Photovoltaic Panel System with Optical Dispersion of Solar Light for Greenhouse Agricultural Applications

Abstract

This paper presents an innovative design of a photovoltaic panel system for agricultural applications, particularly in regions prone to drought and extreme temperatures, known as Agri-PV. The proposed solution utilizes optical elements of divergent lens types to illuminate the ground beneath photovoltaic panels in greenhouse or indoor controlled cultivation areas. The Agri-PV solution improves the ratio between the area occupied by the photovoltaic panels and the total cultivated area therefore the land under the photovoltaic panels is fully cultivable, produces clean electricity that can be used in the agricultural process, reduces solar energy at the ground level up to 16 times, reducing water evaporation from the ground diminishing the summer-extreme temperatures effect on crops. With an optimal vertical layout of the optical lens PV system, areas of minimum illumination can be overlapped to provide a more uniform and consistent light intensity at ground level. The overall illumination uniformity is important for maximizing energy efficiency and maintaining optimal growing conditions in agrivoltaics applications.

1. Introduction

Agriculture is central to sustaining the global population, playing a critical role in providing food, supporting economic development, and sustaining livelihoods. However, the sector faces many challenges. This sector supports people’s lives, is responsible for the population’s well-being, and plays a crucial role in driving the world economy’s development.

As the global population continues to rise, pressure on the food supply system will intensify. According to the United Nations Food and Agriculture Organization (FAO), food production must increase by 60% by 2050 to meet the demands of the growing population [1]. As the global population is projected to reach 9.7 billion by 2050, the demand for food is expected to increase by approximately 50% by 2050 [2]. At the same time, a third of agricultural land is under threat of degradation, a direct consequence of both natural processes and human-induced activities, including poor agricultural practices [1]. This situation has raised concerns about the sustainability of agriculture and the potential for land degradation, underscoring the need for the development of more sustainable agricultural practices to ensure the future of global food security. Maintaining fertile soils and healthy farmland for future generations has never been more crucial than it is now. Currently, there are three challenges to existing agricultural production, as follows: (1) The impact of climate variability and extreme weather on agricultural production [3]. Climate change has exacerbated the risks faced by agriculture globally, affecting production in many regions. Agricultural yields are highly sensitive to temperature fluctuations, drought, and extreme weather events, including floods and storms. Studies show that climate variability has already reduced agricultural productivity in several areas, particularly in regions that are highly dependent on rain-fed agriculture [4]. For example, extreme weather events are responsible for substantial crop loss, leading to food insecurity and economic instability in vulnerable regions [5]; (2) Pressure on the food supply as the global population increases [6]. This demand comes at a time when agricultural land is shrinking, partially due to urbanization and land degradation; (3) Decrease in agricultural land due to desertification [7]; Desertification and soil degradation are significant concerns that threaten the capacity of agricultural lands to produce food. According to the United Nations Convention to Combat Desertification (UNCCD), over 75% of the world’s land area is affected by some form of degradation, resulting in a loss of biodiversity and agricultural productivity. Desertification is often driven by unsustainable agricultural practices, deforestation, and climate change [8]. On the other hand, the increasing global population and rising living standards lead to a rapid increase in the energy required. The traditional reliance on non-renewable energy sources such as fossil fuels has led to resource depletion and contributed to the worsening of climate change through the emission of greenhouse gases (GHGs), particularly CO₂. The agricultural sector is also a significant contributor to global emissions, primarily through the use of synthetic fertilizers, transportation, and livestock production [9]. Transitioning to renewable energy is thus a crucial strategy for mitigating climate change and reducing the environmental impact of agriculture.

Agrivoltaics integrates solar energy production with agriculture, allowing photovoltaic (PV) systems to generate electricity while farmers perform their activities beneath the panels. This dual use of land has the potential to enhance land use efficiency and promote sustainability [10]. The recent decrease in the cost of photovoltaic panels and improvements in solar energy conversion technologies have made solar energy more competitive with other energy sources. Furthermore, the efficiency of agrivoltaics systems has been enhanced with the development of advanced materials and technologies, such as bifacial solar panels, which capture sunlight from both the front and rear sides, improving energy production [11]. Agrivoltaics not only provide renewable energy but can also have positive effects on crop yields. Studies have shown that certain crops benefit from the shading provided by solar panels, which can help reduce water evaporation and lower temperatures during hot summer months, potentially increasing agricultural productivity in drought-prone areas [12,13,14]. Additionally, the revenue generated from selling electricity can help offset the financial risks faced by farmers, making the adoption of solar technologies more financially feasible [15]. Traditional non-renewable energy (energy sources using fossil fuels) has to deal with fossil resource depletion and important greenhouse gas emissions (especially CO₂) as well as excessive environmental pollution. This has prompted a continuous search for efficient alternative solutions for renewable electricity production [16,17,18,19,20].

