Abstract
In this study, we investigated the influence of different solar panel densities (100%, 75%, and 50%) on the photothermal environment beneath photovoltaic (PV) arrays. Our objective was to address the conflict between agricultural productivity and energy generation caused by excessive shading from traditional high-density PV installations. Through structural modifications and environmental monitoring, we analyzed variations in solar radiation, air temperature, and soil temperature across three distinct zones (southern, central, and northern) within a single-span PV array. Results demonstrated that reducing solar panel density significantly enhances solar radiation penetration while moderating microclimatic conditions. Key findings include: (1) Solar radiation intensity follows 50% > 75% > 100% panel density, with the central zone consistently receiving higher radiation; (2) Higher-density panels exhibit stronger daytime cooling effects, whereas nighttime thermal retention remains stable across densities. These insights provide actionable guidelines for optimizing agrivoltaic systems to harmonize energy production and crop growth.
Introduction
Agrivoltaics, the integration of solar panels with agricultural land, has emerged as a sustainable solution to land-use conflicts and renewable energy adoption. However, conventional PV arrays with 100% solar panel density often cast excessive shade, reducing crop yields and land efficiency. Prior studies highlight the trade-off between energy generation and agricultural output, emphasizing the need for balanced solar panel configurations. For instance, Kim et al. (2023) demonstrated that 32% panel density maximizes profitability in dual-use systems, while Gonocruz et al. (2021) reported an 80% rice yield reduction at 27–39% shading.
Our research expands on these findings by systematically testing three solar panel densities (100%, 75%, and 50%) in a real-world agrivoltaic park. We quantify how panel density modulates the photothermal environment, offering practical strategies to enhance both energy output and crop viability.
Methodology
Study Site and Experimental Design
The experiment was conducted in a 46.67-hectare PV agriculture park in southern Jiangsu Province, China (31.62°N, 119.18°E). The baseline structure comprised single-span PV arrays (6.8 m width, 24° tilt) with 100% solar panel density (265 W polycrystalline panels). Structural modifications reduced densities to 75% and 50%, maintaining identical support systems (steel columns, cement foundations).
Environmental Monitoring
We deployed HOBO sensors to measure:
- Solar radiation intensity (0–1,280 W/m², ±10 W/m² accuracy) at 1.0 m above ground.
- Air temperature (-20–70°C, ±0.2°C) and soil temperature (-20–100°C, ±0.15°C) at 0.15 m depth.
Data were recorded every 10 minutes from July 1–20, 2023, across southern, central, and northern zones (Figure 1). Daytime (06:00–18:00) and nighttime (18:00–06:00) periods were analyzed separately.
Results and Discussion
1. Solar Radiation Intensity
Solar radiation beneath PV arrays inversely correlated with solar panel density (Table 1). Open-field radiation averaged 336 W/m², exceeding values under 50%, 75%, and 100% densities by 42.6–188.3 W/m², 59.8–246 W/m², and 72.2–361.4 W/m², respectively. The central zone consistently received higher radiation than peripheral zones, attributed to reduced shading at midday.
Table 1. Average daytime solar radiation intensity (W/m²) across panel densities.
| Date | Open Field | 50% Density | 75% Density | 100% Density |
|---|---|---|---|---|
| July 1 | 486.6 | 322.3 | 269.3 | 186.2 |
| July 5 | 564.3 | 382.6 | 318.3 | 202.9 |
| July 10 | 217.6 | 145.0 | 124.8 | 89.6 |
| July 15 | 200.6 | 130.7 | 103.4 | 83.4 |
| July 20 | 316.1 | 208.0 | 168.0 | 125.2 |
The relationship between solar panel density (DD) and radiation attenuation (II) can be modeled as:I=I0⋅e−kDI=I0⋅e−kD
where I0I0 is open-field radiation, and kk is an attenuation coefficient (empirically derived as 0.012 per % density).
2. Air Temperature Regulation
Higher solar panel densities enhanced daytime cooling but had negligible nighttime effects (Table 2). Open-field daytime temperatures averaged 33.7°C, exceeding 50%, 75%, and 100% densities by 1.4–2.5°C. Nighttime temperatures differed minimally (<0.3°C), indicating that panels retain heat post-sunset.
Table 2. Air temperature (°C) under different solar panel densities.
| Parameter | 50% Density | 75% Density | 100% Density | Open Field |
|---|---|---|---|---|
| Daytime Average | 32.2 | 31.8 | 31.2 | 33.7 |
| Nighttime Average | 26.9 | 27.0 | 27.1 | 26.8 |
| Daily Maximum | 35.0 | 34.5 | 33.5 | 36.4 |
The cooling effect (ΔTΔT) during daytime follows:ΔT=α⋅D+βΔT=α⋅D+β
where α=−0.023α=−0.023°C/% and β=33.7β=33.7°C (open-field baseline).
3. Soil Temperature Dynamics
Soil temperatures beneath panels were consistently lower than open-field values (28.7°C vs. 27.4–28.3°C). The central zone exhibited smaller temperature fluctuations, while peripheral zones varied by up to 1.8°C (Figure 2). Reduced solar panel density increased soil warming, with 50% density showing 0.5–1.1°C higher temperatures than 100% density.
Table 3. Soil temperature (°C) under different solar panel densities.
| Zone | 50% Density | 75% Density | 100% Density | Open Field |
|---|---|---|---|---|
| Southern | 27.6 | 27.4 | 26.9 | 28.7 |
| Central | 28.8 | 28.6 | 28.9 | 28.7 |
| Northern | 27.5 | 27.4 | 27.3 | 28.7 |
Discussion
Our findings align with global agrivoltaic research. For instance, Marrou et al. (2013) observed 18% light reduction under PV arrays, while Ahmed et al. (2022) demonstrated 22–115x higher profits at 90% crop yield retention. The central zone’s superior radiation and thermal stability suggest that partial shading (e.g., 50–75% solar panel density) optimizes conditions for shade-tolerant crops like leafy greens or berries.
Conclusion
This study quantifies how solar panel density shapes the photothermal environment in agrivoltaic systems:
- Radiation Intensity: 50% density maximizes light penetration (113.8 W/m² vs. 66.4 W/m² at 100%).
- Temperature Regulation: Higher densities enhance daytime cooling (ΔT = -0.023°C/% density).
- Soil Stability: Central zones exhibit minimal thermal fluctuations, ideal for root development.
By adopting intermediate solar panel densities (e.g., 50–75%), stakeholders can mitigate land-use conflicts, enhance crop resilience, and sustain energy output. Future work should explore crop-specific responses and long-term soil health under varying solar panel configurations.