Farming with solar panels: The promise of agri-PV in the fight for net zero

As the global push for net-zero emissions increases, scientists are turning to agri-PV – the combination of agriculture and solar energy – to reduce carbon emissions from food production while optimizing both crop yields and energy production .

According to a recent report from the Intergovernmental Panel on Climate Change, agriculture and forestry are the second highest polluters (behind the energy sector), contributing up to 22% of total global CO2₂ Emissions.

“Agrivoltaics is an innovative approach to renewable energy production that could help decarbonise the agricultural industry,” explained Austin Kay from Swansea University. “Essentially, agrivoltaics are solar panels (photovoltaics) combined with agricultural systems, allowing the same piece of land to be used for both electricity generation and food production/land management.”

“This could be as simple as placing traditional photovoltaic systems such as crystalline silicon on pastures with livestock, or it could involve more complex approaches, [such as] Solar panels placed over crop fields or sheltered growing environments such as greenhouses. and polytunnels.”

Agricultural PV and net zero

The impact of this approach, even if implemented on a comparatively small or local scale, could still be staggering. “As the EU only covers 1% of its current agricultural area with agri-PV, it could reach its 2030 capacity targets with these devices alone,” said Kay. “Agri-PV provides locally generated electricity in this way and offers a promising path to decarbonizing the agricultural industry. And if done right, they can be introduced without negatively impacting crop yields.”

But optimizing agri-PV is a challenging task that involves finding the right balance between crop yields and solar energy production. Careful attention must be paid to how light is absorbed, reflected or transmitted by the photovoltaic system and how efficiently the system converts sunlight into electricity while managing the flow of heat and energy.

“[Solar panels] and plants both require light,” Kay added. “The balance between the amount of this light consumed by the photovoltaics and the amount received by the plants is a complex problem that depends on the location, the time of year, the light requirements of the particular crop, the needs of any pollinating insects like bees etc. depends on many [other factors.

“At higher latitudes, [for example]Since there is typically less light available to plants throughout the year, greater light transmission from photovoltaics is likely required. At lower latitudes this is less of a concern as shading effects may be desirable, particularly in the hotter seasons.”

Iron out the details

Kay and his team sought to evaluate the annual electricity production of agricultural PV systems using different types of photovoltaic materials, taking into account factors such as solar cell density, location and ideal crop. Their results provide a basis for developing larger systems that take into account plant needs and environmental factors while focusing on energy efficiency and thermodynamic principles.

“We are using the National Solar Radiation Database (NSRDB), hosted by the National Renewable Energy Laboratory (NREL), to translate the results obtained in the laboratory to real-world scenarios,” said Paul Meredith, co-author of the study. “The NSRDB contains information critical to determining realistic photovoltaic performance, such as temperature and solar radiation.”

By combining real sunlight and temperature data with detailed models, they compared the performance of organic semiconductor-based photovoltaics with traditional silicon-based photovoltaics.

Organic photovoltaics consist of organic (i.e. carbon-based) compounds and are usually semi-transparent, so they can be easily integrated into agricultural PV systems. Their ability to transmit light makes them ideal for modern greenhouses, while silicon photovoltaics, while more efficient at converting sunlight into electricity, are opaque and block light, limiting their use in agricultural environments.

There is also the additional advantage that the optical properties of photovoltaics based on organic semiconductors can be adjusted more easily. “Their optical gaps and transmission properties can be adjusted through their chemical structure, allowing an optimal material to be assigned according to the light requirements of a particular crop,” explained Ardalan Armin, the project leader.

“Organic semiconductor-based photovoltaic systems are also lightweight and flexible, allowing retrofitting of older structures and polytunnels that may not be able to withstand the weight of traditional silicon-based photovoltaic systems,” he added.

A compromise that could be worth it

Overall, they found that while state-of-the-art, silicon-based inorganic solar panels produce more electricity per square meter than their semi-transparent organic counterparts, they took into account factors such as their coverage, weight, flexibility and the efficiency with which the land could be used Technologies could allow them to compete with established inorganic systems.

But there is another caveat to examine: how each material is made must also be considered in the context of sustainability and environmental impact. “What are the environmental costs of our clean energy sources?” asked Kay.

The leading photovoltaic material on the market, monocrystalline silicon solar cells, typically requires temperatures in excess of 1000°C^OC during manufacturing. “Silicon photovoltaics therefore have high embodied energy,” said Kay. “Organic semiconductors and perovskites, on the other hand, can be synthesized from solution at much lower temperatures using techniques such as web printing and slot die coating – similar to newspaper printing. Solution-processable photovoltaic systems therefore have much lower embodied energy.”

Kay says future studies could take into account the light intensity and wavelength requirements of specific plants. But he predicts things are already changing.

“Just this year, the efficiency of organic photovoltaics has exceeded the 20 percent mark, and in the past devices with an operating life of up to 30 years have been produced,” he said. “With these continued improvements and a decline in the cost of synthesizing organic molecules and manufacturing devices, we may one day see fewer agricultural PV projects using traditional silicon photovoltaics and instead larger projects using semi-transparent, organic photovoltaics.”

Reference: Austin M. Kay, et al., On the Performance Limits of Agrivoltaics – From Thermodynamic to Geo-Meteorological Considerations, Solar RRL (2024). DOI: 10.1002/solr.202400456

Post photo credit: Ivan Bandura on Unsplash