Integration of Crops, Livestock, and Solar Panels: A Review of Agrivoltaic Systems

Abstract

This review article focuses on agrivoltaic production systems (AV). The transition towards renewable energy sources, driven by the need to respond to climate change, competition for land use, and the scarcity of fossil fuels, has led to the consideration of new ways to optimise land use while producing clean energy. AV systems not only generate energy but also allow agricultural and livestock yields to be maintained or even increased under PV structures, offering a sustainable production strategy that may be more acceptable to local communities than traditional PV installations. This review assesses the technical feasibility of AV systems, the environmental, economic and social benefits, as well as the challenges faced and the legal framework regulating their implementation. It is highlighted that despite the advantages in land use efficiency and dual food and energy production, there are important challenges related to the initial investment required, the need for technological adaptation, social and regulatory obstacles, or the effects of shading on production. This paper underlines the importance of further research and development of these systems to overcome technical and economic constraints and maximise their potential benefits. It is concluded that although they present significant challenges, AV management offers promising opportunities to improve land efficiency and contribute to several sustainable development goals.

1. Introduction

Context: In recent decades, the need for a transition towards renewable energy sources has been gaining momentum in the face of the growing climate crisis and the depletion of fossil fuels. Electricity consumption grew from 11,000 TWh in 1990 to 26,000 TWh in 2022, and electricity demand is estimated to increase by 9% between 2023 and 2025 [1]. Climate neutrality by 2050 is the main objective of the EU Green Deal [2,3], so this transition to clean energy production is necessary. In order to reach 70% renewable energy production by 2030, Europe needs to produce an additional 48 GW from solar panels [4], which cannot be achieved by rooftop photovoltaic (PV) installations alone. Such installations have gained strength due to the decreasing price of their main component, solar panels, but they are space-intensive, and it is necessary to start mounting PV installations on other soils, such as agricultural land [5]. Using this type of soil to produce PV energy is a sensitive topic: there is competition for land and a conflict between food and fibre production and energy generation [6]. Moreover, the proliferation of such facilities is taking place at full speed, without adequate spatial planning [7], and often faces resistance from local stakeholders [8,9]. In this context, agriphotovoltaic production—also known as solar sharing, agrophotovoltaic, agriphotovoltaic, agrivoltaic, AV, or APV—emerges as an innovative solution that combines PV power generation with agriculture on the same land. In such management, the primary function of these agricultural soils is the production of a crop, while production by PV panels is a secondary use [10]. Given its ability to generate clean energy while maintaining or even improving crop yields, AV is positioned as a key strategy in the search for sustainable production systems. Furthermore, given the inclusion of agricultural production, it may be more widely accepted than traditional solar panel installations: Pascaris et al. [11] found that more than 80% of respondents would be more willing to support the development of PV installations in their communities if agricultural production is integrated into them.

Justification: The review of AV production is crucial at the present time in view of several factors. First, there is a growing concern for soil health and its vision as a potentially renewable resource. This means that we are becoming increasingly aware of the limits of soil use and its fragility, which makes it necessary to implement production methods that maximize efficiency without compromising food and resource security. Second, in recent years, there has been a rapid evolution of PV technology, which has improved the economic and technical feasibility of AV systems. Third, the growing of the agricultural and energy sectors in coexistence models can provide diversified income streams to the landowners while contributing to overall sustainability goals. The interest in this type of technique is reflected in the increasing publication of articles related to the field. For example, a quick Scopus search for publications that include the term agrivoltaics in the title, abstract or keywords will return 337 results, of which 297 are dated from 2021 onwards. This means that almost 90% of the publications are less than four years old. There are two recent reviews on the subject, both published in 2024. However, one of them [12] only includes studies up to 2022, while the other includes articles up to March 2024 [13], but they deal with agroforestry systems focused on fruit trees only. This makes it necessary (given the speed at which this field is expanding) to conduct a new review of the existing literature. These developments underline the importance of compiling and synthesizing current research to guide future implementations and studies.

Objectives: The specific objectives of this article are: (i) review the current status of AV technology and its practical application in diverse agricultural and agroforestry contexts; (ii) assess the environmental, economic, and social benefits derived from the integration of PV with agriculture; (iii) analyse the performance of AV systems; (iv) identify the main challenges and technical constraints facing the adoption of AV production; (v) examine the status of this type of exploitations at the policy level; and (vi) propose directions for future research that can overcome these barriers and maximise the potential of this innovative solution. Through this in-depth analysis, we aim to provide a comprehensive overview that can guide both researchers and decision-makers interested in the convergence of renewable solar energy and sustainable agricultural production, offering examples of AV systems in different parts of the globe and with heterogeneous set-ups, climatic conditions, and crops.

2. Methodology

Methodology: Literature search. To carry out this review of the existing literature on AV production, several academic databases were systematically consulted, including Web of Science, Scopus, PubMed, and Google Scholar. The keywords used for the search were combinations of “agri-voltaics”, “agri-voltaic systems”, “agro-photovoltaics”, “solar energy and agriculture”, and “dual energy and crop production”. Related terms were also used to capture studies on the environmental, economic, social, and crop yield effects associated with the implementation of AV technology. More specific searches were limited to articles published in English and Spanish from 2015 to date to reflect the most current technologies and practices. However, for more generic concepts and more consolidated ideas, as well as to find data from real experiments using AV practices, this search range was extended not only on a temporal level but also to other kinds of materials (books, manuals, journals, etc.).

Criteria and selection process: Several criteria were used to select the articles that form the basis of the review, as outlined below. First, we identified those studies that provide empirical data on the implementation and functioning of AV systems. Secondly, other reviews and analyses that discuss the environmental, economic, or social impacts of AV production were taken into consideration. Thirdly, we looked for articles, legal texts, and reports that provide an insight into the policy context in which these practices take place and the incentives that exist to implement them. Finally, we considered documents related to specific case studies that offer insights into the practical applications and operational challenges of implementing such management.

Initially, on 20 March 2024, a total of 294 published articles were identified through a very simple literature search (only using the term “agrivoltaic” in Scopus). After an initial review of titles, keywords and abstracts, 129 articles were excluded because they did not meet the selection criteria. The remaining articles (165) were subjected to a thorough reading to assess their relevance in detail. Of the initial total, only 58 articles were selected for inclusion in this review. Each article was analysed in depth to extract data on the methodologies employed, main findings, discussion of results, and authors’ conclusions. This information was synthesized to provide a comprehensive overview of current developments, benefits and challenges in AV production. On the other hand, although these 58 articles form the basis of the present review, other sources have been used (Google, Google Scholar, Web of Science, and ResearchGate) on an ad hoc basis to search for specific information and complete data (to fill in the annexes, for example). These sources have been referenced and included in the bibliography (168 references in total, including the ones in the Supplementary Information). However, it is important to note that not all the information considered in these additional 105 sources has been reviewed in detail and included in this paper.

3. Agrivoltaic Production

An AV system, often referred to as “agrivoltaics”, “Agri-PV”, “Agro-PV”, “agri-solar”, “solar sharing” or “pollinator-friendly solar”, depending on the area and specific use [14], can be defined as a technology or management that aims to use land for agricultural (or livestock) purposes and simultaneously generate PV energy. Through such systems, land use efficiency can be increased and a variety of crops and livestock may be used, as might diverse types and models of solar panels and installations [15].

The concept of AV production first emerged in 1981 [16]. This article mentions the compatibility between certain solar energy collectors and some agricultural crops, so that they can coexist in the same area considering certain aspects: the orientation of the solar panels (mono-facial at that time), the distance between the rows of panels to prevent excessive shading, and the possibility of elevating the panels to achieve homogeneous radiation between the crops. The main conclusion of this work was that if energy harvesting by panels is optimised, two-thirds of the radiation would be available for other purposes (e.g., agricultural production). However, the first known system of this kind was created in 2004 in Japan under the nomenclature of “solar sharing” [17]. Nagashima based his design on the light saturation point of a crop, i.e., plants can typically use only a small percentage of incident radiation (3–6% of total solar radiation) to achieve a maximum rate of photosynthesis. In this way, the crops shared the excess solar radiation with the PV systems to generate electricity. On the other hand, the first experimental plot incorporating this type of system dates back to 2010, and was installed in France, near Montpellier [18]. This system had opaque PV modules located 4 m above the ground that generated some shade on the crops. Such systems have spread since that time, especially in the last 5 years, ranging from small family farms to installations in China with outputs of over 700 MW [15].

