RearCPVbif Solar Panels Could Transform Agrivoltaics in Southern Spain

Across southern Spain, an emerging type of solar panel is discreetly changing the rules around who can benefit from sunlight.

Rather than making landowners choose between food production and energy, researchers in Jaén believe sunlight can be shared. Their prototype panels produce substantial electricity while allowing sufficient light through to keep vegetables and fruit trees healthy, growing and productive.

How solar farms began competing with farmland

Europe’s energy transition faces one straightforward but persistent constraint: there is only so much land. The European Union is targeting at least 30% of its energy from renewables by 2030, alongside climate neutrality by 2050. Large-scale solar is vital to this strategy, supported by falling module prices and a surge of manufacturing capacity from China.

However, larger projects have intensified local disputes. Developers seek level, sun-exposed land, while farmers see those same fields as their livelihood. Communities often object when solar installations take the place of pasture or orchards. In certain areas, the choice between solar power and food production has become a prominent issue.

This pressure has helped agrivoltaics gain momentum. Rather than excluding agriculture, agrivoltaic installations raise or spread panels apart so crops, animals or beehives can use the same land. Plants that tolerate shade may benefit from cooler microclimates and less evaporation. Sheep can graze beneath arrays, controlling grass growth, and beekeepers can use solar sites for forage.

Agrivoltaics tries to turn a land‑use conflict into a double harvest: kilowatt‑hours from above, calories from below.

The main engineering difficulty arises when panels are placed immediately above crops. Standard opaque modules obstruct most sunlight, potentially slowing growth, distorting plants or reducing harvests. Although semi-transparent panels are available, they generally sacrifice too much generation capacity to satisfy farmers and investors.

The Jaén team’s approach to semi-transparent solar

Researchers at the University of Jaén in southern Spain have outlined a new system in a recent paper on agrivoltaic technology. They have named it RearCPVbif, short for “Rear Concentrator Photovoltaic bifacial”. Although the name is unwieldy, its principle is simple: transmit light to the plants while recovering some sunlight that would otherwise go unused.

What sets RearCPVbif apart

• It employs bifacial solar cells, which generate electricity from their front and rear surfaces.
• It incorporates rear optical concentrators that direct reflected and scattered light towards the cells’ back side.
• It retains high optical transparency, allowing enough light to reach the crops underneath.

Most semi-transparent PV, often termed STPV, either spaces active material further apart or uses thinner layers. This increases light transmission but lowers electrical production. The Jaén design makes a different compromise: it maintains transparency while extracting additional electricity from light reflected behind the panel.

The researchers report a transparency factor around 60%, a level usually seen as acceptable for many horticultural crops.

This 60% value is significant. Agronomy research indicates that many vegetables begin to struggle when mean light transmission falls far below that point. Above it, certain species can sustain almost normal photosynthesis, particularly where moisture and temperature are properly controlled.

Two essential light measures for crops and electricity

When deciding whether panels can be positioned safely over crops, engineers and agronomists assess two figures, not simply the watt-peak rating on a panel’s label.

• Average visible transmittance (AVT): the proportion of visible light transmitted through a panel.
• Average photosynthetic transmittance (APT): the proportion of wavelengths used by plants for photosynthesis that reaches their leaves.

The Jaén researchers considered both measures. APT is more important to crops than overall solar energy because plants depend chiefly on photosynthetically active radiation (PAR), at wavelengths of roughly 400–700 nanometres. When a panel blocks too much of this range, yields decline, even where ample ultraviolet or infrared light passes through.

Earlier research into greenhouses and shade nets suggests that, depending on the crop, around 60% transmission in the PAR range is the lower threshold for comfortable growth. RearCPVbif was developed with this reference point in mind.

Parameter	Conventional opaque PV	Typical semi-transparent PV	RearCPVbif concept
Light reaching crops	Low (often <20%)	Medium (40–70%)	Around 60% targeted
Electric output per area	High	Medium to low	Medium, boosted by rear concentrators
Crop suitability	Limited	Selective	Designed for a wide range of horticulture

The current state of “transparent” solar

The wider PV sector has pursued transparency through two main routes.

