PDF generated using the open source mwlib toolkit. See http://code.pediapress.com/ for more information. PDF generated at: Wed, 16 May 2012 13:50:17 UTC Solar Energy Green Energy For Green Renovation
1. Solar EnergyGreen Energy For Green Renovation PDF generated
using the open source mwlib toolkit. See
http://code.pediapress.com/ for more information.PDF generated at:
Wed, 16 May 2012 13:50:17 UTC
2. ContentsArticles Sunlight1 Solar energy8 Solar thermal
energy 24 Solar thermal collector41 Photovoltaics50 Photovoltaic
system61 Active solar 72 Passive solar building design73
Daylighting86 Hybrid solar lighting92 Daylight saving time 93
Concentrated solar power112 Air mass (solar energy) 118 Thermal
mass124 Thermal energy storage128 Solar water heating 131 Solar
combisystem 151 Solar architecture154 Solar chimney 154 Solar air
conditioning159 Solar water disinfection164 Solar desalination170
Solar Powered Desalination Unit 172 Solar cooker173 Solar pond184
Salt evaporation pond 186 Solar furnace 188 Solar power 190 Solar
chemical199 Solar vehicle 200 Solar balloon 207 Solar sail211 Solar
power by country226 Solar lamp236
3. Solar tracker237 SolarEdge248 Solar inverter 251 Soil
solarization256 Space-based solar power257 Sustainable energy 272
Community solar farm 285 Urban heat island288References Article
Sources and Contributors 297 Image Sources, Licenses and
Contributors 303Article Licenses License309
4. Sunlight 1Sunlight "Sunshine" redirects here. For natural
lighting of interior spaces by admitting sunlight, see Daylighting.
For solar energy available from sunlight, see Insolation. For other
uses, see Sunlight (disambiguation) and Sunshine
(disambiguation).Sunlight, in the broad sense, is the total
frequencyspectrum of electromagnetic radiation given off by theSun,
particularly infrared, visible, and ultraviolet light.On Earth,
sunlight is filtered through the Earthsatmosphere, and solar
radiation is obvious as daylightwhen the Sun is above the
horizon.When the direct solar radiation is not blocked by clouds,it
is experienced as sunshine, a combination of brightlight and
radiant heat. When it is blocked by the clouds orreflects off of
other objects, it is experienced as diffusedlight.The World
Meteorological Organization uses the term"sunshine duration" to
mean the cumulative time duringwhich an area receives direct
irradiance from the Sun ofat least 120 watts per square
meter.[1]Sunlight may be recorded using a sunshine
recorder,pyranometer or pyrheliometer. Sunlight takes about
8.3minutes to reach the Earth.On average, it takes energy between
10,000 and 170,000 Sunlight shining through clouds, giving rise to
crepuscular rays.years to leave the suns interior and then be
emitted fromthe surface as light.[2]Direct sunlight has a luminous
efficacy of about 93 lumens per watt of radiant flux. Bright
sunlight providesilluminance of approximately 100,000 lux or lumens
per square meter at the Earths surface.Sunlight is a key factor in
photosynthesis, a process vital for many living beings on
Earth.CompositionThe spectrum of the Suns solar radiation is close
to that of a blackbody with a temperature of about 5,800K.[3] The
Sun emits EMradiation across most of the electromagnetic spectrum.
Although theSun produces Gamma rays as a result of the nuclear
fusion process,these super high energy photons are converted to
lower energy photonsbefore they reach the Suns surface and are
emitted out into space. As aresult, the Sun doesnt give off any
gamma rays. The Sun does,however, emit X-rays, ultraviolet, visible
light, infrared, and even radiowaves.[4] When ultraviolet radiation
is not absorbed by the atmosphere Solar irradiance spectrum above
atmosphere andor other protective coating, it can cause damage to
the skin known as at surfacesunburn or trigger an adaptive change
in human skin pigmentation.
5. Sunlight 2The spectrum of electromagnetic radiation striking
the Earths atmosphere spans a range of 100 nm to about 1 mm.This
can be divided into five regions in increasing order of
wavelengths:[5] Ultraviolet C or (UVC) range, which spans a range
of 100 to 280nm. The term ultraviolet refers to the fact thatthe
radiation is at higher frequency than violet light (and, hence also
invisible to the human eye). Owing toabsorption by the atmosphere
very little reaches the Earths surface (Lithosphere). This spectrum
of radiation hasgermicidal properties, and is used in germicidal
lamps. Ultraviolet B or (UVB) range spans 280 to 315nm. It is also
greatly absorbed by the atmosphere, and along withUVC is
responsible for the photochemical reaction leading to the
production of the ozone layer. Ultraviolet A or (UVA) spans 315 to
400nm. It has been traditionally held as less damaging to the DNA,
andhence used in tanning and PUVA therapy for psoriasis. Visible
range or light spans 380 to 780nm. As the name suggests, it is this
range that is visible to the naked eye. Infrared range that spans
700nm to 106 nm (1 mm). It is responsible for an important part of
the electromagneticradiation that reaches the Earth. It is also
divided into three types on the basis of wavelength: Infrared-A:
700nm to 1,400nm Infrared-B: 1,400nm to 3,000nm Infrared-C: 3,000nm
to 1mmCalculationTo calculate the amount of sunlight reaching the
ground, both the elliptical orbit of the Earth and the attenuation
bythe Earths atmosphere have to be taken into account. The
extraterrestrial solar illuminance (Eext), corrected for
theelliptical orbit by using the day number of the year (dn), is
given by[6]where dn=1 on January 1; dn=2 on January 2; dn=32 on
February 1, etc. In this formula dn-3 is used, because inmodern
times Earths perihelion, the closest approach to the Sun and
therefore the maximum Eext occurs aroundJanuary 3 each year. The
value of 0.033412 is determined knowing that the ratio between the
perihelion (0.98328989AU) squared and the aphelion (1.01671033 AU)
squared should be approximately 0.935338.The solar illuminance
constant (Esc), is equal to 128103 lx. The direct normal
illuminance (Edn), corrected for theattenuating effects of the
atmosphere is given by:where c is the atmospheric extinction
coefficient and m is the relative optical airmass.Solar constantThe
solar constant, a measure of flux density, is the amount of
incoming solar electromagnetic radiation per unitarea that would be
incident on a plane perpendicular to the rays, at a distance of one
astronomical unit (AU) (roughlythe mean distance from the Sun to
the Earth). The "solar constant" includes all types of solar
radiation, not just thevisible light. Its average value was thought
to be approximately 1.366kW/m,[7] varying slightly with solar
activity,but recent recalibrations of the relevant satellite
observations indicate a value closer to 1.361kW/m is
morerealistic.[8]
6. Sunlight 3Total (TSI) and spectral solar irradiance (SSI)
upon EarthTotal Solar Irradiance upon Earth (TSI) was earlier
measured by satellite to be roughly 1.366 kilowatts per squaremeter
(kW/m),[7][9][10] but most recently NASA cites TSI as "1361 W/m as
compared to ~1366 W/m from earlierobservations [Kopp et al.,
2005]", based on regular readings from NASAs Solar Radiation and
ClimateExperiment(SORCE) satellite, active since 2003,[11] noting
that this "discovery is critical in examining the energybudget of
the planet Earth and isolating the climate change due to human
activities." Furthermore the SpectralIrradiance Monitor (SIM) has
found in the same period that spectral solar irradiance (SSI) at UV
(ultraviolet)wavelength corresponds in a less clear, and probably
more complicated fashion, with earths climate responses thanearlier
assumed, fueling broad avenues of new research in "the connection
of the Sun and stratosphere, troposphere,biosphere, ocean, and
Earths climate".[11]Intensity in the Solar SystemDifferent bodies
of the Solar System receive light of an intensity inversely
proportional to the square of theirdistance from Sun. A rough table
comparing the amount of solar radiation received by each planet in
the SolarSystem follows (from data in [12]): Planet Perihelion -
Solar radiation Aphelionmaximum and distance (AU) minimum
(W/m)Mercury 0.3075 0.466714,446 6,272Venus 0.7184 0.72822,647
2,576Earth 0.9833 1.017 1,413 1,321Mars1.382 1.666715 492Jupiter
4.950 5.45855.8 45.9Saturn9.048 10.1216.7 13.4Uranus18.38 20.084.04
3.39Neptune 29.77 30.441.54 1.47The actual brightness of sunlight
that would be observed at the surface depends also on the presence
andcomposition of an atmosphere. For example Venus thick atmosphere
reflects more than 60% of the solar light itreceives. The actual
illumination of the surface is about 14,000 lux, comparable to that
on Earth "in the daytime withovercast clouds".[13]Sunlight on Mars
would be more or less like daylight on Earth wearing sunglasses,
and as can be seen in the picturestaken by the rovers, there is
enough diffuse sky radiation that shadows would not seem
particularly dark. Thus itwould give perceptions and "feel" very
much like Earth daylight.For comparison purposes, sunlight on
Saturn is slightly brighter than Earth sunlight at the average
sunset or sunrise(see daylight for comparison table). Even on Pluto
the sunlight would still be bright enough to almost match
theaverage living room. To see sunlight as dim as full moonlight on
the Earth, a distance of about 500 AU (~69light-hours) is needed;
there are only a handful of objects in the solar system known to
orbit farther than such adistance, among them 90377 Sedna and
(87269) 2000 OO67.
