Benchmarking solar power and irradiance forecasting accuracy at Sacramento Municipal Utility District

The Sacramento Municipal Utility District has been working with several commercial forecasters to evaluate the performance of their forecasts in predicting PV output. The work leverages SMUD´s network of 74 irradiance monitoring sites that were installed and are maintained by NEO Virtus Engineering, in addition to measuring output from 8 utility scale PV arrays totaling nearly 100 MW of capacity. The sensor network was designed to mirror the National Digital Forecast Database 5km grid; SMUD sensors were placed in the middle of the grid cells. The work described in this paper examines the state of the art forecasting accuracies for utility scale PV plants and irradiance forecasts over a uniformly spaced geographic area. This study offers insight into the geospatial portion of the forecast, as solar forecasters move to more advanced techniques. The results from this trial drive inputs to how SMUD can improve solar forecast usefulness and implement new tools such as a distributed generation forecast.