New research out of Spain puts a number on one of agrivoltaics’ most debated design questions: how much shading is actually good for crops?
The answer, it turns out, depends heavily on which PV technology you use — and the performance gap between the options is wider than most project developers expect.
The Study
Researchers at Spain’s Murcian Institute for Agricultural and Environmental Research and Development (IMIDA), together with Miguel Hernández University and Italy’s University of Bari, ran a controlled two-season trial over tomato crops in Murcia — a semi-arid Mediterranean climate averaging 30°C in summer and 12°C in winter.
Four identical greenhouses were tested side by side:
- A control greenhouse with standard polyethylene film
- A shading net greenhouse
- A semi-transparent monocrystalline silicon PV greenhouse (PV-Si, 50% light transmission)
- A cadmium telluride thin-film PV greenhouse (PV-TF, 50% light transmission)
Each solar greenhouse had 18 modules — split equally between roof and south façade — with nominal powers of 59 W (PV-Si) and 40 W (PV-TF). Microclimate data including air temperature, humidity, irradiance, and soil conditions were logged at two-minute intervals across both a 120-day winter-spring season and a 98-day spring-summer season.
What the Numbers Show
On energy output, PV-Si outperformed PV-TF by a significant margin:
| System | Winter-Spring (daily avg) | Spring-Summer (daily avg) | Total (2 seasons) |
|---|---|---|---|
| PV-Si (Silicon) | 3.92 kWh | 4.07 kWh | 726.8 kWh |
| PV-TF (CdTe) | 2.58 kWh | 2.79 kWh | 488.4 kWh |
The crop results were equally clear. The key metric tracked was Daily Light Integral (DLI) — the total amount of photosynthetically active light plants receive each day. During the winter-spring season, only the control and PV-Si greenhouses maintained DLI above the minimum threshold needed for healthy tomato development. The PV-TF system let through too little light to sustain optimal growth.
The yield results followed:
- PV-Si: 25% higher tomato fruit weight compared to the control, with more favourable nighttime temperatures and higher soil moisture
- PV-TF: Lower fruit count and smaller average fruit weight in both seasons
The researchers concluded that the PV-Si system “effectively balanced solar radiation management, thermal regulation, and energy production” — and flagged it as the stronger candidate for agrivoltaic applications in Mediterranean and semi-arid environments.
Full study: “Comparative evaluation of semi-transparent monocrystalline silicon and cadmium telluride photovoltaics for tomato cultivation in Mediterranean agrivoltaic greenhouses”, published in Smart Agricultural Technology. Read the original report on pv magazine
What This Means for Agrivoltaic System Design
The study reinforces a principle that experienced agrivoltaic developers already know: shading quantity alone is not the right design target. Light quality and spectral distribution matter just as much.
At 50% nominal transparency, the two panel technologies produced dramatically different DLI outcomes. CdTe thin-film, despite matching silicon on paper transparency, filtered out more of the photosynthetically active spectrum — pushing crops below the growth threshold in winter months.
For open-field agrivoltaic structures, this has direct implications for:
Panel selection. Bifacial monocrystalline glass-glass modules transmit light through inter-panel gaps rather than through the panel itself. The gap-to-panel width ratio becomes the primary DLI control lever.
Row spacing and clearance height. Wider inter-row gaps increase DLI at ground level and create the dappled light patterns that shade-tolerant crops benefit from. Taller clearance (3.5–5 m) allows full-size farm machinery to operate freely and improves air circulation for the crop canopy below.
Seasonal calibration. Winter DLI drops significantly even in Mediterranean climates. Systems designed only for summer performance may leave crops light-starved from November to March — the exact finding the IMIDA team documented with their PV-TF treatment.
Solaracks Agrivoltaic Mounting Systems
Solaracks designs and supplies the elevated racking structures that make dual-use agrivoltaic land viable at commercial scale. Our systems are engineered for:
- 3.5–5 m ground clearance — full tractor and machinery access underneath
- Adjustable inter-row spacing — configurable to crop type and local irradiance data
- Ground screw (helical pile) foundations — no concrete, minimal farmland disruption, fast installation
- HDG steel structure — hot-dip galvanized for 25+ year service life in outdoor agricultural environments
- Wide row gap ratios — designed to maintain DLI above crop-specific thresholds year-round
Talk to the Solaracks team about agrivoltaic mounting for your next project: solaracks.com
Quote and structural design within 24 hours. Load calculations and SAP2000 analysis available on request.