Shading effects in agrivoltaic systems can make the difference in boosting food security in climate change
Over the past few decades, global sustainable policies have focused on the goal of mitigating carbon dioxide emissions, blamed as the main driver of climate change. Notably, almost three-quarters of these emissions emanate from the energy sector [1,2]. This challenge is further exacerbated by human population growth, technological innovation, and rising living standards, factors that collectively contribute to escalating energy demand and increased need for energy production [[3], [4], [5]]. The overarching objective is to achieve zero emissions by the year 2050 [6], compelling countries and decision-makers to prioritize renewable energy production as a central strategy to fight against climate change [7]. To this end, the United Nations (UN) have introduced 17 environmental objectives in the Agenda 2030, with the seventh specifically focusing on i) ensuring access to affordable, reliable, sustainable and modern energy systems for all; ii) increasing the integration of renewable energy into the global energy system; iii) enhancing energy efficiency use [8].
The generation of electricity through photovoltaics emerges as a viable solution to combat climate change, providing significant environmental benefits compared to conventional (fossil) energy production [9]. However, the initial establishment of Ground Photovoltaic Farms (GPF) involved transforming suitable areas, resulting in considerable impacts on crop vegetation loss, biodiversity, and ecosystem services [[9], [10], [11]]. Hence, the establishment of such GPFs has created an environmental paradox. Efforts to mitigate global warming have inadvertently led to localized shifts in land use, detrimentally affecting human well-being in terms of food production. In this context, the application of energy policy contradicted agricultural policy productions [[11], [12], [13], [14], [15]].
Currently, numerous endeavors are underway to facilitate a more sustainable transition in land utilization within GPFs. This involves devising and orchestrating a multifunctional use of solar farms, thereby enhancing their ecological effectiveness. In line with this, agrivoltaics emerge as a solution that seamlessly integrates both agricultural production and energy generation. This entails positioning photovoltaic (PV) panels above agricultural land at a height conducive to cultivation and the use of agricultural machines, or incorporating them into structures like shading installations [[16], [17], [18]].
The integration of PV panels into agricultural settings returns several benefits for crop production (Table 1).
Acknowledging the well-documented decline in leaf net photosynthetic rate under shading conditions, leading to rapid stomatal closure [30], it is important to note that appropriate shading can reduce leaf evapotranspiration. This, in turn, enhances water use efficiency, albeit with variations across plant species. Furthermore, the presence of PV panels helps lower air temperatures beneath them, thus mitigating the impact of the increasing frequency of extreme temperatures associated with climate change. In addition to these effects, the presence of PV panels aids in balancing soil moisture, fostering an environment conducive to plant growth.
Greater biomass, directly linked to enhanced crop productivity, is often associated with eco-physiological adaptations to shade known as Shade Avoidance Syndrome (SAS). This adaptive response involves a reduction in the overall quantity of visible light within the 400–700 nm range, commonly referred as photosynthetically active radiation (PAR) [31,32]. Lately it has been demonstrated that the light spectral distribution affects the biomass accumulation and morphology of horticultural crops. In particular, it has been demonstrated that indoor-growth of lettuce plants achieved maximum accumulation of biomass using a light spectrum that emphasized the red and far-red wavebands and avoided a high spectral irradiance ratio of the blue and green bands [33]. Consequently, the shading effect induces specific morphological and physiological modifications in plants in response to low sunlight [34,35]. Plants, under shading conditions, tend to increase photosynthetic efficiency by expanding leaf area to optimize light usage [36]. Besides, shading leads to an elevation in leaf chlorophyll content while decreasing the chlorophyll a/b ratio, thereby improving plant photosynthetic activity [37]. Singhakumara et al. [38] observed that shade-tolerant plants generally exhibit larger leaf area, higher chlorophyll content, and lower leaf mass per unit area compared to shade-sensitive ones. These findings emphasize the nuanced responses of plants to shading, involving adjustments in various physiological parameters to adapt and optimize their photosynthetic activity under reduced light conditions.
The impact of shade depends on several factors, including plant species, environmental conditions, and crop management. While shading may lead to increased production in certain instances, it might have negative or negligible effects under different conditions [39,40]. In terms of food production, SAS can prove advantageous for specific crops harvested for leaves, stems, or roots [41].
Thus, the behavior of crops cultivated in agrivoltaic systems can exhibit variability, necessitating in-depth studies to understand food security in relation to specific locations, crop types, and employed technologies. Some agronomic crops may be more suitable for the combination of agricultural activities under PV panels than others. Notably, shadow-tolerant crops, such as lettuce, emerge to benefit more from the agrivoltaic system, displaying morphological adaptations without compromising yield [19,20].
While the effects of the shade generated by PV panels on quantitative biomass production have been extensively studied and linked to less water stress [16,18,21,22,25], the correlation between increased biomass, shade and SAS on stimulating edible biomass production remains unexplored in agrivoltaic system. Moreover, the effects of shade on the nutritional composition of plant food, particularly secondary health-promoting metabolites, have received limited attention [40]. These effects could have far-reaching implications for the food security of crops grown under PV panels. Food security, defined as universal access to a sufficient and safe supply of nutritious food, with quality parameters linked to human health promotion [42], encompasses not only the quantity availability of food but also its quality, access, and utilization to promote good health and the stability of these conditions over time [43,44]. It is a critical aspect included in the UN goals, aiming to reduce hunger, malnutrition, and related social and health issues [42]. Currently, climate change compromises food security by reducing water availability for crop production [43,45,46]. Moreover, the water crisis's impact on agricultural production could be exacerbated by the rise in extreme temperatures, potentially overstimulating plant evapotranspiration [45]. In this context, the implementation of agrivoltaic systems emerges as a promising solution, combining increased renewable energy production with enhanced crop production resilience against the impacts of climate change (Table 1).
In this context, pivotal questions arise, forming the basis for a novel sustainable perspective in agrivoltaic application: Can agrivoltaic systems contribute to food security? Can the shade cast by PV panels enhance the yield of edible biomass? Can this shading influence the nutritional quality of the edible biomass, particularly in terms of human health benefits? To address these inquiries, our study focuses on the impact of PV panel-generated shade on chicory crop (Cichorium intybus L., Otrantina variety). Chicory was selected owing to its inclusion in the ESOSCHEME policy, a part of the Community Agricultural Policy (CAP) dedicated to promoting biodiversity conservation. To promote pollination ecosystem services, ESOSCHEME incentivizes farmers to allocate part of their fields on pollination support and not for harvest, in exchange for financial support [47]. Moreover, chicory cultivation has already been undertaken by some agrivoltaics companies in the southern part of the Puglia region in Italy [48]. Therefore, the primary objective of this study was to assess the potential impact of agrivoltaics in maintaining food security under different water availability conditions in an open field trial. Specifically, food security was assessed by measuring crop productivity in terms of edible biomass produced. Crop quality was assessed by examining the concentration of secondary metabolites in the edible biomass, which is important for maintaining human health.
https://www.sciencedirect.com/science/article/abs/pii/S0306261923019293