• Non-selective semi-transparent panels, which make absorbing layers thinner or create microscopic spaces in the active material. These modules transmit more light across the spectrum but generally suffer a major loss of electrical efficiency.
• Wavelength-selective panels, designed to absorb mainly ultraviolet and near-infrared radiation while transmitting visible light. Plants receive much of the light they require, while the panel uses sections of the spectrum that are not useful to human vision.

The Jaén concept is close to the second category, while adding its rear optical concentrators. These components aim to collect rays that initially pass through the module, reflect off crops or soil, then strike the rear of the panel. Bifacial cells can turn this reflected light into additional electricity.

Instead of fighting for each photon on the front surface only, the system harvests the second chance light that the farm would have simply reflected back to the sky.

The approach is also well suited to bright, reflective soils or pale mulches, both of which increase the light available to the rear of the cells.

Keeping crops cooler while solar panels operate

Heat is another limitation when solar modules are suspended above crops. A heated glass canopy may retain warm air, producing an undesirable greenhouse effect. Elevated panel temperatures also reduce electrical performance by lowering cell efficiency.

The Jaén research tracked thermal performance and found that cell temperatures remained below around 70 °C. This avoids the most severe performance reductions and limits the risk of overheating the air immediately beneath the modules. For growers, managing temperature in this way could help plant development follow a more familiar pattern rather than causing stress.

• Cooler panels deliver more consistent output during summer heatwaves.
• Less extreme air temperatures can reduce blossom drop and fruit damage in sensitive crops.
• Animals beneath panels experience a lower heat burden than they would beneath bare metal roofs.

What RearCPVbif could offer farmers and developers

If technologies such as RearCPVbif achieve commercial maturity, they could alter how solar developers view rural land in sunny regions including Andalusia, California and southern Italy. Instead of replacing crops, developers could agree long-term leases in which farming and solar arrays function together.

For farmers, a semi-transparent canopy could reduce certain climate-related risks. Partial shade can lessen heat stress during increasingly common hot periods. Panels may also slow wind at ground level and reduce evaporation. In places where water is costly or scarce, this could make yields more stable.

Rather than paying rent for lost fields, farmers could collect two incomes from the same hectare: one from the harvest, one from electricity.

Actual results will rely on thoughtful crop selection and system configuration. Leafy vegetables, berries and some herbs can perform well under filtered sunlight. Cereal crops and fruit trees that favour full sun may require broader row gaps or taller mounting systems to prevent yield reductions.

Questions still awaiting answers

Like any encouraging laboratory concept, this type of agrivoltaic panel must overcome several obstacles before becoming commonplace above tomato rows or olive saplings.

• Cost of optics: Rear concentrators and bifacial cells increase complexity. Manufacturers must prove that the extra kilowatt-hours compensate for the higher bill of materials.
• Durability: Optical parts need to withstand dust, humidity, hail and cleaning over decades on working farms.
• Maintenance access: Farmers require room for tractors, harvesters and irrigation equipment, affecting array layouts.
• Regulation: Planning policies and agricultural subsidies in Europe and elsewhere still largely treat a field as either agricultural land or a solar site, rather than both.

How to assess agrivoltaic potential on a working farm

Landowners considering similar systems in future can already use several basic checks to inform their thinking, even before this particular technology is fully commercialised.

• Record average solar radiation and temperatures throughout the growing season.
• Establish which farm crops can tolerate partial shade or cooler canopies.
• Model alternative panel densities, targeting at least 60% photosynthetic transmittance where maintaining high yields is most important.
• Estimate water savings from lower evaporation and compare them with any anticipated yield change.

Basic modelling indicates that on hot, highly sunny sites, a small reduction in direct sunlight may sometimes be balanced by reduced heat stress and water savings, especially in high-value horticulture. A dependable electricity income can further change the financial case for marginal or drought-prone land.

For energy planners, agrivoltaic concepts such as the Jaén design expand the range of places capable of hosting solar. Car parks and rooftops will remain important. Nevertheless, semi-transparent bifacial arrays above crops enable solar capacity to expand within existing agricultural areas, rather than displacing farms or moving them onto less appropriate land. In areas facing pressure from climate change and energy targets alike, this shared-sun approach could gradually progress from trials to a standard option when planning the next generation of rural infrastructure.