The call for the timely deployment of renewable energy is becoming more politically prominent as predictions on climate change worsen. Also, the expected population growth of 1.5 billion in the next 15 years raises questions about the resilience of our global energy and food systems. Electricity demand is currently growing faster than population growth, which is leading many to look for synergies between sustainable agriculture and renewable energy.
The typical solar farm, which features ground-mounted solar panels, needs a substantial amount of space to generate electricity at the megawatt level. Agrivoltaics (APV) combines agriculture with electricity generation by farming under a canopy of elevated solar panels. There are some interesting reasons why APV is a potential growth market, but before exploring this, it is important to understand the challenges of solar farms and their respective solutions.
Challenges of Solar Plant Development
Solar panels are considered an established technology, however in the typical solar farm the ground beneath the panels cannot be used for anything, mainly due to the small gaps between rows of panels which are too small for modern farm equipment to pass through. It is possible to convert a typical solar farm to a dual-land use system when it is designated as a living area for grazing farm animals or for beekeeping, for example. This lowers the cost of maintaining vegetation growth without posing a risk to the panels themselves. However, this depends on the farm animal. Pigs, cattle or goats often do pose risk to the panels.
When more space is allowed between the solar panel rows, it is possible to grow crops in between the spaces. This is known as alternating land use because the purpose of the land alternates between ground-mounted solar panels (electricity generation purpose) and crop growth (horticulture purpose). So, it would not be exactly correct to say that alternating land use systems would be agrivoltaics. This is because the land between the rows would be shadowed during certain times of the day, altering the characteristics of the land and the types of crops that can be grown there. Ground-mounted solar panels of any kind simply do not allow for electricity generation and crop growth at the same time on the same areas of land.
Elevating solar panels on a vertical plane is where we begin to see interesting alternatives to traditional solar installations. There are two main APV systems that are in the process of proof of concept and testing. Vertically mounted bifacial solar modules allow for more arable land without a sharp decline in sun exposure (and therefore electricity generation), as bifacial modules can collect solar energy from both sides of the panel.
This system, according to research at Dutch and German Institutes, works particularly well in farming areas suffering from wind erosion, as the vertical installations ‘break’ the wind, reducing the wind speed, and therefore protect the crops that are grown there. The bifacial panels also generate more power per square meter than the traditional monofacial panels without requiring any moving parts which typically raise costs of development significantly.
The more radical and experimental option is stilt mounted solar modules, which would hold monofacial solar panels at a higher vertical. This would allow farming machinery to pass underneath and operate as in a regular farm. In this design, there has to be a specific gap between the crop rows and the stilt rows to ensure the stilts do not bump into the moving machinery. This admittedly leads to an arable land surface loss of about 3-10% percent.
Arable land surface loss refers to areas of land that is suitable for crop growth but is not used for this reason of allowing space for farming machinery.
A piece of research within this type of APV is mounting solar panels using actuators, which would allow for mechanical tilting based on the angle of incidence and plant growth optimisation. This is an extremely advanced system which could maximise electricity generation by perfecting angles of incidence on the solar panels while also shading crops during initial stages of growth.
Plant Physiology and Solar Panel Shading
Contrary to what many people may think, plants growing underneath actuator-mounted solar panels could create crucial optimisations in the future of agriculture. The intuitive conclusion would be that a plant growing under a solar panel would be unable to access the necessary sunlight to grow efficiently. However, research in plant physiology shows that this depends on the crop.
During photosynthesis, plants grow their biomass out of carbon dioxide with the help of chemical energy under the Sun. However, the relationship between sun exposure and biomass growth is not linear: there is a ‘plateau’ point (as in the light saturation point section of the graph below) where the remaining available sunlight cannot be converted into biomass. At the light saturation threshold (or light saturation point),plants struggle to absorb extra energy and enter photoinhibition (final section of the graph below), where they must release energy through evaporating water.
This light saturation point is different for each plant, and certain plants will benefit greatly from shading throughout the day to optimise solar energy consumption, with the extra energy being channelled into electricity generation. The caveat to this is that shade-intolerant plants (plants that require higher levels of sunlight throughout the day), such as red peppers, would probably not be suitable for crops placed under actuator mounted solar panels.