3.1. Current Technologies and Applications

Definition. There is no strict definition for the design of an AV system, but it is usually described as a system where crops are co-located with panels, either directly below, in greenhouse installations, in the form of arcs, or constructions that are placed above the crops in the field, or between rows [19]. In other words, solar panels share ground with crops (arable or woody), but also often include livestock. Therefore, AV systems would include all kinds of agroforestry practices.

Types of AV systems and aspects to be considered when designing them. In the design of an agrivoltaic system, it is important to first consider the type of crop and its light requirements [13], its response to shade, irrigation levels, and parameters related to evapotranspiration and temperature and humidity preservation as well as the type of livestock to be included and its temperature and shade requirements. Some incident light in AV systems is used for energy production and cannot be used by the crops, so it is necessary to select plants that can adapt to lower levels of incident light. One genetic factor that can be considered is the carbon assimilation pathway, which classifies plants into C3, C4, and CAM types [20]. Several C3 species tend to saturate at low levels of photosynthetically active radiation, are shade-tolerant, and are suitable for these systems, as they can grow in reduced-light conditions [21]. However, the effects of low available light should be considered with regards of amount and quality of crop production.

On the other hand, the type of installation and the characteristics of the panels must also be considered: the surface, the angle of inclination, and the height with respect to the ground (Figure 1). These characteristics will influence the efficiency of the panel (η), i.e., the ratio between the power generated and the incident radiation. In addition to the aforementioned parameters, there are other factors that affect η: increasing the temperature of the panel, for example, has a negative effect on the energy yield as well as the surface area of the panel and the degradation of the panel.

The height of the panels in relation to the ground makes it possible to classify the systems into two types [17]: on one hand, there are overhead or stilted AV systems (S-AV), which are those where the PV panels are installed above the crop fields at a certain height (above 2.10 m); on the other hand, there are AVs where the PV panels are installed at a lower height, and the crops are grown between the rows of solar panels. The first case is the most widespread, especially in Reference [22]. It encompasses the installation of solar panels in greenhouses and in agroforestry systems (with the incorporation of livestock), and many of them allow vehicles and animals to pass underneath the installations [23]. Elevated structures have been used in celery, potato, wheat, forage clover, grape, and maize fields, and often achieve higher ground cover ratios because they are independent of the separation required by the crops [24,25,26]. These systems can be designed with specific shading but have the disadvantage of being more bulky, expensive, and difficult to construct. The second case, systems installed at low height between crop rows, have less ground coverage, and are usually built vertically (or at a very low angle). If well planned, they allow the passage of machinery, can be combined with crops that do not have very demanding light requirements, and are frequently cheaper to install. The main problem is that they are not as efficient at capturing solar energy (as they are usually positioned vertically).

In addition to classifying these systems according to height, they can also be classified according to agricultural activity: horticulture, arable farming, and grasslands, which can include sheep [27] or dairy cows [28]. In AV systems, vegetables (tomatoes and lettuce) tend to predominate over other crops such as cereals or berries [12]. This is because many of the AV systems, until now, have focused on installations on greenhouses, or maybe also because of the limited research on other horticultural species. Another classification scheme for such systems is based on the type of solar panels: depending on the mobility of the panels, they can be fixed and use single- or dual-axis tracking (which can be adjusted to optimise the reception of solar radiation) [29]. Depending on the sides that can harness the energy, the panels can be mono- or bifacial. Regarding mobility, tracking PV modules are particularly efficient at capturing solar energy (they can capture 29% more energy than fixed ones) [30], especially those that can move on two axes, as they can follow the path of the sun and program a specific inclination depending on the time of year and latitude [31]. These systems are very interesting in combination with horticulture: crops have a higher added value than in arable farming, for example, and tracking systems can be used to achieve the right amount of shade. This optimization benefits both agricultural production and energy generation, as the tracking systems can adjust to balance the needs of the crops with solar energy capture [29].

On the other hand, to improve the use of solar radiation, bifacial panels that capture solar energy on both sides—taking advantage of both direct light and light reflected from the ground or other nearby surfaces—have been developed. Bifacial panels are more efficient and make better use of energy throughout the day and in various lighting conditions. Bifacial panels are estimated to achieve 80% efficiency in harvesting solar energy [32]. Krexner et al. [5] compared, using life cycle assessment (LCA), stake-mounted systems using two types of panels (mono- and bifacial) with traditional production systems (agricultural and PV). The agricultural production in the AV systems decreased slightly compared to agricultural crops without PV panels: the decrease in crops with mono-facial panels was slightly lower (4%) than in the case of bifacial (9%). On the other hand, the amount of energy generated in the AV systems was also lower than in traditional PV systems: in systems with bifacial panels, only about 34% of energy was produced, while in the system including mono-facial, panels the production reached 47% of what was produced in the PV farm. On the other hand, they concluded that the environmental impact of implementing PV technologies is generally higher than in traditional farming systems due to the need to produce the PV modules.

A classification of PV systems can also be made, considering whether they are open or closed systems (Figure 2) [23]. Open systems would be the former cases (between or above the crops), and closed systems would mainly consist of PV structures integrated on top of greenhouses and require special technical specifications, which are quite different from open systems [33]. In closed systems, solar panels can be placed on top of the greenhouses or on the walls, and there is usually no decrease in production as long as the percentage of coverage is less than 20% [34]. It has been observed that certain crops such as pepper can benefit from the shade effect [35]. The most common problem in these systems is the sacrifice of crop production to maximise electricity production, with coverages of 50–100%, resulting in underutilisation of cropland, something that current policy frameworks aim to avoid [36].

Recent innovations: Regarding solar modules, the development of bifacial panels or tracking systems based on artificial intelligence are only part of the innovations taking place in this field. The evolution of solar panels goes much further with the development of concentrating solar technologies, semi-scenic and organic panels, and photo-electro-chromatic devices, innovations that can facilitate the adoption of AV systems. Concentrator PVs (CPV), for example, are systems that use lenses and mirrors to concentrate sunlight onto small, highly efficient PV cells [37]. They are not yet widely used due to the difficulty of mass-producing them and the associated cost. However, work is underway to integrate concentrated solar power (CPS) and agri-voltaics—agri-CPS. This may be of interest for processes requiring heat, such as desalination, water purification, absorption cooling, or for storing energy to help mitigate the effects of solar energy intermittency (compressed air storage, thermal energy storage, hydropower pumped storage, hydrogen or in the form of batteries) [38]. For example, the linear Fresnel agri-CSP, a concentrated solar power technology that uses linear Fresnel mirrors to capture and concentrate sunlight, has been developed. This system consists of a series of flat or slightly curved mirrors arranged in parallel lines on the ground and oriented to reflect sunlight onto a receiver or collector line located at a certain height above the field of mirrors. This receiver contains a thermal fluid (thermofluid) that is heated to high temperatures by absorbing concentrated solar energy, and is used to drive various integrated subsystems, such as a Li-Br absorption refrigeration cycle, a desalination unit, and other processes requiring heat in agriculture-related activities. Pascaris et al. [11] have proposed a system of this type that meets the energy needs of 86,000 people, generating 484 GWh of electricity, 256 GWh of cooling and 725 GWh of heating. In addition, the system produces 959.06 k-tonnes of fresh water (through a desalination process) and 290.07 tonnes of hydrogen (through an anion exchange membrane electrolyser).

Semi-transparent panels are also being studied for use in AV systems. These panels are typically of two types: those with transparent and opaque parts [39] and those made of materials that allow certain wavelengths to pass through (semi-scenic) [40]. Semi-transparent solar panels represent a promising innovation in agri-voltaics, allowing the simultaneous generation of electricity and plant cultivation under the same surface, considerably reducing the effect of shading: plant chlorophyll mostly uses the red and blue part of the visible spectrum, leaving other wavelengths that can be used for other purposes, such as energy production [41]. In contrast to the more common AV systems, which require spacing to allow light to reach the plants or the use of shade-tolerant species, semi-transparent modules eliminate this need thanks to their spectral selectivity. Zotti et al. [42] conducted a series of experiments with amorphous silicon hydrogenated (a-Si:H) filters mimicking PV panels to study the effect of radiation filtering on lettuce, microalgae, tomato, and basil crops. Under high-intensity irradiation conditions (2187 μmol m⁻² s⁻¹), values that can be reached in Mediterranean areas and near the equator [43], all crops showed a higher growth given the protective capacity of this type of panel. Within this group, semi-transparent organic PV (ST-OPV) panels that selectively absorb infrared light and transmit visible light are included [44]. These materials are in early stages of development, but their flexibility and light weight facilitate their integration into structures such as greenhouses and are compatible with low-cost and sustainable manufacturing processes (module price approx. 7.85 USD m⁻², five years durability). The challenges facing this type of material are the need for improved resistance to adverse weather conditions, i.e., very hot temperatures in summer, as well as the development of efficient light absorbing materials (currently efficiency is around 10%) and large area modules that support large-scale production processes.

