Solar power

Solar power

Overview


Solar energy, radiant light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

 and heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 from the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, has been harnessed by humans since ancient times
Ancient history
Ancient history is the study of the written past from the beginning of recorded human history to the Early Middle Ages. The span of recorded history is roughly 5,000 years, with Cuneiform script, the oldest discovered form of coherent writing, from the protoliterate period around the 30th century BC...

 using a range of ever-evolving technologies. Solar radiation
Non-ionizing radiation
Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule...

, along with secondary solar-powered resources such as wind
Wind power
Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....

 and wave power
Wave power
Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example, electricity generation, water desalination, or the pumping of water...

, hydroelectricity
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

 and biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

, account for most of the available renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

 on earth. Only a minuscule fraction of the available solar energy
Solar constant
The solar constant, a measure of flux density, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit...

 is used.

Solar power
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...

ed electrical generation relies on heat engine
Heat engine
In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...

s and photovoltaics
Photovoltaics
Photovoltaics is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material...

. Solar energy's uses are limited only by human ingenuity.
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Encyclopedia


Solar energy, radiant light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...

 and heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

 from the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

, has been harnessed by humans since ancient times
Ancient history
Ancient history is the study of the written past from the beginning of recorded human history to the Early Middle Ages. The span of recorded history is roughly 5,000 years, with Cuneiform script, the oldest discovered form of coherent writing, from the protoliterate period around the 30th century BC...

 using a range of ever-evolving technologies. Solar radiation
Non-ionizing radiation
Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule...

, along with secondary solar-powered resources such as wind
Wind power
Wind power is the conversion of wind energy into a useful form of energy, such as using wind turbines to make electricity, windmills for mechanical power, windpumps for water pumping or drainage, or sails to propel ships....

 and wave power
Wave power
Wave power is the transport of energy by ocean surface waves, and the capture of that energy to do useful work — for example, electricity generation, water desalination, or the pumping of water...

, hydroelectricity
Hydroelectricity
Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational force of falling or flowing water. It is the most widely used form of renewable energy...

 and biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

, account for most of the available renewable energy
Renewable energy
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides, and geothermal heat, which are renewable . About 16% of global final energy consumption comes from renewables, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from...

 on earth. Only a minuscule fraction of the available solar energy
Solar constant
The solar constant, a measure of flux density, is the amount of incoming solar electromagnetic radiation per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit...

 is used.

Solar power
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...

ed electrical generation relies on heat engine
Heat engine
In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...

s and photovoltaics
Photovoltaics
Photovoltaics is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material...

. Solar energy's uses are limited only by human ingenuity. A partial list of solar applications includes space heating and cooling through solar architecture, potable water via distillation
Solar still
A solar still is a low-tech way of distilling water, powered by the heat of the sun . Two basic types of solar stills are box and pit stills. In a solar still, impure water is contained outside the collector, where it is evaporated by sunlight shining through clear plastic...

 and disinfection
Solar water disinfection
Solar water disinfection, also known as SODIS is a method of disinfecting water using only sunlight and plastic PET bottles. SODIS is a free and effective method for decentralized water treatment, usually applied at the household level and is recommended by the World Health Organization as a viable...

, daylighting
Daylighting
Daylighting is the practice of placing windows or other openings and reflective surfaces so that during the day natural light provides effective internal lighting. Particular attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy...

, solar hot water
Solar hot water
Solar water heating or solar hot water systems comprise several innovations and many mature renewable energy technologies that have been well established for many years...

, solar cooking, and high temperature process heat for industrial purposes.To harvest the solar energy, the most common way is to use solar panels.

Solar technologies are broadly characterized as either passive solar or active solar
Active solar
Active solar technologies are employed to convert solar energy into another more useful form of energy. This would normally be a conversion to heat or electrical energy. Inside a building this energy would be used for heating, cooling, or off-setting other energy use or costs. Active solar uses...

 depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal
Solar thermal energy
Solar thermal energy is a technology for harnessing solar energy for thermal energy . Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat...

 collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass
Thermal mass
Thermal mass is a concept in building design which describes how the mass of the building provides "inertia" against temperature fluctuations, sometimes known as the thermal flywheel effect...

 or light dispersing properties, and designing spaces that naturally circulate air
Ventilation (architecture)
Ventilating is the process of "changing" or replacing air in any space to provide high indoor air quality...

.

Energy from the Sun



The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation
Insolation
Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...

) at the upper atmosphere
Earth's atmosphere
The atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...

. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....

 of solar light at the Earth's surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet.

Earth's land surface, ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

s and atmosphere absorb solar radiation, and this raises their temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation
Atmospheric circulation
Atmospheric circulation is the large-scale movement of air, and the means by which thermal energy is distributed on the surface of the Earth....

 or convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....

. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth's surface, completing the water cycle
Water cycle
The water cycle, also known as the hydrologic cycle or H2O cycle, describes the continuous movement of water on, above and below the surface of the Earth. Water can change states among liquid, vapor, and solid at various places in the water cycle...

. The latent heat
Latent heat
Latent heat is the heat released or absorbed by a chemical substance or a thermodynamic system during a process that occurs without a change in temperature. A typical example is a change of state of matter, meaning a phase transition such as the melting of ice or the boiling of water. The term was...

 of water condensation amplifies convection, producing atmospheric phenomena such as wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...

, cyclone
Cyclone
In meteorology, a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. This is usually characterized by inward spiraling winds that rotate anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale...

s and anti-cyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14 °C. By photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

 green plants convert solar energy into chemical energy
Chemical energy
Chemical energy is the potential of a chemical substance to undergo a transformation through a chemical reaction or, to transform other chemical substances...

, which produces food, wood and the biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....

 from which fossil fuels are derived.
Yearly Solar fluxes & Human Energy Consumption
Solar 3,850,000 EJ
Wind 2,250 EJ
Biomass 3,000 EJ
Primary energy use (2005) 487 EJ
Electricity (2005) 56.7 EJ


The total solar energy absorbed by Earth's atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth's non-renewable resources of coal, oil, natural gas, and mined uranium combined.

Solar energy can be harnessed in different levels around the world. Depending on a geographical location the closer to the equator the more "potential" solar energy is available.

Applications of solar technology



Solar energy refers primarily to the use of solar radiation for practical ends. However, all renewable energies, other than geothermal
Geothermal power
Geothermal energy is thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. Earth's geothermal energy originates from the original formation of the planet and from radioactive decay of minerals...

 and tidal
Tidal power
Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power - mainly electricity....