7. Sunlight 4Surface illuminationThe spectrum of surface
illumination depends upon solar elevation due to atmospheric
effects, with the blue spectralcomponent from atmospheric scatter
dominating during twilight before and after sunrise and sunset,
respectively,and red dominating during sunrise and sunset. These
effects are apparent in natural light photography where
theprincipal source of illumination is sunlight as mediated by the
atmosphere.According to Craig Bohren, "preferential absorption of
sunlight by ozone over long horizon paths gives the zenithsky its
blueness when the sun is near the horizon".[14]See diffuse sky
radiation for more details.Climate effectsFurther information:
Solar variation,Solar dimming,andInsolationOn Earth, solar
radiation is obvious as daylight when the sun is above the horizon.
This is during daytime, and alsoin summer near the poles at night,
but not at all in winter near the poles. When the direct radiation
is not blocked byclouds, it is experienced as sunshine, combining
the perception of bright white light (sunlight in the strict sense)
andwarming. The warming on the body, the ground and other objects
depends on the absorption (electromagneticradiation) of the
electromagnetic radiation in the form of heat.The amount of
radiation intercepted by a planetary body varies inversely with the
square of the distance between thestar and the planet. The Earths
orbit and obliquity change with time (over thousands of years),
sometimes forming anearly perfect circle, and at other times
stretching out to an orbital eccentricity of 5% (currently 1.67%).
The totalinsolation remains almost constant due to Keplers second
law,where is the "areal velocity" invariant. That is, the
integration over the orbital period (also invariant) is
aconstant.If we assume the solar radiation poweras a constant over
time and the solar irradiation given by theinverse-square law, we
obtain also the average insolation as a constant.But the seasonal
and latitudinal distribution and intensity of solar radiation
received at the Earths surface alsovaries.[15] For example, at
latitudes of 65 degrees the change in solar energy in summer &
winter can vary by morethan 25% as a result of the Earths orbital
variation. Because changes in winter and summer tend to offset, the
changein the annual average insolation at any given location is
near zero, but the redistribution of energy between summerand
winter does strongly affect the intensity of seasonal cycles. Such
changes associated with the redistribution ofsolar energy are
considered a likely cause for the coming and going of recent ice
ages (see: Milankovitch cycles).Past variations in solar
irradianceSpace-based observations of solar irradiance started in
1978. These measurements show that the solar constant is
notconstant. It varies with the 11-year sunspot solar cycle. When
going further back in time, one has to rely onirradiance
reconstructions, using sunspots for the past 400 years or
cosmogenic radionuclides for going back 10,000years. Such
reconstructions have been done [16][17][18][19]. These studies show
that solar irradiance does vary withdistinct periodicities such as:
11 years (Schwabe), 88 years (Gleisberg cycle), 208 years (DeVries
cycle) and 1,000years (Eddy cycle).
8. Sunlight 5Life on EarthThe existence of nearly all life on
Earth is fueled by light from the sun.Most autotrophs, such as
plants, use the energy of sunlight, combinedwith carbon dioxide and
water, to produce simple sugarsa processknown as photosynthesis.
These sugars are then used as buildingblocks and in other synthetic
pathways which allow the organism togrow.Heterotrophs, such as
animals, use light from the sun indirectly byconsuming the products
of autotrophs, either by consuming autotrophs,by consuming their
products or by consuming other heterotrophs. TheThis short film
explores the vital connectionsugars and other molecular components
produced by the autotrophs are between Earth and the Sun.then
broken down, releasing stored solar energy, and giving
theheterotroph the energy required for survival. This process is
known as cellular respiration.In prehistory, humans began to
further extend this process by putting plant and animal materials
to other uses. Theyused animal skins for warmth, for example, or
wooden weapons to hunt. These skills allowed humans to harvestmore
of the sunlight than was possible through glycolysis alone, and
human population began to grow.During the Neolithic Revolution, the
domestication of plants and animals further increased human access
to solarenergy. Fields devoted to crops were enriched by inedible
plant matter, providing sugars and nutrients for futureharvests.
Animals which had previously only provided humans with meat and
tools once they were killed were nowused for labour throughout
their lives, fueled by grasses inedible to humans.The more recent
discoveries of coal, petroleum and natural gas are modern
extensions of this trend. These fossilfuels are the remnants of
ancient plant and animal matter, formed using energy from sunlight
and then trapped withinthe earth for millions of years. Because the
stored energy in these fossil fuels has accumulated over many
millions ofyears, they have allowed modern humans to massively
increase the production and consumption of primary energy.As the
amount of fossil fuel is large but finite, this cannot continue
indefinitely, and various theories exist as to whatwill follow this
stage of human civilization (e.g. alternative fuels, Malthusian
catastrophe, new urbanism, peak oil).Cultural aspectsThe effect of
sunlight is relevant to painting, evidenced for instance inworks of
Claude Monet on outdoor scenes and landscapes.Many people find
direct sunlight to be too bright for comfort,especially when
reading from white paper upon which the sun isdirectly shining.
Indeed, looking directly at the sun can causelong-term vision
damage. To compensate for the brightness of sunlight,many people
wear sunglasses. Cars, many helmets and caps areequipped with
visors to block the sun from direct vision when the sunis at a low
angle. Sunshine is often blocked from entering buildingsthrough the
use of walls, window blinds, awnings, shutters or curtains,or by
nearby shade trees.In colder countries, many people prefer sunnier
days and often avoidthe shade. In hotter countries the converse is
true; during the midday Claude Monet: Le djeuner sur lherbehours
many people prefer to stay inside to remain cool. If they do
gooutside, they seek shade which may be provided by trees,
parasols, andso on.
