The Solar Forecast Arbiter: An open source evaluation framework

Department of Hydrology and Atmospheric Sciences
Weekly Colloquium

Thursday, March 26, 2020
4 pm via Zoom, No In-Person Meeting
Zoom Socializing Before Talk ~3:30 pm to 4:00 pm & After Talk ~5:00 pm to 6:00 pm

Zoom Link:

William F. Holmgren
Assistant Research Professor, Department of Hydrology & Atmospheric Sciences
University of Arizona


The Solar Forecast Arbiter is an open source evaluation framework for solar forecasting. The Arbiter enables evaluations of solar irradiance, solar power, and net-load forecasts that are impartial, repeatable, and auditable. The Arbiter structures evaluation problems to match the needs of operational forecast users at electric utilities. This approach allows the Arbiter to compare, in an applied setting, new forecast methods developed under the DOE SETO Solar Forecasting 2 program to existing commercially available forecasts and simple benchmarks. The Arbiter produces forecast analysis reports with figures and metrics that communicate the relative merits of the forecasts. It also includes a data validation toolkit, reference data sources, robust data privacy protocols, and benchmark forecast capabilities based on persistence and processed NOAA NWP model data. The Solar Forecast Arbiter is designed to support the solar forecasting community, but we expect it can be readily extended to support analyses of other types of time series forecasts such as temperature, precipitation, or river flows. This talk will include an outline of the project goals, a live demonstration of the Arbiter capabilities, and a tour of the open source development process.

Readers are encouraged to learn more about the project at, demo the Arbiter at, and review the source code at


William F. Holmgren is an Assistant Research Professor with the Department of Hydrology and Atmospheric Sciences at the University of Arizona. His primary research interests include solar and wind power forecasts using regional weather models, satellite imagery, and ground sensors through open source software development. He received his Master's and Ph.D. degrees in physics from the University of Arizona and currently leads the UA Power Forecasting Group.