| Solar power is the technology of obtaining | | | | batteries at up to 9 A in full, direct |
| usable energy from the light of the Sun. | | | | sunlightSolar cells, also referred to as |
| Solar energy has been used in many | | | | photovoltaic cells, are devices or banks of |
| traditional technologies for centuries and | | | | devices that use the photovoltaic effect of |
| has come into widespread use where other | | | | semiconductors to generate electricity |
| power supplies are absent, such as in remote | | | | directly from sunlight. Until recently, their |
| locations and in space. | | | | use has been limited because of high |
| | | | manufacturing costs. One cost effective use |
| Solar energy is currently used in a number of | | | | has been in very low-power devices such as |
| applications: | | | | calculators with LCDs. Another use has been |
| | | | in remote applications such as roadside |
| Heating (hot water, building heat, cooking) | | | | emergency telephones, remote sensing, |
| | | | cathodic protection of pipe lines, and |
| Electricity generation (photovoltaics, heat | | | | limited "off grid" home power applications. A |
| engines) | | | | third use has been in powering orbiting |
| | | | satellites and other spacecraft. |
| Desalination of seawater. | | | | |
| | | | Total peak power of installed PV is around |
| Its application is spreading as the | | | | 5,300 MW as of the end of 2005.[citation |
| environmental costs and limited supply of | | | | needed] This is only one part of |
| other power sources such as fossil fuels are | | | | solar-generated electric power. For solar |
| realized. | | | | reflector plants see below. |
| | | | |
| Solar radiation reaches the Earth's upper | | | | Declining manufacturing costs (dropping at 3 |
| atmosphere at a rate of 1,366 watts per | | | | to 5% a year in recent years) are expanding |
| square meter (W/m2).[1] However, not all of | | | | the range of cost-effective uses. The average |
| this energy is available for use at ground | | | | lowest retail cost of a large photovoltaic |
| level. While traveling through the | | | | array declined from $7.50 to $4 per watt |
| atmosphere, 6% of the incoming solar | | | | between 1990 and 2005[citation needed]. With |
| radiation (insolation) is reflected and 16% | | | | many jurisdictions now giving tax and rebate |
| is absorbed resulting in a peak irradiance at | | | | incentives, solar electric power can now pay |
| the equator of 1,020 W/m2.[2] Average | | | | for itself in five to ten years in many |
| atmospheric conditions (clouds, dust, | | | | places. "Grid-connected" systems - that is, |
| pollution) further reduce insolation by 20% | | | | systems with no battery that connect to the |
| through reflection and 3% through | | | | utility grid through a special inverter - now |
| absorption.[3] Atmospheric conditions not | | | | make up the largest part of the market. In |
| only reduce the quantity of insolation | | | | 2003 worldwide production of solar cells |
| reaching the earth's surface but also affect | | | | increased by 32%. Between 2000 and 2004 the |
| the quality of insolation by diffusing | | | | increase in worldwide solar energy capacity |
| incoming light and altering its spectrum. | | | | was an annual 60%. 2005 was expected to see |
| | | | large growth again, but shortages of refined |
| The image on the right shows the average | | | | silicon have been hamering production |
| global irradiance calculated from satellite | | | | worldwide since late 2004. Analysts have |
| data collected from 1991 to 1993. For | | | | predicted the similar supply problems during |
| example, in North America the average | | | | 2006 and 2007. |
| insolation lies between 125 and 375 W/m2 (3 | | | | |
| to 9 kWh/m2/day). [4] This is the available | | | | Solar thermal electric power plants |
| power, and not the delivered power. | | | | |
| Photovoltaic panels currently convert about | | | | Solar Two, a concentrating solar power tower |
| 15% of incident sunlight into electricity; | | | | (an example of solar thermal energy applied |
| therefore, a solar panel in the contiguous | | | | to electrical power production).Main article: |
| United States on average delivers 19 to 56 W | | | | Solar thermal energy |
| m2 or 0.45-1.35 kWh/m2/day. [5] The dark | | | | |
| disks on the second image on the right are an | | | | Solar thermal energy can be used to heat a |
| example of the land areas that, if covered | | | | heat exchanger to high temperature and the |
| with 8% efficient solar panels, would produce | | | | heat is used to produce electric power or for |
| slightly more energy in the form of | | | | other industrial purposes. |
| electricity than the total world primary | | | | |
| energy supply in 2003. [6] While average | | | | Power towers |
| insolation and power values offer insight | | | | |
| into solar power's potential on a regional | | | | Power towers (also know as 'central tower' |
| scale, locally relevant conditions need to be | | | | power plants or 'heliostat' power plants |