It is known that the effects of global warming have left their mark, especially on the decrease in agricultural production due to excessively high temperatures at the soil level, which leads to significant evaporation of water from the soil. The effect is all the more intense as the cultivated areas are located in the planet’s warm regions, and the final outcome is the desertification of the soil and a reduction in cultivable areas.

The proposed technical solution’s specific scope encompasses sustainable energy production processes, with applications in stimulating plant growth in agriculture by reducing solar radiation at the soil level, thereby reducing the evaporation of water from the soil necessary for plant development, and increasing the sustainability of farms [21,22,23].

The implementation of Agri-PV in farms requires a long-term evaluation of costs. However, the agricultural application affects the design of the agrivoltaics system due to different cultivation areas, variety, specific geographic and micro-climatic issues, and last but not least, the cost of implementation [24,25,26].

The proposed system fulfills two essential tasks simultaneously: first, it preserves the original agricultural purpose of the agricultural areas, and second, it generates clean solar energy. Since agriculture is a complex system of various factors, the solution chosen for Agri-PV must be tailored to the specific characteristics of the agricultural area, as well as the type of plants cultivated, which enables the optimization of both the technical-ecological and technical-economic potential of the cultivated land [18,27]. Currently, two main applications of Agri-PV are known: interspace PV [28,29] and aerial/overhead PV. In interspace PV technology, the area intended for growing plants is positioned between the rows of solar panels mounted on the ground, in different geometric positions and orientations determined by the sun’s position. The interspace PV solution has the disadvantage of requiring the separation of land intended for mounting photovoltaic panels from cultivated land. In this case, only the distances between the rows of photovoltaic panels allow the cultivation of agricultural land. Also, the land under the photovoltaic panels cannot be cultivated. In the interspace PV solution, crops grow between rows of ground-level modules spaced far apart, permitting machinery to pass through. In the case of the aerial photovoltaic system, crops are grown under the elevated solar modules [30].

The overhead PV solution involves significant gaps between the photovoltaic panels to illuminate the cultivated soil. This solution has the disadvantage that the ratio between the area occupied by the photovoltaic panels and the total area is minimal, so the use of land for electricity production is reduced. The technical problem that the system proposed solves is that the ratio between the surface occupied by the photovoltaic panels and the total surface is improved, and the land surface placed under the photovoltaic panels is fully cultivated [31,32,33].

Apart from the classical Agri-PV mentioned above, several emerging PV technologies for agriculture have emerged in the past few years. The following are examples: The Swiss start-up Insolight developed a system that concentrates the sunlight through lenses on highly efficient solar panels while most of the diffuse sunlight is diverted to the plants [34]. The Franco–German company ASCAA developed organic photovoltaics (OPVs) based on different wavelength-selective transparency absorption properties of PVs. The OPV provides high transparency for the wavelength in the solar spectrum between 400 and 700 nm, where photosynthesis takes place [35]. In the USA, the company Soliculture developed a semi-transparent, low-density crystalline cell made of a luminescent material [36,37,38,39]. In this case, a part of the incident light is absorbed by the luminescent dye while the rest of the light is transmitted to the plants. The OPV modules have been implemented in greenhouses in France [40]. The technology of wavelength-selective concentrating photovoltaics (CPVs) involves coupling the concentrator with a dichroic mirror. These mirrors reflect the near-infrared spectrum allowing the visible spectrum to pass through. The agrivoltaics CPV system has been developed and tested in China, yielding promising results [41]. The TubeSolar German company also developed modules based on the fluorescent tube production of OSRAM/LEDVANCE, providing homogenous shading and lower costs in terms of the mounting structure. Another solution is bifacial photovoltaic arrays, which could significantly increase the energy produced by the PVs by using both sides of the solar panel [42,43,44,45,46].

In [28], it is also concluded that agrivoltaics present a promising solution for addressing the growing demands for both food and energy. However, challenges remain in optimizing these systems for different climates and agricultural settings. Further research is necessary to enhance the integration of PV systems with agricultural practices, improve efficiency, and ensure sustainability. Moreover, optimizing lighting conditions is crucial for enhancing crop productivity in controlled environments. Advances in lighting technologies, such as LEDs, can improve resource efficiency and yields. Future research should focus on fine-tuning these conditions to maximize sustainability and food production [47].

