With the rapid development of the economy, increasing attention has been paid to energy, environment, and food security issues. The importance of optimizing energy structures and achieving clean and low-carbon development has been significantly heightened. Photovoltaic (PV) agriculture, which combines PV power generation with agricultural production activities, can maximize the utilization of land resources and enhance the land value per unit area. However, the shading caused by solar panel can alter the growth environment of crops underneath, thereby having a significant impact on them. Therefore, this study rationally transformed the traditional 100% solar panel coverage ratio into 75% and 50% coverage ratios, using open-air conditions as a control. It primarily focused on the influence of these three different solar panel coverage ratios on the photothermal environment within PV arrays, quantifying their photothermal environmental differences.
Peanut is one of the essential oil and cash crops, with a long history of cultivation and mature planting techniques in China. It has extensive suitable growing areas and independent and controllable production. Peanut has a strong substitute effect on imported soybeans. At the same time, as a temperature-loving crop, peanuts require light. The indirect shading from solar panel can affect their growth. Therefore, it is necessary to study the impact of the three different solar panel coverage ratios on peanut growth under PV arrays.
In this study, peanuts were used as the experimental material. Under field experimental conditions, the effects of ten treatments with 50%, 75%, and 100% solar panel coverage ratios in different areas on the growth and yield of peanuts at maturity were investigated. The study explored the impact of different solar panel coverage ratios on peanut growth under PV arrays, aiming to promote the efficient coupling of PV power generation and agricultural production. This has important theoretical and practical significance for the further sustainable development of PV agriculture.
The main findings are as follows:
- Impact of Different Solar Panel Coverage Ratios on the Photothermal Environment within PV Arrays:
- The solar radiation intensity, daytime air temperature, and soil temperature within PV arrays with different solar panel coverage ratios were significantly lower than those in the control group (CK). The relationship was: 50% > 75% > 100%.
- The soil moisture within PV arrays with different solar panel coverage ratios was higher than that in CK.
- Solar panel played a cooling effect on the internal air during summer days, with the cooling effect improving as the coverage ratio increased. At night, solar panel with different coverage ratios had a certain insulating effect on the internal air.
- Impact of Different Solar Panel Coverage Ratios on the Growth Characteristics of Peanuts at Maturity:
- Reducing the solar panel coverage ratio significantly promoted the growth of peanut agronomic traits such as plant height, stem diameter, root length, lateral branch length, effective branch number, fruit number, pod weight per plant, fresh weight, and dry weight. The relationship was: 50% > 75% > 100%.
- Impact of Different Solar Panel Coverage Ratios on the Physiological Characteristics of Peanuts at Maturity:
- The chlorophyll content of peanuts under different solar panel coverage ratios was lower than that in CK. Local shading of peanuts promoted chlorophyll synthesis in peanut leaves.
- Reducing the solar panel coverage ratio alleviated the impact of solar panel on the net photosynthetic rate (Pn), transpiration rate (Tr), and stomatal conductance (Gs) of peanut leaves, significantly improving their ability to assimilate intercellular CO2 (Ci), which was conducive to the smooth progress of photosynthesis and the accumulation of photosynthetic products in leaves.
- Impact of Different Solar Panel Coverage Ratios on Peanut Yield and Its Composition:
- The relationship between peanut yield and yield indicators under different solar panel coverage ratios was: 50% > 75% > 100%.
- Under the same solar panel coverage ratio, the relationship between peanut yield and yield indicators in different areas was: middle area (MA) > north area (NA) > south area (SA).
The study showed that the growth of peanuts under different solar panel coverage ratios significantly improved with the decrease in solar panel coverage. The growth of peanuts in the MA area was better than that in the SA and NA areas under the same solar panel coverage ratio. With the decrease in solar panel coverage, the growth differences of peanuts in the three areas under the panels were significantly reduced.
1. Research Purpose and Significance
Peanut (Arachis hypogaea L.), also known as the “groundnut,” belongs to the Rosales,Dicotyledoneae, and Fabaceae family. It is an oilseed crop with a long history of cultivation. Peanuts and peanut oil have been prevalent worldwide since the mid-19th century, and they are now one of the six major oilseed crops globally. Peanut cultivation is mainly concentrated in China, India, the United States, Indonesia, and Nigeria. Peanuts are an important source of edible oil and protein in China, with a protein content of over 30% that is easily absorbed by the human body. They are rich in vitamins and minerals that promote brain cell development, enhance memory, and have anti-tumor, anti-aging, and cardiovascular disease prevention effects. Currently, China faces a shortage of oilseed resources, with over 60% of edible oil raw materials relying on imports. Therefore, developing the peanut industry is of great significance.
