There was an error in this gadget

Monday, 27 June 2011

Solar power

Solar power

From Wikipedia, the free encyclopedia
The PS10 concentrates sunlight from a field of heliostats on a central tower.
Renewable energy
Wind Turbine
Biofuel
Biomass
Geothermal
Hydroelectricity
Solar energy
Tidal power
Wave power
Wind power
v · d · e
Solar power is the conversion of sunlight into electricity, either directly using photovoltaics (PV), or indirectly using concentrated solar power (CSP) or to split water and create hydrogen fuel using techniques of artificial photosynthesis. Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaics convert light into electric current using the photoelectric effect.[1]
Commercial concentrated solar power 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 (150 MW) and the Andasol solar power station (100 MW), both in Spain. The 97 MW Sarnia Photovoltaic Power Plant in Canada, is the world’s largest photovoltaic plant.

Applications

Applications

Average insolation showing land area (small black dots) required to replace the world primary energy supply with solar electricity. 18 TW is 568 Exajoule (EJ) per year. Insolation for most people is from 150 to 300 W/m² or 3.5 to 7.0 kWh/m²/day.
Solar power has great potential, but in 2008 supplied less than 0.02% of the world's total energy supply[citation needed]. There are many competing technologies, including 14 types of photovoltaic cells, such as thin film, monocrystalline silicon, polycrystalline silicon, and amorphous cells, as well as multiple types of concentrating solar power. It is too early to know which technology will become dominant.[2]
The earliest significant application of solar cells was as a back-up power source to the Vanguard I satellite in 1958, which allowed it to continue transmitting for over a year after its chemical battery was exhausted.[3] The successful operation of solar cells on this mission was duplicated in many other Soviet and American satellites, and by the late 1960s, PV had become the established source of power for them.[4] Photovoltaics went on to play an essential part in the success of early commercial satellites such as Telstar, and they remain vital to the telecommunications infrastructure today.[5]
The high cost of solar cells limited terrestrial uses throughout the 1960s. This changed in the early 1970s when prices reached levels that made PV generation competitive in remote areas without grid access. Early terrestrial uses included powering telecommunication stations, off-shore oil rigs, navigational buoys and railroad crossings.[6] These off-grid applications accounted for over half of worldwide installed capacity until 2004.[7]
Building-integrated photovoltaics cover the roofs of an increasing number of homes.
The 1973 oil crisis stimulated a rapid rise in the production of PV during the 1970s and early 1980s.[8] Economies of scale which resulted from increasing production along with improvements in system performance brought the price of PV down from 100 USD/watt in 1971 to 7 USD/watt in 1985.[9] Steadily falling oil prices during the early 1980s led to a reduction in funding for photovoltaic R&D and a discontinuation of the tax credits associated with the Energy Tax Act of 1978. These factors moderated growth to approximately 15% per year from 1984 through 1996.[10]
Since the mid-1990s, leadership in the PV sector has shifted from the US to Japan and Europe. Between 1992 and 1994, Japan increased R&D funding, established net metering guidelines, and introduced a subsidy program to encourage the installation of residential PV systems.[11] As a result, PV installations in the country climbed from 31.2 MW in 1994 to 318 MW in 1999,[12] and worldwide production growth increased to 30% in the late 1990s.[13]

Concentrating solar power

Concentrating solar power

Solar troughs are the most widely deployed.
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 [discuss], 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 is heated by the concentrated sunlight, and is then used for power generation or energy storage.[22]
A parabolic trough consists of a linear parabolic reflector that concentrates light onto a receiver positioned along the reflector's focal line. The receiver is a tube positioned right above the middle of the parabolic mirror and is filled with a working fluid. The reflector is made to follow the Sun during the daylight hours by tracking along a single axis. Parabolic trough systems provide the best land-use factor of any solar technology.[23] The SEGS plants in California and Acciona's Nevada Solar One near Boulder City, Nevada are representatives of this technology.[24][25] Compact Linear Fresnel Reflectors are CSP-plants which use many thin mirror strips instead of parabolic mirrors to concentrate sunlight onto two tubes with working fluid. This has the advantage that flat mirrors can be used which are much cheaper than parabolic mirrors, and that more reflectors can be placed in the same amount of space, allowing more of the available sunlight to be used. Concentrating linear fresnel reflectors can be used in either large or more compact plants.[26][27]