The focus of the paper is on an innovative system of photovoltaic panels designed for electricity production, with applications in agriculture, specifically Agri-PV, which utilizes divergent lens optical elements to illuminate the ground beneath the photovoltaic panels for greenhouse and indoor controlled cultivated areas. Moreover, an agrivoltaics system can provide direct protection against environmental factors such as rain, hail, and wind, rather than traditional methods like nets, windbreaks, and other protective solutions. This research introduces an innovative Agri-PV system that integrates divergent lens optical elements to enhance light distribution beneath photovoltaic panels, optimizing greenhouse agriculture. Unlike conventional interspace PV and aerial PV solutions, which either restrict cultivable land or create shading challenges, our approach simultaneously preserves agricultural productivity, reduces soil evaporation, and generates clean energy. Thus, by tailoring the Agri-PV technology to specific agricultural and ecological conditions, this solution optimizes both the technical-ecological and technical-economic potential of cultivated land, contributing to more sustainable and efficient farming practices. Moreover, it preserves agricultural productivity by regulating soil-level solar radiation, reducing water evaporation, and assuring an optimal environment for plant growth.

2. Materials and Methods

2.1. Experimental Setup

The presented Agri-PV system with divergent lenses addresses greenhouses located in areas with excessive solar radiation, with the potential of severe drought, and proposes a possibility to decrease the solar energy at ground level in these greenhouses. Considering that the energy produced can be stored in batteries, this energy can be used to supplement lighting in greenhouses on cloudy days when sunlight is diminished due to weather conditions. The proposed system involves covering greenhouses or closed cultivated spaces with a system of photovoltaic panels separated by a bifocal lens that disperses sunlight under the solar panels in the greenhouse, as in Figure 1.

The Agri-PV lens addresses the critical need for efficient agricultural land use by integrating an advanced Agri-PV system. In areas where dust accumulation on PV systems and lenses is a concern, a design solution could involve utilizing the irrigation water from greenhouses to clean the lenses and PV panels. This could be achieved by incorporating a sprinkler system that simultaneously irrigates the plants and washes the panels, ensuring optimal performance by utilizing available resources. This system features a structure of photovoltaic panels mounted along an axis, with at least one row of divergent lenses positioned between the panels. These lenses are designed with a radius of curvature R and a focal distance f, both precisely matching the length L of the photovoltaic panels, as illustrated in Figure 2 and Figure 3, where 1 and 2 are the two adjacent photovoltaic panels, 3 is the optical divergent lenses while l_p is the width of the PV.

The technical problems that the Agri-PV solution solves are as follows:

• The ratio between the area occupied by the photovoltaic panels and the total area is improved, therefore the land area located under the photovoltaic panels is fully cultivable;
• Produces clean electricity that can be used in the agricultural process—at the limit, a self-sustainable independent agricultural unit can be reached;
• Reduces solar energy at ground level, reducing water evaporation from the ground and diminishing the summer-extreme temperatures’ effect on crops.
• The proposed Agri-PV system allows the greenhouse to be closed and the cultivated interior to be isolated from aggressive environmental factors, especially excessive heat. It requires to use of a greenhouse ventilation system. The electrical energy produced by the photovoltaic panels can thus be used for ventilation, air conditioning with water vapor recovery, and water reuse for crop irrigation. Additionally, the energy can be stored in the battery and may be used for supplementary greenhouse lighting during periods of low solar radiation.

Figure 2 represents the Agri-PV system with divergent lenses for light dispersion, where 1 and 2 are the photovoltaic panels, 3 is the lens, H_L is PV distance to the ground, lp width of the PV, L is and the lens width x. The angle α is the angle of the PVs along the y-axis of the Agri-PV system, and angle β is the angle of the PVs along the x-axis.

The Agri-PV system permits the control of the energy radiated by the sun at ground level by controlling the light intensity. Reducing the amount of solar energy transmitted to these surfaces during the hottest moments of the day reduces heat stress on plants cultivated in environment-controlled greenhouses. As light intensity decreases, electricity generated by PV systems can be supplemented with artificial LED-based lighting to maintain optimal illumination in greenhouses, providing a cost-effective solution. This may compensate for the reduced natural light while regulating photosynthesis to support plant growth, while energy-efficient LED lighting further optimizes conditions, ensuring stable greenhouse production year-round.