Solar energy is one of the most common clean energy sources in nature, characterized by its long-term availability, infiniteness, and widespread presence. It can be directly developed and utilized without geographical restrictions, whether on land, sea, mountains, or islands, without the need for mining and transportation. Photovoltaic power generation utilizes the photovoltaic effect at the semiconductor interface to directly convert solar energy into electrical energy. As a low-carbon emission reduction method, photovoltaic power generation is pollution-free and environmentally friendly during the power generation process, occupying an indispensable position in the context of the dual-carbon goal. The global PV industry has developed rapidly in the 21st century, with the installed PV capacity continuously increasing. However, the development of ground-mounted PV power stations is increasingly constrained by the vast land they occupy. To promote the continuous development of the PV industry, it is urgent to find new suitable regions for large-scale PV installations.
In recent years, global developments have undergone significant changes, with the Russia-Ukraine conflict having a profound and lasting impact. Russia and Ukraine play crucial roles in global food production and supply. Their conflict has further deepened the global food and energy crises. Stimulated by these crises, the integration of agriculture and renewable energy has become a global topic of concern. Therefore, the integration of photovoltaic power generation technology into agricultural production is a natural response, known as PV agriculture. PV agriculture combines green and low-carbon energy with modern agriculture, maximizing the utilization of land resources and significantly increasing the economic value per unit area of land. As a large agricultural country, China’s PV agriculture can not only achieve energy conservation and environmental protection, contributing to the strategic goals of carbon peaking and carbon neutrality, but also promote agricultural transformation, increase farmers’ income, and comprehensively advance rural revitalization. Especially in the Yangtze River Delta region, due to land resource constraints, the combination of PV energy and modern agriculture is bound to further expand.
Scientific research and production practice have jointly proven that environmental factors are significant in influencing peanut yield. Studies have shown that the accumulation of biological mass primarily relies on the capture of light resources, and crop growth requires adequate light conditions. However, the shading from solar panels reduces the average available light for crops, altering their growth environment. Simultaneously, the unreasonable layout of PV arrays exacerbates the negative impact of solar panel shading on crops, resulting in weakened photosynthesis, reduced nutrient accumulation, increased disease incidence, and ultimately lower yields. Therefore, the inability to coordinate agriculture and PV can lead to low land utilization efficiency, ultimately affecting the sustainability of PV agricultural projects. Consequently, balancing PV power generation and agricultural production to create maximum value is the focus of research on the development of this new agricultural industry.
This study used peanuts as the experimental material, rationally transforming the traditional 100% solar panel coverage ratio into 50% and 75% coverage ratios. It investigated the impact of these three different solar panel coverage ratios on the photothermal environment within and outside PV arrays, quantifying their photothermal environmental differences. Through field experiments, the study examined the effect of changes in the photothermal environment under different solar panel coverage ratios on peanut growth. It aims to promote agricultural production quality and efficiency, facilitate the efficient coupling of PV power generation and agricultural production, and steer PV agriculture towards a more sustainable development path.
2. Current Research Status Domestically and Internationally
2.1 Research Status and Progress of PV Agriculture
With the popularization and development of the advantages of PV agriculture, many scholars domestically and internationally have discussed and researched PV agriculture and its key technologies, primarily focusing on the impact of PV module layout design on crop growth. In the implementation of PV agriculture, issues often arise due to unreasonable combinations of agriculture and PV, leading to the inability to achieve a win-win outcome for both PV power generation and agricultural production. Egyptian scholar Hassanien et al. studied the application of solar energy in environmental control, particularly the use of PV facilities in agriculture, and briefly analyzed their economic aspects. They proposed that the current significant challenge in PV agriculture is balancing PV power generation and agricultural output. The development of PV agriculture must simultaneously focus on power generation efficiency and agricultural benefits to ensure that the shading level under solar panels meets crop needs. Japanese scholar Kadowaki et al. investigated the impact of PV array arrangement on crop shading, testing linear and checkerboard PV array layouts with onions as the research object. They found that the fresh and dry weights of onions grown under PV panels were significantly lower than those of control cultivations. Marrou et al. designed PV arrays in full-density and half-density forms, causing approximately 70% and 50% shading effects, respectively, and compared them with open-air conditions to explore changes in lettuce growth morphology under the two density PV array conditions. The results showed that shade-tolerant and cool-loving crops like lettuce can adapt to reduced light exposure, and some crops can achieve higher yields under fluctuating shade. Cossu et al. installed a PV array with a roof area coverage ratio of 12.9% in a greenhouse and explored the impact of linear and checkerboard PV array shading on the growth of hydroponically grown onions. They concluded that crop growth was related to the reduced sunlight.