9. Sunlight 6In Hinduism the sun is considered to be a god as
it is the source of life and energy on earth.SunbathingSunbathing
is a popular leisure activity in which a person sits or lies in
direct sunshine. People often sunbathe incomfortable places where
there is ample sunlight. Some common places for sunbathing include
beaches, open airswimming pools, parks, gardens, and sidewalk cafs.
Sunbathers typically wear limited amounts of clothing or somesimply
go nude. For some, an alternative to sunbathing is the use of a
sunbed that generates ultraviolet light and canbe used indoors
regardless of outdoor weather conditions and amount of sunlight.For
many people with pale or brownish skin, one purpose for sunbathing
is to darken ones skin color (get a sun tan)as this is considered
in some cultures to be beautiful, associated with outdoor activity,
vacations/holidays, and health.Some people prefer naked sunbathing
so that an "all-over" or "even" tan can be obtained, sometimes as
part of aspecific lifestyle.For people suffering from psoriasis,
sunbathing is an effective way of healing the symptoms.Skin tanning
is achieved by an increase in the dark pigment inside skin cells
called melanocytes and it is actually anautomatic response
mechanism of the body to sufficient exposure to ultraviolet
radiation from the sun or fromartificial sunlamps. Thus, the tan
gradually disappears with time, when one is no longer exposed to
these sources.Effects on human healthThe body produces vitamin D
from sunlight (specifically from the UVB band of ultraviolet
light), and excessiveseclusion from the sun can lead to deficiency
unless adequate amounts are obtained through diet.Sunburn can have
mild to severe inflammation effects on skin; this can be avoided by
using a proper sunscreencream or lotion or by gradually building up
melanocytes with increasing exposure. Another detrimental effect of
UVexposure is accelerated skin aging (also called skin
photodamage), which produces a difficult to treat cosmeticeffect.
Some people are concerned that ozone depletion is increasing the
incidence of such health hazards. A 10%decrease in ozone could
cause a 25% increase in skin cancer.[20]A lack of sunlight, on the
other hand, is considered one of the primary causes of seasonal
affective disorder (SAD), aserious form of the "winter blues". SAD
occurrence is more prevalent in locations further from the tropics,
and mostof the treatments (other than prescription drugs) involve
light therapy, replicating sunlight via lamps tuned to
specific(visible, not ultra-violet) wavelengths of light or
full-spectrum bulbs.A recent study indicates that more exposure to
sunshine early in a persons life relates to less risk from
multiplesclerosis (MS) later in life.[21]References[1] "Chapter 8
Measurement of sunshine duration" (http:/ / www. wmo. int/ pages/
prog/ www/ IMOP/ publications/ CIMO-Guide/ CIMOGuide 7th Edition,
2008/ Part I/ Chapter 8. pdf) (PDF). CIMO Guide. World
Meteorological Organization. . Retrieved 2008-12-01.[2] "NASA: The
8-minute travel time to Earth by sunlight hides a thousand-year
journey that actually began in the core" (http:/ /
sunearthday.nasa. gov/ 2007/ locations/ ttt_sunlight. php). NASA,
sunearthday.nasa.gov. . Retrieved 2012-02-12.[3] NASA Solar System
Exploration - Sun: Facts & Figures (http:/ / solarsystem. nasa.
gov/ planets/ profile. cfm?Display=Facts& Object=Sun)retrieved
27 April 2011 "Effective Temperature ... 5777K"[4] "The
Multispectral Sun, from the National Earth Science Teachers
Association" (http:/ / www. windows2universe. org/ sun/
spectrum/multispectral_sun_overview. html). Windows2universe.org.
2007-04-18. . Retrieved 2012-02-12.[5] Naylor, Mark; Kevin C.
Farmer (1995). "Sun damage and prevention" (http:/ / www.
telemedicine. org/ sundam/ sundam2. 4. 1. html).Electronic Textbook
of Dermatology. The Internet Dermatology Society. . Retrieved
2008-06-02.[6] C. KANDILLI and K. ULGEN. "Solar Illumination and
Estimating Daylight Availability of Global Solar Irradiance".
Energy Sources.[7] "Satellite observations of total solar
irradiance" (http:/ / acrim. com/ TSI Monitoring. htm). Acrim.com.
. Retrieved 2012-02-12.[8] G. Kopp; J. Lean (2011). "A new, lower
value of total solar irradiance: Evidence and climate
significance". Geophys. Res. Lett.:
L01706.Bibcode2011GeoRL..3801706K. doi:10.1029/2010GL045777.
10. Sunlight7[9] Willson, R. C., and A. V. Mordvinov (2003),
Secular total solar irradiance trend during solar cycles 2123,
Geophys. Res. Lett., 30(5), 1199,doi:10.1029/2002GL016038 ACR
(http:/ / www. acrim. com/ Reference Files/ Secular total solar
irradiance trend during solar cycles 2123.pdf)[10] "Construction of
a Composite Total Solar Irradiance (TSI) Time Series from 1978 to
present" (http:/ / www. pmodwrc. ch/ pmod.php?topic=tsi/ composite/
SolarConstant). . Retrieved 2005-10-05.[11] "NASA Goddard Space
Flight Center: Solar Radiation" (http:/ / atmospheres. gsfc. nasa.
gov/ climate/ index. php?section=136).Atmospheres.gsfc.nasa.gov.
2012-02-08. . Retrieved 2012-02-12.[12] http:/ / starhop. com/
library/ pdf/ studyguide/ high/ SolInt-19. pdf[13] "The Unveiling
of Venus: Hot and Stifling". Science News 109 (25): 388.
1976-06-19. JSTOR3960800. "100 watts per square meter ...14,000 lux
... corresponds to ... daytime with overcast clouds"[14] Craig F.
Bohren. "Atmospheric Optics" (http:/ / homepages. wmich. edu/
~korista/ atmospheric_optics. pdf). .[15] "Graph of variation of
seasonal and latitudinal distribution of solar radiation" (http:/ /
www. museum. state. il. us/ exhibits/ ice_ages/insolation_graph.
html). Museum.state.il.us. 2007-08-30. . Retrieved 2012-02-12.[16]
Wang et al. (2005). The Astrophysical Journal, Volume 625, issue 1,
pages 522-538, dx.doi.org/10.1086/429689 (http:/ / dx. doi. org/
10.1086/ 429689).[17] Steinhilber et al. (2009), Geophysical
Research Letters, Volume 36, L19704, http:/ / dx. doi. org/ 10.
1051/ 0004-6361/ 200811446[18] Vieira et al. (2011),
Astronomy&Astrophysics, Volume 531, A6, http:/ / dx. doi. org/
10. 1051/ 0004-6361/ 201015843[19] Steinhilber et al.(2012),
Proceedings of the National Academy of Sciences, Early Edition
http:/ / dx. doi. org/ 10. 1073/ pnas. 1118965109[20] Ozone Hole
Consequences (http:/ / www. theozonehole. com/ consequences. htm)
retrieved 30 October 2008[21] "NEUROLOGY 2007;69:381-388" (http:/ /
www. neurology. org/ cgi/ content/ abstract/ 69/ 4/ 381?etoc).
