Solar photovoltaics are a low-emission electricity source, but utility-scale development of ground-mounted PV may displace natural or agricultural land and compromise the land’s ability to provide ecosystem services. Co-locating solar photovoltaics with vegetation (sometimes referred to as “agrivoltaics”) could provide a sustainable solution to meet growing food and energy demands while minimizing the land-use impacts of solar energy. Pilot-scale experiments and modeling studies have shown potential for microclimatic alterations by the solar photovoltaics (PV) and the soil-vegetation components of a co-located system to benefit each other. One predicted co-benefit is cooling of PV modules caused by diversion of sensible heat to latent heat for evapotranspiration in the understory vegetation during the growing season. Field experiments that validate the theorized co-benefits within a utility-scale co-located system are less common. Since a large percentage of current and future land use conversions for utility-scale solar energy developments are estimated to occur on farmlands, validation of co-benefits in utility-scale co-located systems are critical for determining the outcome of co-location in a wide range of physical conditions and optimizing the system design for the environmental co-benefits. In the first study of its kind and scale, three years (2019 – 2021) of microclimate and soil data at three vegetated utility-scale solar plants in Minnesota were tied to the power output data from the corresponding period to examine the influence of ground cover on the PV performance and that of the arrays on the underlying soil and vegetation. Soil moisture, soil temperature, air temperature, relative humidity, wind direction/speed were recorded at a 15-minute interval at three treatments: PV arrays with a vegetated ground cover (“veg PV”), PV arrays with a bare ground cover (“bare PV”), and a nearby open space with the same vegetation as that in veg PV (control). Solar irradiance and cumulative precipitation were also recorded in the control. While air temperature and relative humidity were not significantly different between the veg PV and the bare PV, soil moisture was lowest in the bare PV treatment and comparable between the veg PV and the control. Soil moisture also varied spatially along the transect perpendicular to the array, though the spatial distribution was not consistent between the treatments and different facilities. Soil temperature was the lowest in the veg PV and the highest in the control, implying that the partial shade from the solar array keeps the underlying soils cooler. Cooler soil temperature in PV arrays could be a buffer for plants during periods of drought, which implies that co-located systems could be implemented in ecosystem restoration projects for climate resilience.
In addition to the microclimate variables, panel temperature was also recorded at veg PV and bare PV treatments and electricity generation data from the corresponding treatments during the study period was provided by the operators of the facilities. Neither vegetation-driven panel cooling nor the increased power output was observed in the veg PV: the bare PV had higher output and panel temperatures than the veg PV in the early mornings, which may imply that the observed difference in output may be due to shading of the panels in the veg PV treatment by the co-located vegetation. The differential of total daily production (bare PV – veg PV) was positive on most days, though the mode in a frequency distribution of the differential was centered around a very small positive value. The lack of panel-cooling in the veg PV was determined to be due to the short rainfall interval (1-2 days) during the study period. Because of the frequent rainfalls, evaporation in the bare PV treatment and evapotranspiration process in the veg PV treatment remained in an energy-limited stage, and the water would evaporate more rapidly from the bare soil that is more exposed to sunlight and wind. In a drier environment with infrequent rainfalls, evaporation and evapotranspiration would be moisture-limited most of the times, and plants may be able to transpire water from deeper in the soil over a longer period of time to cool the overlying panels, given enough irrigation. The lack of panel cooling in our field sites implies that such environmental co-benefits are likely to be climate dependent, which indicates the need for further study of the influence of the vegetation on the PV operation and vice-versa at large-scale solar facilities in varying climate zones.
Soil samples were also collected for grain size analysis using laser diffraction and nutrient analysis using standard combustion methods. In the sandy soils at the Chisago facility, the bare PV treatment had significantly less clay portion than the veg PV treatment and the control. On the other hand, the clay percentages did not significantly differ among the three treatments in the other two facilities with higher background clay contents (Atwater and Eastwood). The loss in total carbon, nitrogen, and soil cations was also the most pronounced in the bare PV in a facility with the sandy soil. Maintenance of vegetation or re-vegetation while minimizing land grading may protect the soil’s ability to store carbon and nutrients, and that effect may be magnified in coarse-textured soils or ones whose carbon and nutrient storage capacity is otherwise compromised. Overall, the field investigation found that the occurrence of some of the environmental co-benefits of co-locating PV with vegetation depended on the climate and soil, prompting a need for case-by-case consideration of these variables to identify which of the co-benefits will be achievable.
Extensive solar PV development to meet energy demand and decarbonize the energy grid will significantly impact the landscape. Co-location offers an opportunity to mitigate the potential negative impacts of utility-scale solar energy, while still meeting sustainable development goals. A system dynamics model is developed to compare the regional land occupation, water usage, carbon emissions, and change in soil carbon storage resulting from solar development using two different development strategies: traditional, in which the land is graded and vegetation is removed, and co-location, in which land grading is minimized and the soil is re-vegetated with native vegetation. The model is applied in two water-sensitive semi-arid regions with high technical potential for solar energy where agriculture is an important element of the local economy. First, Rajasthan, India is undergoing rapid expansion of solar PV to address the growing energy demand while meeting sustainable energy development goals in a developing economy. The results show that at the current growth rate of solar energy in Rajasthan, solar energy will grow to more than 500 GW by 2070 and will occupy a land area equivalent to 20% to 95% of the unused land suitable for solar. Second, the Central Valley of California has a mature power system in a mature economy seeking to decarbonize. The results show that the overall capacity of California’s solar energy in 2070 will be less than a fifth of Rajasthan’s and occupy at most 10% of California’s unused land suitable for solar. Consequently, soil carbon loss due to future solar capacity additions under conventional development strategy will be similarly smaller in California than in Rajasthan. Together, the results show that the opportunity for the mitigation of the negative impacts of energy development may be greater in younger economies with a developing grid network. / Geoscience
| Identifer | oai:union.ndltd.org:TEMPLE/oai:scholarshare.temple.edu:20.500.12613/10268 |
| Date | 05 1900 |
| Creators | Choi, Chong Seok, 0000-0002-6860-2038 |
| Contributors | Ravi, Sujith, Davatzes, Nicholas, Kim, Bojeong, Spigler, Rachel |
| Publisher | Temple University. Libraries |
| Source Sets | Temple University |
| Language | English |
| Detected Language | English |
| Type | Thesis/Dissertation, Text |
| Format | 138 pages |
| Rights | IN COPYRIGHT- This Rights Statement can be used for an Item that is in copyright. Using this statement implies that the organization making this Item available has determined that the Item is in copyright and either is the rights-holder, has obtained permission from the rights-holder(s) to make their Work(s) available, or makes the Item available under an exception or limitation to copyright (including Fair Use) that entitles it to make the Item available., http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | http://dx.doi.org/10.34944/dspace/10230, Theses and Dissertations |
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