POWER TOWER

Power towers use an array of flat, movable mirrors (called heliostats) to focus the sun's rays upon a collector tower (the target). The high energy at this point of concentrated sunlight is transferred to a working fluid for conversion to electrical energy in a heat engine, or in some instances, stored for nighttime usage, in order to provide a more continuous output.Parabolic troughsParabolic troughA long row of parabolic mirrors concentrates sunlight on a tube filled with a heat transfer fluid (usually oil). As with the power tower, this heated oil is used to power a conventional steam turbine, or stored for nighttime use. The largest operating solar power plant, as of 2007, is one of the SEGS parabolic trough systems in the Mojave Desert in California, USA (see Solar power plants in the Mojave Desert).Concentrating collector with steam engineSolar energy converted to heat in a concentrating collector can be used to boil water into steam (as is done in nuclear and coal power plants) to drive a steam engine or steam turbine. The concentrating collector can be a trough collector, parabolic collector, or power tower.
A parabolic solar collector concentrating the sun's rays on the heating element of a Stirling engine. The entire unit acts as a solar tracker.Solar energy converted to heat in a concentrating (dish or trough parabolic) collector can be used to drive a Stirling engine, a type of heat engine which uses a sealed working gas (i.e. a closed cycle) and does not require a water supply.Until recently, a solar Stirling system held the record for converting solar energy into electricity (30% at 1,000 watts per square meter). Such concentrating systems produce little or no power in overcast conditions and incorporate a solar tracker to point the device directly at the sun. That record has been broken by a so-called concentrator solar cell produced by Boeing-Spectrolab which claims a conversion efficiency of 40.7 percent.

SOLAR COOKING

Solar Cookers use sunshine as a source of heat for cooking
as an alternative to fire.
A solar box cooker traps the sun's energy in an insulated
box; such boxes have been successfully used for cooking,
pasteurization and fruit canning. Solar cooking is helping
many developing countries, both reducing the demands for
local firewood and maintaining a cleaner breathing
environment for the cooks.
The first known western solar oven is attributed to Horace
de Saussure in 1767, which impressed Sir John Herschel
enough to build one for cooking meals on his astronomical
expedition to the Cape of Good Hope in Africa in 1830.
Today, there are many different designs in use around the
world.

SOLAR HEATING

Solar hot water systems use sunlight to heat water. They may be used to heat domestic hot water, for space heating or to heat swimming pools. These systems are composed of solar thermal collectors, a storage tank and a circulation loop. The three basic classifications of solar water heaters are:• Batch systems which consist of a tank that is directly heated by sunlight. These are the oldest and simplest solar water heater designs, however; the exposed tank can be vulnerable to cooldown. • Active systems which use pumps to circulate water or a heat transfer fluid.• Passive systems which circulate water or a heat transfer fluid by natural circulation. These are also called thermosiphon systems.
A Trombe wall is a passive solar heating and ventilation system consisting of an air channel sandwiched between a window and a sun-facing wall. Sunlight heats the air space during the day causing natural circulation through vents at the top and bottom of the wall and storing heat in the thermal mass. During the evening the Trombe wall radiates stored heat.A transpired collector is an active solar heating and ventilation system which consists of a perforated sun-facing wall. The wall acts as a solar thermal collector and pre-heats air as it is drawn into the building's ventilation system through the perforations. These systems are inexpensive and commercial models have achieved efficiencies above 70%. Most systems pay for themselves within 4-8 years.

TECHNOLOGIES

Types of technologies
Solar design in architecture
Solar heating systems
Solar cooking
Solar lighting
Photovoltaics
Solar thermal electric power plants
Solar updraft tower
Solar pond
Power towers
Solar chemical

SOLAR POWER

Solar power (also known as solar energy) is the technology of obtaining usable energy from the light of the sun. Solar energy has been used in many traditional technologies for centuries, and has come into widespread use where other power supplies are absent, such as in remote locations and in space.Solar energy is currently used in a number of applications:• Heat (hot water, building heat, cooking)• Electricity generation (photovoltaics, heat engines)• Desalination of seawater
Map of global solar energy resources. The colours show the average available solar energy on the surface during 1991 to 1993. For comparison, the dark disks represent the land area required to supply the primary energy demand in the year 2010 using currently available technology (i.e. with a conversion efficiency of 8%).Solar radiation reaches the Earth's upper atmosphere at a rate of 1366 watts per square meter (W/m2). The first map shows how the solar energy varies in different latitudes.While traveling through the atmosphere 6% of the incoming solar radiation (insolation) is reflected and 16% is absorbed resulting in a peak irradiance at the equator of 1,020 W/m². Average atmospheric conditions (clouds, dust, pollutants) further reduce insolation by 20% through reflection and 3% through absorption. Atmospheric conditions not only reduce the quantity of insolation reaching the Earth's surface but also affect the quality of insolation by diffusing incoming light and altering its spectrum.