Neurology.org. 2007-07-24. .Retrieved 2012-02-12.Further reading
Hartmann, Thom (1998). The Last Hours of Ancient Sunlight. London:
Hodder and Stoughton. ISBN0-340-82243-0.External links Solar
radiation - Encyclopedia of Earth
(http://www.eoearth.org/article/Solar_radiation) Total Solar
Irradiance (TSI) Daily mean data
(http://www.ngdc.noaa.gov/stp/solar/solarirrad.html) at thewebsite
of the National Geophysical Data Center Construction of a Composite
Total Solar Irradiance (TSI) Time Series from 1978 to present
(http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant)
by World Radiation Center,Physikalisch-Meteorologisches
Observatorium Davos (pmod wrc) A Comparison of Methods for
Providing Solar Radiation Data to Crop Models and Decision Support
Systems(http://www.macaulay.ac.uk/LADSS/papers.html?2002),
Rivington et al. Evaluation of three model estimations of solar
radiation at 24 UK stations
(http://www.macaulay.ac.uk/LADSS/papers.html?2005), Rivington et
al. High resolution spectrum of solar radiation
(http://bass2000.obspm.fr/solar_spect.php) from Observatoire
deParis Measuring Solar Radiation
(http://avc.comm.nsdlib.org/cgi-bin/wiki_grade_interface.pl?Measuring_Solar_Radiation)
: A lesson plan from the National Science Digital Library. Websurf
astronomical information
(http://websurf.nao.rl.ac.uk/surfbin/first.cgi): Online tools for
calculatingRising and setting times of Sun, Moon or planet, Azimuth
of Sun, Moon or planet at rising and setting, Altitudeand azimuth
of Sun, Moon or planet for a given date or range of dates, and
more. An Excel workbook
(http://www.ecy.wa.gov/programs/eap/models/solrad.zip) with a solar
position andsolar radiation time-series calculator; by Greg
Pelletier (http://www.ecy.wa.gov/programs/eap/models.html) DOE
information (http://rredc.nrel.gov/solar/spectra/am1.5/) about the
ASTM standard solar spectrum forPV evaluation. ASTM Standard
(http://www.astm.org/Standards/G173.htm) for solar spectrum at
ground level in the US(latitude ~ 37 degrees).
11. Sunlight8 Detailed spectrum of the sun
(http://apod.nasa.gov/apod/ap100627.html) at Astronomy Picture of
the Day(http://apod.nasa.gov/apod/archivepix.html).Solar
energySolar energy, radiant light and heat fromthe sun, has been
harnessed by humans sinceancient times using a range of
ever-evolvingtechnologies. Solar energy technologiesinclude solar
heating, solar photovoltaics,solar thermal electricity and
solararchitecture, which can make considerablecontributions to
solving some of the mosturgent problems the world now
faces.[1]Solar technologies are broadly characterizedas either
passive solar or active solardepending on the way they capture,
convertand distribute solar energy. Active solartechniques include
the use of photovoltaic Nellis Solar Power Plant in the United
States, one of the largest photovoltaic powerpanels and solar
thermal collectors to plants in North America.harness the energy.
Passive solar techniquesinclude orienting a building to the
Sun,selecting materials with favorable thermal mass or light
dispersing properties, and designing spaces that naturallycirculate
air.In 2011, the International Energy Agency said that "the
development of affordable, inexhaustible and clean solarenergy
technologies will have huge longer-term benefits. It will increase
countries energy security through relianceon an indigenous,
inexhaustible and mostly import-independent resource, enhance
sustainability, reduce pollution,lower the costs of mitigating
climate change, and keep fossil fuel prices lower than otherwise.
These advantages areglobal. Hence the additional costs of the
incentives for early deployment should be considered learning
investments;they must be wisely spent and need to be widely
shared".[1]Energy from the SunThe Earth receives 174petawatts (PW)
of incoming solar radiation(insolation) at the upper atmosphere.[2]
Approximately 30% is reflectedback to space while the rest is
absorbed by clouds, oceans and landmasses. The spectrum of solar
light at the Earths surface is mostlyspread across the visible and
near-infrared ranges with a small part inthe
near-ultraviolet.[3]Earths land surface, oceans and atmosphere
absorb solar radiation, andthis raises their temperature. Warm air
containing evaporated waterfrom the oceans rises, causing
atmospheric circulation or convection.About half the incoming solar
energy reaches theWhen the air reaches a high altitude, where the
temperature is low, Earths surface.
12. Solar energy9water vapor condenses into clouds, which rain
onto the Earths surface, completing the water cycle. The latent
heat ofwater condensation amplifies convection, producing
atmospheric phenomena such as wind, cyclones andanti-cyclones.[4]
Sunlight absorbed by the oceans and land masses keeps the surface
at an average temperature of14C.[5] By photosynthesis green plants
convert solar energy into chemical energy, which produces food,
wood andthe biomass from which fossil fuels are derived.[6]Yearly
Solar fluxes & Human Energy ConsumptionSolar[7] 3,850,000EJWind
[8] 2,250EJBiomass[9] 3,000EJPrimary energy use (2005)[10]
487EJElectricity (2005)[11] 56.7EJThe total solar energy absorbed
by Earths atmosphere, oceans and land masses is approximately
3,850,000exajoules(EJ) per year.[7] In 2002, this was more energy
in one hour than the world used in one year.[12][13]
Photosynthesiscaptures approximately 3,000EJ per year in
biomass.[9] The amount of solar energy reaching the surface of
theplanet is so vast that in one year it is about twice as much as
will ever be obtained from all of the Earthsnon-renewable resources
of coal, oil, natural gas, and mined uranium combined.[14]Solar
energy can be harnessed in different levels around the world.
Depending on a geographical location the closerto the equator the
more "potential" solar energy is available.[15]Applications of
solar technologySolar energy refers primarily to the use of solar
radiation for practicalends. However, all renewable energies, other
than geothermal andtidal, derive their energy from the sun.Solar
technologies are broadly characterized as either passive or
activedepending on the way they capture, convert and distribute
sunlight.Active solar techniques use photovoltaic panels, pumps,
and fans toconvert sunlight into useful outputs. Passive solar
techniques includeselecting materials with favorable thermal
properties, designing spacesthat naturally circulate air, and
referencing the position of a building toAverage insolation showing
land area (smallblack dots) required to replace the world
primarythe Sun. Active solar technologies increase the supply of
energy andenergy supply with solar electricity. 18 TW isare
considered supply side technologies, while passive solar 568
Exajoule (EJ) per year. Insolation for mosttechnologies reduce the
need for alternate resources and are generallypeople is from 150 to
300 W/m2 or 3.5 to 7.0considered demand side
technologies.[16]kWh/m2/day.
13. Solar energy10Architecture and urban planningSunlight has
influenced building design since the beginning ofarchitectural
history.[18] Advanced solar architecture and urbanplanning methods
were first employed by the Greeks and Chinese, whooriented their
buildings toward the south to provide light andwarmth.[19]The
common features of passive solar architecture are
orientationrelative to the Sun, compact proportion (a low surface
area to volumeratio), selective shading (overhangs) and thermal
mass.[18] When theseDarmstadt University of Technology in
Germanyfeatures are tailored to the local climate and environment
they canwon the 2007 Solar Decathlon in Washington,produce well-lit
spaces that stay in a comfortable temperature range.D.C. with this
passive house designed specifically[17]Socrates Megaron House is a
classic example of passive solarfor the humid and hot subtropical
climate.design.[18] The most recent approaches to solar design use
computermodeling tying together solar lighting, heating and
ventilation systems in an integrated solar design
package.[20]Active solar equipment such as pumps, fans and
switchable windows can complement passive design and improvesystem
performance.Urban heat islands (UHI) are metropolitan areas with
higher temperatures than that of the surrounding environment.The
higher temperatures are a result of increased absorption of the
Solar light by urban materials such as asphalt andconcrete, which
have lower albedos and higher heat capacities than those in the
natural environment. Astraightforward method of counteracting the
UHI effect is to paint buildings and roads white and plant trees.