| assessed to determine the solar potential of | | | | (power towers)) use an array of flat, |
| a specific site. | | | | moveable mirrors (called heliostats) to focus |
| | | | the sun's rays upon a collector tower (the |
| A recent concern is global dimming, an effect | | | | target). The high energy at this point of |
| of pollution that is allowing less sunlight | | | | concentrated sunlight is transferred to a |
| to reach the Earth's surface. It is | | | | substance that can store the heat for later |
| intricately linked with pollution particles | | | | useage. |
| and global warming, and it is mostly of | | | | |
| concern for issues of global climate change, | | | | Concentrating collector with steam engine |
| but is also of concern to proponents of solar | | | | |
| power because of the existing and potential | | | | Solar energy converted to heat in a |
| future decreases in available solar energy. | | | | concentrating collector can be used to boil |
| The order of magnitude is about 4% less solar | | | | water into steam (as is done in nuclear and |
| energy available at sea level over the | | | | coal power plants) to drive a steam engine or |
| timeframe 1961–90, mostly from | | | | steam turbine. The concentrating collector |
| increased reflection from clouds back into | | | | can be an trough collector, parabolic |
| outer space. | | | | collector, or power tower. |
| | | | |
| After passing through the Earth's atmosphere, | | | | Concentrating collector with Stirling engine |
| most of the sun's energy is in the form of | | | | |
| visible and Infrared radiations. Plants use | | | | A parabolic solar collector concentrating the |
| solar energy to create chemical energy | | | | sun's rays on the heating element of a |
| through photosynthesis. Humans regularly use | | | | Stirling engine. The entire unit acts as a |
| this energy burning wood or fossil fuels, or | | | | solar tracker.Solar energy converted to heat |
| when simply eating the plants. | | | | in a concentrating (dish or trough parabolic) |
| | | | collector can be used to drive a Stirling |
| Types of technologies | | | | engine. The Stirling engine is a type of heat |
| | | | engine which uses a sealed working gas (i.e. |
| Many technologies have been developed to make | | | | a closed cycle) and does not require a water |
| use of solar radiation. Some of these | | | | supply. |
| technologies make direct use of the solar | | | | |
| energy (e.g. to provide light, heat, etc.), | | | | A solar Stirling system holds the record for |
| while other technologies produce electricity. | | | | converting solar energy into electricity (30 |
| | | | percent at 1,000 watts per square meter). |
| Solar design in architecture | | | | Such concentrating systems produce little or |
| | | | no power in overcast conditions and |
| Solar heating systems | | | | incorporate a solar tracker to point the |
| | | | device directly at the sun. |
| Solar hot water systems use sunlight to heat | | | | |
| water. These systems may be used to heat | | | | Solar updraft tower |
| domestic hot water or for space heating. | | | | |
| These systems are basically composed of solar | | | | A solar updraft tower is a relatively |
| thermal collectors and a storage tank.[8] The | | | | low-tech solar thermal power plant where air |
| three basic classifications of solar water | | | | passes under a very large agricultural glass |
| heaters are: | | | | house (between 2 and 8 km in diameter), is |
| | | | heated by the sun and channeled upwards |
| Active systems which use pumps to circulate | | | | towards a convection tower. It then rises |
| water or a heat transfer fluid. | | | | naturally and is used to drive turbines, |
| | | | which generate electricity. |
| Passive systems which circulate water or a | | | | |
| heat transfer fluid by natural circulation. | | | | Energy tower |
| These are also called thermosiphon systems. | | | | |
| | | | An energy tower is an alternative proposal to |
| Batch systems using a tank directly heated by | | | | the solar updraft tower. The energy tower is |
| sunlight. | | | | driven by spraying water at the top of the |
| | | | tower, evaporation of water causes a |
| A Trombe wall is a passive solar heating and | | | | downdraft by cooling the air thereby |
| ventilation system consisting of an air | | | | increasing its density, driving windturbines |
| channel sandwiched between a window and a | | | | at the bottom of the tower. It requires a hot |
| sun-facing wall. Sunlight heats the air space | | | | arid climate and large quantities of water |
| during the day causing natural circulation | | | | (seawater may be used for this purpose) but |
| through vents at the top and bottom of the | | | | it does not require the large glass house of |
| wall and storing heat in the thermal mass. | | | | the solar updraft tower. |
| During the evening the trombe wall radiates | | | | |
| stored heat.[9] | | | | Solar pond |
| | | | |