Domestic scholars Zhao Qunfa et al. studied the impact of PV panels with different shading densities on the growth and development of autumn-sown cucumbers. By laying three densities of PV panels, they clarified that different shading density PV panels had no impact on cucumber growth indicators. When the PV panels provided 60% shading, the main quality indicators of cucumbers significantly increased and reached their maximum values. The sustainable development of PV agriculture requires combining the characteristics of PV facilities to find suitable crop varieties for planting. Huang Yanguo et al. studied the impact of shading conditions in PV agriculture on the agronomic traits, yield, and quality of Chinese herbal medicines, selecting three herbal medicines and establishing a controlled experiment. The results showed that the yield of Pinellia ternata under shading conditions was 34% higher than that of the control, while the yields of Glycyrrhiza uralensis and Radix Isatidis were slightly lower than those of the control. In 2018, American scholar Hassanpour et al. discussed the impact of PV panels on the environment of frequently water-stressed unirrigated grasslands, quantifying the impact of PV panels on microclimate, soil moisture, water use, and biomass productivity. The results showed that areas under PV panels maintained higher soil moisture, with a 90% increase in later biomass and a 328% improvement in water efficiency. Wu Longfei et al. compared the impact of PV modules on the microenvironment of ordinary greenhouses and PV greenhouses and on the net photosynthetic rate of strawberry leaves. The results showed that the internal air temperature of PV greenhouses was always lower than that of ordinary greenhouses, which was beneficial to the improvement of the net photosynthetic rate of strawberry leaves. In 2021, Hua Yongxin et al. conducted an adaptability study on PV arrays of the same height but with different structures, selecting multiple common vegetables for planting under PV panels and setting up同步种植 comparison tests in open spaces around the power station. The results showed that the erection of PV panels had a certain impact on lighting conditions. Although the tested crops could adapt to the growth environment within PV power stations to obtain output, their yields and quality were affected to varying degrees.
2.2 Research Status and Progress on the Photothermal Environment of PV Agriculture
PV agriculture is a green and environmentally friendly industrial model that combines PV power generation with agricultural production. However, due to the lack of practical experience and unclear changes in the photothermal environment, it is prone to blind development and resource waste. Therefore, exploring the complex impact of PV modules on their photothermal environment is beneficial for the benign development of PV agriculture.
Currently, the development of PV agriculture is still in the exploratory stage, with most scholars focusing on research in the field of PV greenhouses. The coupled development of PV power generation and open-field planting still requires continuous innovation and exploration. Chen Xugen et al. proposed a novel PV power generation greenhouse and raindrop irrigation system that could adjust the orientation of PV panels based on the light intensity outside the greenhouse, enhancing power generation efficiency. In 2013, Zhao Xue et al. continuously tested and analyzed the photothermal environment of PV greenhouses, comparing them with plastic film solar greenhouses. The results showed that although the light environment in PV solar greenhouses was approximately 20% weaker than that in plastic film solar greenhouses, there were no significant differences in tomato yield and quality between the two greenhouses. Canadian scholar Bambara et al. used semi-transparent PV to verify the energy model of a greenhouse concept. This model was used to compare the energy performance of comprehensive greenhouses and vertical farm concepts, both employing semi-transparent PV. The results showed that the solar power generation of vertical farms was 49% less than that of greenhouses, with a 31% reduction in heating consumption, while their cooling energy demands were roughly equal. In 2016, Italian scholar Cossu et al. proposed an algorithm that could calculate the cumulative direct and diffuse radiation in PV greenhouse areas over desired time intervals and at different canopy heights. This algorithm could be applied to various PV greenhouse types and provide a decision support tool for identifying the most suitable plant species based on their lighting needs. Ye Lin et al. studied the impact of different PV module materials such as amorphous silicon, monocrystalline silicon, and polycrystalline silicon on the greenhouse photothermal environment and established controlled experiments. The results showed that the greenhouse with amorphous silicon had smaller temperature and humidity fluctuations and higher light transmittance, making it more suitable for the development needs of PV agriculture in Ningxia. Moroccan scholar Ezzaeri et al. studied the impact of PV panels on the photothermal environment within greenhouses. The PV panel area accounted for 10% of the total roof area. The results showed that the PV panel occupancy rate in the greenhouse had no significant impact on climatic parameters. Wang Biao et al. used Ecotect software to explore the impact of PV modules on the lighting radiation environment for crop growth at different times and under different solar altitude angles, clarifying that PV greenhouses were suitable for crop growth and further providing a reliable theoretical basis for the optimal design of PV greenhouses.
