Validation of simulated irradiance and power for the Western Wind and Solar Integration Study. Phase II.

The Western Wind and Solar Integration Study (WWSIS) Phase II seeks to quantify the effects on thermal generation plants that may result from integration onto the transmission network of variable generation sources, including wind and solar power plants. The study assumes a large number of additional generating resources, including utility-scale photovoltaic (PV), concentrating solar power (CSP) plants, distributed PV, and wind generation, are added to the grid. Power balance simulations are performed for a study period of one year to quantify the operating costs associated with the additional levels of variable generation. For the WWSIS Phase II study, time series of power output from hypothetical solar plants were calculated from simulated time series of one-minute irradiance at each plant’s location. For all types of solar power, the key input to these calculations is the time series of irradiance at one-minute time steps for calendar year 2006 averaged over the spatial extent of each hypothetical solar plant. Measurements of irradiance at with this temporal and spatial resolution are not available. National Renewable Energy Laboratory staff devised methods to simulate the required irradiance. To build confidence in the conclusions of this study, Sandia National Laboratories conducted validation of the algorithm used to simulate irradiance, and performed a qualitative review of the methods that calculate power from irradiance. We concluded that the simulated power output from utility-scale solar plants was reasonable for the purposes of the WWSIS Phase II study.