17:15 〜 19:15
[AGE34-P16] Effect of Photovoltaic Panels on Soil Water and Temperature Dynamics
キーワード：ソーラーシェアリング、太陽光発電
1. Introduction
In recent years, interest in renewable energy has been rising due to growing awareness of global warming. Photovoltaic (PV) systems dominate the renewable energy use in Japan (Siecker et al., 2017). However, commercial adoption remains limited in Japan because the land is very small and the land suitable for PV systems is also suitable for agriculture. Therefore, solar sharing systems are gaining attention. This system combines agriculture and power generation by installing PV panels on cultivation fields.
The shading effect of PV panels, however, cannot be ignored with this system. According to Yue et al. (2021), soil moisture content increases during the rainy season and soil temperature increases in winter and decreases in summer in arid areas. However, there are few studies investigating the effect on soil moisture and temperature by PV panels in temperate regions such as Japan. This study therefore aims to clarify the effect of shade of PV panels on soil water and energy dynamics.
2. Methods
2.1 Measurements
The experimental site is located at TUAT FM Fuchu. Three observation points were set up: one with a high density of PV panels (H), one with a low density of PV panels (L), and one with no panels (C). Sensors were installed at the midpoint of the PV Panels (NO), directly below the PV panels (PV), and at the point affected by rainfall from the PV panels (CR). Sensors were installed at 10 cm intervals up to a depth of 40 cm. The observation period was from June 25 to December 9, 2024, with the measurement interval was 10 minutes.
2.2 Simulation
HYDRUS-2D (Šimůnek et al., 2018) was used in this research. HYDRUS-2D is a versatile program that can simultaneously solve the governing equation of liquid water and water vapor flow, as well as energy transport. The program was modified to account for PV panel shading.
The top boundary conditions for water flow were determined from AMeDAS data, while the boundary conditions for energy transport were determined by solving the surface energy balance equation.
3. Results and Discussion
3.1 Measurements
The monthly averaged soil temperature was lower at the site installed PV panels compared to no panels site both in August and November. This result indicates that PV panels have a cooling effect on soil. The difference between H and L differs greatly between August and November. In summer, sun’s altitude is higher and shadows are shorter. Therefore, solar radiation reaching the soil varies significantly with PV panel density. As a result, a large difference is expected between H and L. On the other hand, sun’s altitude is lower and shadows are longer in winter. Consequently, the shading duration between H and L is similar in winter.
3.2 Simulation
Simulated soil temperature data at the NO point from June 25 to July 22, 2024, were compared to observations. Similar to the observation, the soil temperature was lower in H than in C. However, the simulated values differ significantly from observed values. Soil hydraulic and thermal properties need to be adjusted for better prediction.
4. Conclusions
The seasonal difference became clear from the observations. The measured relationship between H and C was reproduced by simulation with modified HYDRUS. Observations in the presence of crops and measurements of radiation under PV panels are expected to improve simulation accuracy. More accurate simulation might better estimate soil moisture dynamics and temperature changes.
References
Siecker, J., et al., 2017. Renewable and Sustainable Energy Reviews, 79, pp.192-203.
Yue, S., et al., 2021. Environmental Science and Pollution Research, 28, pp.17506-17518.
In recent years, interest in renewable energy has been rising due to growing awareness of global warming. Photovoltaic (PV) systems dominate the renewable energy use in Japan (Siecker et al., 2017). However, commercial adoption remains limited in Japan because the land is very small and the land suitable for PV systems is also suitable for agriculture. Therefore, solar sharing systems are gaining attention. This system combines agriculture and power generation by installing PV panels on cultivation fields.
The shading effect of PV panels, however, cannot be ignored with this system. According to Yue et al. (2021), soil moisture content increases during the rainy season and soil temperature increases in winter and decreases in summer in arid areas. However, there are few studies investigating the effect on soil moisture and temperature by PV panels in temperate regions such as Japan. This study therefore aims to clarify the effect of shade of PV panels on soil water and energy dynamics.
2. Methods
2.1 Measurements
The experimental site is located at TUAT FM Fuchu. Three observation points were set up: one with a high density of PV panels (H), one with a low density of PV panels (L), and one with no panels (C). Sensors were installed at the midpoint of the PV Panels (NO), directly below the PV panels (PV), and at the point affected by rainfall from the PV panels (CR). Sensors were installed at 10 cm intervals up to a depth of 40 cm. The observation period was from June 25 to December 9, 2024, with the measurement interval was 10 minutes.
2.2 Simulation
HYDRUS-2D (Šimůnek et al., 2018) was used in this research. HYDRUS-2D is a versatile program that can simultaneously solve the governing equation of liquid water and water vapor flow, as well as energy transport. The program was modified to account for PV panel shading.
The top boundary conditions for water flow were determined from AMeDAS data, while the boundary conditions for energy transport were determined by solving the surface energy balance equation.
3. Results and Discussion
3.1 Measurements
The monthly averaged soil temperature was lower at the site installed PV panels compared to no panels site both in August and November. This result indicates that PV panels have a cooling effect on soil. The difference between H and L differs greatly between August and November. In summer, sun’s altitude is higher and shadows are shorter. Therefore, solar radiation reaching the soil varies significantly with PV panel density. As a result, a large difference is expected between H and L. On the other hand, sun’s altitude is lower and shadows are longer in winter. Consequently, the shading duration between H and L is similar in winter.
3.2 Simulation
Simulated soil temperature data at the NO point from June 25 to July 22, 2024, were compared to observations. Similar to the observation, the soil temperature was lower in H than in C. However, the simulated values differ significantly from observed values. Soil hydraulic and thermal properties need to be adjusted for better prediction.
4. Conclusions
The seasonal difference became clear from the observations. The measured relationship between H and C was reproduced by simulation with modified HYDRUS. Observations in the presence of crops and measurements of radiation under PV panels are expected to improve simulation accuracy. More accurate simulation might better estimate soil moisture dynamics and temperature changes.
References
Siecker, J., et al., 2017. Renewable and Sustainable Energy Reviews, 79, pp.192-203.
Yue, S., et al., 2021. Environmental Science and Pollution Research, 28, pp.17506-17518.