2.2. Theoretical Approach

To highlight the effects of light incidence angles on ground illumination through the optical dispersion system, a small-scale experimental model was created in the laboratory It was thus possible to simulate the effect of the apparent movement of the sun during the day, angle α, and of the azimuth in the annual position of the sun, angle β.

It was considered that the light in the greenhouses reaches the ground level only through the lenses mounted between the PVs. The system that allows for the illumination of the soil beneath solar panels used in agriculture takes into account the light distribution of the diverging biconcave lens, as presented schematically in Figure 3.

The light geometry for a divergent bifocal lens used in the Agri-PV system seeks to determine the geometric dimensions of the lens, the radius of curvature R, the lens width x, and the focal distance f, so that the system allows the complete illumination of the ground under the solar panel positioned at a distance H_L from the ground, determined by the technological requirements for growing plants. According to Figure 3, in the triangles ABC and ADE meet Equations (1) and (2) [48]:

$${\displaystyle \frac{\mathrm{x}}{\mathrm{l}}}={\displaystyle \frac{\mathrm{f}}{\mathrm{f}+\mathrm{H}}}$$

(1)

$$\mathrm{f}={\displaystyle \frac{\mathrm{R}}{2·\left(\frac{{\mathrm{n}}_{\mathrm{L}}}{{\mathrm{n}}_{\mathrm{A}}}-1\right)}}$$

(2)

where n_L and n_A are the refraction index for lens material (Clear Plexiglass—n_L = 1.5) and for air (n_A = 1), respectively. The focal distance f ≈ R (thin lens). According to the lens dimension, to simplify the calculus, we considered the system as a thin lens (with a minimum thickness of 5 mm).

Considering that the lens is made of glass, in this case of a thicker lens, the focal distance will be calculated accordingly. We opted for divergent lenses to disperse the light.

The lens width x can be expressed as follows:

$$\mathrm{x}=2·\mathrm{R}·\sin {\displaystyle \frac{\phi }{2}}$$

(3)

where α is the angle of the con light in point A (α= φ/2):

$$\sin {\displaystyle \frac{\phi }{2}}={\displaystyle \frac{\mathrm{l}}{\sqrt{{\left(\mathrm{H}+\mathrm{R}\right)}^2+{\mathrm{l}}^2}}}$$

(4)

$${\displaystyle \frac{\mathrm{x}}{2}}={\displaystyle \frac{\mathrm{R}·\mathrm{l}}{\sqrt{{\left(\mathrm{H}+\mathrm{R}\right)}^2+{\mathrm{l}}^2}}}$$

(5)

For a distance H_L = 3 m from the ground, lp = 0.7 m, and R = 0.05 m, the lens width results in x = 0.012 m. By multiplying Equation (1) with panel length L, it can be found the ratio between the area of lens S_L and the panel area S_p:

$${\displaystyle \frac{{\mathrm{S}}_{\mathrm{L}}}{{\mathrm{S}}_{\mathrm{p}}}}={\displaystyle \frac{\mathrm{R}}{\mathrm{R}+\mathrm{H}}}$$

(6)

$$\mathrm{K}={\displaystyle \frac{{\mathrm{S}}_{\mathrm{p}}}{{\mathrm{S}}_{\mathrm{L}}}}=1+{\displaystyle \frac{\mathrm{H}}{\mathrm{R}}}$$

(7)

For the considered parameters, the panel area resulted in S_p = 60 * S_L.

The theoretical analysis highlights the feasibility of determining the ground-illuminated area by optimizing the geometric parameters of the lens (R, x) or by vertically adjusting the position of the Agri-PV panel system, which comprises the panel and lens. In Figure 4, the evolution of the ratio between the illuminated area of the ground and the area of the lens K = S_p/S_L, depending on the parameters H and R, is presented, where the following values are considered:

R (the lens radius): R1 = 0.04 m; R2 = 0.05 m; R3 = 0.06 m; R4 = 0.08 m; R5 = 0.1 m.

H (the distance to the ground of PVs): H1 = 1 m; H2 = 1.5 m; H3 = 2 m; H4 = 2.5 m; H5 = 3 m.

Based on the specific agricultural technological requirements, the radius of curvature of the lens (R) and the lens width (x) can be determined, or, if allowed by the design of the Agri-PV system, the distance (H) from the ground can be adjusted by vertically repositioning the lens-panel assembly. Given that the luminous intensity I_x (lx) is defined as the ratio of the luminous flux (cd) to the illuminated area (I_x = cd/m²), the variation in luminous intensity at ground level is also influenced by the evolution of the area ratio S_p/S_L.

