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WATUSO - 834134;info:eu-repo/grantAgreement/EC/H2020/834134

Abstract:

Sustainable crop production and the continued profitability of agriculture in Europe are increasingly perceived as two opposing goals. The desire to continue traditional farming while reducing chemical inputs and fossil energy consumption brings with it many challenges. Also, the changing climate challenges agriculture in many new ways: jeopardizing harvests, pressuring growers to adopt new management practices or changing cropping systems entirely. To remain relevant and competitive, new ways of crop production will need to be considered. An ever-increasing global population and rise in energy demand stands in stark contrast with the available renewable energy in our electricity mix. Despite sustained efforts, the transition away from fossil fuels progresses at an insufficient pace. Additionally, increased opposition against nuclear energy leads to a re-uptake of gas- and coal-fired power stations, further increasing greenhouse gas emissions. To reach, or even approach our climate goals, solar- and wind energy production must be increased. Agrivoltaic (AV) production systems can serve as a bridge between agricultural sustainability and climate change challenges. By integrating solar panels on agricultural land, provided careful design choices are made, crop production can be maintained while solar energy generation can be expanded. Under AV, plants experience a modified microclimate characterized by reduced solar irradiance, changed temperatures and shifted precipitation inputs. Solar energy generation almost exclusively relies on crystalline silicon solar cells. New approaches such as perovskite-silicon tandem cells or wavelength selective technology show promise for continuing PV efficiency growth. A variety of solar panel types are available for AV. Fuel production directly from solar energy and ambient water has become a reality with the development of hydrogen panels. The use of hydrogen fuel can be a key factor in overcoming the energy density and storage problems associated with electric PV. By capturing water from the air, H2 panels thrive alongside transpiring crops. Where additional light transmission may be required, a range of semitransparent options are available. AV systems can make use of semitransparent modules, since they represent a useful tool for fine-tuning irradiance levels for the crops. One of the biggest challenges of implementing AV as a new sustainable farming system, is knowing the impact on crop productivity ahead of time and dealing with the uncertainty of fluctuating energy prices, both impacting profitability. We first performed an extensive literature search related to all the constraints that determine an AV system. Practical farming constraints, such as the use of heavy machinery, or intensive manual labor leads to a variety of AV system requirements. The variation in shade tolerance among commonly cultivated crops requires tailor-made AV system designs to optimize both energy production and agricultural yield. We distinguish three types of crop responses under AV. Crops such as maize or strawberry tolerate shade only to a limited extent and exhibit a steep decline in productivity with increasing shade. Other crops such as pear, grass or blackcurrant decrease in yield but at a much slower rate. Finally, there are crops that exhibit some level of shade tolerance, such as blueberry or raspberry. Another challenge for AV systems is determining its place in the landscape. Selecting suitable sites for AV systems requires the consideration of many factors and stakeholders' requirements. A GIS multi criteria decision analysis of Flanders revealed 60 % of its agricultural land as suitable for AV. All crops contended with important restrictions due to the proximity of heritage sites or areas of significant natural value. Most of the fruit cropping area reached AV suitability scores exceeding 0.95 out of a max of 1, while arable crops and vegetables scored on average 0.12 points lower. Despite contending with a highly fragmented landuse, agrivoltaic systems can supply up to 200 TWh of electricity per year- 4 times the current yearly electrical consumption of Flanders. Besides assessing the theoretical suitability of crops and determining the geographical selection of ideal farming plots for AV implementation, we also conducted field trials on several different AV systems in Flanders. We evaluated two experimental agrivoltaic pilot sites on arable farmland as well as an AV setup in a mature pear orchard. On the fist arable site, we investigated static and single-axis tracked bifacial modules paired to sugar beet, an important industry crop, at a light reduction of 15-20 %. Beets proved challenging to manage in practice due to weed and fungal pressure, with yields that were reduced by 11-19 % depending on position. Roots were found to be smaller but maintained sugar levels. The other arable AV pilot assessed the potential of wheat under an elevated agrivoltaic system at 22-30 % shading using traditional PV modules and hydrogen panels. Wheat suffered higher losses of 33-46 %. Smaller grains with high protein content were recorded under AV. Collectively, arable crops reached a land equivalent ratio (LER) between 1.00 and 1.22. In a third field experiment, we evaluated pear agrivoltaics under semitransparent PV cover. Fruit production represents a much smaller fraction of the agricultural landscape in Flanders. However, fruits have a much higher economical value per hectare, and are often cultivated in long-term orchards. In a pioneering agrivoltaic pilot installation, three consecutive growing seasons of 'Conference' pears were evaluated under Agrivoltaics, with a yearly average light reduction of 24 %. We examined how the microclimate changes under AV with regard to canopy air temperature, pear yield, and fruit quality. The AV system was found to increase nighttime air temperatures during periods of frost by 0.5°C, and temper higher temperature peaks during a hot summer period. Fruit yield was consistently reduced by 15% over the 3 years of trial, without impacting postharvest quality or storability. However, a discrepancy in fruit shape was observed under AV, leading to an increased percentage (93 % increase on average) in bottle-shaped pears and a caliber that was decreased by 5mm. Despite these changes, the AV system was found to have no effects on flowering and fruit development, and flower and fruit abscission, but it delayed leaf senescent in the fall. It also offered some additional protection against sunburn. In conclusion, innovative crop production systems such as AV, often require initial fine-tuning and engineering to enable implementation to the fullest potential. By selecting an appropriate location, establishing a profitable energy use-case and implementing it for an appropriate shade-tolerant crop with the right light penetration percentage, agrivoltaic systems can contribute to advances in modern farming. This way, it has the potential to provide benefits for the cultivated crops (protection against climate change events), while expanding the amount of sustainable electricity production by means of PV in a local and rural community. Our research and practical experiences suggest that agrivoltaics not only represent a viable solution to the challenges faced by farmers, but also offer a viable pathway towards harmonizing energy production with profitable crop production. With carefully chosen system designs and crop types, agrivoltaics can improve land use efficiency, sustain or enhance crop yields, and contribute to the dual objectives of energy sustainability and food security.