Usingthese methods, a hypothetical "cool communities" program in
Los Angeles has projected that urban temperaturescould be reduced
by approximately 3C at an estimated cost of US$1billion, giving
estimated total annual benefitsof US$530million from reduced
air-conditioning costs and healthcare savings.[21]Agriculture and
horticultureAgriculture and horticulture seek to optimize the
capture of solarenergy in order to optimize the productivity of
plants. Techniques suchas timed planting cycles, tailored row
orientation, staggered heightsbetween rows and the mixing of plant
varieties can improve cropyields.[22][23] While sunlight is
generally considered a plentifulGreenhouses like these in the
Westlandmunicipality of the Netherlands grow vegetables,resource,
the exceptions highlight the importance of solar energy to fruits
and flowers.agriculture. During the short growing seasons of the
Little Ice Age,French and English farmers employed fruit walls to
maximize thecollection of solar energy. These walls acted as
thermal masses and accelerated ripening by keeping plants
warm.Early fruit walls were built perpendicular to the ground and
facing south, but over time, sloping walls weredeveloped to make
better use of sunlight. In 1699, Nicolas Fatio de Duillier even
suggested using a trackingmechanism which could pivot to follow the
Sun.[24] Applications of solar energy in agriculture aside from
growingcrops include pumping water, drying crops, brooding chicks
and drying chicken manure.[25][26] More recently thetechnology has
been embraced by vinters, who use the energy generated by solar
panels to power grape presses.[27]Greenhouses convert solar light
to heat, enabling year-round production and the growth (in enclosed
environments)of specialty crops and other plants not naturally
suited to the local climate. Primitive greenhouses were first
usedduring Roman times to produce cucumbers year-round for the
Roman emperor Tiberius.[28] The first moderngreenhouses were built
in Europe in the 16th century to keep exotic plants brought back
from explorationsabroad.[29] Greenhouses remain an important part
of horticulture today, and plastic transparent materials have
alsobeen used to similar effect in polytunnels and row covers.
14. Solar energy 11Solar lightingThe history of lighting is
dominated by the use of natural light. TheRomans recognized a right
to light as early as the 6th century andEnglish law echoed these
judgments with the Prescription Act of1832.[30][31] In the 20th
century artificial lighting became the mainsource of interior
illumination but daylighting techniques and hybridsolar lighting
solutions are ways to reduce energy consumption.Daylighting systems
collect and distribute sunlight to provide interiorillumination.
This passive technology directly offsets energy use byreplacing
artificial lighting, and indirectly offsets non-solar energy use
Daylighting features such as this oculus at the topby reducing the
need for air-conditioning.[32] Although difficult to of the
Pantheon, in Rome, Italy have been in usequantify, the use of
natural lighting also offers physiological and since
antiquity.[32]psychological benefits compared to artificial
lighting.Daylightingdesign implies careful selection of window
types, sizes and orientation; exterior shading devices may be
consideredas well. Individual features include sawtooth roofs,
clerestory windows, light shelves, skylights and light tubes.
Theymay be incorporated into existing structures, but are most
effective when integrated into a solar design package thataccounts
for factors such as glare, heat flux and time-of-use. When
daylighting features are properly implementedthey can reduce
lighting-related energy requirements by 25%.[33]Hybrid solar
lighting is an active solar method of providing interior
illumination. HSL systems collect sunlight usingfocusing mirrors
that track the Sun and use optical fibers to transmit it inside the
building to supplementconventional lighting. In single-story
applications these systems are able to transmit 50% of the direct
sunlightreceived.[34]Solar lights that charge during the day and
light up at dusk are a common sight along walkways.[35]
Solar-chargedlanterns have become popular in developing countries
where they provide a safer and cheaper alternative to
kerosenelamps.[36]Although daylight saving time is promoted as a
way to use sunlight to save energy, recent research has been
limitedand reports contradictory results: several studies report
savings, but just as many suggest no effect or even a net
loss,particularly when gasoline consumption is taken into account.
Electricity use is greatly affected by geography,climate and
economics, making it hard to generalize from single
studies.[37]
15. Solar energy 12Solar thermalSolar thermal technologies can
be used for water heating, space heating, space cooling and process
heatgeneration.[38]Water heatingSolar hot water systems use
sunlight to heat water. In low geographicallatitudes (below
40degrees) from 60 to 70% of the domestic hot wateruse with
temperatures up to 60C can be provided by solar heatingsystems.[39]
The most common types of solar water heaters areevacuated tube
collectors (44%) and glazed flat plate collectors (34%)generally
used for domestic hot water; and unglazed plastic collectors(21%)
used mainly to heat swimming pools.[40]As of 2007, the total
installed capacity of solar hot water systems isapproximately
154GW.[41] China is the world leader in theirdeployment with 70GW
installed as of 2006 and a long term goal of210GW by 2020.[42]
Israel and Cyprus are the per capita leaders in theuse of solar hot
water systems with over 90% of homes using them.[43] Solar water
heaters facing the Sun to maximizeIn the United States, Canada and
Australia heating swimming pools isgain.the dominant application of
solar hot water with an installed capacityof 18GW as of
2005.[16]Heating, cooling and ventilationIn the United States,
heating, ventilation and air conditioning (HVAC)systems account for
30% (4.65EJ) of the energy used in commercialbuildings and nearly
50% (10.1EJ) of the energy used in residentialbuildings.[33][44]
Solar heating, cooling and ventilation technologiescan be used to
offset a portion of this energy.Thermal mass is any material that
can be used to store heatheat fromthe Sun in the case of solar
energy. Common thermal mass materialsinclude stone, cement and
water. Historically they have been used inarid climates or warm
temperate regions to keep buildings cool by Solar House #1 of
Massachusetts Institute ofabsorbing solar energy during the day and
radiating stored heat to theTechnology in the United States, built
in 1939,cooler atmosphere at night. However they can be used in
cold used seasonal thermal storage for year-roundtemperate areas to
maintain warmth as well. The size and placement ofheating.thermal
mass depend on several factors such as climate, daylightingand
shading conditions. When properly incorporated, thermal mass
maintains space temperatures in a comfortablerange and reduces the
need for auxiliary heating and cooling equipment.[45]A solar
chimney (or thermal chimney, in this context) is a passive solar
ventilation system composed of a verticalshaft connecting the
interior and exterior of a building. As the chimney warms, the air
inside is heated causing anupdraft that pulls air through the
building. Performance can be improved by using glazing and thermal
massmaterials[46] in a way that mimics greenhouses.Deciduous trees
and plants have been promoted as a means of controlling solar
heating and cooling. When plantedon the southern side of a
building, their leaves provide shade during the summer, while the
bare limbs allow light topass during the winter.[47] Since bare,
leafless trees shade 1/3 to 1/2 of incident solar radiation, there
is a balancebetween the benefits of summer shading and the
corresponding loss of winter heating.[48] In climates with
significant
16. Solar energy13heating loads, deciduous trees should not be
planted on the southern side of a building because they will
interferewith winter solar availability. They can, however, be used
on the east and west sides to provide a degree of summershading
without appreciably affecting winter solar gain.[49]Water
treatmentSolar distillation can be used to make saline or brackish
water potable.The first recorded instance of this was by 16th
century Arabalchemists.[50] A large-scale solar distillation
project was firstconstructed in 1872 in the Chilean mining town of
Las Salinas.[51] Theplant, which had solar collection area of
4,700m2, could produce up to22,700L per day and operated for
40years.[51] Individual still designsinclude single-slope,
double-slope (or greenhouse type), vertical,conical, inverted
absorber, multi-wick, and multiple effect.[50] Thesestills can
operate in passive, active, or hybrid modes. Double-slope Solar
water disinfection in Indonesiastills are the most economical for
decentralized domestic purposes,while active multiple effect units
are more suitable for large-scaleapplications.[50]Solar water
disinfection (SODIS) involves exposing water-filled
plasticpolyethylene terephthalate (PET) bottles to sunlight for
severalhours.[52] Exposure times vary depending on weather and
climate froma minimum of six hours to two days during fully
overcastconditions.[53] It is recommended by the World Health
Organization asa viable method for household water treatment and
safe storage.[54]Over two million people in developing countries
use this method fortheir daily drinking water.[53]Small scale solar
powered sewerage treatment plant.Solar energy may be used in a
water stabilisation pond to treat wastewater without chemicals or
electricity. A further environmentaladvantage is that algae grow in
such ponds and consume carbon dioxide in photosynthesis, although
algae mayproduce toxic chemicals that make the water
unusable.[55][56]CookingSolar cookers use sunlight for cooking,
drying and pasteurization. Theycan be grouped into three broad
categories: box cookers, panel cookersand reflector cookers.[57]
The simplest solar cooker is the box cookerfirst built by Horace de
Saussure in 1767.[58] A basic box cookerconsists of an insulated
container with a transparent lid. It can be usedeffectively with
partially overcast skies and will typically reachtemperatures of
90150C.[59] Panel cookers use a reflective panel todirect sunlight
onto an insulated container and reach temperatures The Solar Bowl
in Auroville, India, concentratescomparable to box cookers.