, derive their energy from the sun.

Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.

Architecture and urban planning



Sunlight has influenced building design since the beginning of architectural history. Advanced solar architecture and urban planning methods were first employed by the Greeks
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

 and Chinese, who oriented their buildings toward the south to provide light and warmth.

The common features of passive solar architecture are orientation relative to the Sun, compact proportion (a low surface area to volume ratio), selective shading (overhangs) and thermal mass. When these features are tailored to the local climate and environment they can produce well-lit spaces that stay in a comfortable temperature range. Socrates'
Socrates
Socrates was a classical Greek Athenian philosopher. Credited as one of the founders of Western philosophy, he is an enigmatic figure known chiefly through the accounts of later classical writers, especially the writings of his students Plato and Xenophon, and the plays of his contemporary ...

 Megaron House is a classic example of passive solar design. The most recent approaches to solar design use computer modeling tying together solar lighting
Daylighting
Daylighting is the practice of placing windows or other openings and reflective surfaces so that during the day natural light provides effective internal lighting. Particular attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy...

, heating and ventilation
Solar air conditioning
Solar air conditioning refers to any air conditioning system that uses solar power.This can be done through passive solar, solar thermal energy conversion and photovoltaic conversion . The U.S...

 systems in an integrated solar design package. Active solar
Active solar
Active solar technologies are employed to convert solar energy into another more useful form of energy. This would normally be a conversion to heat or electrical energy. Inside a building this energy would be used for heating, cooling, or off-setting other energy use or costs. Active solar uses...

 equipment such as pumps, fans and switchable windows can complement passive design and improve system 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 and concrete, which have lower albedo
Albedo
Albedo , or reflection coefficient, is the diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it...

s and higher heat capacities
Heat capacity
Heat capacity , or thermal capacity, is the measurable physical quantity that characterizes the amount of heat required to change a substance's temperature by a given amount...

 than those in the natural environment. A straightforward method of counteracting the UHI effect is to paint buildings and roads white and plant trees. Using these methods, a hypothetical "cool communities" program in Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...

 has projected that urban temperatures could be reduced by approximately 3 °C at an estimated cost of US$1 billion, giving estimated total annual benefits of US$530 million from reduced air-conditioning costs and healthcare savings.

Agriculture and horticulture



Agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...

 and horticulture
Horticulture
Horticulture is the industry and science of plant cultivation including the process of preparing soil for the planting of seeds, tubers, or cuttings. Horticulturists work and conduct research in the disciplines of plant propagation and cultivation, crop production, plant breeding and genetic...

 seek to optimize the capture of solar energy in order to optimize the productivity of plants. Techniques such as timed planting cycles, tailored row orientation, staggered heights between rows and the mixing of plant varieties can improve crop yields. While sunlight is generally considered a plentiful resource, the exceptions highlight the importance of solar energy to agriculture. During the short growing seasons of the Little Ice Age
Little Ice Age
The Little Ice Age was a period of cooling that occurred after the Medieval Warm Period . While not a true ice age, the term was introduced into the scientific literature by François E. Matthes in 1939...

, French and English
Solar power in the United Kingdom
Solar power is a minor source of renewable energy in the United Kingdom. , about 200 megawatts of solar photovoltaic power have been installed in the UK, capable of producing about 200 gigawatt hours per year of electricity. In April 2010, the UK instituted a feed-in tariff, offering at...

 farmers employed fruit walls to maximize the collection 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 were developed to make better use of sunlight. In 1699, Nicolas Fatio de Duillier
Nicolas Fatio de Duillier
Nicolas Fatio de Duillier was a Swiss mathematician known for his work on the zodiacal light problem, for his very close relationship with Isaac Newton, for his role in the Newton v. Leibniz calculus controversy, and for originating the "push" or "shadow" theory of gravitation...

 even suggested using a tracking mechanism
Solar tracker
A solar tracker is a generic term used to describe devices that orient various payloads toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices....

 which could pivot to follow the Sun. Applications of solar energy in agriculture aside from growing crops include pumping water, drying crops, brooding chicks and drying chicken manure. More recently the technology has been embraced by vinters, who use the energy generated by solar panels to power grape presses.

Greenhouse
Greenhouse
A greenhouse is a building in which plants are grown. These structures range in size from small sheds to very large buildings...

s 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 used during Roman times to produce cucumbers year-round for the Roman emperor Tiberius
Tiberius
Tiberius , was Roman Emperor from 14 AD to 37 AD. Tiberius was by birth a Claudian, son of Tiberius Claudius Nero and Livia Drusilla. His mother divorced Nero and married Augustus in 39 BC, making him a step-son of Octavian...

. The first modern greenhouses were built in Europe in the 16th century to keep exotic plants brought back from explorations abroad. Greenhouses remain an important part of horticulture today, and plastic transparent materials have also been used to similar effect in polytunnel
Polytunnel
A polytunnel is a tunnel made of polyethylene used to grow plants that require a higher temperature and/or humidity than that which is available in the environment....

s and row cover
Row cover
In horticulture, row cover is any material used as a protective covering to shield plants, usually vegetables, primarily from the undesirable effects of cold and wind, and also from insect damage....

s.

Solar lighting



The history of lighting is dominated by the use of natural light. The Romans recognized a right to light as early as the 6th century
Corpus Juris Civilis
The Corpus Juris Civilis is the modern name for a collection of fundamental works in jurisprudence, issued from 529 to 534 by order of Justinian I, Eastern Roman Emperor...

 and English law echoed these judgments with the Prescription Act of 1832. In the 20th century artificial lighting
Lighting
Lighting or illumination is the deliberate application of light to achieve some practical or aesthetic effect. Lighting includes the use of both artificial light sources such as lamps and light fixtures, as well as natural illumination by capturing daylight...

 became the main source of interior illumination but daylighting techniques and hybrid solar lighting solutions are ways to reduce energy consumption.

Daylighting
Daylighting
Daylighting is the practice of placing windows or other openings and reflective surfaces so that during the day natural light provides effective internal lighting. Particular attention is given to daylighting while designing a building when the aim is to maximize visual comfort or to reduce energy...

 systems collect and distribute sunlight to provide interior illumination. This passive technology directly offsets energy use by replacing artificial lighting, and indirectly offsets non-solar energy use by reducing the need for air-conditioning. Although difficult to quantify, the use of natural lighting also offers physiological and psychological benefits compared to artificial lighting. Daylighting design implies careful selection of window types, sizes and orientation; exterior shading devices may be considered as well. Individual features include sawtooth roofs, clerestory windows
Clerestory
Clerestory is an architectural term that historically denoted an upper level of a Roman basilica or of the nave of a Romanesque or Gothic church, the walls of which rise above the rooflines of the lower aisles and are pierced with windows. In modern usage, clerestory refers to any high windows...