| A transpired collector is an active solar | | | | A solar pond is a relatively low-tech, low |
| heating and ventilation system consisting of | | | | cost approach to harvesting solar energy. The |
| a perforated sun-facing wall which acts as a | | | | principle is to fill a pond with 3 layers of |
| solar thermal collector. The collector | | | | water: |
| pre-heats air as it is drawn into the | | | | |
| building's ventilation system through the | | | | A top layer with a low salt content |
| perforations. These systems are inexpensive | | | | |
| and commercial models have achieved | | | | An intermediate insulating layer with a salt |
| efficiencies above 70 percent. Most systems | | | | gradient, which sets up a density gradient |
| pay for themsleves within 4-8 years. | | | | that prevents heat exchange by natural |
| | | | convection in the water. |
| Solar cooking | | | | |
| | | | A bottom layer has with a high salt content |
| Solar Cookers use sunshine as an alternative | | | | which reaches a temperature approaching 90 |
| to fire for cooking.A solar box cooker traps | | | | degrees Celsius. |
| the Sun's energy in an insulated box; such | | | | |
| boxes have been successfully used for | | | | The different densities in the layers because |
| cooking, pasteurization and fruit canning. | | | | of their salt content prevent convection |
| Solar cooking is helping many developing | | | | currents developing which would normally |
| countries, both reducing the demands for | | | | transfer the heat to the surface and then to |
| local firewood and maintaining a cleaner | | | | the air above. The heat trapped in the salty |
| environment for the cooks. The first known | | | | bottom layer can be used for different |
| western solar oven is attributed to Horace de | | | | purposes, such as heating of buildings, |
| Saussure in 1767, which impressed Sir John | | | | industrial processes, or generating |
| Herschel enough to build one for cooking | | | | electricity. There is one in use at Bhuj, |
| meals on his astronomical expedition to the | | | | Gujarat, India and another at the University |
| Cape of Good Hope in Africa in 1830. Today, | | | | of Texas El Paso. |
| there are many different designs in use | | | | |
| around the world. | | | | Solar chemical |
| | | | |
| Solar lighting | | | | Solar chemical refers to a number of possible |
| | | | processes that harness solar energy by |
| Solar lighting or daylighting is the use of | | | | absorbing sunlight in a chemical reaction in |
| natural light to provide illumination. | | | | a way similar to photosynthesis in plants but |
| Daylighting offsets energy use in electric | | | | without using living organisms. No practical |
| lighting systems and reduces the cooling load | | | | process has yet emerged. |
| on HVAC systems. Although difficult to | | | | |
| quantify, the use of natural light also | | | | A promising approach is to use focused |
| offers physiological and psychological | | | | sunlight to provide the energy needed to |
| benefits. Builiding orientation, exterior | | | | split water into its constituent hydrogen and |
| shading, sawtooth roofs, clerestory windows, | | | | oxygen in the presence of a metallic catalyst |
| light shelves, skylights and light tubes are | | | | such as zinc. |
| among the many daylighting features. These | | | | |
| features may be incorporated in existing | | | | While metals, such as zinc, have been shown |
| structures but are most effective when | | | | to drive photoelectrolysis of water, more |
| integrated in a solar design package which | | | | research has focused on semiconductors. |
| accounts for factors such as glare, heat | | | | Further research has examined transition |
| gain, heat loss and time-of-use. Achitectural | | | | metal compounds, in particular titanium, |
| trends increasingly favor daylighting as a | | | | niobium and tantalum oxides.[citation needed] |
| cornerstone of sustainable design. | | | | Unfortunately, these materials exhibit very |
| | | | low efficiencies, because they require |
| Daylight saving time (DST) can be seen as a | | | | ultraviolet light to drive the |
| method of utilising solar energy by matching | | | | photoelectrolysis of water. Current materials |
| available sunlight to the hours of the day in | | | | also require an electrical voltage bias for |
| which it is most useful. DST energy savings | | | | the hydrogen and oxygen gas to evolve from |
| have been estimated to reduce total | | | | the surface, another disadvantage. Current |
| electricity use in California by .5% (3400 | | | | research is focusing on the development of |
| MWh) and peak electricity use by 3% (1000 | | | | materials capable of the same water splitting |
| MW). | | | | reaction using lower energy visible light. |
| | | | |
| Photovoltaics | | | | It is also possible to use solar energy to |
| | | | drive industrial chemical processes without a |
| The solar panels (photovoltaic arrays) on | | | | requirement for fossil fuel. |
| this small yacht at sea can charge the 12 V | | | | |