Reflector cookers use various sunlight on a movable receiver to
produce steamconcentrating geometries (dish, trough, Fresnel
mirrors) to focus light for cooking.on a cooking container. These
cookers reach temperatures of 315Cand above but require direct
light to function properly and must be repositioned to track the
Sun.[60]The solar bowl is a concentrating technology employed by
the Solar Kitchen in Auroville, Pondicherry, India, wherea
stationary spherical reflector focuses light along a line
perpendicular to the spheres interior surface, and a
17. Solar energy 14computer control system moves the receiver
to intersect this line. Steam is produced in the receiver at
temperaturesreaching 150C and then used for process heat in the
kitchen.[61]A reflector developed by Wolfgang Scheffler in 1986 is
used in many solar kitchens. Scheffler reflectors are
flexibleparabolic dishes that combine aspects of trough and power
tower concentrators. Polar tracking is used to follow theSuns daily
course and the curvature of the reflector is adjusted for seasonal
variations in the incident angle ofsunlight. These reflectors can
reach temperatures of 450650C and have a fixed focal point, which
simplifiescooking.[62] The worlds largest Scheffler reflector
system in Abu Road, Rajasthan, India is capable of cooking up
to35,000 meals a day.[63] As of 2008, over 2,000 large Scheffler
cookers had been built worldwide.[64]Process heatSolar
concentrating technologies such as parabolic dish, trough and
Scheffler reflectors can provide process heat forcommercial and
industrial applications. The first commercial system was the Solar
Total Energy Project (STEP) inShenandoah, Georgia, USA where a
field of 114 parabolic dishes provided 50% of the process heating,
airconditioning and electrical requirements for a clothing factory.
This grid-connected cogeneration system provided400kW of
electricity plus thermal energy in the form of 401kW steam and
468kW chilled water, and had a onehour peak load thermal
storage.[65]Evaporation ponds are shallow pools that concentrate
dissolved solids through evaporation. The use of evaporationponds
to obtain salt from sea water is one of the oldest applications of
solar energy. Modern uses includeconcentrating brine solutions used
in leach mining and removing dissolved solids from waste
streams.[66]Clothes lines, clotheshorses, and clothes racks dry
clothes through evaporation by wind and sunlight withoutconsuming
electricity or gas. In some states of the United States legislation
protects the "right to dry" clothes.[67]Unglazed transpired
collectors (UTC) are perforated sun-facing walls used for
preheating ventilation air. UTCs canraise the incoming air
temperature up to 22C and deliver outlet temperatures of 4560C.[68]
The short paybackperiod of transpired collectors (3 to 12years)
makes them a more cost-effective alternative than glazed
collectionsystems.[68] As of 2003, over 80 systems with a combined
collector area of 35,000m2 had been installed worldwide,including
an 860m2 collector in Costa Rica used for drying coffee beans and a
1,300m2 collector in Coimbatore,India used for drying
marigolds.[26]Solar powerSolar power is the conversion of sunlight
into electricity, either directlyusing photovoltaics (PV), or
indirectly using concentrated solar power(CSP). CSP systems use
lenses or mirrors and tracking systems tofocus a large area of
sunlight into a small beam. PV converts light intoelectric current
using the photoelectric effect.Commercial CSP plants were first
developed in the 1980s, and the 354MW SEGS CSP installation is the
largest solar power plant in theworld and is located in the Mojave
Desert of California. Other largeThe PS10 concentrates sunlight
from a field ofCSP plants include the Solnova Solar Power Station
(150 MW) and theheliostats on a central tower.Andasol solar power
station (100 MW), both in Spain. The 214 MWCharanka Solar Park in
India, is the worlds largest photovoltaic plant.
18. Solar energy 15Concentrated solar powerConcentrating Solar
Power (CSP) systems use lenses or mirrors and tracking systems to
focus a large area ofsunlight into a small beam. The concentrated
heat is then used as a heat source for a conventional power plant.
Awide range of concentrating technologies exists; the most
developed are the parabolic trough, the concentratinglinear fresnel
reflector, the Stirling dish and the solar power tower. Various
techniques are used to track the Sun andfocus light. In all of
these systems a working fluid is heated by the concentrated
sunlight, and is then used for powergeneration or energy
storage.[69]PhotovoltaicsA solar cell, or photovoltaic cell (PV),
is a device that converts lightinto electric current using the
photoelectric effect. The first solar cellwas constructed by
Charles Fritts in the 1880s.[70] In 1931 a Germanengineer, Dr Bruno
Lange, developed a photo cell using silver selenidein place of
copper oxide.[71] Although the prototype selenium cellsconverted
less than 1% of incident light into electricity, both ErnstWerner
von Siemens and James Clerk Maxwell recognized theimportance of
this discovery.[72] Following the work of Russell Ohl inthe 1940s,
researchers Gerald Pearson, Calvin Fuller and Daryl Chapin80 MW
Okhotnykovo Solar Park in Ukraine.created the silicon solar cell in
1954.[73] These early solar cells cost286USD/watt and reached
efficiencies of 4.56%.[74]Solar chemicalSolar chemical processes
use solar energy to drive chemical reactions.These processes offset
energy that would otherwise come from a fossilfuel source and can
also convert solar energy into storable andtransportable fuels.
Solar induced chemical reactions can be dividedinto thermochemical
or photochemical.[75] A variety of fuels can beproduced by
artificial photosynthesis.[76] The multielectron catalyticNREL
compilation of best research solar cellchemistry involved in making
carbon-based fuels (such as methanol)efficiencies from 1976 to
2010from reduction of carbon dioxide is challenging; a feasible
alternativeis hydrogen production from protons, though use of water
as the source of electrons (as plants do) requires masteringthe
multielectron oxidation of two water molecules to molecular
oxygen.[77] Some have envisaged working solar fuelplants in coastal
metropolitan areas by 2050- the splitting of sea water providing
hydrogen to be run through adjacentfuel-cell electric power plants
and the pure water by-product going directly into the municipal
water system.[78]Hydrogen production technologies been a
significant area of solar chemical research since the 1970s. Aside
fromelectrolysis driven by photovoltaic or photochemical cells,
several thermochemical processes have also beenexplored. One such
route uses concentrators to split water into oxygen and hydrogen at
high temperatures(2300-2600C).[79] Another approach uses the heat
from solar concentrators to drive the steam reformation ofnatural
gas thereby increasing the overall hydrogen yield compared to
conventional reforming methods.[80]Thermochemical cycles
characterized by the decomposition and regeneration of reactants
present another avenue forhydrogen production. The Solzinc process
under development at the Weizmann Institute uses a 1MW solar
furnaceto decompose zinc oxide (ZnO) at temperatures above 1200C.
