already under pressure from all sides. Food production, nature, housing, infrastructure, industry, and increased energy production require space, a limited treasure. Large solar parks can provide quite a bit of energy, but the land on which they are built is lost to agriculture or other land uses. At most, some measly grass struggles in the shade under the panels. After all, the energy from the sun can only be used once for crops to grow via photosynthesis or for generating energy.

At least, that is still the prevailing philosophy today, explains Bram Van de Poel, bioengineer and professor of plant physiology at the Department of Biosystems at KULeuven. “It is really a pity to sacrifice valuable farmland just for solar panels. We believe that agriculture and energy can be combined. That is the idea behind Agrivolaics, finding a place for solar within agriculture. This is a challenge because these systems have to be developed in such a way that it allows sufficient light to pass through for crops. Our cut-off line is a harvest loss of less than 20 per cent, otherwise cultivation won't be economically feasible any longer.”

The mobile solar panel of the brothers Dogterom is an exception. Other experiments with Agrivoltaics are based on fixed systems. Van de Poel and his team currently manage three test sites at different locations across Belgium. One site combines pears with solar panels, on the other two sugar beets and wheat are grown. Pears are an important crop in certain regions in Belgium, just like sugar beets. Pears and other fruits are ideal for Agrivoltaics because they last for at least a decade on a field. As a result, a more permanent solar installation is possible. Pears are prone to damage from hail and intense sunlight. Many farmers already use protective shields, which would work well with solar.

“The trial with pear trees in Bierbeek has been running for more than one season, so we have data. We measure a reduction in yield of 16%. The pears are also slightly smaller, but the quality is good. That is in line with the expectations we had. The installation does take away some of the sunlight, but the crop loss is limited.”

Designing an installation that generates enough solar energy to be economically profitable while simultaneously sparing the harvest is no easy task, says Van de Poel. “In a conventional solar park, every square centimetre is crammed with panels, what grows underneath is of no interest. Agrivoltaics follows the opposite logic. It is the crop that has priority. The installation must allow sufficient light to pass through to make agriculture not only possible but thriving.”

Rotating solar panels are being tested as a means of adjusting the amount of light according to the needs of the plants.

Protection against hail

A certain loss of yield is difficult to avoid with fixed solar panels. But well-designed systems may offer benefits that balance out crop losses. “In our experiment with pear trees, the panels act like a roof over the rows of trees. This protects the fruits against hail and the blossoms against spring frost because it is half a degree to one degree warmer under the panels. Shade on the hottest summer days is also a plus. These elements of crop protection somewhat compensate for the loss of yield.”

There are several ways to combine solar panels and agriculture. Integrating panels with other constructions, such as canopy shades and hail nets, is an option. Another possibility is to install vertical panels between the agricultural crops. “We are also investigating the potential of rotating solar installations,” says Van de Poel. “This system has the advantage of adjusting the amount of light according to the needs of the plant. More light during periods of growth, less during heat and drought. A large part of our research focuses on developing models that can predict the yield and impact of solar installations.”

It is possible to integrate solar panels into other agricultural practices, but it is not easy, Van de Poel continues. “Installations can hinder the farmer when he must work the field with agricultural vehicles. This poses a problem for crops such as potatoes or wheat where the farmer uses large machines. It's less of an issue in orchards, which often stand for twenty years. Crop rotation does not play a role in these modes of cultivation.”

Farming under panels can be difficult where large machinery is needed. Here, a farmer fertilises a wheat field under a photovoltaic panel in Liaocheng, China. (Photo by Zhang Zhenxiang/VCG via Getty Images)

Complex interaction between plants and sunlight

Hellen Elissen, a researcher in renewable biomass and renewable energy at Wageningen University & Research, acknowledges that combining solar energy and agriculture is not an easy exercise. Elissen, who also coordinates the Sunbiose project, discovered that in a series of experiments in merging solar energy and agriculture, found out that a surprisingly large range of factors influences the interaction between solar panels and crops.³

“With Sunbiose, we are mainly looking into integrating solar panels in fruit cultivation, although there is also an experiment running with a pasture mixture of clover and grass. We also experiment with types of panels that allow certain wavelengths of the sunlight to pass through while using others to generate energy, and with mathematical models to predict the impact of structures on the harvest without having to run experiments every time.” Currently, panels are being developed that use only certain wavelengths of sunlight while letting others pass through for plant growth. They produce less energy than conventional panels, but they can be used on greenhouse roofs, for example.