2.3 Response Mechanism of Peanut Growth to Photothermal Environmental Conditions
Chen Xiaoshu et al. proved through a low-temperature stress experiment on peanut seedlings that peanuts prefer warmth and require higher temperatures during their growth process. In 2017, Xie Minghui et al. used pot experiments to study the impact of different temperatures, soil moisture, and sowing depths on peanut seed germination and seedling growth. The conclusions were that increased temperature could enhance peanut emergence rate, plant height, lateral branch number, above- and belowground fresh weights, chlorophyll content, and root activity. Specifically, when the soil relative humidity was 60%, the emergence rate and seedling growth of peanuts were superior to those at 40% and 80% relative humidity. At 80% soil relative humidity, the rotting rate of peanut seeds significantly increased, especially under high temperatures and deep sowing conditions. The most suitable sowing depth was 4-6 cm.
In 2016, Yang Shunguo et al. conducted shading treatment experiments on peanuts and found that shading increased the main stem height, shortened lateral branches, reduced the number of branches, decreased dry matter accumulation, reduced the relative chlorophyll content of leaves, and lowered the photosynthetic rate, particularly during the later growth stages. Overall, these changes were detrimental to the normal growth of peanuts, ultimately leading to reduced yields. Zhang Tianyu et al. studied the impact of different mulching materials on peanut growth and found that mulching could significantly increase soil water content, regulate soil temperature, accelerate peanut photosynthesis, and enable a more reasonable distribution of dry matter, thereby increasing peanut yield. Gao Guoqing et al. statistics indicated that drought-induced peanut yield reductions averaged over 20% of the national total yield. Zhang Zhimeng et al. used artificial simulations of drought conditions to discover that the degree and duration of water stress significantly impacted peanut plant morphology, biomass accumulation, and physiological indicators, with notable interspecific differences. Dai Liangxiang et al. adopted full-growth-period artificial water control pot experiments and found that soil water stress affected the mineral element content of peanut kernels. The above analysis of the impact of photothermal environmental conditions on peanut crop growth shows that this crop is suitable for planting in high summer temperatures and is not conducive to growing under shading conditions, having specific requirements for temperature and humidity. In recent years, China’s peanut imports have also increased. Planting peanuts under solar panel can expand the effective production area of peanuts and serve as a typical case for exploring the combination of PV power generation and agricultural production, with practical industrial demand and research significance.
3. Existing Problems
In summary, domestic and international research on the photothermal environmental conditions of PV agriculture and their impact on crop growth has been extensively carried out. However, current research on the impact of PV panel layout density and arrangement on crop growth is almost entirely theoretical, with few reports on the practical application effects of PV power generation and crop production. Therefore, experiments on different PV panel arrangements and laying densities are needed to deeply explore the adaptive performance of peanuts to PV panel shading.
Since light, temperature, soil temperature, and soil water play vital roles in the crop growth process, it is essential to study the changes in the photothermal environment under different solar panel coverage ratios in field environments and their impact on peanut growth and development. Simultaneously, research on how to promote the coordinated development of PV power generation and agricultural production, and create maximum value for the balanced development of the industry, is of great theoretical and practical significance for the healthy and sustainable development of PV agriculture in China.
Compared with foreign countries, domestic research on PV agriculture started relatively late, and most studies have focused more on PV greenhouses. There is less systematic research on the integration of open PV systems with agriculture. Additionally, peanuts are important economic crops, and research on the impact of PV panel shading on their growth is rare both domestically and internationally. Furthermore, from a crop cultivation perspective, peanuts possess good growth characteristics and are easy to cultivate and manage. Peanuts are also light-loving crops, and shading from PV panels has a significant impact on their growth. Therefore, selecting peanuts as the research object to explore the impact of different PV panel coverage ratios on the photothermal environment within the PV array and on their growth, physiology, and yield, can supplement the lack of basic theoretical research and poor practical application effects in PV agriculture. This research has unique significance.
In summary, this study aims to address the following gaps in existing research:
- Practical Application of PV Panel Density and Arrangement: Current research primarily focuses on theoretical analyses, lacking experimental validation of the practical effects of different PV panel densities and arrangements on crop growth. This study aims to bridge this gap through field experiments.
- Field Environment Photothermal Environment Study: It is crucial to understand how photothermal environments change under different PV panel coverage ratios in field settings and how these changes affect peanut growth and development.
- Coordinated Development of PV and Agriculture: Promoting the coordinated development of PV power generation and agricultural production is essential for creating maximum value and ensuring the balanced development of the industry. This study explores strategies to achieve this goal.
- Research on Light-Loving Crops like Peanuts: Given the lack of research on the impact of PV shading on light-loving crops like peanuts, this study specifically focuses on peanuts to provide insights into their adaptive performance under different PV panel coverage ratios.
- Systematic Research on Open PV Systems: Unlike most studies that focus on PV greenhouses, this research examines open PV systems, which are more prevalent in practical applications, to provide a more comprehensive understanding of PV agriculture.
By addressing these gaps, this study aims to contribute to the further development of PV agriculture towards sustainability, providing theoretical and practical guidance for the efficient coupling of PV power generation and agricultural production.