Finaly, Chang et al. [45] recently introduced a photoelectrochromatic device based on tungsten oxide and graphene quantum dots operating in the near infrared (NIR-PECD) into closed AV systems. This system makes it possible to autonomously regulate the temperature inside a greenhouse, as these materials change their opacity to light depending on the electric current passing through them. This can be very beneficial both for crops, by protecting them from the most intense hours of sunlight, and for energy generation. By increasing the opacity of the panels, it also increases their efficiency in capturing energy.

3.2. Environmental, Economic, and Social Benefits of AV Systems

AV systems are associated with a number of benefits at various levels: they have a positive environmental impact, they have associated economic and social advantages, and they can contribute to improved productivity and land efficiency. On this last point, the improvement of productivity and land efficiency, there is still controversy, and much depends on the studies considered.

Environmental impact: AV systems offer multiple environmental benefits, mainly due to their ability to optimise the use of natural resources and improve the climatic resilience of agricultural ecosystems—in particular, in very hot climates and arid and semi-arid regions. The implementation of AV leads to a notable reduction in irrigation needs and erosion (water and wind) [15] and can retain more water during the summer [46]. Depending on the level of shading, this can save up to 29% water [47] and, in addition, moderate the temperature under the panel [48]. Warmann et al. [49] used the Penman–Monteith evapotranspiration model in several areas of the southeastern USA and concluded that the reduction in water consumption can be as much as 30–40% in AV systems. In addition, the systems evaluated found that afternoon shade could benefit shade-tolerant species in hot, dry conditions. Grapes cultivated under panels had higher photosynthesis rate at midday with respect to full sun grapes [26].

Plant evapotranspiration has been observed to contribute to the decrease in the temperature of solar panels and improve their efficiency [50]. Some studies have pointed out as a benefit a reduction in evapotranspiration in regions where accessible light is between 50% and 70% of total sun exposure [51,52]. Under shaded conditions, photosynthetic rate is reduced and stomatal closure occurs [53], which reduces crop water loss, which can be advantageous in climates with high temperatures and intense solar radiation of in a climate change scenario [54]. This is especially relevant for crops that experience these problems during flowering or grain-filling. For that reason, under water stress conditions, some crops such as maize and rice can benefit from the presence of panels, increasing crop production [55].

This type of management is also a potential tool for creating climate-change-resilient ecosystems by protecting soil, crops, and animals against solar radiation and extreme weather events such as drought, frost, hail, heavy rain, and heat waves [56]. The systems used in Agostini et al. [57] stabilise maize crops by better controlling temperature and heat. Barron-Gafford et al. [55] observed that solar panels in AV systems experienced lower diurnal temperatures and less variation than in traditional installations due to the balance between latent heat from plant transpiration and sensible heat from bare soil radiation. This resulted in a reduction of the temperature of the panels by 8.9 °C during the daytime in the growing season. Considering that the panels used were most efficient at temperatures below 30 °C, applying the system advisor model [58], it was calculated that temperature reductions in the growing months increased energy generation by 3%, which translates to 1% annually.

These systems can also have positive effects on the production of certain crops, as it has been shown that the lack of light is often accompanied by an increase in leaf area to optimise the use of light [59]. In overhead AV systems, the panels can be strategically placed to partially cover the crops for optimal light hours. In addition, keeping the soil cultivated reduces wind erosion and can help reduce fouling of the PV panels [60], which occurs in PV plants where the soil is bare or sparsely vegetated [61,62].

Finally, the reduced sunlight intensity and lower temperatures under the panels can favour the growth of shade-tolerant plants, promoting crop biodiversity and providing habitats for beneficial insects and wildlife [63]. This physiological adaptation is known as shade avoidance syndrome (SAS) and can increase the yield of crops that are used for leaves, stems, or roots [64]. Certain species such as lettuce show promise for inclusion in AV [52]. Studies with chicory in southern Italy have also shown very positive results: Semeraro et al. [54] observed an increase in edible yield of 69% under shaded conditions, suggesting that plants are influenced by the SAS. In addition, plants that enjoyed fewer hours of light had a higher chlorophyll a/b ratio than the control, an adaptation that allowed them to take better advantage of red light, which is more penetrating and can reach the leaves [65]. In addition, by modifying soil conditions and causing changes in the microclimate (altering temperature, humidity and UV exposure), have effects on soil microbial communities, altering bacterial and fungal balances and affecting the decomposition of organic matter [66]. Bai et al. [67] observed an alteration in the composition of soil microbial communities: the relative abundance of Actinobacteriota decreased under the solar panels, while the abundance of Proteobacteria, Acidobacteriota and Methylomirabilota increased.

Economic and social impact: On an economic and social level, such systems can be very beneficial for rural communities—for income diversification, improving access to electricity, and achieving greater economic stability—and even for solar panel developers [31]. AV systems promote income diversification, introducing new sources of income for farms and supporting the economics of the agricultural sector [68]. By providing clean energy to sustain agricultural activities that currently rely on fossil fuels, these systems contribute to reducing the environmental impact of agriculture [69]. In addition, they can increase the economic value of agroecosystems through multifunctional activities that provide greater income resilience [70]. Crop price stability is also favoured by AV systems, which can support crop production with reduced costs and increased food production [55]. Sojib Ahmed et al. [71] studied the economics of AV systems in rice fields, and considering the higher net benefit of PVs, they observed that if 90% of rice production is maintained, the benefits generated by these systems are in the order of 22 to 115 times higher than those generated by rice production alone.

AV systems can help to recover the decreasing area of cultivated land and maintain food production in a scenario of global population growth [72] and in areas where agricultural land is abandoned. The systems used by Agostini et al. [57] are mounted on crops and minimise land occupation. In addition, through LCA, they have been found to have similar environmental performance to conventional PV systems. AVP systems can also increase land value and improve energy production. In Thailand, for example, the growth and yield of bok choy and electricity production were studied, and it was observed that crops under the panels could reduce the temperature of the panels and increase the efficiency of the panels and electricity production [73].

AV systems can play an important role in reducing the budget for irrigation or solar panel cleaning [74]. On the one hand, water used to maintain the efficiency of the panels can be used to irrigate crops, and on the other hand, agrivoltaic systems can provide the energy needed to maintain pumping and irrigation systems. This is particularly critical in areas with electricity shortages, where reliable power supply is essential for maintaining agricultural productivity. Additionally, appropriate design of PV panels can facilitate water management by serving as channels to distribute or store rainwater, which is particularly useful in regions with variable rainfall patterns, such as India’s monsoon climate, where rainfall is concentrated between June and September, with two dry periods in between) [70]. This dual functionality not only supports the direct energy needs of farms but also enhances water management capabilities, thereby contributing to overall farm efficiency and sustainability. In a SWOT analysis carried out for AV systems in Brazil [15], a number of economic and social strengths have been identified, including: the solar energy sector is booming, making it a very promising area for investment; there are many countries with agricultural economies that could benefit greatly from the associated income diversification; there are increasing incentives for such management; there is increasing attention to climate change; and there is a growing demand for renewable energy production systems in rural areas. On the other hand, they point out as main weaknesses the lack of knowledge about AV technology, the lack of literature or experimental areas, the need for initial investment in infrastructure and components, and the lack of technological knowledge and expertise. They also point out as opportunities the possibility of new sources of funding, there is room for technological development, for agricultural production (especially in semi-arid areas), the creation of jobs and business models, the possibility of creating associations that share production, or the resilience of the families involved in agriculture. Finally, they point out as threats the competition for land, the lack of guidelines and regulations, the scarce education on the issue, and the low investment power of rural communities.

3.3. Agricultural and Energy Yields

On this point, there is still some disagreement among the authors on the advantages of AVs in terms of yield. It is important to consider that in order to set up an AV system, it is necessary to install solar panels, which requires a part of the land and which uses part of the light from the crops. Therefore, crop yields are expected to decrease slightly in some cases, which is compensated by energy generation. As will be seen in later sections, current legal frameworks aim to keep the drop in crop yields in AV systems to less than 10–20%, so as not to compromise food supply.

