Hourly data about electric power generation illustrate the variability of wind and solar sources relative to the comparatively smooth output from other generation methods.
The California ISO, which operates the electric power system for most of California, provides these hourly data for generation sources that are eligible renewable resources under California's Renewable Portfolio Standard (RPS).
"Power produced by geothermal, biomass, biogas, and small hydro generators can be ... increased, decreased, or controlled to remain fairly constant," the U.S. Energy Information Administration notes. Wind and solar are subject to the conditions of the moment.