, light shelves, skylights and light tube
Light tube
Light tubes or light pipes are used for transporting or distributing natural or artificial light. In their application to daylighting, they are also often called sun pipes, sun scopes, solar light pipes, sky lights or daylight pipes.Generally speaking, a light pipe or light tube may refer to:* a...

s. They may be incorporated into existing structures, but are most effective when integrated into a solar design
Passive solar building design
In passive solar building design, windows, walls, and floors are made to collect, store, and distribute solar energy in the form of heat in the winter and reject solar heat in the summer...

 package that accounts for factors such as glare, heat flux and time-of-use. When daylighting features are properly implemented they can reduce lighting-related energy requirements by 25%.

Hybrid solar lighting
Hybrid Solar Lighting
Hybrid solar lighting or hybrid lighting systems combine the use of solar with artificial light for interior illumination by channelling sunlight through fiber optic cable bundles to provide solar light into rooms without windows or skylights, and by supplementing this natural light with...

 is an active solar
Active solar
Active solar technologies are employed to convert solar energy into another more useful form of energy. This would normally be a conversion to heat or electrical energy. Inside a building this energy would be used for heating, cooling, or off-setting other energy use or costs. Active solar uses...

 method of providing interior illumination. HSL systems collect sunlight using focusing mirrors that track the Sun
Solar tracker
A solar tracker is a generic term used to describe devices that orient various payloads toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices....

 and use optical fiber
Optical fiber
An optical fiber is a flexible, transparent fiber made of a pure glass not much wider than a human hair. It functions as a waveguide, or "light pipe", to transmit light between the two ends of the fiber. The field of applied science and engineering concerned with the design and application of...

s to transmit it inside the building to supplement conventional lighting. In single-story applications these systems are able to transmit 50% of the direct sunlight received.

Solar lights that charge during the day and light up at dusk are a common sight along walkways. Solar-charged lanterns have become popular in developing countries where they provide a safer and cheaper alternative to kerosene lamps.

Although daylight saving time
Daylight saving time
Daylight saving time —also summer time in several countries including in British English and European official terminology —is the practice of temporarily advancing clocks during the summertime so that afternoons have more daylight and mornings have less...

 is promoted as a way to use sunlight to save energy, recent research has been limited and reports contradictory results: several studies report savings, but just as many suggest no effect or even a net loss, particularly when gasoline
Gasoline
Gasoline , or petrol , is a toxic, translucent, petroleum-derived liquid that is primarily used as a fuel in internal combustion engines. It consists mostly of organic compounds obtained by the fractional distillation of petroleum, enhanced with a variety of additives. Some gasolines also contain...

 consumption is taken into account. Electricity use is greatly affected by geography, climate and economics, making it hard to generalize from single studies.

Solar thermal


Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation.

Water heating




Solar hot water systems use sunlight to heat water. In low geographical latitudes (below 40 degrees) from 60 to 70% of the domestic hot water use with temperatures up to 60 °C can be provided by solar heating systems. The most common types of solar water heaters are evacuated 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.

As of 2007, the total installed capacity of solar hot water systems is approximately 154 GW. China is the world leader in their deployment with 70 GW installed as of 2006 and a long term goal of 210 GW by 2020. Israel and Cyprus
Cyprus
Cyprus , officially the Republic of Cyprus , is a Eurasian island country, member of the European Union, in the Eastern Mediterranean, east of Greece, south of Turkey, west of Syria and north of Egypt. It is the third largest island in the Mediterranean Sea.The earliest known human activity on the...

 are the per capita leaders in the use of solar hot water systems with over 90% of homes using them. In the United States, Canada and Australia heating swimming pools is the dominant application of solar hot water with an installed capacity of 18 GW as of 2005.

Heating, cooling and ventilation




In the United States, heating, ventilation and air conditioning
HVAC
HVAC refers to technology of indoor or automotive environmental comfort. HVAC system design is a major subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer...

 (HVAC) systems account for 30% (4.65 EJ) of the energy used in commercial buildings and nearly 50% (10.1 EJ) of the energy used in residential buildings. Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy.

Thermal mass is any material that can be used to store heat—heat from the Sun in the case of solar energy. Common thermal mass materials include stone, cement and water. Historically they have been used in arid climates or warm temperate regions to keep buildings cool by absorbing solar energy during the day and radiating stored heat to the cooler atmosphere at night. However they can be used in cold temperate areas to maintain warmth as well. The size and placement of thermal mass depend on several factors such as climate, daylighting and shading conditions. When properly incorporated, thermal mass maintains space temperatures in a comfortable range and reduces the need for auxiliary heating and cooling equipment.

A solar chimney (or thermal chimney, in this context) is a passive solar ventilation system composed of a vertical shaft connecting the interior and exterior of a building. As the chimney warms, the air inside is heated causing an updraft that pulls air through the building. Performance can be improved by using glazing and thermal mass materials in a way that mimics greenhouses.

Deciduous
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...

 trees and plants have been promoted as a means of controlling solar heating and cooling. When planted on the southern side of a building, their leaves provide shade during the summer, while the bare limbs allow light to pass during the winter. Since bare, leafless trees shade 1/3 to 1/2 of incident solar radiation, there is a balance between the benefits of summer shading and the corresponding loss of winter heating. In climates with significant heating loads, deciduous trees should not be planted on the southern side of a building because they will interfere with winter solar availability. They can, however, be used on the east and west sides to provide a degree of summer shading without appreciably affecting winter solar gain.

Water treatment




Solar distillation can be used to make saline
Saline water
Saline water is a general term for water that contains a significant concentration of dissolved salts . The concentration is usually expressed in parts per million of salt....

 or brackish water
Brackish water
Brackish water is water that has more salinity than fresh water, but not as much as seawater. It may result from mixing of seawater with fresh water, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root "brak," meaning "salty"...

 potable. The first recorded instance of this was by 16th century Arab alchemists. A large-scale solar distillation project was first constructed in 1872 in the Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

an mining town of Las Salinas. The plant, which had solar collection area of 4,700 m2, could produce up to 22,700 L per day and operated for 40 years. Individual still
Still
A still is a permanent apparatus used to distill miscible or immiscible liquid mixtures by heating to selectively boil and then cooling to condense the vapor...

 designs include single-slope, double-slope (or greenhouse type), vertical, conical, inverted absorber, multi-wick, and multiple effect. These stills can operate in passive, active, or hybrid modes. Double-slope stills are the most economical for decentralized domestic purposes, while active multiple effect units are more suitable for large-scale applications.