Nevertheless, these advanced APV opportunities highlight an important problem, which is that plants can suffer from too much sunlight when they reach their light saturation thresholds. This can lead to the equivalent of sunburn and heat stress, causing increased levels of water evaporation. This inevitably leads to suboptimal crop growth and horticulture, an issue that will likely take a significant toll on food security in the coming years.
According to a report from the Fraunhöfer Institute for Solar Energy in Germany, nearly all crops can be cultivated under solar panels in APV systems, with the caveat of some yield loss of these shade-intolerant plants during the autumn and winter seasons. They estimate that there is up to 1700 GW of technical potential in deploying APV across Germany. During a RESOLA project, conducted for two years in the Bodensee and funded by the BMBF, during the relatively wet and cold year of 2016, APV crop yield was 25% less than reference fields that did not have solar panels. However, in the relatively dry and hot years of 2017 and 2018, APV systems offered higher crop yields “for winter wheat, potatoes and celery”. This may signal the high applicability of APV in hot and arid regions, which are often the most vulnerable to food security issues.
The Netherlands is the second largest exporter of food resources in the world, second only to the United States. The agricultural company GroenLeven, a subsidiary of major developer BayWa, has started several pilot APV projects with fruit farmers. In their largest pilot, a large 4-hectare raspberry farm in Babberich was converted to a 2MW APV farm, with the remaining area kept as traditional farmland for the raspberries. Raspberries are shade-tolerant fruit that are typically grown in rows (making it suitable for a solar installation) and are typically covered with some sort of plastic to protect them from the elements and prevent them squashing.
In the project, the raspberries were grown directly under stilt mounted solar panels facing east and west alternately to maximise solar ray yields and protect the raspberries from the wind. They used monofacial panels with larger spacing than in a typical solar farm to allow more of the light to get through.
It was found that the yield and quality of raspberries grown in APV environments was the same or enhanced as in the typical plastic covering environment. This also reaps benefits for farmers because they save work from managing the plastic tunnels that normally cover the raspberries. These plastic tunnels are easily crushed or damaged by summer storms and hail. This forces farmers to harvest fruit that cannot be sold, and with climate change leading to more unpredictable climates, these problems can significantly harm a farmer’s ability to make a living. Under the stilt mounted solar panels, the raspberries under the panels sustained no damage, while the raspberries in the reference field were mostly destroyed. Also, the temperature under the solar panels in the APV field was several degrees cooler than in the reference field without solar panels. This shade makes working easier and more pleasant for farming workers, allows for greater diversity of crop cultivation (as a farmer can create cooler environments by adding vertically mounted solar panels to specific patches of land), and importantly reduces water use in irrigation by 50%, reducing costs of cultivation and demand on water resources.
Interestingly, there is a benefit to the solar panels from the crops as well. In GroenLeven’s project, they found that since the crops are evaporating water at a limited rate (as they are less likely to reach their light saturation points, this keeps the panels cool which maintains the energy efficiency of the panels. The cooler a panel can be, the more solar energy it can convert to electricity. This optimises revenues for a farmer between electricity generation and crop cultivation and meets both growing demands of food and electricity.
That being said, a lot of research on APV is still needed for conclusive evidence to be drawn. Projects are fairly limited, with most projects only done with shade-tolerant crops like spinach, tomatoes, potatoes, lettuce etc. This means the compelling case for APV is somewhat limited at present.
The Future of APV
APV does seem to create an efficient and necessary synergy between efficient agriculture and renewable energy generation. If Europe was to convert just a fraction of current agricultural land into APV systems, we would be able to meet a significant portion of our energy needs, while also improving crop yields for shade-tolerant plants and even slow down soil degradation. Additionally, areas such as the Middle East, which would benefit from integrated crop shade and reduced water consumption, could stimulate their agricultural sectors significantly through APV.
However, though there are clear synergies between farming and energy production, farmers may be slow to embrace the technology due to lack of expertise in energy, causing anxiety concerning how solar panels may affect their crops. Unfortunately, one of the main barriers is likely to be the NIMBY effect (Not In My Backyard). This is a psychological barrier to technological advance in renewable energy as many do not take well to industrialisation in their area or near their home. A common example is the visual impact and noise pollution issues common when installing wind turbines.
In agriculture, there are also a range of strict and complex regulations that dictate a farmer’s access to subsidies. APV installation may have a range of issues penetrating the market for these reasons, particularly in the EU. As part of agricultural policy, EU direct payments (grants), are given to “land used primarily for agriculture”. Whether an APV farm loses its eligibility for this subsidy has not yet been clarified by the EU Institutions.
