Tag Archive for: solar-suitable crops

By Lee Walston and Heidi Hartmann, Argonne National Laboratory

Pollinator habitat at a solar facility in Minnesota. Photo: Lee Walston, Argonne National Laboratory.

Many of us have witnessed regional land-use transformations towards renewable energy in the last decade. As the fastest growing electricity generating sector in the U.S., solar energy development has grown more than 20x in the past decade and is projected to be the dominant renewable source of electricity by 2040. The recent DOE Solar Futures Study predicts that over 1 terawatt (TW) of utility-scale solar electricity developments will be required to meet net-zero clean-energy objectives in the U.S. by 2050 (Figure 1). This represents a solar land-use footprint of over 10 million acres across the U.S. – roughly the combined area  of Connecticut, Massachusetts, and Rhode Island.

Figure 1. Source: Solar Futures Study

A fundamental question we all face is how to balance solar energy development with other land uses such as agriculture. Given the current and projected land-use requirements, sustained development of solar energy will depend on finding renewable energy solutions that optimize the combined outputs of energy production, ecosystem services, and other land uses. Dual land-use approaches that co-locate solar energy with other forms of land uses, such as agriculture or habitat restoration, have emerged as promising strategies to improving the landscape compatibility of solar energy. The establishment of native pollinator-friendly vegetation at solar facilities (“solar-pollinator habitat”) is one strategy to improve the multifunctionality of these lands that not only provide renewable energy but also offer several ecosystem service benefits such as: (1) biodiversity conservation; (2) stormwater and erosion control; (3) carbon sequestration; and (4) benefits to nearby agricultural fields.

Understanding the true ecosystem service benefits of solar-pollinator habitat will require field studies in different geographic regions to examine the methods of solar-pollinator habitat establishment and link these processes with measured ecosystem service outputs. Given the time required to conduct these direct field studies, most discussions of solar-pollinator habitat thus far have centered on qualitative ecosystem outcomes. Fortunately, there are ways to quantitatively understand some of these potential outcomes. Native habitat restoration has been a focus of scientific research for many years, and we can use these studies to understand the regional methods for solar pollinator habitat establishment (e.g., types of seed mixes, vegetation management) and relate these habitat restoration activities with quantifiable ecosystem responses. For example, there are decades of research on the restoration of the prairie grassland systems in the Midwest and Great Plains – regions that have seen losses of over 90% of their native grasslands due to agricultural expansion.

Because many solar facilities in the Midwest are sited on former agricultural fields, research on ecological restoration of former agricultural fields could be very useful in understanding the establishment and performance of solar-pollinator habitat in the same region. We can look to these studies as surrogate study systems for solar-pollinator habitat and utilize the data from these studies to make inferences on the ecosystem outcomes of solar-pollinator habitat. Along with a team of research partners, we recently took this approach to quantify the potential ecosystem services of solar-pollinator habitat in the Midwest. Our goal was to understand how solar energy developments co-located with pollinator-friendly native vegetation may improve ecosystem services compared to other traditional land uses. We began by reviewing the literature to collect a range of data on vegetation associated with three different land uses: agriculture, solar-turfgrass, and solar-pollinator habitat. The data for each land use included information on vegetation types, root depths, carbon storage potential, and evapotranspiration, to name a few.  

We then developed ecosystem service models for each land use scenario. The land uses corresponded to the following scenarios (Figure 2):

1. Agriculture scenario (baseline “pre-solar” land use);

2. Solar-turfgrass (“business as usual” solar-turfgrass land use) and

3. Solar-pollinator habitat (grassland restoration at solar sites).

We mapped and delineated 30 solar sites in the Midwest and used the InVEST modeling tool to model the following four ecosystem services across all sites and land-use scenarios:

Figure 2. Illustration of land use scenarios at each solar site. Source: Walston et al., 2021.

Our results, published in the journal Ecosystem Services, found that, compared to traditional agricultural land uses, solar facilities with sitewide co‑located, pollinator‑friendly vegetation produced a three-fold increase in pollinator habitat quality and a 65% increase in carbon storage potential. The models also showed that solar-pollinator habitat increased the site’s potential to control sedimentation and runoff by more than 95% and 19%, respectively (Figure 3). This study suggests that in regions where native grasslands have been lost to farming and other activities native grassland restoration at solar energy facilities could represent a win‑win for energy and the environment.

What do these results mean? We hope these results can help industry, communities, regulators, and policymakers better understand the potential ecosystem benefits of solar-pollinator habitat. These findings may be used to build cooperative relationships between the solar industry and surrounding communities to better integrate solar energy into agricultural landscapes. While our study provides a quantitative basis for understanding these potential ecosystem benefits, additional work is needed to validate model results and collect the primary data that would support economic evaluations to inform solar-native grassland business decisions for the solar industry and quantify the economic benefits of services provided to nearby farmers, landowners, and other stakeholders.

Figure 3. Average ecosystem service values for the thirty Midwest solar facilities modeled with InVEST: (A) pollinator supply; (B) carbon storage; (C) sediment export; and (D) water retention. Source: Walston et al. 2021.

