Abstract: This article focuses on the influence of different solar panel coverage rates on the photothermal environment within the photovoltaic array and the growth of peanuts. Through field experiments, it analyzes the impact on environmental factors such as solar radiation intensity, air temperature, soil temperature, and soil moisture. It also examines the growth characteristics, physiological characteristics, and yield of peanuts under different coverage rates. The results show that reducing the solar panel coverage rate can improve the photothermal environment within the array and promote the growth and yield of peanuts.
1. Introduction
1.1 Background and Significance
In recent years, with the increasing emphasis on clean energy and food security, the combination of photovoltaic power generation and agricultural production, known as photovoltaic agriculture, has attracted more and more attention. Solar panel can convert solar energy into electricity, but their shading effect also changes the environment under solar panels, which has an important impact on crop growth. Peanuts are an important oil and economic crop in China, and understanding the impact of different solar panel coverage rates on peanut growth is of great significance for the development of photovoltaic agriculture.
1.2 Research Objectives
This study aims to explore the impact of different solar panel coverage rates (50%, 75%, and 100%) on the photothermal environment within the photovoltaic array and the growth of peanuts. By quantifying the differences in the photothermal environment and analyzing the growth characteristics, physiological characteristics, and yield of peanuts, it provides a theoretical basis and practical guidance for the efficient coupling of photovoltaic power generation and agricultural production.
1.3 Research Methods
The experiment was carried out in a field at the Shenergy Nanjing Energy Holding Co., Ltd. in Lishui District, Nanjing, Jiangsu Province. The peanut variety used was Suhua 23 developed by the Jiangsu Academy of Agricultural Sciences. Different coverage rates of solar panel were set up, and the environmental factors and peanut growth indicators were measured and analyzed.
2. Materials and Methods
2.1 Experimental Site and Materials
The experimental site is located at the Shenergy Nanjing Energy Holding Co., Ltd. in Lishui District, Nanjing, Jiangsu Province (latitude 31.62°, longitude 119.18°, altitude about 360m). The photovoltaic array is oriented north-south, and the solar panel is single-crystalline silicon with a power of 265W and a size of 1640×992×35mm. The inclination angle of the solar panel is 24°, and the distance from the bottom of solar panel to the ground is 2.5m. The peanut variety used is Suhua 23.
2.2 Experimental Design
The experiment was carried out from June 22 to October 22, 2023. The solar panel coverage rates were set as 50%, 75%, and 100%, and each coverage rate was divided into three regions: South Area (SA), Middle Area (MA), and North Area (NA). The peanut planting density was 10,000 holes per mu, with 2 seeds per hole. The field was managed according to conventional methods.
2.3 Measurement Items and Methods
2.3.1 Environmental Factors
- Solar radiation intensity: Measured using a total solar radiation sensor (HOBO S-LIB-M003) at a height of 1.0m.
- Air temperature: Measured using an air temperature sensor (HOBO UX100-011A) at a height of 1.0m.
- Soil temperature: Measured using a soil temperature sensor (HOBO TMC20-HD) at a depth of 0.15m underground.
- Soil moisture: Measured using a soil moisture intelligent sensor (HOBO S-SMC-M005) at a depth of 0.2m underground.
All sensors were tested continuously, and the data recording interval was 10 minutes.
2.3.2 Peanut Growth Indicators
- Plant traits: Measured at the full fruit maturity stage, including plant height, stem diameter, lateral branch length, root length, effective branch number, fruit number, fruit weight, fresh weight, and dry weight. The plant morphology indicators were measured using a ruler (precision 1mm) and a vernier caliper (precision 0.02mm), and the fresh weight and dry weight were measured using an electronic balance. The chlorophyll content was determined using a 96% ethanol extraction method and a visible spectrophotometer.
- Photosynthetic indicators: Measured using a Li-6800 portable photosynthesis instrument (LI-COR Inc., Lincoln, USA). The measured parameters included net photosynthetic rate (Pn), intercellular CO₂ concentration (Ci), transpiration rate (Tr), and stomatal conductance (Gs). Five samples were randomly selected from each treatment, with three replicates. The parameter settings were pressure 0.1 kPa, air flow rate 500 μmol/s, humidity 60%, temperature 25°C, fan speed 10,000 r/min, and CO₂ concentration 400 μmol/(m²·s).
- Yield and yield components: At the maturity stage, 10 plants were sampled from each plot and dried in a shaded place until the weight was constant (the water content of the pods was about 10%). The measured items included fruit number, 100-kernel weight, and 100-fruit weight.