When assessing an AV system, it is necessary to look at both crop or livestock production and energy generation. [68] examined different AV systems and concluded that crop yield is highly dependent on crop type, location, panel shading rate and specific climatic conditions in the year of study. For example, in warm areas such as Tucson, chiltepin showed a 150% increase in yield with 70–80% shading [55]. On the other hand, in Santiago de Chile, broccoli yield was reduced by 29% with 30% shading [75]. The results are mixed not only regarding yield but also where changes in crop quality are considered—there is no clear trend. With crops such as lettuce, in areas such as Almeria (southern Spain, very hot and dry climate), using a 22% cover crop significantly increased yield and also increased the fresh weight, dry matter, number of leaves, maximum length, and dry matter of roots both in spring and summer. Another study in Amaliada, southwestern Greece shows a small (non-significant) increase in plant fresh weight under 20% shade as well as a significant increase in leaf area. A decrease in plant transpiration was also observed, which is associated with cooler and wetter shaded conditions [76]. Another study, carried out in Montpellier, shows opposite results, especially when using systems that produce canopies with too much shade (around 50%). However, when the coverage is lower, around 30%, yields do not drop as much (between 1 and 19% compared to the control). In the latter case, there are varieties such as Lactuca sativa acephala sp. “Kiribati” and Lactuca sativa acephala sp. “Emocion”, which produce even higher yields [77].

The same is true for tomato—there are rather different results [12]. A study conducted at a research centre north of Tucson, AZ, USA under extreme heat conditions found that the number of S. lycopersicum var. cerasiforme fruits (a heat-sensitive variety) doubled under the shade of the panels. Additionally, 65% more CO₂ was absorbed, and water use efficiency was also 65% greater [55]. In the same study, the authors observed that Capsicum annuum var. glabriusculum, a variety used to growing in the shade, captured 33% more CO₂ and tripled fruit production under the panels, and jalapeño production (Capsicum annuum var. annuum) had 157% greater water use efficiency under the panels while maintaining production. Cossu et al. [78] also conducted a study with tomato (Solanum lycopersicum L., cv. Shire) in a greenhouse by covering part of the roof and walls with solar panels (reducing radiation by 58–73%) and observed reductions in yield, both total (22%) and marketable production (18%), but not in dry matter. The authors also point out that despite this decrease, electricity production is economically more profitable (on the order of 11 times more profitable), so this type of system can compensate for the decrease in production. López-Díaz et al. [79] observed a significant decrease in tomato production for different % shading: 15, 39 and 50% were associated with yield decreases of 10, 29, and 39%, respectively. In a vineyard with 75% of shade in northern Italy, a reduction in grape production was observed (<15%) along with an increase in titratable acidity, an important parameter for wine production [26].

In Table S1 of the Supplementary Information, a summary of actual experiments evaluating the yield of different crops in AV systems against controls is presented, and a reduction in yield is observed in most cases (more than 80% of the studies consulted). In almost 40% of the cases, the reduction is more than 20%, and in the most extreme cases, the reduction is up to 88% [80]. In many crops, a direct relationship between percent shade and yield reduction can be observed (Figure 3).

Regarding livestock, Andrew et al. [27] found no difference in lamb production in an AV system compared to the control and no variation in animal behaviour. Another study with cows showed similar results—no differences in milk production and milk quality but differences in animal activity. The peak activity of the cows was reduced on very hot days, as the animals were sheltering under the panels [81].

While the above are studies that directly measure yield, other methods can be used to determine the yield of AV systems, such as holistic simulations that assess crop yields under varying environmental conditions, taking into account plant-soil interactions, cultivation techniques and microclimatic parameters [17,82]; simpler methods by modelling photosynthetically active radiation under crops [83]; or considering the incident spectral irradiance together with the spectral absorption of the plants, which allows calculating the amount of CO₂ absorbed by the crop in a given period [84]. Mouhib et al. [46] modelled the performance of bifocal PV panels on olive crops, considering different tilt angles (0 to 90°) and various heights (from 3 to 4.5 m), and found that energy production reaches a maximum when the tilt of the panels approaches the latitude of the site. Between 0 and 60° of inclination, the panels’ performance is always above 80%, but performance decreases to 50% when approaching 90°. There are hardly any differences when considering the height, but the yield at 4.5 m is slightly higher.

To facilitate comparisons regarding yield in AV systems, when more than one use has to be considered, it is usually done in land equivalent ratios (LERs) [18]:

$$\mathrm{L}\mathrm{E}\mathrm{R}={\displaystyle \frac{{\mathrm{Y}\mathrm{i}\mathrm{e}\mathrm{l}\mathrm{d}}_{\mathrm{C}\mathrm{r}\mathrm{o}\mathrm{p}\left(\mathrm{A}\mathrm{V}\right)}}{{\mathrm{Y}\mathrm{i}\mathrm{e}\mathrm{l}\mathrm{d}}_{\mathrm{C}\mathrm{r}\mathrm{o}\mathrm{p}\left(\mathrm{C}\mathrm{o}\mathrm{n}\mathrm{v}\right)}}}+{\displaystyle \frac{{\mathrm{Y}\mathrm{i}\mathrm{e}\mathrm{l}\mathrm{d}}_{\mathrm{E}\mathrm{l}\mathrm{e}\mathrm{c}\left(\mathrm{A}\mathrm{V}\right)}}{{\mathrm{Y}\mathrm{i}\mathrm{e}\mathrm{l}\mathrm{d}}_{\mathrm{E}\mathrm{l}\mathrm{e}\mathrm{c}\left(\mathrm{C}\mathrm{o}\mathrm{n}\mathrm{v}\right)}}}$$

where Yield_Crop(AV) is the yield of the crop in AV system; Yield_Crop(Conv) is the yield of the crop in conventional (single-use) system; Yield_Elec(AV) is the yield of the solar panels in AV system; and Yield_Crop(Conv) is the yield of the solar panels in conventional (single-use) system [47]. LER was selected as the main indicator because it provides a comprehensive, quick, and easy-to-understand overview of the benefits and drawbacks of AV systems compared to non-dual systems.

A system in which only one type of product (either agricultural or electrical energy) is generated has a LER of 1, while AV systems usually have values above this [18,83,85]. For example, Mouhib et al. [46] found that the LER of a PV installation in Spain was between 0.5 and 1 (considering different setups); an olive farm in the same area was around 0.8; and an AV system combining both was between 1.3 and 1.7 (considering different heights and angles for the panels). Similar observations have been made with vineyards: the LER in AV systems was between 1.27 and 1.5 [86]. In Belgium, LER values in AV systems of 0.97 to 1.22 have been observed in wheat fields [87]. In this case, AV systems do not seem to be very efficient and would need to be optimised: on one hand, it seems that wheat (Triticum aestivum) is more sensitive to shading (only 54–67% of the control is achieved) compared to sugar beet (the yield of this crop is always above 80%); on the other hand, bifacial panels are less efficient at collecting solar energy than those that can change their inclination following the path of the sun (76% and 114%, respectively, compared to the control). Some models have found that in hot and dry areas, AV systems can achieve LER values of 2 or even higher, especially if the assemblies are designed to maximise electrical energy production (e.g., by properly orienting the solar panels) [49]. In Figure 4, the LER of several European studies have been plotted (more information can be found in Table S2 of the supplementary information). Something similar has been pointed out in a study by Willockx et al. [88], where it has been estimated (theoretically) that in areas of Southern Europe, LER values higher than 2 are found. A trend towards a higher LER is observed in the Mediterranean area, perhaps associated with a higher number of daylight hours: more energy can be produced without sacrificing too much space or resources for agricultural production. In addition, these soils benefit more from shade, which can have a positive impact on soil fertility, moisture preservation, and biodiversity.

3.4. Challenges and Limitations

Adelhardt et al. [89] conducted an analysis of risks related to AV systems in Sub-Saharan Africa using the PESTLE approach [90], which considers political, economic, social, technological, legal, and environmental aspects and whose results can be taken into account in many other parts of the world. Through a literature search and semi-structured interviews, they identified the following:

• Political: political instability and likelihood of collapse within a short period; bribery and corruption; lack of political support (i.e., disinterest from public institutions); regulatory barriers such as high taxes or legislation penalising the inclusion of PV installations in agricultural fields; uncertainty (political and legislative); and a bureaucracy characterised by complex approval processes [87,91].
• Economic: limited availability of market data for the products generated; lack of local capacity (and market) structures and dependence on imports (e.g., for spare parts); restrictive monopoly position of national energy suppliers; high initial investment; lack of financial resources and limited access to finance; long payback period; and financial insecurity (caused by weather, volatility of prices, etc.) [89,91,92].
• Social: lack of social acceptance associated, for example, with food security; reluctance to invest; complexity of coordination and planning processes; lack of knowledge and education; relationships marked by conflicts of interest; lack of inclusion and participatory schemes; historical inequality; previous negative experiences; adaptation to local practices; limited local stakeholder network; insufficient commitment; and individual opportunism [15,91,92].
• Technological: incompatibility with local requirements and those of the required system; construction marked by lack of skilled labour and limitations in quality control; risks related to maintenance, theft of technological components; or negative shadow effects [93,94].
• Legal: unclear land use rights; costs associated with litigation; and uncertainty of asset ownership [89,91,95].
• Environmental: direct or indirect damage to soil/crops and reduced agricultural profit [33].

