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Solar energy is the transformation of heat, the energy that comes from the sun. It has been used for thousands of years in many different ways by people all over the world. The oldest uses of solar energy is for heating, cooking, and drying. Today, it is also used to make electricity where other power supplies are not there, such as in places far away from where people live, and in outer space.
It is becoming cheaper to make electricity from solar energy. Because the Sun always gives heat, solar energy can be considered a renewable energy and an alternative to non-renewable resources like coal and oil.
Solar energy is used today in a number of ways:
- As heat for making hot water, heating buildings and cooking
- To generate electricity with solar cells or heat engines
- To take the salt away from sea water.
- To use sun rays for drying clothes and towels.
- It is used by plants for the process of photosynthesis.
- To use in cooking (solar cookers).
Energy from the Sun
After passing through the Earth's atmosphere, most of the Sun's energy is in the form of visible light and infrared light radiation. Plants convert the energy in sunlight into chemical energy (sugars and starches) through the process of photosynthesis. Humans regularly use this store of energy in various ways, as when they burn wood off fossil fuels, or when simply eating plants, fish and animals.
Solar radiation reaches the Earth's upper atmosphere with the power of 1366 watts per square meter (W/m2). Since the Earth is round, the surface nearer its poles is angled away from the Sun and receives much less solar energy than the surface nearer the equator.
At present, solar cell panels convert, at best, about 15% of the sunlight hitting them into electricity. The dark disks in the third diagram on the right are imaginary examples of the amount of land that, if covered with 8% efficient solar panels, would produce slightly more energy in the form of electricity than the world needed in 2003. 
Types of technologies
Many technologies have been developed to make use of solar radiation. Some of these technologies make direct use of the solar energy (e.g. to provide light, heat, etc.), while others produce electricity.
Solar power plants
Solar power plants convert sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP). Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaics converts light into electric current using the photoelectric effect.
|Photovoltaic power station||Country||Site co-ordinates||Nominal
|Notes and references|
|Topaz Solar Farm||USA||500||installed capacity as of June 2019.|
|Desert Sunlight Solar Farm||USA||500||Commissioned since November 2013 toward final capacity 550 MW|
|Longyangxia Dam Solar Park||China||320||Completed December 2013|
|Solar Star I and II||USA||309||Under construction, 579MW when completed|
|California Valley Solar Ranch||USA||292||399||First 130MW connected Feb 2013.|
|Agua Caliente Solar Project||USA||290||626||completed April 2014|
|Antelope Valley Solar Ranch||USA||266||230 MWAC. Has received government loan guarantee|
Concentrated solar thermal
|9||Palma del Rio||Spain||100|||
Solar cooking uses the Sun as the source of energy instead of standard cooking fuels such as charcoal, coal or gas. Solar cookers are an inexpensive and environmentally sound alternative to traditional ovens. They are becoming widely used in areas of the developing world where deforestation is an issue, financial resources to purchase fuel are limited, and where open flames would pose a serious risk to people and the environment. Solar cookers are covered with a glass plate. They achieve a higher temperature by using mirrors to focus the rays of the sun.
Liquid-based systems heat water or an antifreeze solution in a "hydronic" collector, whereas air-based systems heat air in an "air collector." Both air and liquid systems can supplement forced air systems.
Solar cells can be used to generate electricity from sunlight. It is a device that converts light energy into electrical energy. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight, while the term photovoltaic cell is used when the light source is unspecified.
Solar cells have many applications. They have long been used in situations where electrical power from the grid is unavailable, such as in remote area power systems, Earth-orbiting satellites and space probes, consumer systems, e.g. handheld calculators or wrist watches, remote radiotelephones and water pumping applications. A large no. of solar cells are combined in an arrangement called solar cell panel that can deliver enough electricity for practical use. Electricity produced by solar panels can be stored in rechargeable solar batteries, which is then drawn upon when required.
- A solar panel in the contiguous United States on average delivers 19 to 56 W/m² or 0.45 - 1.35 (kW·h/m²)/day."us_pv_annual_may2004.jpg". National Renewable Energy Laboratory, US. http://www.nrel.gov/gis/images/us_pv_annual_may2004.jpg. Retrieved 2006-09-04.
- International Energy Agency - Homepage
- Technologies: From silicon to the solar cell.
- The Tribune: California Valley's Topaz Solar Farm now producing electricity
- SolarServer: CPI completes massive hybrid solar PV/hydro plant in Western China
- Solar Star Project, Japan DG Demand Drive SunPower's Q3, Forbes, 10/31/2014
- Energy Division Resolution E-4229
- U.S. Solar Market Trends 2013, IREC, July 2014
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- "130MW energized". California Valley Solar Ranch. http://www.californiavalleysolarranch.com/. Retrieved Feb 2013.
- RPS Project Status Table - February Update
- World's Largest Operational Solar PV Project, Agua Caliente, Achieves 250 Megawatts of Grid-Connected Power
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- World’s Biggest Solar PV Plant a Feather in DOE’s Cap, Pete Danko, greentechmedia, May 2, 2014
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- Project Overview
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- Ivanpah Solar Electric Generating System, http://www.nrel.gov/csp/solarpaces/project_detail.cfm/projectID=62, retrieved 2014-02-18
- SEGS Power Stations, http://www.nrel.gov/csp/troughnet/power_plant_data.html, retrieved 2010-03-20
- Abengoa Solar: Abengoa’s Solana, the US’s first large-scale solar plant with thermal energy storage system, begins commercial operation
- CSP World
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- (in Spanish) Lokalizacion de Centrales Termosolares en Espana
- ACS LAUNCHES THE OPERATION PHASE OF ITS THIRD DISPATCHABLE 50 MW THERMAL POWER PLANT IN SPAIN, EXTRESOL-1
- VALLE 1 and VALLE 2
- Active Solar Heating
- "Solar Batteries | Natural Solar" (in en-US). Natural Solar. https://naturalsolar.com.au/solar-batteries/. Retrieved 2018-11-01.
- Solar Energy Industries Association is the national trade association for the US solar energy industry and has information on current commercial technologies and market developments.
- Direct solar U.S. Department of Energy: Energy Efficiency and Renewable Energy - Thermal water splitting
- U.S. Department of Energy: Energy Efficiency and Renewable Energy Solar History Timeline
- National Renewable Energy Laboratory: Concentrating Solar Power (CSP)
- Solar energy in the News
- ESTIF - European Solar Thermal Industry organization (statistics, market situation)
- Solar perspectives in Italy - Information on the Italian Solar Market
- Online article by scientist Jonathan G. Dorn, July 22-2008 The solar thermal power industry experienced a surge in 2007, with 100 megawatts of new capacity worldwide.
- Applications of solar energy Some different techniques to have to maximum utilization of the available solar power.