Solar energy is energy that is present in sunlight. It has been used for thousands of years in many different ways by people all over the world. As well as its traditional human uses in heating, cooking, and drying, it is used today to make electricity where other power supplies are absent, such as in remote places and in space. It is becoming cheaper to make electricity from solar energy and in many situations it is now competitive with energy from coal or oil.
Energy use [change]
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 seawater.
Energy from the Sun [change]
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 or fossil fuels, or when simply eating plants, fish and animals.
Solar radiation reaches the Earth's upper Earth's 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 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 [change]
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 [change]
Solar power plants strive to 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.
Solar cooking [change]
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 heating [change]
The sun may be used to heat water instead of electricity or gas. There are two basic types of active solar heating systems based on the type of fluid — either liquid or air — that is heated in the solar energy collectors. (The collector is the device in which a fluid is heated by 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 [change]
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.
Other pages [change]
- 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.
- Active Solar Heating
Other websites [change]
- The Climate Change Guide easy-to-understand information on Solar energy
- 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
- Prometheus Institute for sustainable development
- 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.
- Earth for Energy, make your own solar panels