Solar water disinfection
Disinfection
Disinfectants are substances that are applied to non-living objects to destroy microorganisms that are living on the objects. Disinfection does not necessarily kill all microorganisms, especially nonresistant bacterial spores; it is less effective than sterilisation, which is an extreme physical...

 (SODIS) involves exposing water-filled plastic polyethylene terephthalate
Polyethylene terephthalate
Polyethylene terephthalate , commonly abbreviated PET, PETE, or the obsolete PETP or PET-P, is a thermoplastic polymer resin of the polyester family and is used in synthetic fibers; beverage, food and other liquid containers; thermoforming applications; and engineering resins often in combination...

 (PET) bottles to sunlight for several hours. Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions. It is recommended by the World Health Organization
World Health Organization
The World Health Organization is a specialized agency of the United Nations that acts as a coordinating authority on international public health. Established on 7 April 1948, with headquarters in Geneva, Switzerland, the agency inherited the mandate and resources of its predecessor, the Health...

 as a viable method for household water treatment and safe storage. Over two million people in developing countries use this method for their daily drinking water.

Solar energy may be used in a water stabilisation pond to treat waste water without chemicals or electricity. A further environmental advantage is that algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 grow in such ponds and consume carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 in photosynthesis, although algae may produce toxic chemicals that make the water unusable.

Cooking



Solar cookers use sunlight for cooking, drying and pasteurization
Pasteurization
Pasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food...

. They can be grouped into three broad categories: box cookers, panel cookers and reflector cookers. The simplest solar cooker is the box cooker first built by Horace de Saussure in 1767. A basic box cooker consists of an insulated container with a transparent lid. It can be used effectively with partially overcast skies and will typically reach temperatures of 90–150 °C. Panel cookers use a reflective panel to direct sunlight onto an insulated container and reach temperatures comparable to box cookers. Reflector cookers use various concentrating geometries (dish, trough, Fresnel mirrors) to focus light on a cooking container. These cookers reach temperatures of 315 °C and above but require direct light to function properly and must be repositioned to track the Sun.

The solar bowl is a concentrating technology employed by the Solar Kitchen in Auroville
Auroville
Auroville is an "experimental" township in Viluppuram district in the state of Tamil Nadu, India, near Pondicherry in South India. It was founded in 1968 by Mirra Alfassa and designed by architect Roger Anger...

, Pondicherry, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, where a stationary spherical reflector focuses light along a line perpendicular to the sphere's interior surface, and a computer control system moves the receiver to intersect this line. Steam is produced in the receiver at temperatures reaching 150 °C and then used for process heat in the kitchen.

A reflector developed by Wolfgang Scheffler
Wolfgang Scheffler
Born 1956 in Innsbruck, Austria, and recipient of a Special Recognition Award at the 2006 Nuclear-Free Future Award, Wolfgang Scheffler is the inventor/promoter of Scheffler Reflectors, large, flexible parabolic reflecting dishes that concentrate sunlight for solar cooking in community kitchens,...

 in 1986 is used in many solar kitchens. Scheffler reflectors are flexible parabolic dishes that combine aspects of trough and power tower concentrators. Polar tracking is used to follow the Sun's daily course and the curvature of the reflector is adjusted for seasonal variations in the incident angle of sunlight. These reflectors can reach temperatures of 450–650 °C and have a fixed focal point, which simplifies cooking. The world's largest Scheffler reflector system in Abu Road, Rajasthan
Rajasthan
Rājasthān the land of Rajasthanis, , is the largest state of the Republic of India by area. It is located in the northwest of India. It encompasses most of the area of the large, inhospitable Great Indian Desert , which has an edge paralleling the Sutlej-Indus river valley along its border with...

, India is capable of cooking up to 35,000 meals a day. As of 2008, over 2,000 large Scheffler cookers had been built worldwide.

Process heat


Solar concentrating technologies such as parabolic dish, trough and Scheffler reflectors can provide process heat for commercial and industrial applications. The first commercial system was the Solar Total Energy Project
Solar Total Energy Project
The Solar Total Energy Project was the world’s first and largest solar thermal cogeneration project having an industrial application. Built and operated during the 1980s in Coweta County, Georgia, STEP used solar energy to provide electricity and process heat to a manufacturing facility.Developed...

 (STEP) in Shenandoah, Georgia, USA where a field of 114 parabolic dishes provided 50% of the process heating, air conditioning and electrical requirements for a clothing factory. This grid-connected cogeneration system provided 400 kW of electricity plus thermal energy in the form of 401 kW steam and 468 kW chilled water, and had a one hour peak load thermal storage.

Evaporation ponds are shallow pools that concentrate dissolved solids through evaporation
Evaporation
Evaporation is a type of vaporization of a liquid that occurs only on the surface of a liquid. The other type of vaporization is boiling, which, instead, occurs on the entire mass of the liquid....

. The use of evaporation ponds to obtain salt from sea water is one of the oldest applications of solar energy. Modern uses include concentrating brine solutions used in leach mining and removing dissolved solids from waste streams.

Clothes line
Clothes line
A clothes line or washing line is any type of rope, cord, or twine that has been stretched between two points , outside or indoors, above the level of the ground. Clothing that has recently been washed is hung along the line to dry, using clothes pegs or clothes pins...

s, clotheshorse
Clotheshorse
A clotheshorse or clothes horse, sometimes called a clothes rack, drying horse, winterdyke, clothes maiden, drying rack, Frostick, or airer, refers to a frame upon which clothes are hung after washing to enable them to dry...

s, and clothes racks dry clothes through evaporation by wind and sunlight without consuming electricity or gas. In some states of the United States legislation protects the "right to dry" clothes.

Unglazed transpired collectors (UTC) are perforated sun-facing walls used for preheating ventilation air. UTCs can raise the incoming air temperature up to 22 °C and deliver outlet temperatures of 45–60 °C. The short payback period of transpired collectors (3 to 12 years) makes them a more cost-effective alternative than glazed collection systems. As of 2003, over 80 systems with a combined collector area of 35,000 m2
Square metre
The square metre or square meter is the SI derived unit of area, with symbol m2 . It is defined as the area of a square whose sides measure exactly one metre...

 had been installed worldwide, including an 860 m2 collector in Costa Rica
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....

 used for drying coffee beans and a 1,300 m2 collector in Coimbatore
Coimbatore
Coimbatore , also known as Kovai , is the second largest city in the Indian state of Tamil Nadu. It is a major commercial centre in Tamil Nadu and is known as the "Manchester of South India"....