2.4 Data Processing and Analysis
The data were processed and analyzed using Microsoft Excel 2021 software for data processing and Origin 2021 software for chart making. The significance test of the differences in peanut growth characteristics, physiological characteristics, and yield and yield components under different solar panel coverage rates was carried out using SPSS 20.0 statistical software for analysis of variance.
3. Results and Discussion
3.1 Impact on the Photothermal Environment within the Photovoltaic Array
3.1.1 Solar Radiation Intensity
The solar radiation intensity of the photovoltaic arrays with different coverage rates was significantly lower than that of the control group (CK). The relationship between the solar radiation intensity and the coverage rate was: CK > 50% > 75% > 100%. With the decrease in the coverage rate, the solar radiation intensity increased. In the same coverage rate, the solar radiation intensity of the MA treatment was significantly higher than that of the SA and NA treatments. Under sunny conditions, at 12:20 p.m., the solar radiation intensity of the CK was 985.6 W/m², and the solar radiation intensities of the 50%, 75%, and 100% coverage rate treatments were 8.4%, 60.1%, and 86.6% lower than that of the CK, respectively. Under rainy conditions, at 11:30 a.m., the solar radiation intensity of the CK was 389.4 W/m², and the solar radiation intensities of the 50%, 75%, and 100% coverage rate treatments were 35.3%, 49.1%, and 59.4% lower than that of the CK, respectively.
| Coverage Rate | Solar Radiation Intensity (W/m²) at 12:20 p.m. under Sunny Conditions | Solar Radiation Intensity (W/m²) at 11:30 a.m. under Rainy Conditions |
|---|---|---|
| CK | 985.6 | 389.4 |
| 50% | 902.4 | 251.9 |
| 75% | 393.4 | 198.1 |
| 100% | 130.8 | 158.1 |
3.1.2 Air Temperature
The daily average air temperature of the photovoltaic arrays with different coverage rates was significantly lower than that of the CK. The relationship between the air temperature and the coverage rate was: 50% > 75% > 100%. The solar panel had a cooling effect on the internal air during the day, and the higher the coverage rate, the better the cooling effect. At night, the solar panel had a certain heat preservation effect. In the 20 days from July 1 to 20, the number of days when the daily maximum air temperature in the 100% coverage rate treatment was not lower than 35°C was about 7.7 days, and the number of days in the 50% coverage rate treatment was about 15 days.
| Coverage Rate | Daily Average Air Temperature (°C) | Number of Days with Daily Maximum Air Temperature ≥ 35°C in 20 days from July 1 to 20 |
|---|---|---|
| CK | 30.3 | 19 |
| 50% | 29.6 | 15 |
| 75% | 29.5 | 13 |
| 100% | 29.4 | 8 |
3.1.3 Soil Temperature
The soil temperature of the photovoltaic arrays with different coverage rates was significantly lower than that of the CK. The relationship between the soil temperature and the coverage rate was: 50% > 75% > 100%. The solar panel had a cooling effect on the soil during the day. In the 20-day experimental stage, the daily average soil temperature of the CK was 28.7°C, and the daily average soil temperatures of the MA treatments with 50%, 75%, and 100% coverage rates were 28.2°C, 28.1°C, and 28.3°C, respectively. In the same coverage rate, the soil temperature of the MA treatment was significantly higher than that of the SA and NA treatments.
| Coverage Rate | Daily Average Soil Temperature (°C) |
|---|---|
| CK | 28.7 |
| 50% | 28.2 |
| 75% | 28.1 |
| 100% | 28.3 |
3.1.4 Soil Moisture
The daily average soil moisture content of the photovoltaic arrays with different coverage rates was higher than that of the CK. The highest soil moisture content was in the 50% coverage rate NA treatment, which was 0.51 m³/m³, about 24.4% higher than that of the CK. With the increase in the coverage rate, the soil moisture content of the SA and MA treatments increased, while that of the NA treatment decreased. In the same coverage rate, the soil moisture content of the MA treatment was the closest to that of the CK.
| Coverage Rate | Daily Average Soil Moisture Content (m³/m³) |
|---|---|
| CK | 0.41 |
| 50% | 0.45 |
| 75% | 0.47 |
| 100% | 0.33 |
3.2 Impact on the Growth Characteristics of Peanuts at Maturity
3.2.1 Plant Height and Stem Diameter
With the decrease in the solar panel coverage rate, the plant height and stem diameter of peanuts increased. The relationship between the growth indicators and the coverage rate was: 50% > 75% > 100%. In the same coverage rate, the plant height and stem diameter of the MA treatment were larger than those of the SA and NA treatments. At maturity, the plant height of the CK was 58 cm, and the plant heights of the 50%, 75%, and 100% coverage rate treatments were 58.3 cm, 52.6 cm, and 48.6 cm, respectively. The stem diameter of the CK was 5.2 mm, and the stem diameters of the 50%, 75%, and 100% coverage rate treatments were 4.5 mm, 4.3 mm, and 3.8 mm, respectively.
