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Solar energy

Solar energy

Solar energy is radiant light and heat from the sun that is harnessed using a range of technologies.


Solar energy is electromagnetic radiation emitted by the sun that can be harnessed using a range of technologies. In total, 173,000 terawatts (trillion watts) of solar energy continuously strikes the Earth. Estimates by the US Department of Energy state the amount of sunlight hitting the Earth's surface in an hour and a half is enough to handle the world's energy consumption for a full year.

As much as 54 percent of incoming sunlight reaching the Earth is absorbed or reflected by the Earth's atmosphere. Of the light that strikes the surface, 50 percent is in the visible spectrum, 45 percent is infrared (IR) radiation, and the remainder is made of small amounts of (UV) and other forms of electromagnetic radiation.

Diagram showing the interaction of solar energy with the Earth.
Solar technologies

Solar technologies can harness this energy for a range of uses, including generating electricity, providing light or a comfortable interior environment, and heating water for domestic, commercial, or industrial use. The following are the three main technologies harnessing solar energy:

  • Photovoltaics (PV)—the direct conversion of light into electricity using semiconductors commonly through solar panels
  • Concentrating solar power (CSP)—the use of mirrors to reflect and concentrate sunlight to heat fluid in a receiver in order to generate electricity
  • Solar heating and cooling—the use of solar energy for direct space or water heating without electricity generation

In 2020, the global cumulative solar PV capacity reached 773.2 gigawatts, an increase of 138 gigawatts of new PV capacity compared with the year before. In 2021, 23.6 GWdc of solar PV capacity was installed in the US, bringing the total capacity to 121.4 GWdc—enough to power 23.3 million American homes. This increase accounts for 46 percent of all new electricity-generating capacity added in the US in 2021, the third year in a row that solar has made up the largest share of new electricity generating capacity. In 2021, 3.9 percent of all US electricity generation came from solar energy.


The University of South Wales breaks the record for solar cell efficiency, reaching 34.5 percent.
US National Renewable Energy Laboratory (NREL) in collaboration with SpectroLab Inc. create a solar cell with 33.3 percent efficiency.
Pacific Gas & Electric completes installation of the first grid-supported PV system in Kerman, California.
Researchers at the Universiry of South Wales achieve 20 percent efficiency for silicon cells.
First megawatt-scale PV power station goes on line in Hisperia, California, developed by ARCO Solar.
Solar One a 10-megawatt central-receiver demonstration unit begins operations, establishing the feasibility of CSP.

The project is led by the US Department of Energy with an industry consortium.

Paul MacCready builds Solar Challenger, the first aircraft powered by solar energy.

MacCready flew the aircraft across the English Channel.

ARCO Solar become the first company to produce more than 1 megawatt of PV modules in a year.
President Jimmy Carter installs solar panels on the White House.
US Department of Energy launches the Solar Energy Research Institute - National Renewable Energy Laboratory.

The federal facility is dedicated to harnessing solar energy.

Further Resources


NREL Energy Basics: Solar


August 31, 2020


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