Of all these risks, the ones that stakeholders are most concerned about, i.e., the ones that would have the greatest impact and likelihood of occurring, are the financial ones: lack of financial resources, limited access to finance, and high start-up costs. The problem of theft is also of great concern, while lack of social acceptance or low political support would be more secondary problems (with less impact and lower likelihood).

Technical challenges: AV systems present a number of technical challenges that are crucial to their implementation and sustainability. These challenges range from the design of the installations to the implications on crop quality and landscape, as well as the use of machinery and maintenance of the solar panels.

With regard to design, two main constraints are often pointed out (especially in arable crops): on one hand, installations must be compatible with the light requirements of a multitude of crops (if rotations are used, for example);on the other hand, they must not interfere with management practices and machinery use, which are often optimised and highly dependent on farmer preferences, terrain, and climate [87]. The problem of shading has been shown in Figure 3 and is of particular concern in certain areas where daylight hours are limited: for example, in Belgium, one of the main sugar beet producers in Europe, there is a linear relationship between crop yield and decreased shading [96] Similar patterns have also been observed in wheat crops, for which lack of light causes yield losses in the UK [97] and Argentina [98]. However, in areas with excess light, such as the Mediterranean area, the effect of shading can be the opposite, and grain yield can increase by up to 19% [99]. Touil et al. [100] found that 25% shading does not necessarily affect crop growth and quality.

On the other hand, there is also some concern about reduced crop quality if shading is increased: Sytar et al. [101] found that exposure to sunlight increases the amount of flavonoids in sugar beet leaves; and a reduction in total soluble solids has been observed in a winegrape vineyard in Italy [26]. Reher et al. [87] found less chlorophyll in sugar beet leaves in AV systems compared to the control, but this was not the case for wheat crop quality: grain number per tiller, thousand-kernel weight, and grain protein content all showed similar results. In the case of protein content, it was even significantly higher in one of the seasons under AV management. Regarding the use of machinery under the solar panels, in addition to space limitations, problems have arisen with self-driving machinery that loses the GPS signal under the modules, which can lead to poor seed distribution in the plot [102].

Aspects related to the installation and maintenance of AV systems can be considered limitations. For example, soil damage caused by compaction or erosion during the installation of AV systems (which can have negative effects on crop yields), the associated loss of land, which can be around 10% of the land in arable crops [87]. This is not the case in tree orchards, where panels can be placed without taking up space [93]. On the other hand, damage to solar panels caused by agricultural machinery or animals can also occur. Large machinery used for planting or harvesting can inadvertently strike the panels, causing physical damage, and livestock can also pose risks by potentially damaging the panels. These problems increase the fire risk, especially under hot and dry conditions. Additionally, electrical faults, such as failures in grounding systems, can lead to sparks that may ignite flammable materials, further increasing the risk of fire [94]. Moreover, issues related to operator security, such as the risk of accidents during installation and maintenance due to the height and positioning of panels, must be carefully managed. In addition, dust accumulation, aggravated by wind erosion in open fields, can reduce the efficiency of the panels and necessitate frequent cleaning [70]. The chemicals used in these cleaning processes could have undesirable effects on nearby crops, potentially affecting their growth and yield. Although self-cleaning panels [103] or the use of water for crop irrigation [19] can mitigate some of these problems, careful planning and management are essential to minimising risks.

In addition to operational and maintenance challenges, the disposal of used equipment, especially solar panels, raises significant environmental concerns. When solar panels reach the end of their life cycle (typically 25–30 years), they must be properly disposed of to avoid environmental damage. Improper disposal can lead to the release of hazardous materials such as cadmium and lead, which are present in some types of panels [104]. It is therefore crucial to develop and implement effective recycling programmes and guidelines to manage this problem. Increasing attention is now being paid to the recycling and reuse of decommissioned panel materials to reduce the environmental impact. These efforts not only mitigate the potential damage of disposal but also contribute to the circular economy by recovering valuable materials for future use.

Landscape transformation is another important consideration in the design of AV systems. Sirnik et al. [105] developed an analytical framework to determine ten indicators of landscape change that can be associated with AV systems. This allowed them to analyse four farms of this type, determine which effects are most common, and develop a series of policy considerations and recommendations. They concluded that when designing such systems, it is important to pay attention to, for example, changes in crop types, crop patterns, fencing, supporting infrastructure, openness (a characteristic that relates to the amount of landscape that can be observed from a height of 1.6 metres), changes in cropping patterns, etc. Another more recent study [33], compares the landscape quality of two AV systems in the Netherlands, one overhead and the other inter-crop, considering three factors—use, experiential, and future based on the Vitrubian triplet—by linking them to four social interests: economic, social, ecological, and cultural. Use value refers to functional adequacy and efficiency, experiential value to identity and meaning, and future value to efficiency and sustainability over time. On the other hand, economic interest concerns land use efficiency, social interest concerns combating inequality, ecological interest concerns sustainable design, and cultural interest concerns human experience. Biró-Varga et al. [33] found that there is a decline in both systems for experiential value and an increase for future value. On the other hand, use value increases for intercrop systems and decreases for overhead. Some preference was found by respondents for intercrop systems.

Economic constraints: As mentioned above, economic constraints are also significant and of most concern to stakeholders, especially those aspects related to the initial investment, the long periods needed to amortise this investment, and financial insecurity [89]. After all, there is no regulatory framework to protect these farms, and they are highly susceptible to market changes associated with the variability of crop and electricity prices as well as to the effects of climate fluctuations [106]. To make these systems more viable (large-scale) and reduce investment risks, a fixed power sales tariff or power purchase agreement is needed [107].

Another major aspect to consider is the feasibility and the need for financial support through subsidies. Reher et al. [87] calculated the LCOE (levelized cost of electricity) in three different AVs and compared them to a PV production control: the control had a cost of 79 € MWh⁻¹, lower than the three tested systems (vertical bifacial, single axis tracking and overhead/elevated), which had costs of 117.88 and 176 € MWh⁻¹, respectively. The first two systems are quite competitive, but the elevated system could not operate without subsidies. In a similar study, compared other AV systems, with different panel densities (full density and half density) and with two types of movement depending on the position of the sun (mono-axial tracking and bi-axial tracking) and obtained similar results. AV systems are more economically viable than PV (generating 5–40% more revenue), but to be competitive with purely agricultural systems in economic terms, they require additional incentives of USD 0.02 to USD 0.06 per kWh generated. The low profitability of AV systems, compared to crop-only systems, is often caused by decreasing crop yields, which has also been observed in pear fields: electricity production could not compensate for a 16% decrease in yield [93]. In apple cultivation, the economic forecasts are similar: for AV apple production to be viable, these systems depend on state aid and mechanisms such as FIT (feed-in-tariff) price [92].

There is one economic aspect that is not often considered when planning the transition to AV systems: the impact on land valuation. Changes in land use to accommodate agri-PV systems can affect the valuation of agricultural land, increasing costs, and with new tax obligations. This can result in a more complex economic balance sheet compared to operations dedicated exclusively to one or the other activity [91].

Social barriers: The constraints that exist in this regard relate to the low acceptance of such systems by farmers, livestock keepers, and the community at large and the lack of education and knowledge on the subject.

Firstly, the lack of a legal framework, high initial costs, lack of a formal definition, or little research create uncertainty among stakeholders, decreasing interest and willingness to invest in such systems [91]. There are concerns about the sustainability of such systems, given the lack of large-scale successful examples and practical issues, such as the need to clean solar panels using some kind of detergent, or that there is parasitic competition between crop production and energy, where one may be disadvantaged to the benefit of the other. This includes concerns about prioritising energy production over agriculture due to differences in remuneration [95]. This study also shows farmers’ concerns that such systems will increase inequalities and that only the wealthy will be able to benefit from them. Finally, acceptance may also be influenced by the possible visual impact on the landscape.

