page_title: Variable renewable energy
section_title: Solar power
hierarchical_section_title: Variable renewable energy / Sources / Solar power
caption_attribution_description: English: Solar Stirling engine — solar power in the Mojave Desert, San Bernardino County, California. Credits Source: http://www.wapa.gov/es/pubs/esb/1998/98Aug/at_solargen.htm
context_page_description: Variable renewable energy is a renewable energy source that is non-dispatchable due to its fluctuating nature, like wind power and solar power, as opposed to a controllable renewable energy source such as dammed hydroelectricity, or biomass, or a relatively constant source such as geothermal power.
context_section_description: Solar power is more predictable than wind power and less variable – while there is never any solar power available during the night, and there is a reduction in winter, the only unknown factors in predicting solar output each day is cloud cover, frost and snow. Many days in a row in some locations are relatively cloud free, just as many days in a row in either the same or other locations are overcast – leading to relatively high predictability. Wind comes from the uneven heating of the earth's surface, and can provide about 1% of the potential energy that is available from solar power. 86,000 TW of solar energy reaches the surface of the world vs. 870 TW in all of the world's winds. Total world demand is roughly 12 TW, many times less than the amount that could be generated from potential wind and solar resources. From 40 to 85 TW could be provided from wind and about 580 TW from solar.
  Intermittency inherently affects solar energy, as the production of renewable electricity from solar sources depends on the amount of sunlight at a given place and time.  Solar output varies throughout the day and through the seasons, and is affected by dust, fog, cloud cover, frost or snow.  Many of the seasonal factors are fairly predictable, and some solar thermal systems make use of heat storage to produce grid power for a full day.
  Intermittency: In the absence of an energy storage system, solar does not produce power at night or in bad weather and varies between summer and winter. When intended to produce electricity only for peak air conditioning loads in the summer, there is no intermittency; in the winter can be complemented with wind power for peak loads.
  Capacity factor Photovoltaic solar in Massachusetts 12–15%.  Photovoltaic solar in Arizona 19%. Thermal solar parabolic trough with storage 56%. Thermal solar power tower with storage 73%.
  The impact of intermittency of solar-generated electricity will depend on the correlation of generation with demand. For example, solar thermal power plants such as Nevada Solar One are somewhat matched to summer peak loads in areas with significant cooling demands, such as the south-western United States. Thermal energy storage systems like the small Spanish Gemasolar Thermosolar Plant can improve the match between solar supply and local consumption. The improved capacity factor using thermal storage represents a decrease in maximum capacity, and extends the total time the system generates power.
caption: Dish Stirling
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