3. Results and Discussion

To investigate the effects of bifocal divergent lenses on the area covered by solar panels, an experimental setup was designed comprising a closed enclosure, referred to as a dark box, with dimensions of height H = 25 cm, length l = 35 cm, and width w = 23 cm. The described experiments, as well as the performed measurements, were conducted in the year 2024. The lens was made of four bifocal divergent lenses with dimensions 6 cm × 1.5 cm fabricated from Plexiglass and mounted on the upper section of the box, as illustrated in Figure 5. The experimental setups involved two configurations: (1) positioning the dark box under a lamp at a predefined distance H_L, with light perpendicular to the lens assembly, and (2) exposing the dark box directly to sunlight, where the incident angle of sunlight varied throughout the day but was initially aligned as closely as possible to perpendicular to the lens assembly. For each configuration, light intensity was measured using a calibrated light meter to assess the dispersion effect of the lenses on the panel area. Additionally, the distance between the light source and the lenses was monitored to ensure consistent experimental conditions. In our study, the Gossen MavoSpec Base was used to assess light intensity within the experimental setup. This spectrometer provided precise measurements of illuminance (lux), ensuring an accurate evaluation of the lighting conditions in our greenhouse model. The device was chosen for its ability to measure the spectral power distribution and its sensitivity and accuracy ensured reliable data collection for both artificial and natural lighting scenarios within our setup.

As proposed in this study, the Agri-PV system with divergent lenses is particularly suitable for greenhouses in regions characterized by excessive solar radiation and a high risk of severe droughts. In such areas, combining high solar energy input and water scarcity can challenge crop growth and energy efficiency. Integrating divergent lenses with photovoltaic systems enables a controlled reduction of solar radiation at ground level within the greenhouse. This reduction can help maintain optimal temperature and light conditions for plant growth, mitigating the adverse effects of overheating and excessive light intensity on crops. Moreover, the system enhances energy efficiency by capturing and converting solar energy into electricity, which can be used to power irrigation systems or supplemental artificial lighting, further enhancing crop yield.

3.1. Assessment of Controlled Illumination Using an Artificial Light Source

In the first setup, the dark box was positioned beneath a lamp at a distance H_L = 30 cm from the box lid, with light directed perpendicular to the lens assembly. The lamp used in the experiment is specifically designed for solar panel testing. For the experiment, a solar module CO3208-1B with a solar altitude emulator allowing to investigation of a variety of irradiation scenarios and incidence angle of light towards PVs has been used. The system uses a 500 W halogen lamp with a dimmer, providing 100 klx on the divergent lens at the top of the box, and can simulate adjustable module inclination, adjustable solar altitude, and adjustable solar azimuth.

As shown in Figure 6, the light spectrum emitted by the halogen lamp exhibits a higher intensity in the wavelength range corresponding to the red region of the spectrum. As this is a characteristic feature of halogen lamps, which typically emit more energy in the red portion of the spectrum compared to other wavelengths, we considered this spectral characteristic in our analysis, as the red light is known to play a significant role in plant growth. If a halogen lamp generates light with a red-shifted spectrum, the temperature drop at ground level through the optical system is significant (a difference in temperature of 10–13 °C).

Considering the relative movement of the Sun or the potential rotation of the photovoltaic panels in the y0z-plane, light intensity measurements of the illuminated area in the x0y-plane were taken for three angle values α = 0°, 23°, and 40°, as illustrated in Figure 7.

It was observed that the maximum luminous intensity occurs when the light source is perpendicular to the lens surface. The reduction of the light intensity was more than 10 times at the simulated ground level, at the bottom of the box. The maximum luminous intensity was recorded in the perpendicular direction under the divergent lenses, reaching a value of 7 klx. The luminous intensity decreases as the distance from the point of maximum illumination increases, reaching a value of 1 klx at a distance of 15 cm from the origin. In order to scale up the system to real dimensions, Equation (6) can be used; Equation (6) shows the ratio between the area of the lens and the area of the PV panel as a function of distance to the ground. The reduction of the luminous intensity at ground level can be obtained by an appropriate ratio between the area of the lens and the area of the PV panel, depending on the height of the PV position relative to the ground (Figure 4a). As plant growth is highly dependent on specific wavelengths, particularly in the photosynthetically active radiation range, the proposed system is based on the dispersion of sunlight.

