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Solar explained Where solar is found and used

Solar energy is sunshine

Sunshine is radiant energy from the sun. The amount of solar radiation, or solar energy, that the earth receives each day is many times greater than the total amount of all energy that people consume each day. However, on the earth's surface, solar energy is a variable and intermittent energy source. Nevertheless, use of solar energy, especially for electricity generation, has increased significantly in the United States and around the world in the past 30 years.

Solar energy resources vary by location

The availability and intensity of solar radiation on the earth’s surface varies by time of day and location. In general, the intensity of solar radiation at any location is greatest when the sun is at its highest apparent position in the sky—at solar noon—on clear, cloudless days.

Latitude, climate, and weather patterns are major factors that affect insolation—the amount of solar radiation received on a given surface area during a specific amount of time. Locations in lower latitudes and in arid climates generally receive higher amounts of insolation than other locations. Clouds, dust, volcanic ash, and pollution in the atmosphere affect insolation levels at the surface. Buildings, trees, and mountains may shade a location during different times of the day in different months of the year. Seasonal (monthly) variations in solar resources increase with increasing distance from the earth’s equator.

The type of solar collector also determines the type of solar radiation and level of insolation that a solar collector receives. Concentrating solar collector systems, such as those used in solar thermal-electric power plants, require direct solar radiation, which is generally greater in arid regions with few cloudy days. Flat-plate solar thermal and photovoltaic (PV) collectors are able to use global solar radiation, which includes diffuse (scattered) and direct solar radiation. Learn more about solar radiation.

In general, a solar energy collector with a tracking system will have higher levels of daily and annual insolation than a solar collector in a fixed position. Learn more about PV collector tilt angles and PV collector tracking systems.

The two maps below show U.S. average annual solar radiation in kilowatthours (kWh) per square meter per day (kWh/m2/d) for direct normal irradiance (DNI) used by concentrating solar energy collectors and global horizontal irradiance (GHI) used by flat-plate solar collectors. The world map below shows average daily global solar radiation on a horizontal flat surface.

Map of the United states showing annual direct normal (solar) irradiance with the largest levels in the southwestern United States.

Source: National Renewable Energy Laboratory, U.S. Department of Energy

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Map of the United States showing global horizontal (solar) irradiance with the largest levels in the southwestern United States.

Source: National Renewable Energy Laboratory, U.S. Department of Energy

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World Map of Solar Resources showing greatest concentration in the southern portion of the Northern Hemisphere, South America, Africa, the Middle East, southern Eurasia, the South Pacific, and Australia

World map of solar resources

Source: United Nations Environment Programme (UNEP), NASA Surface meteorology and Solar Energy (SSE), 2008.

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Where solar energy is used

Insolation levels are important for the technical and economic performance of solar energy systems. The availability of financial and other incentives for solar energy are also major factors that influence where solar energy systems are installed. Net metering has been especially important in encouraging the installation of PV systems on homes and businesses.

The U.S. Energy Information Administration (EIA) estimates that solar energy use in the United States increased from about 0.06 trillion British thermal units (Btu) in 1984 to about 1,044 trillion Btu in 2019. Total solar electricity generation increased from about 5 million kWh in 1984, nearly all from utility-scale solar thermal-electric power plants (power plants with at least one megawatt (MW) of electricity generation capacity), to about 107,057 million (104 billion) kWh in 2019, of which 64% was from utility-scale PV power plants, 33% was from small-scale (or distributed) PV systems (systems with less than one MW generation capacity), and 3% was from utility-scale solar thermal-electric power plants.

The maps below show total annual solar electricity generation in each state from utility-scale solar power plants and estimated electricity generation from small-scale PV systems. Most small-scale PV systems are installed on building rooftops. Residential sector small-scale PV systems accounted for 60% of total small-scale PV electricity generation in 2019.

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According to EIA’s International Energy Outlook 2019 Reference case, total world solar electricity generation was about 33 billion kWh in 2010 and 894 billion kWh in 2018, of which the U.S. produced about 11% and China produced about 36%.

Last updated: April 2, 2020