Increasing energy demands and the drive towards low carbon (C) energy sources has prompted a rapid increase in ground-mounted solar parks across the world. This represents a significant global land use change with implications for the hosting ecosystems that are poorly understood. In order to investigate the effects of a typical solar park on the microclimate and ecosystem processes, we measured soil and air microclimate, vegetation and greenhouse gas emissions for twelve months under photovoltaic (PV) arrays, in gaps between PV arrays and in control areas at a UK solar park sited on species-rich grassland. Our results show that the PV arrays caused seasonal and diurnal variation in air and soil microclimate. Specifically, during the summer we observed cooling, of up to 5.2 °C, and drying under the PV arrays compared with gap and control areas. In contrast, during the winter gap areas were up to 1.7 °C cooler compared with under the PV arrays and control areas. Further, the diurnal variation in both temperature and humidity during the summer was reduced under the PV arrays. We found microclimate and vegetation management explained differences in the above ground plant biomass and species diversity, with both lower under the PV arrays. Photosynthesis and net ecosystem exchange in spring and winter were also lower under the PV arrays, explained by microclimate, soil and vegetation metrics. These data are a starting point to develop understanding of the effects of solar parks in other climates, and provide evidence to support the optimisation of solar park design and management to maximise the delivery of ecosystem services from this growing land use.

Global energy demand is increasing as greenhouse gas driven climate change progresses, making renewable energy sources critical to future sustainable power provision. Land-based wind and solar electricity generation technologies are rapidly expanding, yet our understanding of their operational effects on biological carbon cycling in hosting ecosystems is limited. Wind turbines and photovoltaic panels can significantly change local ground-level climate by a magnitude that could affect the fundamental plant–soil processes that govern carbon dynamics. We believe that understanding the possible effects of changes in ground-level microclimates on these phenomena is crucial to reducing uncertainty of the true renewable energy carbon cost and to maximize beneficial effects. In this Opinions article, we examine the potential for the microclimatic effects of these land-based renewable energy sources to alter plant–soil carbon cycling, hypothesize likely effects and identify critical knowledge gaps for future carbon research. Land use change for land-based renewables (LBR) is global, widespread and predicted to increase. Understanding of microclimatic effects is growing, but currently incomplete, and subsequent effects on plant–soil C cycling, greenhouse gas (GHG) emissions and soil C stocks are unknown. We urge the scientific community to embrace this research area and work across disciplines, including plant–soil ecology, terrestrial biogeochemistry and atmospheric science, to ensure we are on the path to truly sustainable energy provision.

To date, the impacts of agriphotovoltaic (APV) condition on the production yield of crop have been studied; however, the effect of APV production on the sensorial quality and consumer acceptability of the produce remains unexplored. Therefore, to address this knowledge gap, we cultivated “Winter Storm” cabbage under solar panels and in open field in 2020. The weight and diameter reduction rate of fresh cabbage grown under APV condition compared to open field conditions were 9.7% and 1.2%, respectively. The levels of glucosinolates and their hydrolysis products were not significantly different in the fresh cabbage between the two conditions. The amount of volatile organic compounds, which may affect the perception of smell, were significantly higher in the cabbage juice prepared from the ones grown in open-field conditions than in the juice prepared from cabbages grown under APV conditions. However, untrained subjects could not distinguish the difference in the quality of the 2 sets of cabbage juices in the triangle test. Regardless of the distinguishing features of color, aroma, and taste, the subjects did not have any preference between the two different cabbage juices.

The growing need for clean energy and food production are favoring the use of underused spaces, such as rooftops. This study aims to demonstrate the compatibility of the use of rooftops both for the production of photovoltaic energy and for the production of food, despite the fact that both compete for the same resource, sunlight (rooftop agrivoltaic). The results show that in these environmental conditions, the cultivation of plants that demand little sunlight, such as lettuce, is compatible with the shading produced by photovoltaic panels.

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 article describes a planned three-year study (2019-2022) to understand the effect of shading below solar panels in apple production. This study will include tree water status, irrigation requirements, and fruit growth. The first-year results of the study are included.  

This thesis examines the crop outputs for Swiss chard, kale, pepper, and broccoli in an agrisolar system with different gap spacings between solar panel clusters. It concludes that the biomass crop yields of agrisolar plots are restricted significantly for Swiss chard, kale, or pepper compared against the full-sun control plot yields but not for broccoli stem and leaf yields.

This article concerns research conducted at a 100-m2 experimental farm with three sub-configurations: no modules (control), low module density, and high module density. In each configuration, 9 stalks/m2 were planted 0.5 m apart. The biomass of corn stover grown in the low-density configuration was larger than that of the control configuration by 4.9%. Also, the corn yield per square meter of the low-density configuration was larger than that of the control by 5.6%. 

This article reviews factors that influence solar PV and agronomic management in agrisolar systems. The authors conclude that several adjustments for crop selection and management are needed due to light limitation, microclimate condition beneath the solar structure, and solar structure constraints. The authors also conclude that a systematic irrigation system is required to prevent damage to the solar panel structure.