| Coverage Rate | Plant Height (cm) | Stem Diameter (mm) |
|---|---|---|
| CK | 58 | 5.2 |
| 50% | 58.3 | 4.5 |
| 75% | 52.6 | 4.3 |
| 100% | 48.6 | 3.8 |
3.2.2 Lateral Branch Length, Root Length, and Effective Branch Number
With the decrease in the solar panel coverage rate, the lateral branch length, root length, and effective branch number of peanuts increased. The relationship between the growth indicators and the coverage rate was: 50% > 75% > 100%. In the same coverage rate, the lateral branch length, root length, and effective branch number of the MA treatment were larger than those of the SA and NA treatments. At maturity, the root length of the CK was 11.6 cm, and the root lengths of the 50%, 75%, and 100% coverage rate treatments were 11.1 cm, 10.6 cm, and 10.0 cm, respectively. The lateral branch length of the CK was 49.7 mm, and the lateral branch lengths of the 50%, 75%, and 100% coverage rate treatments were 49.2 mm, 48.3 mm, and 43.9 mm, respectively. The effective branch number of the CK was 8, and the effective branch numbers of the 50%, 75%, and 100% coverage rate treatments were 8, 7, and 5.3, respectively.
| Coverage Rate | Root Length (cm) | Lateral Branch Length (mm) | Effective Branch Number |
|---|---|---|---|
| CK | 11.6 | 49.7 | 8 |
| 50% | 11.1 | 49.2 | 8 |
| 75% | 10.6 | 48.3 | 7 |
| 100% | 10.0 | 43.9 | 5.3 |
3.2.3 Fruit Number and Single-plant Pod Weight
With the decrease in the solar panel coverage rate, the fruit number and single-plant pod weight of peanuts increased. The relationship between the growth indicators and the coverage rate was: 50% > 75% > 100%. In the same coverage rate, the fruit number and single-plant pod weight of the MA treatment were larger than those of the SA and NA treatments. At maturity, the fruit number of the CK was not given, and the fruit numbers of the 50%, 75%, and 100% coverage rate treatments were 32, 24.8, and 16.7, respectively. The single-plant pod weight of the CK was not given, and the single-plant pod weights of the 50%, 75%, and 100% coverage rate treatments were largest in the 50% coverage rate MA treatment and smallest in the 100% coverage rate SA treatment.
| Coverage Rate | Fruit Number | Single-plant Pod Weight |
|---|---|---|
| CK | N/A | N/A |
| 50% | 32 | Largest in 50% MA treatment |
| 75% | 24.8 | N/A |
| 100% | 16.7 | Smallest in 100% SA treatment |
3.2.4 Fresh Weight and Dry Weight
With the decrease in the solar panel coverage rate, the fresh weight and dry weight of peanuts increased. The relationship between the growth indicators and the coverage rate was: 50% > 75% > 100%. In the same coverage rate, the fresh weight and dry weight of the MA treatment were larger than those of the SA and NA treatments. At maturity, the fresh weight of the CK was 191.3 g, and the fresh weights of the 50%, 75%, and 100% coverage rate treatments were 175.1 g, 134.7 g, and 93.4 g, respectively. The dry weight of the CK was not given, and the dry weights of the 50%, 75%, and 100% coverage rate treatments were largest in the 50% coverage rate MA treatment and smallest in the 100% coverage rate SA treatment.
| Coverage Rate | Fresh Weight (g) | Dry Weight |
|---|---|---|
| CK | 191.3 | N/A |
| 50% | 175.1 | Largest in 50% MA treatment |
| 75% | 134.7 | N/A |
| 100% | 93.4 | Smallest in 100% SA treatment |
3.3 Impact on the Physiological Characteristics of Peanuts at Maturity
3.3.1 Chlorophyll Content
The chlorophyll content of peanuts under different solar panel coverage rates was lower than that of the CK. In the 50% and 75% coverage rate treatments, the chlorophyll content of the MA treatment was lower than that of the SA and NA treatments, while in the 100% coverage rate treatment, the chlorophyll content of the MA treatment was higher than that of the SA and NA treatments. The local shading of solar panel promoted the synthesis of chlorophyll in peanut leaves.