Similar results for the variation in light intensity were obtained with respect to the distance y. This reflects the fact that the same distribution of light intensity is obtained for the apparent motion of the sun relative to the Earth (variation of the angle of incidence of light during the day). As the angle α decreases, the maximum light intensity at y = 0 cm also decreases, with intensity variations measured at distances y = {−15, −10, −5, 0, 5, 10, 15} cm. Additionally, in all cases, the light intensity decreases along the y-direction, with the minimum measured value corresponding to a y-coordinate equal to the width of the photovoltaic panel, l.

The light intensity of the illuminated area in the xy plane was measured for three different values of angle β (0°—horizontal, 23°, 40°). The results are presented in Figure 8. Similarly, in this case, the reduction in light intensity was more than 10 times at the simulated ground level.

It was observed that the maximum luminous intensity is achieved when the light source is perpendicular to the lens surface. As the angle β decreases, the maximum light intensity at x = 0 also decreases. Similar results for the light intensity were obtained for the variation with distance x. This reflects the fact that the same distribution of light intensity is obtained for the apparent motion of the sun relative to the earth (variation of the angle of incidence of light during the year), the differences being around 10 ÷ 15%. Moreover, across all cases, the minimum intensity is observed at the boundary of the illuminated area, enhancing our expectation for the predictability of light distribution with varying Sun angles. These results highlight the importance of optimizing lens orientation and positioning to maximize light utilization in agrivoltaics applications, ensuring consistent illumination for plant growth throughout seasonal changes.

The intensity of light at ground level, and thereby the amount of solar energy available, can be varied by adjusting the position of the solar panels along the z-axis, due to changes in the distribution and concentration of light transmitted and dispersed. As the panels are elevated or descended, the geometric dispersion of light flowing through the optical system varies, affecting both the illuminated area and the intensity dispersion.

The study demonstrates that adjusting the height of solar panels has a significant impact on the geometric dispersion of light, influencing both the size of the illuminated area and the distribution of light intensity. When the panels are positioned higher, the light spreads over a broader area but with reduced intensity, whereas lowering the panels concentrates the light on a smaller region, increasing its intensity. This relationship, illustrated in Figure 9, reveals that light intensity along the z-axis follows a second-order polynomial function, indicating a nonlinear correlation between panel height and ground-level illumination. These results highlight the importance of precise panel height optimization to balance light distribution and intensity, thereby ensuring optimal growing conditions for crops while maintaining efficient energy generation in agrivoltaics systems.

A second approach to assessing light intensity at ground level, both with and without the use of divergent lenses, involved employing a mini solar test panel with dimensions of 6 cm × 6 cm, positioned at ground level, while it was exposed directly to sunlight. In this setup, the current intensity, I (mA), generated by the photovoltaic (PV) test panel was measured using a milliammeter connected to the solar panel’s output. The experimental results outlined in Figure 10 highlight the impact of integrating divergent lenses into the solar radiation dispersion system. Under identical conditions, the mini-solar test system with divergent lenses demonstrates a noticeable decrease in the maximum solar energy intensity at the ground reference point (x, y, z = 0) by a factor of approximately 16 compared to the system without lenses. This is due to the light being redistributed over a larger area, rather than being concentrated at a single point. Therefore, this emphasizes the efficiency of the optical system in controlling light dispersion, which is particularly desirable in agrivoltaics applications where excessive solar radiation could hamper plant growth. Thus, by dispersing the light more evenly, soil evaporation is reduced, maintaining optimal growing conditions and improving the overall efficiency of the PV system.

For the direct evaluation of the temperature with and without the divergent lens, a metal plate measuring 23 × 30 cm was exposed to light radiation with the lens and through direct exposure. The effects of light radiation were highlighted by measuring the temperature on a black metal plate using a FLIR T650sc thermal imaging camera. The thermal images of the metal plate with and without the lens are shown in Figure 11. It was observed that the temperature of the plate exposed directly to the light radiation from the lamp was 13.3 °C higher than the temperature of the plate exposed to light that passed through the divergent lens.

Figure 12 presents a graphical representation of the total light intensities received by two adjacent photovoltaic panels, PV-1 and PV-2. By summing the individual light intensities measured for each panel, the figure allows for a direct comparison of their performance under identical experimental conditions. This combined intensity analysis is crucial for understanding how light distribution varies when panels are positioned in proximity, as overlapping illumination zones can lead to a more uniform energy capture or potential shading effects. Additionally, the results provide insights into optimizing panel alignment to maximize solar energy utilization and minimize intensity fluctuations across the photovoltaic array.