There are other regulatory risks that also play into bureaucracy which can slow down growth of the APV sector. In the EU, the solar panel modules are considered a physical structure under building regulation laws, meaning one needs a building permit to begin an APV project. Also, in Germany, there is a lot of red tape around building structures in rural areas. It can only go ahead if it the building structure falls under a list of public interests. It has not yet been considered by any German authority whether APV should be on that public interests list.
Finally, as with any major renewable project, the issue of investment costs and ability to sell is a major contributor to growth or stagnation. APV systems admittedly do not generate as much electricity as traditional ground-mounted solar farms per square metre, making the cost/MWh up to 20% higher. If the ownership between the solar panels and the farm is split (eg. a developer owns the panels, a farmer owns/generates profit from the arable land), it is unlikely to be economical for either party. This will also play into a farmer’s willingness to install APV as they are likely reluctant to take on operational costs. Likewise, if the farmer does own the solar array, he or she may choose to optimise in one direction. Put simply, they may choose to optimise the solar array for crop cultivation and only prioritise energy generation to make up for shortfalls in crop yield, or benefit from spikes in energy prices. This would minimise the synergistic effects outlined as a key driver of APV’s value.
Nevertheless, there are reasons to be hopeful. Though the NIMBY effect among local stakeholders has caused a delay in many renewable energy projects, this is often overcome over time. An example is the large biogas plants that are now relatively commonplace in Germany but were previously opposed by farmers and local communities.
For this reason, the growth of APV, to prevent immovable backlash, must be controlled and strategic. Regions such as the Netherlands and Germany, with expertise in agricultural systems and existing pilot projects, should likely lead the way in developing proof of success within the technology. Additionally, there are a range of developers who may build solar parks under the guise of agriculture and claim that it fits within the APV model. It is important, therefore, to be extremely clear about what counts as APV (vertical bifacial mounted, stilt mounted, and actuator mounted panels), and communicate this to farmers who may be targeted for potential projects. Overall, garnering community support and trust, as well as sector support and trust, will be essential to the growth of this technology in the future.
The Fraunhöfer Institute in Germany sets out the following recommendations for the future of APV:
1. Agrivoltaics should be deployed mainly where synergistic effects can be achieved, for instance reducing the water demand for crop production.
2. To maintain proper local support, agrivoltaics systems should preferably be operated by local farms, energy cooperatives or regional investors.
This article has sought to show that these two recommendations are very important and the local political economy of APV can be extremely complex. Though a promising concept that is potentially vital in the context of climate change mitigation and the urgency of the energy transition, government subsidies are likely necessary to make APV competitive with other renewable energy technologies. Regulation relating to APV is complex and slow changing, creating inertia that makes farmers reluctant and developers anxious about regulatory and technical risk. However, the potential to grow human crops with greater yield, or even biofuel crops such as corn, offers an attractive case for giving APV a try, particularly with the growing issue of global food security.
If governments, farmers and investors can find an economical way to generate one of the cheapest types of renewable energy with efficient advancements in agriculture, this movement towards APV could be a game changer which creates synergies between renewable energy deployment, efficient agriculture, soil regeneration or even reforestation.
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1. Fraunhofer ISE, APV-RESOLA – Agrophotovoltaic - A Contribution to Resource-Efficient Land Use
2. https://agri-pv.org/en/, Solar and energy transition
3. BayWa r.e. grows AgriPV across the Netherlands, https://www.baywa-re.com/en/news/details/baywa-re-grows-agripv-across-the-netherlands
4. Energy Innovation Policy & Technology LLC, How “Agrivoltaics” Can Provide More Benefits Than Agriculture And Solar Photovoltaics Separately, https://energyinnovation.org/2021/11/01/how-agrivoltaics-can-provide-more-benefits-than-agriculture-and-solar-photovoltaics-separately/
5. Semchenko et. al, Positive effect of shade on plant growth: amelioration of stress or active regulation of growth rate, Journal of Ecology, British Ecological Society, Volume 100 (2), 12 December 2011.
6. Weselek et. al, Agrophotovoltaic systems: applications, challenges, and opportunities. A review, Agronomy for Sustainable Development 39, Article 35, 2019.