, India used for drying marigolds.

Solar power



Solar power is the conversion of sunlight into electricity
Electricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...

, either directly using photovoltaics
Photovoltaics
Photovoltaics is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material...

 (PV), or indirectly using concentrated solar power (CSP). CSP systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. PV converts light into electric current using the photoelectric effect
Photoelectric effect
In the photoelectric effect, electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as photoelectrons...

.

Commercial CSP plants were first developed in the 1980s, and the 354 MW SEGS CSP installation is the largest solar power plant in the world and is located in the Mojave Desert of California. Other large CSP plants include the Solnova Solar Power Station
Solnova Solar Power Station
The Solnova Solar Power Station is a large CSP power station made up of five separate units of each. The facility is located at the Solar Platform, in Sanlúcar la Mayor, in Spain, the same area where the PS20 solar power tower is also located...

 (150 MW) and the Andasol solar power station (100 MW), both in Spain. The 97 MW Sarnia Photovoltaic Power Plant
Sarnia Photovoltaic Power Plant
Sarnia Photovoltaic Power Plant near Sarnia, Ontario in Canada, is as of September 2010 the world's largest photovoltaic plant with 80 MWp....

 in Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, is the world’s largest photovoltaic plant.

Concentrated solar power


Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as a heat source for a conventional power plant. A wide range of concentrating technologies exists; the most developed are the parabolic trough, the concentrating linear fresnel reflector, the Stirling dish and the solar power tower. Various techniques are used to track the Sun and focus light. In all of these systems a working fluid
Working fluid
A working fluid is a pressurized gas or liquid that actuates a machine. Examples include steam in a steam engine, air in a hot air engine and hydraulic fluid in a hydraulic motor or hydraulic cylinder...

 is heated by the concentrated sunlight, and is then used for power generation or energy storage.

Photovoltaics


A solar cell
Solar cell
A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....

, or photovoltaic cell (PV), is a device that converts light into electric current using the photoelectric effect
Photoelectric effect
In the photoelectric effect, electrons are emitted from matter as a consequence of their absorption of energy from electromagnetic radiation of very short wavelength, such as visible or ultraviolet light. Electrons emitted in this manner may be referred to as photoelectrons...

. The first solar cell was constructed by Charles Fritts
Charles Fritts
Charles Fritts was an American inventor credited with creating the first working solar cell in 1883.Fritts coated the semiconductor material selenium with an extremely thin layer of gold...

 in the 1880s. In 1931 a German engineer, Dr Bruno Lange, developed a photo cell using silver selenide in place of copper oxide. Although the prototype selenium
Selenium
Selenium is a chemical element with atomic number 34, chemical symbol Se, and an atomic mass of 78.96. It is a nonmetal, whose properties are intermediate between those of adjacent chalcogen elements sulfur and tellurium...

 cells converted less than 1% of incident light into electricity, both Ernst Werner von Siemens
Ernst Werner von Siemens
Ernst Werner Siemens, von Siemens since 1888, was a German inventor and industrialist. Siemens' name has been adopted as the SI unit of electrical conductance, the siemens...

 and James Clerk Maxwell
James Clerk Maxwell
James Clerk Maxwell of Glenlair was a Scottish physicist and mathematician. His most prominent achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and optics into a consistent theory...

 recognized the importance of this discovery. Following the work of Russell Ohl
Russell Ohl
Russell Shoemaker Ohl was an American engineer who is generally recognized for patenting the modern solar cell ....

 in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

 solar cell in 1954. These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6%.

Solar chemical



Solar chemical processes use solar energy to drive chemical reactions. These processes offset energy that would otherwise come from a fossil fuel source and can also convert solar energy into storable and transportable fuels. Solar induced chemical reactions can be divided into thermochemical or photochemical. A variety of fuels can be produced by artificial photosynthesis
Artificial photosynthesis
Artificial photosynthesis is a chemical process that replicates the natural process of photosynthesis, a process that converts sunlight, water, and carbon dioxide into carbohydrates and oxygen. The term is commonly used to refer to any scheme for capturing and storing the energy from sunlight in...

. The multielectron catalytic chemistry involved in making carbon-based fuels (such as methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...

) from reduction of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 is challenging; a feasible alternative is hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 production from protons, though use of water as the source of electrons (as plants do) requires mastering the multielectron oxidation of two water molecules to molecular oxygen. Some have envisaged working solar fuel plants in coastal metropolitan areas by 2050- the splitting of sea water providing hydrogen to be run through adjacent fuel-cell electric power plants and the pure water by-product going directly into the municipal water system.

Hydrogen production
Hydrogen production
Hydrogen production is the family of industrial methods for generating hydrogen. Currently the dominant technology for direct production is steam reforming from hydrocarbons. Many other methods are known including electrolysis and thermolysis...

 technologies been a significant area of solar chemical research since the 1970s. Aside from electrolysis driven by photovoltaic or photochemical cells, several thermochemical processes have also been explored. One such route uses concentrators to split water into oxygen and hydrogen at high temperatures (2300-2600 °C). Another approach uses the heat from solar concentrators to drive the steam reformation
Steam reforming
Fossil fuel reforming is a method of producing hydrogen or other useful products from fossil fuels such as natural gas. This is achieved in a processing device called a reformer which reacts steam at high temperature with the fossil fuel. The steam methane reformer is widely used in industry to...

 of natural gas thereby increasing the overall hydrogen yield compared to conventional reforming methods. Thermochemical cycles characterized by the decomposition and regeneration of reactants present another avenue for hydrogen production. The Solzinc process under development at the Weizmann Institute
Weizmann Institute of Science
The Weizmann Institute of Science , known as Machon Weizmann, is a university and research institute in Rehovot, Israel. It differs from other Israeli universities in that it offers only graduate and post-graduate studies in the sciences....

 uses a 1 MW solar furnace to decompose zinc oxide
Zinc oxide
Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

 (ZnO) at temperatures above 1200 °C. This initial reaction produces pure zinc, which can subsequently be reacted with water to produce hydrogen.

Sandia's
Sandia National Laboratories
The Sandia National Laboratories, managed and operated by the Sandia Corporation , are two major United States Department of Energy research and development national laboratories....