Vidotto et al. [15] point to the lack of technological knowledge and expertise as social weaknesses of AV systems. They also see as threats the lack of education on the subject, and the low investment capacity of rural communities, where these systems can be very beneficial. Another study has identified the complexity and difficulty of understanding these systems as one of the problems: it creates uncertainty about their usefulness and feasibility [95].

Other limitations: As mentioned at the beginning of this section, there are other constraints to the implementation of AV systems. Chatzipanagi et al. [91] mention that in addition to the technical, economic, and social challenges, there is also a challenge at the regulatory level, as AV systems are not yet well incorporated into national strategic plans for CAP (common agricultural policy) and national policies. Furthermore, there is no clear definition or universal standards at the EU level, which causes lack of coordination and exploitation of legal loopholes, where conventional PV systems on agricultural land are considered as AVs as they only partially comply with the requirements.

The integration of AV systems with centralized electricity grids is also a significant challenge. This includes the connection of new installations to the grid and the capacity of grids to handle the additional load generated by AV systems, especially in rural areas with limited electricity infrastructure. The capacity of grids to handle the additional load generated by AV systems may be limited. Furthermore, the costs associated with connection and possible upgrading of existing electricity infrastructure represent additional barriers and it is critical to develop a clear regulatory framework that addresses these challenges, ensuring that AV systems can be efficiently integrated into existing electricity grids without compromising grid stability or the economic viability of farms.

Strategies to mitigate challenges, risks, and constraints: It is important to develop strategies that holistically take into account the environmental, economic, social and political challenges facing AVs. Chatzipanagi et al. [91] draw a number of conclusions on strategies to be followed to mitigate the challenges associated. Firstly, it is essential to clearly define what is considered an AV system and to establish a European standard that follows harmonised policies. In this regard, the boundaries between traditional PV production and AV need to be clearly delineated. It is also crucial that these types of systems are prioritised over the maintenance of agricultural activity rather than energy production and that farms or plots that include these systems are not excluded from the strategic plans of the CAP. Research and planning must be two pillars of progress in AV; it is necessary to look for crops that are efficient in these scenarios, and to plan the systems to be more effective in capturing energy, maintaining an acceptable temperature for crops and livestock, improving humidity preservation, etc. The development of a quality standard, including third-party monitoring systems, can contribute to the evaluation of the efficiency of such systems. The results of Adelhardt et al. [89] show that in Sub-Saharan Africa, financing measures for initial installations would be necessary, while in the long term, sustainable and viable income generation is essential. It would be interesting to simplify the investment processes for such systems or to develop business models that include landowners, farmers, and developers of PV installations. The importance of the context, both social and environmental, is also pointed out: it is important to know the local culture so that the implemented systems do not present problems as well as to adapt the management to local crops. It is essential to include end-users in the planning and development of these systems as well as to implement education and training programmes to mitigate the risks of failure. Although this study has been conducted for a specific area, these strategies have many options to work (adapted) in other contexts, as similar measures are also mentioned in Chatzipanagi et al. [91].

3.5. Policies, Regulatory Framework, and Incentive Programmes

At the global level, AV systems have generated a great deal of political interest, as they are aligned with several United Nations Sustainable Development Goals (SDGs) [89]:

• SDG2. Zero hunger, boosting food generation in the face of the challenges of climate change and water scarcity;
• SDG3. Health and well-being, expanding food production while maintaining nutritional quality (taking into account secondary metabolites);
• SDG7. Affordable and clean energy, expanding renewable energy with little or no reduction in arable land use;
• SDG9. Industry, innovation and infrastructure, driving creative solutions that merge energy generation with agriculture, using technologies that enhance the services provided by agroecosystems;
• SDG12. Responsible production and consumption, simultaneously increasing energy and agricultural production, while minimising land degradation and water consumption;
• And SDG13. Climate action, reducing CO2 emissions resulting from human activities, including those associated with agriculture [54].

These are the most affected, but there may be effects on more SDGs (in 14 out of 17), as concluded by Cuppari et al. [19] in their study, in which they perform a SWOT analysis of dual systems (AV) versus single-use systems (agricultural or PV installations), considering the different SDGs. In this work, they consider that AV systems can also contribute to the following SDGs: SDG1 (zero poverty), by increasing farmers’ profits, supplementing agricultural income with that generated by solar panels; SDG4 (quality education), AV systems present the opportunity to bring electricity to educational facilities far from electricity supply or with few resources; SDG6 (clean water and sanitation), by reducing evapotranspiration rates and taking advantage of the water used to clean the panels for irrigation; SDG8 (decent work and economic growth), electricity generation in rural areas can be used to power training centres and micro-enterprises; SDG10 (reduced inequalities), diversifying and increasing the benefits for small farmers; and SDG15 (life on land) as, by integrating two systems into one, the land footprint of single solar energy production is reduced, and the impact of human (agricultural) activities can be reduced. These authors also point out that there is a threat to SDG5 (gender equality)—there is a possibility that adding electricity sources for lighting could extend working hours for women.

Despite this interest, this is a novel type of management, and there is still no legal framework. However, some countries have begun to legislate on the issue. Government support is motivated by several factors, such as improving land productivity, increasing farm incomes or supporting national development programmes [19].

In Japan, legislation has been in place since 2013, when an official ordinance was published setting out the conditions for converting agricultural systems to AVs [108]. This included, for example, demonstrating that the conversion would not negatively affect agricultural production (no more than 20% reduction in production), the minimum height of the panels so as not to hinder machinery activities, or the need to include easily removable structures. On the other hand, producers of energy through PV systems can sell the electricity generated under the FIT as long as they meet a number of criteria. In 2021, related legislation was updated to facilitate the creation of such systems [109]. This has been facilitated by the lack of available land in the country. The new guidelines consider AV systems to be those that are planned as such from the very beginning, so it is not enough to include crops or livestock in purely PV installations—agricultural and livestock production must be prioritised. This is because AV systems are legally considered to be agricultural systems and carry a number of associated tax benefits. In contrast to Japan are other Asian countries, such as South Korea where the Agricultural Land Law prohibits such initiatives even though they have to import energy from other countries and 95% of their energy production is associated with fossil fuels. However, reforms to this law have been proposed over the last few years, and—according to the final proposal that is expected to be approved soon—each farmer is allowed to produce up to 100 kW. In addition, the government will give priority to the purchase of electricity generated by these means, and financial support for their installation is envisaged [110].

In other countries, such as France, there is no official legislation on the subject. In 2021, the French Agency for Environmental and Energy Management (ADEME) defined a set of guidelines on this type of management through its website [111], including generic information on concepts, characterisation of systems, production, and the state of the art in general. However, a law on the subject is being developed [15]. This new law will include aspects related to long-term maintenance, and, as in the Japanese case, will emphasise that the main activity of such systems must be agriculture and that PV installations must have benefits for crop cultivation or animal welfare. The German government favours AV systems, with incentives including a technology bonus for every kWh generated by these systems as well as guaranteed grid access and FIT under the Renewable Energy Sources Act in addition to continuing to benefit from 85% of the standard subsidies offered by the EU’s CAP. However, a legal framework does not yet exist in this country [112], but a document has been published (as in other countries) to standardise measurements in AV systems [29]. Similarly, in Italy, guidelines have been published to classify AV systems, distinguish between different typologies, and categorise those eligible for state incentives [15]. Croatia has adopted specific legislation, and its new laws give farmers the capacity to install PV infrastructure on farmland, allowing for the simultaneous production of energy and agricultural activities [113]. It also opens the door to financial support and other incentives for the adoption of solar energy production systems in a variety of locations, including active cropland, disused land, and permanently cultivated areas such as vineyards and olive groves.

In the US, the Department of Energy (DOE) has allocated USD 15 million in research funds to assess the feasibility of AVs for farmers, the solar industry and communities [114]. Not only that, but many states are also promoting such projects through research and incentive programmes. For example, the state of Massachusetts, through its Solar Massachusetts Renewable Target (SMART) programme, has implemented a FIT supplement of USD 0.06 per additional kWh for solar power producers who feed energy into the grid through AV systems.

In short, specific regulations for AV are still under development despite the growth that these systems are experiencing. However, countries such as Japan, the USA and France have already launched national funding programmes to encourage the adoption of these innovative systems. The need to ensure that agricultural production does not decline, and that crop damage does not occur, is underlined by legal requirements. In countries such as Italy and Germany, existing guidelines emphasise the importance of maintaining primary agricultural activity when introducing AV technology, with requirements for production planning and crop maintenance.

