Agri­v­oltaics: How does it impact crop yield?

Standing between energy and food crops, agri­v­oltaics takes a middle route, offering the poten­tial for improved land use effi­ciency. However, the ques­tion remains: Will agri­cul­tural produc­tivity meet expec­ta­tions? The Furrow spoke with farmers who have embraced this approach.

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.

The untreated areas under the modules serve to promote biodi­ver­sity.
Amance, France: It is not easy to main­tain the yield level when 40 % of the area is in shade.

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.

In 2022, Sylvain Raison’s soyabeans produced an average yield with better nutri­tional values.

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.

Wheat harvest in Donaueschingen: RTK steering systems are a must in agri-PV systems.

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.

At Finca Daramezas, the oper­ating times of the machines were adapted to the orien­ta­tion of the panels.

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.