This initial reaction produces pure zinc, which cansubsequently be
reacted with water to produce hydrogen.[81]Sandias Sunshine to
Petrol (S2P) technology uses the high temperatures generated by
concentrating sunlight alongwith a zirconia/ferrite catalyst to
break down atmospheric carbon dioxide into oxygen and carbon
monoxide (CO).
19. Solar energy 16The carbon monoxide can then be used to
synthesize conventional fuels such as methanol, gasoline and jet
fuel.[82]A photogalvanic device is a type of battery in which the
cell solution (or equivalent) forms energy-rich
chemicalintermediates when illuminated. These energy-rich
intermediates can potentially be stored and subsequently reactedat
the electrodes to produce an electric potential. The
ferric-thionine chemical cell is an example of
thistechnology.[83]Photoelectrochemical cells or PECs consist of a
semiconductor, typically titanium dioxide or related
titanates,immersed in an electrolyte. When the semiconductor is
illuminated an electrical potential develops. There are twotypes of
photoelectrochemical cells: photoelectric cells that convert light
into electricity and photochemical cells thatuse light to drive
chemical reactions such as electrolysis.[84]A combination
thermal/photochemical cell has also been proposed. The Stanford
PETE process uses solar thermalenergy to raise the temperature of a
thermionic metal to about 800C to increase the rate of production
of electricity toelectrolyse atmospheric CO2 down to carbon or
carbon monoxide which can then be used for fuel production, andthe
waste heat can be used as well.[85]Solar vehiclesDevelopment of a
solar powered car has been an engineering goalsince the 1980s. The
World Solar Challenge is a biannualsolar-powered car race, where
teams from universities and enterprisescompete over 3021 kilometres
(unknown operator: ustrongmi)across central Australia from Darwin
to Adelaide. In 1987, when it wasfounded, the winners average speed
was 67 kilometres per hour(unknown operator: ustrongmph) and by
2007 the winnersaverage speed had improved to 90.87 kilometres per
hour (unknownoperator: ustrongmph).[86] The North American Solar
Challengeand the planned South African Solar Challenge are
comparablecompetitions that reflect an international interest in
the engineering andAustralia hosts the World Solar Challenge
wheredevelopment of solar powered vehicles.[87][88]solar cars like
the Nuna3 race through a 3021km(unknown operator: ustrongmi) course
fromSome vehicles use solar panels for auxiliary power, such as for
air Darwin to Adelaide.conditioning, to keep the interior cool,
thus reducing fuelconsumption.[89][90]In 1975, the first practical
solar boat was constructed in England.[91] By 1995, passenger boats
incorporating PVpanels began appearing and are now used
extensively.[92] In 1996, Kenichi Horie made the first solar
poweredcrossing of the Pacific Ocean, and the sun21 catamaran made
the first solar powered crossing of the Atlantic Oceanin the winter
of 20062007.[93] There are plans to circumnavigate the globe in
2010.[94]In 1974, the unmanned AstroFlight Sunrise plane made the
first solarflight. On 29 April 1979, the Solar Riser made the first
flight in a solarpowered, fully controlled, man carrying flying
machine, reaching analtitude of 40 feet (unknown operator:
ustrongm). In 1980, theGossamer Penguin made the first piloted
flights powered solely byphotovoltaics. This was quickly followed
by the Solar Challengerwhich crossed the English Channel in July
1981. In 1990 Eric ScottRaymond in 21 hops flew from California to
North Carolina usingHelios UAV in solar powered flight.solar
power.[95] Developments then turned back to unmanned aerial
20. Solar energy 17vehicles (UAV) with the Pathfinder (1997)
and subsequent designs, culminating in the Helios which set the
altituderecord for a non-rocket-propelled aircraft at 29524 metres
(unknown operator: ustrong ft) in 2001.[96] TheZephyr, developed by
BAE Systems, is the latest in a line of record-breaking solar
aircraft, making a 54-hour flightin 2007, and month-long flights
are envisioned by 2010.[97]A solar balloon is a black balloon that
is filled with ordinary air. As sunlight shines on the balloon, the
air inside isheated and expands causing an upward buoyancy force,
much like an artificially heated hot air balloon. Some
solarballoons are large enough for human flight, but usage is
generally limited to the toy market as the surface-area
topayload-weight ratio is relatively high.[98]Solar sails are a
proposed form of spacecraft propulsion using large membrane mirrors
to exploit radiation pressurefrom the Sun. Unlike rockets, solar
sails require no fuel. Although the thrust is small compared to
rockets, itcontinues as long as the Sun shines onto the deployed
sail and in the vacuum of space significant speeds caneventually be
achieved.[99]The High-altitude airship (HAA) is an unmanned,
long-duration, lighter-than-air vehicle using helium gas for
lift,and thin film solar cells for power. The United States
Department of Defense Missile Defense Agency has contractedLockheed
Martin to construct it to enhance the Ballistic Missile Defense
System (BMDS).[100] Airships have someadvantages for solar-powered
flight: they do not require power to remain aloft, and an airships
envelope presents alarge area to the Sun.Energy storage
methodsSolar energy is not available at night, and energy storage
is animportant issue because modern energy systems usually
assumecontinuous availability of energy.[101]Thermal mass systems
can store solar energy in the form of heat atdomestically useful
temperatures for daily or seasonal durations.Thermal storage
systems generally use readily available materials with Solar Twos
thermal storage system generatedhigh specific heat capacities such
as water, earth and stone. electricity during cloudy weather and at
night.Well-designed systems can lower peak demand, shift
time-of-use tooff-peak hours and reduce overall heating and
coolingrequirements.[102][103]Phase change materials such as
paraffin wax and Glaubers salt are another thermal storage media.
These materialsare inexpensive, readily available, and can deliver
domestically useful temperatures (approximately 64C). The"Dover
House" (in Dover, Massachusetts) was the first to use a Glaubers
salt heating system, in 1948.[104]Solar energy can be stored at
high temperatures using molten salts. Salts are an effective
storage medium becausethey are low-cost, have a high specific heat
capacity and can deliver heat at temperatures compatible
withconventional power systems. The Solar Two used this method of
energy storage, allowing it to store 1.44TJ in its68m3 storage tank
with an annual storage efficiency of about 99%.[105]Off-grid PV
systems have traditionally used rechargeable batteries to store
excess electricity. With grid-tied systems,excess electricity can
be sent to the transmission grid, while standard grid electricity
can be used to meet shortfalls.Net metering programs give household
systems a credit for any electricity they deliver to the grid. This
is oftenlegally handled by rolling back the meter whenever the home
produces more electricity than it consumes. If the netelectricity
use is below zero, the utility is required to pay for the extra at
the same rate as they charge consumers.[106]Other legal approaches
involve the use of two meters, to measure electricity consumed vs.