 Sunshine to Petrol (S2P) technology uses the high temperatures generated by concentrating sunlight along with a zirconia/ferrite
Ferrite (iron)
Ferrite or alpha iron is a materials science term for iron, or a solid solution with iron as the main constituent, with a body centred cubic crystal structure. It is the component which gives steel and cast iron their magnetic properties, and is the classic example of a ferromagnetic material...

 catalyst to break down atmospheric carbon dioxide into oxygen and carbon monoxide
Carbon monoxide
Carbon monoxide , also called carbonous oxide, is a colorless, odorless, and tasteless gas that is slightly lighter than air. It is highly toxic to humans and animals in higher quantities, although it is also produced in normal animal metabolism in low quantities, and is thought to have some normal...

 (CO). The carbon monoxide can then be used to synthesize conventional fuels such as methanol, gasoline and jet fuel.

A photogalvanic device is a type of battery in which the cell solution (or equivalent) forms energy-rich chemical intermediates when illuminated. These energy-rich intermediates can potentially be stored and subsequently reacted at the electrodes to produce an electric potential. The ferric-thionine chemical cell is an example of this technology.

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 two types of photoelectrochemical cells: photoelectric cells that convert light into electricity and photochemical cells that use light to drive chemical reactions such as electrolysis
Electrolysis
In chemistry and manufacturing, electrolysis is a method of using a direct electric current to drive an otherwise non-spontaneous chemical reaction...

.

A combination thermal/photochemical cell has also been proposed. The Stanford PETE process uses solar thermal energy to raise the temperature of a thermionic metal to about 800C to increase the rate of production of electricity to electrolyse atmospheric CO2 down to carbon or carbon monoxide which can then be used for fuel production, and the waste heat can be used as well.

Solar vehicles


Development of a solar powered car has been an engineering goal since the 1980s. The World Solar Challenge
World Solar Challenge
The World Solar Challenge is a solar-powered car race which covers through the Australian Outback, from Darwin to Adelaide.The race attracts teams from around the world, most of which are fielded by universities or corporations although some are fielded by high schools...

 is a biannual solar-powered car race, where teams from universities and enterprises compete over 3021 kilometres (1,877.2 mi) across central Australia from Darwin
Darwin, Northern Territory
Darwin is the capital city of the Northern Territory, Australia. Situated on the Timor Sea, Darwin has a population of 127,500, making it by far the largest and most populated city in the sparsely populated Northern Territory, but the least populous of all Australia's capital cities...

 to Adelaide
Adelaide
Adelaide is the capital city of South Australia and the fifth-largest city in Australia. Adelaide has an estimated population of more than 1.2 million...

. In 1987, when it was founded, the winner's average speed was 67 kilometres per hour (41.6 mph) and by 2007 the winner's average speed had improved to 90.87 kilometres per hour (56.46 mph).
The North American Solar Challenge and the planned South African Solar Challenge
South African Solar Challenge
The South African Solar Challenge is an alternative fuel vehicle auto racing challenge in South Africa, with classes for hybrid vehicles, electric vehicles, solar vehicles, and biofuel-powered vehicles. The first challenge was run in 2008, and it will run every two years thereafter. The race...

 are comparable competitions that reflect an international interest in the engineering and development of solar powered vehicles.

Some vehicles use solar panels for auxiliary power, such as for air conditioning, to keep the interior cool, thus reducing fuel consumption.

In 1975, the first practical solar boat was constructed in England. By 1995, passenger boats incorporating PV panels began appearing and are now used extensively. In 1996, Kenichi Horie
Kenichi Horie
is a Japanese solo yachtsman. Horie first rose to prominence when he became the first person to sail solo across the Pacific Ocean in 1962. He has made other significant solo voyages, usually involving boats exhibiting some sort of environmentally friendly theme, including his 2008 voyage across...

 made the first solar powered crossing of the Pacific Ocean, and the sun21 catamaran made the first solar powered crossing of the Atlantic Ocean in the winter of 2006–2007. There are plans to circumnavigate the globe in 2010.
In 1974, the unmanned AstroFlight Sunrise
AstroFlight Sunrise
The AstroFlight Sunrise was an unmanned experimental electric aircraft technology demonstrator and the first aircraft to fly on solar power....

 plane made the first solar flight. On 29 April 1979, the Solar Riser made the first flight in a solar powered, fully controlled, man carrying flying machine, reaching an altitude of 40 feet (12.2 m). In 1980, the Gossamer Penguin made the first piloted flights powered solely by photovoltaics. This was quickly followed by the Solar Challenger
Solar Challenger
|-See also:-External links:*...

which crossed the English Channel in July 1981. In 1990 Eric Scott Raymond
Eric Scott Raymond
Eric Raymond is a Certified Flight Instructor, Glider pilot, hang gliding pilot and Designer of Solar powered Aircraft. University education in Photography and Aerospace engineering...

 in 21 hops flew from California to North Carolina using solar power. Developments then turned back to unmanned aerial vehicles (UAV) with the Pathfinder (1997) and subsequent designs, culminating in the Helios
Helios Prototype
The NASA Pathfinder, NASA Pathfinder Plus, NASA Centurion and NASA Helios Prototype were an evolutionary series of solar- and fuel-cell-system-powered unmanned aerial vehicles. AeroVironment, Inc. developed the vehicles under NASA's Environmental Research Aircraft and Sensor Technology program...

which set the altitude record for a non-rocket-propelled aircraft at 29524 metres (96,863.5 ft) in 2001. The Zephyr
QinetiQ Zephyr
Zephyr is a lightweight solar-powered UAV which was originally designed and built by the QQ1 "Edge of Space" team who were sponsored by the United Kingdom defence firm, Qinetiq. It is of carbon-fibre construction, and uses sunlight to charge a lithium sulphur battery during the day, which powers...

, developed by BAE Systems
BAE Systems
BAE Systems plc is a British multinational defence, security and aerospace company headquartered in London, United Kingdom, that has global interests, particularly in North America through its subsidiary BAE Systems Inc. BAE is among the world's largest military contractors; in 2009 it was the...

, is the latest in a line of record-breaking solar aircraft, making a 54-hour flight in 2007, and month-long flights are envisioned by 2010.

