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The advantages of solar energy

Solar power is the technology of obtainingbatteries 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 manyphotovoltaic cells, are devices or banks of
traditional technologies for centuries anddevices that use the photovoltaic effect of
has come into widespread use where othersemiconductors to generate electricity
power supplies are absent, such as in remotedirectly 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 ofhas 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, heatlimited "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 the5,300 MW as of the end of 2005.[citation
environmental costs and limited supply ofneeded] This is only one part of
other power sources such as fossil fuels aresolar-generated electric power. For solar
realized.reflector  plants  see  below.
Solar radiation reaches the Earth's upperDeclining manufacturing costs (dropping at 3
atmosphere at a rate of 1,366 watts perto 5% a year in recent years) are expanding
square meter (W/m2).[1] However, not all ofthe range of cost-effective uses. The average
this energy is available for use at groundlowest retail cost of a large photovoltaic
level. While traveling through thearray declined from $7.50 to $4 per watt
atmosphere, 6% of the incoming solarbetween 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 atincentives, solar electric power can now pay
the equator of 1,020 W/m2.[2] Averagefor 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% throughutility grid through a special inverter - now
absorption.[3] Atmospheric conditions notmake up the largest part of the market. In
only reduce the quantity of insolation2003 worldwide production of solar cells
reaching the earth's surface but also affectincreased by 32%. Between 2000 and 2004 the
the quality of insolation by diffusingincrease 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 averagesilicon have been hamering production
global irradiance calculated from satelliteworldwide since late 2004. Analysts have
data collected from 1991 to 1993. Forpredicted the similar supply problems during
example, in North America the average2006  and  2007.
insolation lies between 125 and 375 W/m2 (3
to 9 kWh/m2/day). [4] This is the availableSolar  thermal  electric  power  plants
power, and not the delivered power.
Photovoltaic panels currently convert aboutSolar 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 contiguousto electrical power production).Main article:
United States on average delivers 19 to 56 WSolar  thermal  energy
m2 or 0.45-1.35 kWh/m2/day. [5] The dark
disks on the second image on the right are anSolar thermal energy can be used to heat a
example of the land areas that, if coveredheat exchanger to high temperature and the
with 8% efficient solar panels, would produceheat is used to produce electric power or for
slightly more energy in the form ofother  industrial  purposes.
electricity than the total world primary
energy supply in 2003. [6] While averagePower  towers
insolation and power values offer insight
into solar power's potential on a regionalPower towers (also know as 'central tower'
scale, locally relevant conditions need to bepower 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 effecttarget). The high energy at this point of
of pollution that is allowing less sunlightconcentrated sunlight is transferred to a
to reach the Earth's surface. It issubstance that can store the heat for later
intricately linked with pollution particlesuseage.
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 potentialSolar 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 solarwater into steam (as is done in nuclear and
energy available at sea level over thecoal power plants) to drive a steam engine or
timeframe 1961–90, mostly fromsteam turbine. The concentrating collector
increased reflection from clouds back intocan 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 useA parabolic solar collector concentrating the
solar energy to create chemical energysun's rays on the heating element of a
through photosynthesis. Humans regularly useStirling engine. The entire unit acts as a
this energy burning wood or fossil fuels, orsolar 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  technologiesengine. The Stirling engine is a type of heat
engine which uses a sealed working gas (i.e.
Many technologies have been developed to makea closed cycle) and does not require a water
use of solar radiation. Some of thesesupply.
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  architectureSuch concentrating systems produce little or
no power in overcast conditions and
Solar  heating  systemsincorporate 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 heatSolar  updraft  tower
domestic hot water or for space heating.
These systems are basically composed of solarA solar updraft tower is a relatively
thermal collectors and a storage tank.[8] Thelow-tech solar thermal power plant where air
three basic classifications of solar waterpasses 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 circulatetowards 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 bythe 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 anddowndraft by cooling the air thereby
ventilation system consisting of an airincreasing its density, driving windturbines
channel sandwiched between a window and aat the bottom of the tower. It requires a hot
sun-facing wall. Sunlight heats the air spacearid 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 theit 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 solarA solar pond is a relatively low-tech, low
heating and ventilation system consisting ofcost approach to harvesting solar energy. The
a perforated sun-facing wall which acts as aprinciple is to fill a pond with 3 layers of
solar thermal collector. The collectorwater:
pre-heats air as it is drawn into the
building's ventilation system through theA  top  layer  with  a  low  salt  content
perforations. These systems are inexpensive
and commercial models have achievedAn intermediate insulating layer with a salt
efficiencies above 70 percent. Most systemsgradient, 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 alternativewhich reaches a temperature approaching 90
to fire for cooking.A solar box cooker trapsdegrees  Celsius.
the Sun's energy in an insulated box; such
boxes have been successfully used forThe different densities in the layers because
cooking, pasteurization and fruit canning.of their salt content prevent convection
Solar cooking is helping many developingcurrents developing which would normally
countries, both reducing the demands fortransfer the heat to the surface and then to
local firewood and maintaining a cleanerthe air above. The heat trapped in the salty
environment for the cooks. The first knownbottom layer can be used for different
western solar oven is attributed to Horace depurposes, such as heating of buildings,
Saussure in 1767, which impressed Sir Johnindustrial processes, or generating
Herschel enough to build one for cookingelectricity. There is one in use at Bhuj,
meals on his astronomical expedition to theGujarat, 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  lightingSolar chemical refers to a number of possible
processes that harness solar energy by
Solar lighting or daylighting is the use ofabsorbing sunlight in a chemical reaction in
natural light to provide illumination.a way similar to photosynthesis in plants but
Daylighting offsets energy use in electricwithout using living organisms. No practical
lighting systems and reduces the cooling loadprocess  has  yet  emerged.
on HVAC systems. Although difficult to
quantify, the use of natural light alsoA promising approach is to use focused
offers physiological and psychologicalsunlight to provide the energy needed to
benefits. Builiding orientation, exteriorsplit 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 aresuch  as  zinc.
among the many daylighting features. These
features may be incorporated in existingWhile metals, such as zinc, have been shown
structures but are most effective whento drive photoelectrolysis of water, more
integrated in a solar design package whichresearch has focused on semiconductors.
accounts for factors such as glare, heatFurther research has examined transition
gain, heat loss and time-of-use. Achitecturalmetal compounds, in particular titanium,
trends increasingly favor daylighting as aniobium 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 aultraviolet light to drive the
method of utilising solar energy by matchingphotoelectrolysis of water. Current materials
available sunlight to the hours of the day inalso require an electrical voltage bias for
which it is most useful. DST energy savingsthe hydrogen and oxygen gas to evolve from
have been estimated to reduce totalthe surface, another disadvantage. Current
electricity use in California by .5% (3400research is focusing on the development of
MWh) and peak electricity use by 3% (1000materials capable of the same water splitting
MW).reaction  using  lower  energy visible light.
PhotovoltaicsIt is also possible to use solar energy to
drive industrial chemical processes without a
The solar panels (photovoltaic arrays) onrequirement for fossil fuel.
this small yacht at sea can charge the 12 V



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