UC San Diego

Utility-scale solar energy has become a popular solution for the renewable energy market and has proven to drive down the cost of energy by introducing competition to the marketplace, however there remains potential for unforeseen impacts. In recent years, more research has been targeted at exploring the impacts of USSE and its effect on climate conditions - both global with climate simulations [16], [7], [11] and at the local level as a threat to ecosystems [20], [12].

In this model, the local ground temperature and respective mass transfer rates are simulated under varied conditions, including an open ground-sky interface and ground behavior with a panel overhead. A sensitivity analysis is also performed to assess the impact of ground emissivity, local wind speed, and relative humidity on local conditions. Further, the relative surface fluxes are evaluated to compare the change in albedo effect in the presence of photovoltaic panels, heliostat panels, to an open ground-sky interface.

Ground surface flux depends heavily on radiative heat transfer with no panel over- head, and depends almost completely on convective heat transfer with a panel overhead, showing hundreds of Watts of flux reduced during the daytime. With a panel overhead, ground temperatures are reduced by up to 40 K during the day, due to shading; during the nighttime the panel keeps the ground temperature warmer by up to 20 K due to lack of radiative exchange with the sky. Increased ground temperature during the nighttime can be resolved by rotating the panels perpendicular to the ground surface, though this has an unknown effect on local wind patterns. Mass transfer rates, specifically evaporation, are reduced up to an order of magnitude during the daytime with the presence of a panel overhead the ground surface; nighttime cases, with no intervention such as rotating the panels, show a lack of condensation formation on the ground surface with panels overhead.

The overall surface flux of the panels when compared to the ground is significantly reduced, especially in the heliostat case, where over 1000 W m−2 is reflected onto either a collector or back to space in the shortwave portion of the spectrum. PV panels show about 100 W m−2 lower surface flux than the open ground. Both panel cases contribute less surface flux to the atmosphere, suggesting lower radiative forcing than the open ground-sky interface.