3.6. AV Systems around the World

Such technologies have been implemented with varying degrees of success in different parts of the world; the first support scheme for such technologies was launched in Japan in 2012 and was soon followed by other countries, such as China, Germany, and South Korea. This section will present the status of such management, as well as lessons learned, in various regions of the world. In a review conducted in 2024 (including work up to the end of 2022), the authors determined that all AV studies were located in the northern hemisphere [12]. It appears that in addition to optimal weather conditions, the cost of facilities is often a limiting factor. However, as shown in some research projects below, case studies are beginning to appear in South America and Australia.

Asia: In Japan, about 2000 such systems had been installed by 2021 [109], and the electricity production of such systems is estimated to be between 500,000 and 600,000 MWh. This is an energy production associated with more than 120 types of crops. The scale of farms in Japan is small; they are usually farms with an area of less than 0.1 ha, occupying a total area of 560 ha. In South Korea, pending approval of the amendment to the Korean Agricultural Land Law that prohibits any use of agricultural land other than for farming, there are a number of pilot experiments (44), of which implementation began in 2016 [110]. The aim of such systems is to give farmers a new source of income. China is the country with the highest energy production associated with such systems: in 2021, it generated 1900 MW, of which 700 MW is generated in the Gobi Desert, in goji berry crops [56]. In the coming years, energy production is estimated to reach 10 GW, mainly through the use of solar panels directly integrated on greenhouses [115].

Europe: In France, there has been an increase in companies offering AV-related services, as they are backed by the French government, which encourages competitive AV-related contracts. In 2021, the government allocated 40 MW of power generation capacity to this type of project in an energy auction. This number doubled in 2023: of the 180 MW of projects selected for a new tender, 80 MW included AV systems [116]. Right now, the country has about 200 projects already installed, but many more are in the planning phase. Some examples of such systems are installed on fruit tree crops: for example, apple trees were grown under different levels of shading in the south of France, and a decrease in irrigation needs was observed, as was protection against freezing damage [117]. In 2022, Germany had an AV system production of 14 GWp of the 80 GWp produced by PV farms. The German government aims to increase solar energy production to 215 GWp by 2030 and is therefore encouraging such initiatives [56]. In Italy, some experiments with this type of technology have also been carried out, and AV systems have been found to be suitable for olive [118] and grape [26] crops. This conclusion has been reached in other Mediterranean areas, such as in Spain—Fernández-Solas et al. [119] are evaluating the feasibility of AV systems in olive trees in the south of the peninsula, considering different olive varieties (“Picual”, “Manzanilla” and “Chemlali”) and exploring different configurations of bifacial PV systems. In Belgium, given the limited terrain and fragmented fields, such systems have a lot of potential both for sugar beet and wheat crops [87]. Small increases in LER were observed in both trials, no losses in crop quality were observed, but a significant decrease in yield was observed. It is concluded that there is a need to improve the efficiency of these systems.

America: In the USA, there are already projects of this type both on experimental plots and at commercial level, and in this country, the production of PV energy on livestock farms (with sheep grazing) is being prioritised with the aim of facilitating pollination [114]. The “Innovative Solar Practices Integrated with Rural Economies and Ecosystems” (InSPIRE) project has been underway in the UK since 2015 and has supported AV research, analysing more than 25 pilot projects across the country [14]. In 2022, the findings of this study were published, focusing on several important aspects for the implementation of AV—such as the configuration of solar modules and the selection of PV technologies—with the aim of establishing guidelines for the effective development of this technology. In 2017, Chile inaugurated the first AV project in Latin America: three systems with a total capacity of 13 kWp, aiming to provide shade to protect plants from the sun and dehydration. This project, supported by the local government and the Fraunhofer Institute Chile, has shown positive results in both agricultural productivity and energy generation [56]. A number of innovative AV systems have also been installed in Brazil [15]. For example, the Ecolume project has designed a system for family units in the semi-arid region that combines energy generation with the production of vegetables, fish in tanks and chickens [120]. It produces 17 types of vegetables using an aquaponics system, two animal proteins for school consumption, and umbu seedlings for reforestation of the Caatinga. These are 24 m² systems, which can produce about 4800 kWh year⁻¹, 130 kg of fish, 730 free-range eggs, 336 kg of vegetables, and 200 units of native seedlings. This production could generate an annual income of approximately USD 2000, demonstrating a sustainable and profitable model for family farming in the region. Other projects in this country include the use of AV technology to generate energy and maintain irrigation [121]; CCampo (https://www.dgrv.coop/es/publicaciones-2/ccampo-un-proyecto-piloto-de-agrivoltaica-en-brasil/, accessed on 12 August 2024) pilot uses AV systems to produce peppers, kale, coriander, and chives and uses the energy produced to reduce processing costs for certain products.

Africa: There are not many AV installations on the African continent reported in the literature. However, there are some publications by researchers working on theoretical models to assess the economic viability and land use efficiency of such systems. Bhandari et al. [122] have considered the implementation of a 0.15 ha AV system in a village in Niger (West Africa), a reference area because its characteristics represent local farming practices. The authors compared four scenarios—traditional rain-fed, irrigated with diesel pumps, irrigated with solar pumps, and the AV system—and developed an economic feasibility model, collecting bibliographic data and through surveys, to understand management, crops, expenses, markets, etc. The study concludes that the AV system would have a LER between 1.33 and 1.13 (the latter considering a 20% crop loss due to shading) and could be used to provide electricity to 400 houses in the studied village (assuming a demand of 323 kWh year⁻¹). Randle-Boggis et al. [123] also point to the possibilities of implementing AV systems in East Africa. They propose multidisciplinary research and the development of pilot projects in Kenya, Uganda, and Tanzania to generate empirical evidence and support the development of AV technology. In Kenya, for example, in Kajiado County, the pilot is intended to be installed at the Latia Resource Centre, an agribusiness centre dedicated to farmer training. It is in a semi-arid area, will have a capacity of 56 kWp, and will be equipped with a rainwater harvesting system to optimise water use and improve agricultural production under water scarcity conditions. On the other hand, the system to be implemented at Sustainable Agriculture Tanzania, a non-profit agricultural training centre (in the Morogoro area), will be designed for semi-arid areas and will have a capacity of 35 kWp. In addition to the rainwater harvesting system, similar to the previous case, battery storage will be included. It is also important to mention some projects in the area that have already started working with AV systems: the Watermed4.0 (“Efficient use and management of conventional and non-conventional water resources through smart technologies applied to improve the quality and safety of Mediterranean agriculture in semi-arid areas”) and the APV-MaGa (“Agrophotovoltaics for Mali and The Gambia: Sustainable Electricity Production by Integrated Food, Energy and Water Systems”). In the framework of the Watermed4.0 project, an AV system is being tested in Algeria, in potato, strawberry, and apple orchards in order to reduce irrigation needs (due to shading), cover electricity needs in isolated areas, and implement automated irrigation systems. The AV-MaGa project focuses on improving the supply of food, water, and electricity in Mali and Gambia through AV systems. Five pilot systems will be implemented in these regions, where the demand for solar energy is increasing, but the limited availability of arable land creates land use conflicts and water management challenges. The aim is to assess the capacity of these systems to sustain crop production and evaluate their economic viability as well as to develop economic models that improve local livelihoods.

Australia: AV systems have not been developed much on this continent either, but there are some case studies, such as the one built in 2021 in Perth [124]. It is a closed system, a greenhouse with an area of 300 m² and equipped with 153 highly transparent solar windows in different configurations (varying inclination and orientation) to study energy yield and plant growth. Compared to a control PV system, the solar windows offer slightly lower yields. However, the effect of this glazing on the crops in the greenhouse is not specified in the mentioned study. On the other hand, grazing systems combined with PV production have been common in Australia since 2015, and by 2020, there were at least 13 large-scale solar farms grazing sheep in Australia. Thornton [124], using the APSIM (Agricultural Production Systems sIMulator) model, studied pasture biomass production in AV systems, and concluded that in subtropical systems, biomass production can be higher when compared to full sun conditions: between 8 and 15%, depending on the type of installation.