electricity produced. Thisis less common due to the increased
installation cost of the second meter.Pumped-storage
hydroelectricity stores energy in the form of water pumped when
energy is available from a lowerelevation reservoir to a higher
elevation one. The energy is recovered when demand is high by
releasing the water to
21. Solar energy 18run through a hydroelectric power
generator.[107]Development, deployment and economicsBeginning with
the surge in coal use which accompanied the Industrial Revolution,
energy consumption has steadilytransitioned from wood and biomass
to fossil fuels. The early development of solar technologies
starting in the 1860swas driven by an expectation that coal would
soon become scarce. However development of solar
technologiesstagnated in the early 20thcentury in the face of the
increasing availability, economy, and utility of coal
andpetroleum.[108]The 1973 oil embargo and 1979 energy crisis
caused a reorganization of energy policies around the world
andbrought renewed attention to developing solar
technologies.[109][110] Deployment strategies focused on
incentiveprograms such as the Federal Photovoltaic Utilization
Program in the US and the Sunshine Program in Japan. Otherefforts
included the formation of research facilities in the US (SERI, now
NREL), Japan (NEDO), and Germany(Fraunhofer Institute for Solar
Energy Systems ISE).[111]Commercial solar water heaters began
appearing in the United States in the 1890s.[112] These systems saw
increasinguse until the 1920s but were gradually replaced by
cheaper and more reliable heating fuels.[113] As withphotovoltaics,
solar water heating attracted renewed attention as a result of the
oil crises in the 1970s but interestsubsided in the 1980s due to
falling petroleum prices. Development in the solar water heating
sector progressedsteadily throughout the 1990s and growth rates
have averaged 20% per year since 1999.[41] Although
generallyunderestimated, solar water heating and cooling is by far
the most widely deployed solar technology with anestimated capacity
of 154GW as of 2007.[41]The International Energy Agency has said
that solar energy can make considerable contributions to solving
some ofthe most urgent problems the world now faces:[1]The
development of affordable, inexhaustible and clean solar energy
technologies will have hugelonger-term benefits. It will increase
countries energy security through reliance on an
indigenous,inexhaustible and mostly import-independent resource,
enhance sustainability, reduce pollution, lowerthe costs of
mitigating climate change, and keep fossil fuel prices lower than
otherwise. Theseadvantages are global. Hence the additional costs
of the incentives for early deployment should beconsidered learning
investments; they must be wisely spent and need to be widely
shared.[1]In 2011, the International Energy Agency said that solar
energy technologies such as photovoltaic panels, solar waterheaters
and power stations built with mirrors could provide a third of the
worlds energy by 2060 if politicianscommit to limiting climate
change. The energy from the sun could play a key role in
de-carbonizing the globaleconomy alongside improvements in energy
efficiency and imposing costs on greenhouse gas emitters. "The
strengthof solar is the incredible variety and flexibility of
applications, from small scale to big scale".[114]
22. Solar energy19ISO StandardsThe International Organization
for Standardization has established a number of standards relating
to solar energyequipment. For example, ISO 9050 relates to glass in
building while ISO 10217 relates to the materials used in
solarwater heaters.Notes[1] "Solar Energy Perspectives: Executive
Summary" (http:/ / www. webcitation. org/ 63fIHKr1S) (PDF).
International Energy Agency. 2011.Archived from the original
(http:/ / www. iea. org/ Textbase/ npsum/ solar2011SUM. pdf) on
2011-12-03. .[2] Smil (1991), p. 240[3] "Natural Forcing of the
Climate System" (http:/ / www. grida. no/ climate/ ipcc_tar/ wg1/
041. htm#121). Intergovernmental Panel on ClimateChange. .
Retrieved 2007-09-29.[4] "Radiation Budget" (http:/ / marine.
rutgers. edu/ mrs/ education/ class/ yuri/ erb. html). NASA Langley
Research Center. 2006-10-17. .Retrieved 2007-09-29.[5] Somerville,
Richard. "Historical Overview of Climate Change Science" (http:/ /
www. ipcc. ch/ pdf/ assessment-report/ ar4/ wg1/ar4-wg1-chapter1.
pdf) (PDF). Intergovernmental Panel on Climate Change. . Retrieved
2007-09-29.[6] Vermass, Wim. "An Introduction to Photosynthesis and
Its Applications" (http:/ / photoscience. la. asu. edu/ photosyn/
education/ photointro.html). Arizona State University. . Retrieved
2007-09-29.[7] Smil (2006), p. 12[8] Archer, Cristina; Jacobson,
Mark. "Evaluation of Global Wind Power" (http:/ / www. stanford.
edu/ group/ efmh/ winds/ global_winds. html).Stanford. . Retrieved
2008-06-03.[9] "Energy conversion by photosynthetic organisms"
(http:/ / www. fao. org/ docrep/ w7241e/ w7241e06. htm#TopOfPage).
Food andAgriculture Organization of the United Nations. . Retrieved
2008-05-25.[10] "World Consumption of Primary Energy by Energy Type
and Selected Country Groups, 1980-2004" (http:/ / www. eia. doe.
gov/ pub/international/ iealf/ table18. xls). Energy Information
Administration. . Retrieved 2008-05-17.[11] "World Total Net
Electricity Consumption, 1980-2005" (http:/ / www. eia. doe. gov/
iea/ elec. html). Energy Information Administration. .Retrieved
2008-05-25.[12] Solar energy: A new day dawning? (http:/ / www.
nature. com/ nature/ journal/ v443/ n7107/ full/ 443019a. html)
retrieved 7 August 2008[13] Powering the Planet: Chemical
challenges in solar energy utilization (http:/ / web. mit. edu/
mitpep/ pdf/ DGN_Powering_Planet. pdf)retrieved 7 August 2008[14]
Exergy (available energy) Flow Charts (http:/ / gcep. stanford.
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27. Solar energy24External links "How do Photovoltaics Work?"
(http://science.nasa.gov/headlines/y2002/solarcells.htm). NASA.
Solar Energy Back in the Day
(http://www.life.com/image/first/in-gallery/43861/solar-energy-back-in-the-day)
- slideshow by Life magazine Compendium of Solar Cooker Designs
(http://solarcooking.wikia.com/wiki/Compendium_of_solar_cooker_designs)
U.S. Solar Farm Map (1 MW or Higher)
(http://www.solarpowerworldonline.com/u-s-solar-farm-map/)Solar
thermal energySolar thermal energy (STE) is a technology
forharnessing solar energy for thermal energy (heat). Solarthermal
collectors are classified by the United StatesEnergy Information
Administration as low-, medium-, orhigh-temperature collectors.
Low-temperature collectorsare flat plates generally used to heat
swimming pools.Medium-temperature collectors are also usually flat
platesbut are used for heating water or air for residential
andcommercial use. High-temperature collectors concentratesunlight
using mirrors or lenses and are generally used forelectric power
production. STE is different from andmuch more efficient
than[1][2][3] photovoltaics, which Solar thermal system for water
heating in Santorini, Greece.converts solar energy directly into
electricity. Whileexisting generation facilities provide only 600
megawatts of solar thermal power worldwide in October 2009,
[4]plants for an additional 400 megawatts are under construction
and development is underway for concentrated solarpower projects
totalling 14,000 megawatts.[5]Low-temperature collectorsOf the
21000000 square feet (unknown operator: ustrong m2) of solar
thermal collectors produced in the UnitedStates in 2007, 16000000
square feet (unknown operator: ustrong m2) were of the
low-temperature variety.[6]Low-temperature collectors are generally
installed to heat swimming pools, although they can also be used
for spaceheating. Collectors can use air or water as the medium to
transfer the heat to their destination.Heating, cooling, and
ventilation