Renewable energy production variability by hour of day, and by season (graph)

– …illustrate the variability of wind and solar generation relative to the comparatively smooth output from other generation sources

– Power produced by geothermal, biomass, biogas, and small hydro generators can be easily dispatched, meaning it can be either increased, decreased, or controlled to remain fairly constant.

– Wind resources are often more available at night.

– Solar power is not generated until the sun comes up, and can increase and decrease quickly as the sun rises, sets, or is blocked by cloud cover. However, much of California’s utility-scale solar capacity is based on concentrating solar technology, which embodies enough thermal storage to continue generating power for a few hours after the sun goes down

– The variability of wind and solar power generation leads to challenges in power system operations and planning.

– The contribution towards total generation from eligible renewable resources also varies seasonally. For the dates charted above, the amount of renewable generation as a percentage of the total generation ranges from 8% on Oct 18, 2011 to 14% on May 9, 2011.

via – Today in Energy, EIA