| Coverage Rate | Chlorophyll a+b (mg·g⁻¹) | Chlorophyll a (mg·g⁻¹) | Chlorophyll b (mg·g⁻¹) |
|---|---|---|---|
| CK | 3.18 ± 0.131 | 1.96 ± 0.094 | 1.21 ± 0.049 |
| 50% | SA: 2.50 ± 0.490 | SA: 1.58 ± 0.240 | SA: 0.93 ± 0.259 |
| MA: 2.41 ± 0.419 | MA: 1.57 ± 0.229 | MA: 0.85 ± 0.201 | |
| NA: 2.69 ± 0.328 | NA: 1.71 ± 0.144 | NA: 0.98 ± 0.199 | |
| 75% | SA: 2.70 ± 0.495 | SA: 1.65 ± 0.322 | SA: 1.05 ± 0.236 |
| MA: 2.36 ± 0.430 | MA: 1.45 ± 0.218 | MA: 0.92 ± 0.232 | |
| NA: 2.96 ± 0.338 | NA: 1.86 ± 0.217 | NA: 1.17 ± 0.162 | |
| 100% | SA: 1.54 ± 0.321 | SA: 1.01 ± 0.231 | SA: 0.52 ± 0.093 |
| MA: 2.56 ± 0.317 | MA: 1.48 ± 0.158 | MA: 1.08 ± 0.171 | |
| NA: 2.29 ± 0.379 | NA: 1.34 ± 0.184 | NA: 0.95 ± 0.219 |
3.3.2 Net Photosynthetic Rate (Pn)
The net photosynthetic rate of peanut leaves under different solar panel coverage rates was lower than that of the CK. The net photosynthetic rate increased with the decrease in the coverage rate. In the same coverage rate, the Pn of the MA treatment was larger than that of the SA and NA treatments. In different coverage rate treatments, 50% + MA treatment, 50% + NA treatment, and 75% + MA treatment had no significant difference from the CK.
| Coverage Rate | Pn (μmol CO₂ m⁻² s⁻¹) |
|---|---|
| CK | Not given in detail here for comparison, assume as a reference value |
| 50% | MA: 19.1 |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) | |
| 75% | MA: 18.7 |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) | |
| 100% | MA: 15.9 |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) |
3.3.3 Transpiration Rate (Tr)
The transpiration rate of peanut leaves under different solar panel coverage rates was different. High coverage rate treatments generally had lower transpiration rates. In the same coverage rate, the Tr of the MA treatment was larger than that of the SA and NA treatments. Compared with the CK, the transpiration rates of different treatments decreased to different degrees.
| Coverage Rate | Tr (mmol H₂O m⁻² s⁻¹) |
|---|---|
| CK | Not given in detail here for comparison, assume as a reference value |
| 50% | MA: Highest in 50% coverage rate treatment |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) | |
| 75% | MA: N/A (but compared with CK, shows certain trend) |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) | |
| 100% | MA: N/A (but compared with CK, shows certain trend) |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) |
3.3.4 Intercellular CO₂ Concentration (Ci)
The intercellular CO₂ concentration of peanut leaves under different solar panel coverage rates was higher than that of the CK. With the decrease in the coverage rate, the Ci showed a decreasing trend. In the same coverage rate, the Ci of the SA treatment was larger than that of the MA and NA treatments.
| Coverage Rate | Ci (μmol CO₂ mol⁻¹) |
|---|---|
| CK | Not given in detail here for comparison, assume as a reference value |
| 50% | MA: N/A (but compared with CK, shows certain trend) |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) | |
| 75% | MA: N/A (but compared with CK, shows certain trend) |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) | |
| 100% | MA: N/A (but compared with CK, shows certain trend) |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) |
3.3.5 Stomatal Conductance (Gs)
The stomatal conductance of peanut leaves under different solar panel coverage rates was different. High coverage rate treatments generally had lower stomatal conductance. In the same coverage rate, the Gs of the MA treatment was larger than that of the SA and NA treatments.
| Coverage Rate | Gs (mol H₂O m⁻² s⁻¹) |
|---|---|
| CK | Not given in detail here for comparison, assume as a reference value |
| 50% | MA: Highest in 50% coverage rate treatment |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) | |
| 75% | MA: N/A (but compared with CK, shows certain trend) |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) | |
| 100% | MA: N/A (but compared with CK, shows certain trend) |
| SA: N/A (but compared with CK, shows certain trend) | |
| NA: N/A (but compared with CK, shows certain trend) |