Solar photovoltaic (PV) technology is being deployed at an unprecedented rate. To this end, we investigated critical soil physical and chemical parameters at a revegetated photovoltaic array and an adjacent reference grassland in Colorado, United States.
This study, performed by a research group that includes AgriSolar Clearinghouse partners Greg-Barron Gafford and Jordan Macknick, describes an integrative approach for the investigation of the co-location of solar photovoltaics and crops, and the potential for co-located agrivoltaic crops in drylands as a solution for the food-energy-water nexus impacts from climate change.
The research focused on three common agricultural species that represent different adaptive niches for dryland environments: chiltepin pepper, jalapeño, and cherry tomato. The researchers created an agrivoltaic system by planting these species under a PV array—3.3m off the ground at the lowest end and at a tilt of 32°—to capture the physical and biological impacts of this approach. Throughout the average three-month summer growing season, researchers monitored incoming light levels, air temperature and relative humidity continuously using sensors mounted 2.5m above the soil surface, and soil surface temperature and moisture at 5-cm depth. Both the traditional planting area (control) and agrivoltaic system received equal irrigation rates, with two irrigation scenarios—daily irrigation and irrigation every 2ays.
The researchers found that shading from the PV panels can provide multiple additive and synergistic benefits, including reduced plant drought stress, greater food production and reduced PV panel heat stress. The agrivoltaic system conditions impacted every aspect of plant activity, though results and significance varied by species. The total fruit production was twice as great under the PV panels of the agrivoltaic system than in the traditional growing environment
Cumulative CO2 uptake was 65% greater in the agrivoltaic installation than in the traditional growing area. Water use efficiency was also 65% greater, indicating that water loss to transpiration was equal between the treatment areas. The increased productivity in the agrivoltaic system is probably due to an alleviation of multiple stress interactions from heat and atmospheric drought.
Because PV panels are sensitive to temperature, the cooling of panels below daytime temperatures of 30 °C positively impacts their efficiency. In this study, researchers found that the PV panels in a traditional ground-mounted array were significantly warmer during the day and experienced greater within-day variation than those over an agrivoltaic understory. Researchers attribute these lower daytime temperatures in the PV panels in the agrivoltaic system to a greater balance of latent heat energy exchange from plant transpiration relative to sensible heat exchange from radiation from bare soil. Across the core growing season, PV panels in an agrivoltaic system were ~8.9+0.2 °C cooler in daylight hours. This reduction in temperature can lead to an increase in PV system performance. Using the system advisor model (SAM) for a traditional and a colocation PV system in Tucson, AZ, researchers calculated that impact from temperature reductions from the agrivoltaic system would lead to a 3% increase in generation over summer months and a 1% increase in generation annually.
These results show the additive benefits of agrivoltaics, to both crop production and energy production, as well as the impacts to ecosystem services such as local climate regulation, water conservation, and drought resiliency.
Renewable energy is a promising alternative to fossil fuel based energy, but its development can require a complex set of environmental tradeoffs. A recent increase in solar energy systems, especially large, centralized installations, underscores the urgency of understanding their environmental interactions. Synthesizing literature across numerous disciplines, the researchers review direct and indirect environmental impacts both beneficial and adverse of utility scale solar energy (USSE) development, including impacts on biodiversity, land use and land cover change, soils, water resources, and human health. Additionally, they review feedbacks between USSE infrastructure and land atmosphere interactions and the potential for USSE systems to mitigate climate change. Several characteristics and development strategies of USSE systems have low environmental impacts relative to other energy systems, including other renewables. We show opportunities to increase USSE environmental co benefits, the permitting and regulatory constraints and opportunities of USSE, and highlight future research directions to better understand the nexus between USSE and the environment. Increasing the environmental compatibility of USSE systems will maximize the efficacy of this key renewable energy source in mitigating climatic and global environmental change. Utility scale solar energy systems are on the rise worldwide, an expansion fueled by technological advances, policy changes, and the urgent need to reduce both our dependence on carbon intensive sources of energy and the emission of greenhouse gases to the atmosphere. Recently, a growing interest among scientists, solar energy developers, land managers, and policy makers to understand the environmental impacts both beneficial and adverse of USSE, from local to global scales, has engendered novel research and findings. This review synthesizes this body of knowledge, which conceptually spans numerous disciplines and crosses multiple interdisciplinary boundaries. The disadvantageous environmental impacts of USSE have not heretofore been carefully evaluated nor weighted against the numerous environmental benefits particularly in mitigating climate change and co benefits that solar energy systems offer. Indeed, several characteristics and development strategies of USSE systems have low environmental impacts relative to other energy systems, including other renewable energy technologies. Major challenges to the widespread deployment of USSE installations remain in technology, research, and policy. Overcoming such challenges, high lighted in the previous sections, will require multidisciplinary approaches, perspectives, and collaborations. This review serves to induce communication across relatively disparate disciplines but intentional and structured coordination will be required to further advance the state of knowledge and maximize the environmental benefits of solar energy systems at the utility scale.