4. Discussion

4.1. Synthesis of Findings

Throughout this review, advances in the implementation of AV systems—a practice in which crops and livestock share space with the production of PV energy through solar panels—have been analysed. Studies on the subject have increased exponentially over the last five years, with many revealing the effectiveness of AV systems, which offer benefits for both crops and energy production, demonstrated by obtaining LERs greater than 1 in the majority of cases. The best yields are usually obtained by selecting those animal and plant species that are best adapted to the conditions of shade, temperature, and humidity that are obtained when PV installations are carried out. Furthermore, these systems are becoming more efficient through innovations in the installations both in the design of and adaptation to each context, with different assemblies depending on the needs of the crop, and through innovative solar panels. These panels use bifacial panels or systems that use artificial intelligence to track the sun and maximise the use of direct light and albedo or transparent/semi-transparent panels made with cheaper organic components, which disrupt the capture of light by the crops to a lesser extent. In most cases, AV systems do not fundamentally alter the core technology of agricultural production. Some require minor adaptations, such as adjusting irrigation systems or crop selection to align with the shading provided by solar panels. These adjustments are necessary to optimize the coexistence of energy and crop production but do not constitute a radical departure from traditional agricultural practices.

On the other hand, governments and public entities are also showing interest in this type of technology and are beginning to introduce this kind of system into the legislation of several countries. In addition, AV systems are being promoted through financial incentives, and there has been a growing interest in economic models that seek to integrate energy production with agriculture without compromising the viability of both. In many countries, for example, the focus is on designing these systems with appropriate planning, adapted very locally, and trying to avoid the conversion of pure PV installations into AV systems. This potential competition for space, and for light, is a constant concern noted in many of the studies reviewed. In addition, the aim is to keep the reduction of agricultural production below 10 to 20%, to avoid compromising food security and reach a balance that ensures that the technology does not violate the principles of traditional agriculture but rather augments it with dual production capabilities. This potential competition for space, and for light, is a constant concern noted in many of the studies reviewed.

Considering this, what are the implications of implementing AV systems? Such systems can provide a new source of income for farmers, help achieve sustainable production, and bring energy to off-grid areas. Creating AV systems instead of agricultural ones can also improve the climate resilience of many ecosystems that are at risk in a climate change scenario. However, there is still much room for improvement not only from a technological point of view, with the creation of more efficient PV systems, but also with further experimentation. Many of the existing theoretical models need to be expanded and implemented in practical case studies, where the interaction between crops and livestock, environmental variables, and the efficiency of dual production can be analysed. In addition, there is a need to increase the acceptance of such systems, which may face similar opposition to conventional PV systems.

4.2. Knowledge Gaps and Future Areas to Explore

Given the limited number of established studies on AV systems, there are numerous areas that require improvement and consideration to deepen our understanding of AVs. These include the establishment of case studies with a wider variety of crops and in diverse geographical areas, greater inclusion of livestock aspects, advances in technology and modelling, integration of environmental conservation practices, and greater inclusion of AV systems in the development of policies, incentives, and business models.

We can consider the implementation of AV systems that integrate environmental conservation practices away from conventional models or utilise degraded or underutilised land. In cases where land is not suitable for food production, it could be used for the generation of other types of materials. It would also be beneficial to conduct research that addresses soil health holistically, considering other ecosystem services in addition to production, such as carbon storage, biodiversity conservation, and water storage, and filtration [125]. It is crucial, for example, to study the effects of AV on pollinator behaviour [33].

It is imperative to diversify the types of crops used in AV systems. To date, AV studies have mainly included berries and have almost completely omitted perennial crops, although the latter might be more promising due to their lower sensitivity to shade compared to vegetables and cereals [12,13]. Long-term studies would be beneficial to assess the performance of different crop varieties and to determine which ones are more adaptable. In addition, it would be fruitful to focus research on the incorporation of livestock into AV systems, exploring the interaction between animals, forage, and solar panels [126]. Knowledge is still scarce on the effects of shading on heat stress and its possible contribution to improve animal production.

In terms of technological innovations, it would be interesting to incorporate aerial imagery, advanced remote sensing techniques and geospatial analysis tools to facilitate modelling and identify changes in the landscape [105]. Integrating precision agriculture tools, such as advanced sensors, drones, and Internet of Things technologies, can significantly enhance the monitoring of AV systems. These technologies enable real-time tracking of soil conditions and microclimate, facilitating informed decision-making to optimize both agricultural production and energy generation. The use of aerial imagery and geospatial analysis can identify patterns and changes in the landscape, contributing to more efficient and sustainable management of AV systems [127]. Kumpanalaisatit et al. [128] suggest putting effort into developing advanced mathematical models that enable optimisation of AV systems and help select crops for specific climatic conditions and at specific shading levels. Decision support tools are also interesting to optimise the placement, orientation of panels, or the overall design of the system [125]. It would also be interesting to design solar panels adapted to the specific needs of certain crop species, allowing the passage of light frequencies beneficial for plant growth and capturing those frequencies that crops do not use [12]. In this regard, Krexner et al. [5] point out that the manufacture of solar panels using only renewable energy and more efficient materials needs to be promoted in order to reduce the environmental impact.

The interrelationships that are established in such systems are also a field of research to be considered. Aspects such as temperature and humidity variations under the panels, and the associated savings, need to be explored. Consideration should also be given to how crops or livestock affect the conditions under the panels, especially the materials and their durability [129], and also the effect of cooling caused by agriculture on energy production [130].

With a view to the development of circular economy systems, it would also be interesting to carry out environmental impact studies that cover the entire life cycle of AV systems and the recycling possibilities of both panels and structures [5]. A standardisation of LCAs for AV would be very useful.

Effective implementation of AV systems requires a number of key strategic measures to ensure their long-term success and sustainability. First, the development and establishment of a robust and specific legal framework governing the operation and deployment of AV systems is crucial. This framework must address both energy and agricultural needs, ensuring that the integration of both activities is conducted in a harmonious and win–win manner for all parties involved. Secondly, it is essential to provide adequate funding for research and development projects that explore the potential of AV systems under various environmental and geographical conditions. This investment in R&D will allow AV systems to be adapted and optimised to the wide diversity of ecosystems and farming practices, improving their efficiency and economic viability. In addition, the creation of specific credit lines and other financial incentives is essential to encourage the adoption of AV systems by farmers and energy developers. These financial incentives can facilitate the initial investment required for the installation of AV systems, making this innovative technology accessible to a larger number of farmers, especially small and medium-scale producers. Finally, the promotion and development of training and capacity building programmes in AV technology are crucial in preparing a new generation of farmers, technicians, and professionals. These programmes should focus not only on the technical aspects of AV systems but also on their environmental, social, and economic implications, providing the necessary skills and knowledge to maximise the benefits of this integrated technology [15].

5. Conclusions

This article has comprehensively reviewed the most recent research and current status of AV systems, which combine agricultural and/or livestock activity with solar energy generation. These systems have been shown to be viable and offer multiple environmental, economic and social benefits, contributing significantly to global sustainability goals. AV systems are effective in reducing water consumption (up to 40%), can help moderate crop temperatures (cooling crops by up to 8.9 °C during daytime) and significantly improve the efficiency of solar panels (up to 1% annually).

Despite their many advantages, AV systems face a number of challenges, including the need to adapt system design to various agronomic and climatic contexts, and shading management to optimise both agricultural and energy production. In Europe, for example, it is essential to focus on optimising the integration of AV systems in intensive agricultural landscapes and exploring the potential of multi-cropping systems. In Africa, research could prioritise improving water use efficiency and increasing resilience to climate change. In Asia, particularly in densely populated countries, the emphasis could be on maximising land use efficiency and integrating AV systems with existing farming practices. Meanwhile, in North and South America, studies could explore the economic viability of large-scale AV systems and their role in supporting sustainable development in rural areas. In addition, advanced technologies need to be integrated to enhance their efficiency and sustainability. The issues of operating electrical equipment, such as ensuring the safety and reliability of installations in diverse environments, need careful consideration. They also face economic barriers, such as the high initial investment required, and social barriers, including lack of acceptance by local communities and insufficient knowledge and adequate training programmes.

To facilitate the implementation of these systems, it is crucial to further advance in research and development programmes that improve the efficiency and sustainability of AV farms. It is also essential to develop policies and regulatory frameworks that support their expansion, including economic incentives, subsidies and guaranteed tariffs for the energy generated. Diversifying the types of crops used in AV systems and including livestock aspects are also critical areas for future research. Incorporating advanced technologies such as remote sensing and geospatial analysis tools will enhance the modelling and optimization of these systems. These systems, with proper management, are positioned to play a crucial role in the future of sustainable agriculture and renewable energy production. AV adoption is expected to increase as technology evolves and market conditions become more favourable. However, active collaboration between researchers, technology developers, policymakers, farmers, livestock producers, and other stakeholders is essential to overcoming current challenges and achieving the full potential of AV systems.