Through optimal positioning of the panels, it is possible to achieve nearly constant ground illumination. This is evident from the trendline, marked in red, which demonstrates a stable intensity profile across the measured area. The data suggest that optimal panel arrangement can minimize fluctuations in light intensity, thereby improving the consistency of energy capture from the illuminated surface.

3.2. Assessment of Natural Illumination Under Direct Sunlight

In the second experimental setup, the dark box was positioned directly under sunlight, with the light incident perpendicular to the lens assembly. The luminous intensity of the sunlight, measured outside the dark box at the level of the lenses, was recorded as 114 klx.

Light intensity was measured along the y-axis, and the variation of light intensity concerning the distance y is presented in Figure 13. It can be observed that, when using divergent lenses, the maximum light intensity at ground level decreases by a factor of four. Similar to the experimental setup with the lamp, the light intensity follows a second-degree polynomial function, decreasing towards the edges of the dark box. This behavior highlights the distribution of light intensity across the illuminated area and the impact of the divergent lenses on the intensity profile.

Figure 14 illustrates the spectral analysis of sunlight, showing the distribution of light intensity over different wavelengths as measured in our experimental setup. The output reveals a relatively uniform spectral distribution compared to the lamp used in previous experiments, which exhibited a higher intensity in the red wavelength range. Therefore, it directly affects the efficiency of the PV system and the amount of light that is dispersed to the ground. The spectral composition of the incident sunlight provides insight into variations in energy availability at ground level with and without diverging lenses, thereby strengthening the relevance of spectral profiles in optimizing the performance of the Agri-PV system.

Unlike the spectrum of light produced by the lamp, the spectrum of sunlight exhibits a more uniform light intensity across all wavelengths, indicating a broader and more continuous range of energy. In a similar manner, a mini solar test panel with dimensions of 6 cm × 6 cm was utilized to measure solar energy at ground level, both with and without the use of divergent lenses. The current intensity generated by the photovoltaic (PV) test panel was measured using a milliampere meter connected to the panel’s output, providing a direct measurement of the electrical output in response to the incident solar radiation. The data shown in Figure 15 depict the effect of the divergent lenses on the electrical output of the mini solar test panel, comparing its performance with and without the optical elements under identical experimental conditions. This comparison illustrates how solar energy redistribution impacts energy conversion efficiency. The results indicate that the maximum solar energy at ground level (x, y, z = 0) is reduced by a factor of about 8 when diverging lenses are used. This significant reduction demonstrates the ability of lenses to alter the spectral distribution of light, dispersing it over a wider area instead of concentrating it at a single point. This effect is essential in agrivoltaics applications, where controlled light dispersion can prevent excessive shading while ensuring suitable power generation. Furthermore, this highlights the importance of optimizing lens design and panel positioning to achieve a uniform distribution of solar energy for optimal agricultural productivity and PV efficiency.

The observed gap, relative to the previous case where the energy reduction was measured using the solar test panel (resulting in a 16-fold decrease), can be attributed to differences in the spectral characteristics of the light sources. By contrast to the artificial lamp, which exhibited a higher intensity in certain wavelength intervals, natural sunlight has a broader and more evenly dispersed spectrum. Therefore, as the efficiency of PV panels is wavelength-dependent, particularly with higher wavelengths, the spectral composition of the light source inherently affects the measured energy savings. The light spectrum of the lamp exhibits a more uniform distribution of light intensity over all wavelengths, while the solar light contains a broader range of wavelengths, making the solar panels more sensitive to higher wavelengths. The efficiency of photovoltaic panels is well known to decrease for wavelengths extending into the infrared region, where energy conversion is less efficient. This spectral gap is likely to account for the observed difference in energy reduction between the two configurations. This gap highlights the importance of considering spectral properties when assessing light transmission and energy distribution in Agri-PV systems.

As in the previous experimental setup, the temperature was measured directly with and without the use of the divergent lens by exposing the same metal plate (23 × 30 cm) to light radiation both through the lens and directly. Temperature measurements were acquired using a FLIR T650sc thermal imaging camera, which provided high-resolution thermal images of the plate under both conditions. The resulting thermal images of the metal plate, with and without the diverging lens, are shown in Figure 16, illustrating the differences in temperature distribution associated with each exposure method.

As in the previous case, it has been observed that the temperature of the metal plate exposed to direct sunlight is 10 °C higher than the temperature of the plate exposed to light traveling through the diverging lens. For the research hypothesis, it is assumed that the sun behaves as a light source at an effectively infinite distance, resulting in nearly constant light intensity at both the lens surface and the ground. This uniform exposure to light at both points allows a more accurate comparison of the temperature differences observed when using divergent lenses.