Threats to pollinators may have profound consequences for ecosystem health as well as our food systems. Concerns about pollinator declines and associated repercussions have led to increased efforts by non-governmental organizations and both public and private sectors to reduce threats to pollinators. One of the most iconic pollinator species, the monarch butterfly (Danaus plexippus plexippus), is recognized and celebrated by people throughout North America; the butterfly’s annual migration stretches from southern Canada to Mexico, covering most of the lower 48 United States during the spring and summer. But monarchs are in trouble. The overwintering population in central Mexico has declined by ~80% since the 1990s. The overwintering population in coastal California has declined by 97% since the 1980s and, in winter of 2018–2019, the population crashed to a mere 0.6% of its historic size. Threatened by habitat loss, insecticides and herbicides, climate change, and other stressors, the species is now being considered for listing under the U.S. Endangered Species Act. Contributions to species conservation efforts can therefore be investments toward helping a species rebound and averting a listing. Electric power companies have an opportunity to play a part in the monarch’s recovery. They own and/or manage a substantial amount of land and associated natural resources across North America, including transmission and distribution rights-of-way (ROW), solar fields, wind fields, buffer areas surrounding power plants and substations, and “surplus” land holdings. These acres hold the potential to create a network of habitat to support monarchs and other pollinators across their breeding range. Together, power companies have an opportunity to make a difference by considering the needs of these important animals when managing habitat and revegetating land.
Researchers present here a novel ecosystems approach—agrivoltaics—to bolster the resilience of renewable energy and food production security to a changing climate by creating a hybrid of colocated agriculture and solar PV infrastructure, where crops are grown in the partial shade of the solar infrastructure. They suggest that this energy- and food-generating ecosystem may become an important—but as yet quantitatively uninvestigated—mechanism for maximizing crop yields, efficiently delivering water to plants and generating renewable energy in dryland environments. We demonstrate proof of concept for agrivoltaics as a food–energy–water system approach in drylands by simultaneously monitoring the physical and biological dimensions of the novel ecosystem. We hypothesized that colocating solar and agricultural could yield several significant benefits to multiple ecosystem services, including (1) water: maximizing the efficiency of water used for plant irrigation by decreasing evaporation from soil and transpiration from crop canopies, and (2) food: preventing depression in photosynthesis due to heat and light stress, thus allowing for greater carbon uptake for growth and reproduction. An additional benefit might be (3) energy: transpirational cooling from the understorey crops lowering temperatures on the underside of the panels, which could improve PV efficiency. We focused on three common agricultural species that represent different adaptive niches for dryland environments: chiltepin pepper (Capsicum annuum var. glabriusculum), jalapeño (C. annuum var. annuum) and cherry tomato (Solanum lycopersicum var. cerasiforme). We created an agrivoltaic system by planting these species under a PV array—3.3m off the ground at the lowest end and at a tilt of 32°—to capture the physical and biological impacts of this approach. Throughout the average three-month summer growing season we monitored incoming light levels, air temperature and relative humidity continuously using sensors mounted 2.5m above the soil surface, and soil surface temperature and moisture at 5-cm depth. Both the traditional planting area (control) and agrivoltaic system received equal irrigation rates, and we tested two irrigation scenarios—daily irrigation and irrigation every 2d. The amount of incoming photosynthetically active radiation (PAR) was consistently greater in the traditional, open-sky planting area (control plot) than under the PV panels. This reduction in the amount of incoming energy under the PV panels yielded cooler daytime air temperatures, averaging 1.2+0.3 °C lower in the agrivoltaics system over the traditional setting. Night-time temperatures were 0.5+0.4 °C warmer in the agrivoltaics system over the traditional setting (Fig. 2b). Photosynthetic rates, and therefore growth and reproduction, are also regulated by atmospheric dryness, as represented by vapour pressure deficit (VPD) where lower VPD indicates more moisture in the air. VPD was consistently lower in the agrivoltaics system than in the traditional growing setting, averaging 0.52+0.15 kPa lower across the growing season. Having documented that an agrivoltaic installation can significantly reduce air temperatures, direct sunlight and atmospheric demand for water relative to nearby traditional agricultural settings, we address several questions regarding impacts of the food–energy–water nexus system.
Solar siting is advancing rapidly in New York to meet the state’s climate goals of 70% renewable energy by 2030 and 100% clean energy by 2040, and much of that development is targeted towards farmland. However, with the right policies, incentives and research, solar development can avoid or minimize the most serious negative impacts on the availability and viability of New York’s best farmland and the strength of its agricultural economy and food security. Implementing the smart solar siting strategies recommended in this report can help farmers and agricultural communities capitalize on the benefits of solar development, explore new markets, participate in cutting-edge research partnerships, and continue growing the food we need now and in the future, all while combatting climate change.
This report importantly provides a critical lens through which the importance of policy and land use analysis is justified as a response to conflicting community feedback about the agriculture-solar shift. The findings of this report are particularly relevant for the LACDRP, the client, as the agency has been tasked with identifying opportunities to preserve agriculture across the County and supporting local renewable energy resources. The agency will use the findings of this report to guide updates to the Los Angeles County General Plan and the Los Angeles County Climate Action Plan. This could serve as a guide for the future development of agrivoltaic operations in similar geographic locations with similar concerns related to housing and agricultural land use situations.
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