A solar balloon
Solar balloon
A solar balloon is a balloon that gains buoyancy when the air inside is heated by the sun's radiation, usually with the help of black or dark balloon material. The heated air inside the solar balloon expands and has lower density than the surrounding air. As such, a solar balloon is similar to a...

 is a black balloon that is filled with ordinary air. As sunlight shines on the balloon, the air inside is heated and expands causing an upward buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

 force, much like an artificially heated hot air balloon
Hot air balloon
The hot air balloon is the oldest successful human-carrying flight technology. It is in a class of aircraft known as balloon aircraft. On November 21, 1783, in Paris, France, the first untethered manned flight was made by Jean-François Pilâtre de Rozier and François Laurent d'Arlandes in a hot air...

. Some solar balloons are large enough for human flight, but usage is generally limited to the toy market as the surface-area to payload-weight ratio is relatively high.

Solar sail
Solar sail
Solar sails are a form of spacecraft propulsion using the radiation pressure of light from a star or laser to push enormous ultra-thin mirrors to high speeds....

s are a proposed form of spacecraft propulsion using large membrane mirror
Membrane mirror
Membrane mirrors are mirrors made on thin films of material, such as metallized PET film. They can be used as components in adaptive optics systems....

s to exploit radiation pressure from the Sun. Unlike rockets, solar sails require no fuel. Although the thrust is small compared to rockets, it continues as long as the Sun shines onto the deployed sail and in the vacuum of space significant speeds can eventually be achieved.

The High-altitude airship
High-altitude airship
The United States Department of Defense Missile Defense Agency contracted Lockheed Martin to construct a high-altitude airship to enhance its Ballistic Missile Defense System ....

 (HAA) is an unmanned, long-duration, lighter-than-air vehicle using helium
Helium
Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

 gas for lift, and thin film
Thin film
A thin film is a layer of material ranging from fractions of a nanometer to several micrometers in thickness. Electronic semiconductor devices and optical coatings are the main applications benefiting from thin film construction....

 solar cells for power. The United States Department of Defense
United States Department of Defense
The United States Department of Defense is the U.S...

 Missile Defense Agency has contracted Lockheed Martin
Lockheed Martin
Lockheed Martin is an American global aerospace, defense, security, and advanced technology company with worldwide interests. It was formed by the merger of Lockheed Corporation with Martin Marietta in March 1995. It is headquartered in Bethesda, Maryland, in the Washington Metropolitan Area....

 to construct it to enhance the Ballistic Missile Defense System (BMDS). Airships have some advantages for solar-powered flight: they do not require power to remain aloft, and an airship's envelope presents a large area to the Sun.

Energy storage methods




Solar energy is not available at night, and energy storage is an important issue because modern energy systems usually assume continuous availability of energy.

Thermal mass systems can store solar energy in the form of heat at domestically useful temperatures for daily or seasonal durations
Seasonal thermal store
A seasonal thermal store is a store designed to retain heat deposited during the hot summer months for use during colder winter weather...

. Thermal storage systems generally use readily available materials with high specific heat capacities such as water, earth and stone. Well-designed systems can lower peak demand
Peak demand
Peak demand is used to refer to a historically high point in the sales record of a particular product. In terms of energy use, peak demand describes a period of strong consumer demand.- Peak load :...

, shift time-of-use to off-peak hours and reduce overall heating and cooling requirements.

Phase change materials such as paraffin wax and Glauber's salt are another thermal storage media. These materials are inexpensive, readily available, and can deliver domestically useful temperatures (approximately 64 °C). The "Dover House" (in Dover, Massachusetts
Dover, Massachusetts
Dover is a town in Norfolk County, Massachusetts, United States. The population was 5,589 at the 2010 census.Located about southwest of downtown Boston, Dover is a residential town nestled on the south banks of the Charles River. Almost all of the residential zoning requires or larger...

) was the first to use a Glauber's salt heating system, in 1948.

Solar energy can be stored at high temperatures using molten salt
Molten salt
Molten salt refers to a salt that is in the liquid phase that is normally a solid at standard temperature and pressure . A salt which is normally liquid at STP is usually called a room temperature ionic liquid, although technically molten salts are a class of ionic liquids.-Uses:Molten salts have...

s. Salts are an effective storage medium because they are low-cost, have a high specific heat capacity and can deliver heat at temperatures compatible with conventional power systems. The Solar Two used this method of energy storage, allowing it to store 1.44 TJ in its 68 m3
Cubic metre
The cubic metre is the SI derived unit of volume. It is the volume of a cube with edges one metre in length. An alternative name, which allowed a different usage with metric prefixes, was the stère...

 storage tank with an annual storage efficiency of about 99%.

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
Grid-tied electrical system
A grid-tied electrical system, also called tied to grid or grid tie system, is a semi-autonomous electrical generation or grid energy storage system which links to the mains to feed excess capacity back to the local mains electrical grid...

, while standard grid electricity can be used to meet shortfalls. Net metering
Net metering
Net metering is an electricity policy for consumers who own renewable energy facilities or V2G electric vehicles. "Net", in this context, is used in the sense of meaning "what remains after deductions" — in this case, the deduction of any energy outflows from metered energy inflows...

 programs give household systems a credit for any electricity they deliver to the grid. This is often legally handled by 'rolling back' the meter whenever the home produces more electricity than it consumes. If the net electricity use is below zero, the utility is required to pay for the extra at the same rate as they charge consumers. Other legal approaches involve the use of two meters, to measure electricity consumed vs. electricity produced. This is less common due to the increased installation cost of the second meter.

Pumped-storage hydroelectricity
Pumped-storage hydroelectricity
Pumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps...

 stores energy in the form of water pumped when energy is available from a lower elevation reservoir to a higher elevation one. The energy is recovered when demand is high by releasing the water to run through a hydroelectric power generator.

Development, deployment and economics


Beginning with the surge in coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...

 use which accompanied the Industrial Revolution
Industrial Revolution
The Industrial Revolution was a period from the 18th to the 19th century where major changes in agriculture, manufacturing, mining, transportation, and technology had a profound effect on the social, economic and cultural conditions of the times...

, energy consumption has steadily transitioned from wood and biomass to fossil fuel
Fossil fuel
Fossil fuels are fuels formed by natural processes such as anaerobic decomposition of buried dead organisms. The age of the organisms and their resulting fossil fuels is typically millions of years, and sometimes exceeds 650 million years...

s. The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. However development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and petroleum
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...

.