The first results show a mixed picture, says Elissen. “We see a slight drop in yield for raspberries, but on the other hand, they benefit from the shade provided by panels on the hottest days of the year. There are currently several hectares of this combination, which is almost economically profitable. Strawberries seem much more sensitive to shade, which makes it more difficult to find the right balance.”

It is not easy to determine which plants are suitable for Agrivoltaics. In periods of intense sunlight, crops like strawberries can benefit from shade. Sunlight and day length differ from place to place, so solar-food combinations must be adapted. There is a lot that depends on the existing agricultural practices. The installation should not interfere with the use of agricultural machines. Farmers who already use greenhouses or protective shields can combine solar with their existing structures. It is more challenging to install a large-scale solar system on smaller agricultural plots than on vast fields.

What requires more research is the long-term impact on the soil, says Elissen. “We monitor the organic matter content in the soil, as well as the presence of a number of indicator species, such as earthworms and nematodes, which tell us something about the health of life in the soil. We also look at the soil structure and presence of nutrients.”

“The physiology of the plant requires more attention as well. In our experiment with raspberries, we see that the leaves of the plant grow faster and the sugar content of the fruit changes. Another example is lettuce. It will grow faster in the shade, because the leaves create more surface area to absorb more of the available light.”

Tailor-made solutions

The body of research on combining solar with agriculture is still in its infancy, but it won't be a one-size-fits-all solution, says Elissen. “The interaction between plants, sunlight and shade are very complex. Ultimately, you can only use light once, either for energy or for the plant. This can be reconciled for a number of crops by removing light when the plant does not need it or is even damaged by too strong sunlight.”

“Systems will be tailor-made, and I am hesitant to say for sure that it is going to be a success. Every crop, every soil type and every climate requires a different approach. In regions with a hot and dry climate, panels can offer great advantages such as more shade, a better microclimate and better moisture management. But all of this is still under investigation.”

Apart from a wide range of technological and agricultural aspects, there is also the question of how large-scale applications of Agrivoltaics will change the landscape. Large construction projects of solar parks and wind turbines are often met with opposition from the public reluctant to see such industrial-looking constructions being built.

“That is indeed a point of concern,” says Bram Van de Poel. “The rural character of a region can be lost by implanting such structures, and that is not desirable everywhere. In places where not much remains of the rural landscape anyway, this issue poses less of a problem. For some crops, farmers are already using all kinds of constructions to protect the crop, such as shade roofs or hail nets. These can easily be replaced by systems that combine solar panels without further affecting the landscape. The whole idea still needs to catch on.”

Aerial view of sheep grazing under solar panels, Spain. Condensation builds up on the panels during warm temperatures, dripping onto the surrounding grass. This can help to keep grazing areas healthy during periods of drought.

Food remains priority

Back to the fields in Oude-Tonge of the Dogterom farm, the mobile solar panel that slowly creeps between the rows of sugar beets is just one piece of a broader vision to achieve a fully autonomous company, says Jacob Jan Dogterom. “Eventually, we aim to go off-grid and become completely energy and CO2 neutral. It's achievable within ten years to disconnect from the electricity grid and provide our own energy, both for harvesting and storing our products, and for the use of agricultural vehicles.”

Perhaps, even more, it is possible, Dogterom continues. “Energy from the sun or the wind that we don't need at a certain moment can be stored as hydrogen. In regions with a lot of space, agriculture will eventually be able to supply energy to citizens or companies.”

Professor Van de Poel sees potential in the long term for farmers to supply energy beyond the needs of their farms. “Currently, solar energy systems are primarily aimed at meeting the energy demand of agricultural companies. That can be done differently, although it will take some time. The technology is still under development, and investments are higher than fixed installations. Legislation to supply electricity to the grid must also be sorted out.”

“I don't have a crystal ball, but it is quite possible that Agrivoltaics will be implemented in many places around the world within a decade. Vineyards in the south of Europe, for example, are ideal. It concerns extensive plots, more sun and the benefits of panels to protect crops are greater. In a country like Belgium, applications will have to be more custom made, because there is less open space available. If we equip one percent of all cultivated land with such systems, agriculture could become energy neutral, but we must be vigilant that agriculture and food production remain the priority. Ultimately, the farmer must have the last say in this story.”