- Solar Energy Definition: Solar energy is defined as the light and heat from the Sun, created by nuclear fusion reactions.
- Solar Energy Production: The Sun produces solar energy by converting hydrogen into helium, emitting large amounts of heat and light.
- Renewable and Pollution-Free: Solar energy is a renewable and pollution-free source of energy, consistently available from the Sun.
- Historical Development: The first solar collector, made in 1767, started the development of solar energy technology.
- Modern Applications: Large-scale solar farms, like those in India and China, show the extensive use of solar energy for electricity production.
Solar Energy System
Solar energy is the Sun’s light and heat, produced by core fusion that converts about 600 million tonnes of hydrogen to helium each second. That process releases heat and electromagnetic radiation. Most of the heat stays in the Sun and keeps fusion going, while radiation, including visible, infrared and ultraviolet light, leaves into space. Solar energy arrives as sunlight after that nuclear process. The Sun, like other stars, is a large sphere of hydrogen and helium. In the core, hydrogen fuses to helium at about 7 × 1011 kg per second.
Heat from the Sun’s centre spreads out and reaches the photosphere, where the temperature is about 5800 K. Stefan-Boltzmann’s law then sets the total power the surface radiates and the solar power that reaches Earth. Solar energy systems now generate electricity and also heat water or cook food. Most of India’s electricity still comes from coal-fired thermal power plants, though that generation share is no longer a fixed 65%. Coal stocks are finite, so solar systems are one way to cut that dependence.
A solar energy system collects that radiation. The Sun sits at the centre of the solar system and radiates at a fairly steady rate, so the resource is renewable and does not emit combustion pollutants at the collector. Earth does not receive or use the Sun’s full output, for reasons such as:
- Earth rotates on its polar axis, so any site sees day and night.
- The atmosphere absorbs and scatters part of the incoming radiation.
- Earth is about one astronomical unit from the Sun, so only a tiny fraction of the solar output hits the planet.
Even after those losses, the flux at Earth’s surface is enough to generate electricity without combustion at the array. That lets grids cut some use of Thermal Power Plants and gas plants and leave more coal and oil in the ground. Solar generation has grown in many countries, but it is not yet the main source everywhere, and the electricity is not free: panels, inverters and land still have a cost.
Sunlight at the collector has no fuel cost. The array still needs a capital outlay. After that, maintenance is usually light. Typical module warranties run 25 to 30 years; many arrays keep producing after that at a lower output, rather than for a guaranteed 40 to 50 years.
History of Solar Energy
The first widely cited solar collector was an insulated box with three glass layers, built in 1767 by the Swiss scientist Horace-Benedict de Saussure. The box became known as an early solar oven and reached about 230 degrees Fahrenheit. In 1839 Edmond Becquerel, in France, reported the photovoltaic effect: two electrodes in an electrolyte produced more current when lit. Later work raised the electricity that could be taken from sunlight, and that research is still going on.
In 1873, Willoughby Smith reported photoconductivity in selenium. In 1887 Heinrich Hertz showed that ultraviolet light could help a spark jump between two electrodes. In 1891 Clarence Kemp patented an early solar water heater. Charles Fritts had already built a selenium solar cell in 1883, not 1893. In 1908 William J. Bailey made a copper-coil collector in an insulated box. In 1958 Vanguard 1 used solar cells in space. In the 1970s Exxon’s Solar Power Corporation cut the cost of making silicon panels, a turning point in the history of solar energy. In 1977 the US opened the Solar Energy Research Institute, now NREL. In 1981 Paul MacCready’s Solar Challenger flew on solar power. In 1982 Australia ran early solar-powered cars such as the Quiet Achiever. By then commercial plants were already measured in megawatts, not 20 kilowatts.
In 1999 Spectrolab and NREL reported a concentrator triple-junction cell at 32.3% efficiency, not 36%. A 36.9% Spectrolab cell followed in 2003. Mid-2010s parks such as Gujarat’s Charanka cluster (then about 600 MW) and the Golmud area in China were large for that decade. Both have been passed by later multi-gigawatt projects.