The 1973 oil embargo
1973 oil crisis
The 1973 oil crisis started in October 1973, when the members of Organization of Arab Petroleum Exporting Countries or the OAPEC proclaimed an oil embargo. This was "in response to the U.S. decision to re-supply the Israeli military" during the Yom Kippur war. It lasted until March 1974. With the...

 and 1979 energy crisis
1979 energy crisis
The 1979 oil crisis in the United States occurred in the wake of the Iranian Revolution. Amid massive protests, the Shah of Iran, Mohammad Reza Pahlavi, fled his country in early 1979 and the Ayatollah Khomeini soon became the new leader of Iran. Protests severely disrupted the Iranian oil...

 caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies. Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the US (SERI, now NREL), Japan (NEDO
New Energy and Industrial Technology Development Organization
The New Energy and Industrial Technology Development Organization , also known as NEDO, is Japan's largest public management organization promoting research and development as well as deployment of industrial, energy and environmental technologies. In 2003, NEDO was reorganized as an Independent...

), and Germany
Solar power in Germany
Germany is one of the world's top photovoltaics installers, with a solar PV capacity as of May 2011 of more than 18,000 megawatts .The German solar PV industry installed 7,400 MW from nearly one-quarter million individual systems in 2010, and solar PV provided 12 TWh of electricity in 2010, about...

 (Fraunhofer Institute for Solar Energy Systems ISE
Fraunhofer Society
The Fraunhofer Society is a German research organization with 60 institutes spread throughout Germany, each focusing on different fields of applied science . It employs around 18,000, mainly scientists and engineers, with an annual research budget of about €1.65 billion...

).

Commercial solar water heaters began appearing in the United States in the 1890s. These systems saw increasing use until the 1920s but were gradually replaced by cheaper and more reliable heating fuels. As with photovoltaics, solar water heating
Solar water heating
Solar water heating or solar hot water systems comprise several innovations and many mature renewable energy technologies that have been well established for many years...

 attracted renewed attention as a result of the oil crises in the 1970s but interest subsided in the 1980s due to falling petroleum prices. Development in the solar water heating sector progressed steadily throughout the 1990s and growth rates have averaged 20% per year since 1999. Although generally underestimated, solar water heating and cooling is by far the most widely deployed solar technology with an estimated capacity of 154 GW as of 2007.

ISO Standards


The International Organization for Standardization
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

 has established a number of standards relating to solar energy equipment. For example, ISO 9050 relates to glass in building while ISO 10217 relates to the materials used in solar water heaters.

See also


  • Airmass
    Airmass
    In astronomy, air mass is the optical path length through Earth’s atmosphere for light from a celestial source. As it passes through the atmosphere, light is attenuated by scattering and absorption; the more atmosphere through which it passes, the greater the attenuation. Consequently, celestial...


  • Community solar farm
    Community solar farm
    A community solar farm or solar garden is a solar power installation that accepts capital from and provides credit for the output and tax benefits to individual and other investors. The power output of the farm is credited to the investors in proportion to their investment, with adjustments to...

  • Desertec
    Desertec
    DESERTEC is a concept proposed by the DESERTEC Foundation for making use of solar energy and wind energy. This concept will be implemented in North Africa and the Middle East by the consortium Dii GmbH, formed by a group of European companies and the DESERTEC Foundation...

  • Energy storage
    Energy storage
    Energy storage is accomplished by devices or physical media that store some form of energy to perform some useful operation at a later time. A device that stores energy is sometimes called an accumulator....

  • Global dimming
    Global dimming
    Global dimming is the gradual reduction in the amount of global direct irradiance at the Earth's surface that was observed for several decades after the start of systematic measurements in the 1950s. The effect varies by location, but worldwide it has been estimated to be of the order of a 4%...

  • Greasestock
    Greasestock
    Greasestock is an American event held yearly in Yorktown Heights, New York. It is one of the largest alternative fuel, renewable energy, and low-energy green vehicle exhibitions in the United States. Exhibitors showcase a variety of alternative energy vehicles, as well as exhibits with a...

  • Green electricity
  • Heliostat
    Heliostat
    A heliostat is a device that includes a mirror, usually a plane mirror, which turns so as to keep reflecting sunlight toward a predetermined target, compensating for the sun's apparent motions in the sky. The target may be a physical object, distant from the heliostat, or a direction in space...

  • List of conservation topics
  • List of renewable energy organizations
  • List of solar energy topics
  • List of solar thermal power stations
  • Photovoltaic cell
  • Photovoltaic module
    Photovoltaic module
    A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...

  • Renewable heat
    Renewable heat
    Renewable heat is an application of renewable energy and it refers to the renewable generation of heat, rather than electrical power ....

  • Solar Decathlon
    Solar Decathlon
    The U.S. Department of Energy Solar Decathlon is an international competition that challenges 20 collegiate teams to design, build, and operate the most attractive, effective, and energy-efficient solar-powered house...

  • Solar easement
    Solar Easement
    A solar easement is a right, expressed as an easement, restriction, covenant, or condition contained in any deed, contract, or other written instrument executed by or on behalf of any landowner for the purpose of assuring adequate access to direct sunlight for solar energy systems.- Features :A...

  • Solar flower tower
    Solar flower tower
    AORA's Solar Flower Tower is a hybrid power generator that utilizes solar and alternative fuels, including diesel fuel, natural gas, liquefied natural gas, biogas, and other biofuels, to provide a constant green power source targeted for community-sized production. A module, dubbed the Solar Flower...

  • Solar lamp
    Solar lamp
    A solar lamp is a portable light fixture composed of a LED lamp, a photovoltaic solar panel, and a rechargeable battery.Outdoor lamps are used for lawn and garden decorations. Indoor solar lamps are also used for general illumination .Solar lights are used for decoration, and come in a wide variety...

  • Solar power satellite
  • Solar pond
    Solar pond
    A solar pond is a pool of saltwater which acts as a large-scale solar thermal energy collector with integral heat storage for supplying thermal energy...

  • Solar tracker
    Solar tracker
    A solar tracker is a generic term used to describe devices that orient various payloads toward the sun. Payloads can be photovoltaic panels, reflectors, lenses or other optical devices....

  • Soil solarization
    Soil solarization
    Soil solarization is an environmentally friendly method of using solar power for controlling disease agents in the soil by mulching the soil and covering it with tarp, usually with a transparent polyethylene cover, to trap solar energy....

  • Sun
    Sun
    The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

  • Timeline of solar cells
    Timeline of solar cells
    The timeline of solar cells begins in the 19th century when it is observed that the presence of sunlight is capable of generating usable electrical energy. Solar cells have gone on to be used in many applications...

  • Trombe wall
    Trombe wall
    A Trombe wall is a sun-facing wall separated from the outdoors by glass and an air space, which absorbs solar energy and releases it selectively towards the interior at night. The essential idea was first explored by Edward S. Morse and patented by him in 1881...


  • External links