Table 1. Energy reduction for both experimental configurations.

Energy Measurement	Energy Reduction Lamp Light	Energy Reduction Sun Light
Light intensity ratio IL/Ig (lx/lx)	14	5
PV test panel IL/Ig (mA/mA)	16	8
Temperature gradient ΔT (°C)	10	10

summarizes the main results for the two tested configurations.

The observed differences between the two experimental configurations—one using a lamp as a light source and the other exposing the black box directly to sunlight—can be assigned to the distinct geometrical characteristics of the light sources. The light emitted by the lamp exhibits a conical geometric dispersion in space, resulting in a variation in light intensity throughout the illuminated area. However, the light from the sun, due to its great distance from the Earth, maintains an almost uniform intensity over the distance z from the lens to the ground. This uniformity of sunlight intensity also contributes to the differences observed in the experimental results. The light intensity remains within a suitable range for photosynthesis, ensuring adequate plant development. Additionally, temperature reduction can be beneficial in preventing heat stress, especially in warm climates.

This Agri-PV at a real accurate scale depends on installation costs, maintenance expenses, and potential yields. The initial investment includes photovoltaic panels, the optical system, and a supporting structure for the PVs. We opted for divergent lenses to disperse the light. Future studies will explore the feasibility of Fresnel lenses in similar applications, as well as create a ray tracing diagram of the transmission and dispersion phenomena for the diverging lens. Moreover, the system provides dual benefits in terms of renewable energy production and sustained agricultural productivity. The light intensity at ground level provided by the optical system ensures adequate plant growth, which can increase crop yields. The return on investment (ROI) depends on factors such as energy production income and improved agricultural yields. Further research will conduct a detailed cost-benefit analysis based on specific regional conditions, aimed at assessing the long-term cost-effectiveness and feasibility of the Agri-PV system.

4. Conclusions

Overall, this study concludes that the proposed Agri-PV solution offers a sustainable and innovative approach to integrating PV systems in agriculture. The experiment was carried out in two stages: (1) exposure of the PV system and diverging lenses to natural solar radiation, to highlight the full spectral distribution of sunlight and the effect of the light dispersion at a predetermined distance from the ground in the experimental model; (2) exposure of the miniaturized model to artificial light from a lamp, to analyze the effects of the angle of incidence of light during the relative motion of the sun, through variations of alpha and beta angles, concerning the solar displacement during the year and seasonal changes. The divergent lenses placed between the solar panels allow a significant reduction of solar energy at ground level, up to 16 times less. The maximum luminous intensity, recorded at 7 klx, was observed in the perpendicular direction beneath the divergent lenses. As the distance from this peak increases, the luminous intensity gradually decreases. At a distance of 15 cm from the point of maximum illumination, the intensity decreases to 1 klx. This evolution in light intensity follows a pattern influenced by the dispersion of light through the divergent lenses, which cause the light to spread out over a larger area, reducing its concentration. To achieve a suitable vertical positioning of the optical lens-PV system, the areas of minimum illumination may be overlapped to attain a constant light intensity on the ground. The light intensity was decreased by 14 times in the laboratory model, and the energy produced by the mini solar PV test was reduced by 16 times. In the case of the monitored temperature, it decreased by 10 degrees for the divergent lens system. The results can be extrapolated to the real scale of a greenhouse to assess their impact on PV system performance and energy efficiency in a real agricultural environment. This paper addresses a solution to reduce the light radiation at ground level in greenhouses, in areas where the solar radiation is excessive, the output energy of the PV corresponds to the technical characteristics of the PV, and the incident solar radiation. The results obtained in this study represent an essential starting point for our future research aimed at developing an integrated Agri-PV system with dispersive lenses, applicable at full scale. The electrical energy produced by the photovoltaic panels can be used for greenhouse ventilation, air conditioning with water vapor recovery, and reuse for crop irrigation. Eventually, the energy can be stored in the battery and used for additional greenhouse lighting during periods of low solar radiation. Compared to other Agri-PV solutions, our system optimizes land-use efficiency by allowing simultaneous energy generation and agricultural production without significantly shading crops. Unlike conventional Agri-PV which may reduce crop yields due to excessive shading, our approach balances energy and agricultural outputs, making it a suitable solution for sustainable farming. Future studies will investigate the impact of dusting on optical performance and explore potential cleaning solutions, while real-world test conditions will provide valuable insights into long-term maintenance requirements. Future research will include spectral analysis to ensure that the dispersed light remains optimal for photosynthesis.