Photovoltaics

Photovoltaics

11 MW Serpa solar power plant in Portugal
A solar cell, or photovoltaic cell (PV), is a device that converts light into electric current using the photoelectric effect. The first solar cell was constructed by Charles Fritts in the 1880s.[30] In 1931 a German engineer, Dr Bruno Lange, developed a photo cell using silver selenide in place of copper oxide.[31] Although the prototype selenium cells converted less than 1% of incident light into electricity, both Ernst Werner von Siemens and James Clerk Maxwell recognized the importance of this discovery.[32] Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954.[33] These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6%.[34]

Economics

Economics

The U.S. Energy Information Administration calculates that, all-told, electricity from a Solar PV plants costs 4 times that of conventional coal.[67] Bloomberg New Energy Finance in March 2011, put the 2010 cost of solar panels at $1.80 per watt, but estimated that the price would decline to $1.50 per watt by the end of 2011.[68] Nevertheless, there are exceptions-- Nellis Air Force Base is receiving photoelectric power for about 2.2 ¢/kWh and grid power for 9 ¢/kWh.[69][70] Also, since PV systems use no fuel and modules typically last 25 to 40 years, the International Conference on Solar Photovoltaic Investments, organized by EPIA, has estimated that PV systems will pay back their investors in 8 to 12 years.[71] As a result, since 2006 it has been economical for investors to install photovoltaics for free in return for a long term power purchase agreement. Fifty percent of commercial systems were installed in this manner in 2007 and it is expected that 90% will by 2009.[72]
Concentrated Solar Power (CSP) facilities produce power more cheaply than photovoltaic systems and may eventually be price-competitive with conventional power plants. The Ivanpah Solar Power Facility is expected to produce power at costs comparable to natural gas.[73]
Additionally, governments have created various financial incentives to encourage the use of solar power. Renewable portfolio standards impose a government mandate that utilities generate or acquire a certain percentage of renewable power regardless of increased energy procurement costs.

Energy storage methods

Energy storage methods

This energy park in Geesthacht, Germany, includes solar panels and pumped-storage hydroelectricity.
Seasonal variation of the output of the solar panels at AT&T Park in San Francisco
Solar energy is not available at night, making energy storage an important issue in order to provide the continuous availability of energy.[79] Both wind power and solar power are intermittent energy sources, meaning that all available output must be taken when it is available and either stored for when it can be used, or transported, over transmission lines, to where it can be used. Wind power and solar power tend to be somewhat complementary, as there tends to be more wind in the winter and more sun in the summer, but on days with no sun and no wind the difference needs to be made up in some manner.[80] The Institute for Solar Energy Supply Technology of the University of Kassel pilot-tested a combined power plant linking solar, wind, biogas and hydrostorage to provide load-following power around the clock, entirely from renewable sources.[81]
Solar energy can be stored at high temperatures using molten salts. 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 storage tank, enough to provide full output for close to 39 hours, with an efficiency of about 99%.[82]

Experimental solar power

Experimental solar power

Concentrating photovoltaics in Catalonia, Spain
Concentrated photovoltaics (CPV) systems employ sunlight concentrated onto photovoltaic surfaces for the purpose of electrical power production. Solar concentrators of all varieties may be used, and these are often mounted on a solar tracker in order to keep the focal point upon the cell as the Sun moves across the sky.[86] Luminescent solar concentrators (when combined with a PV-solar cell) can also be regarded as a CPV system. Luminescent solar concentrators are useful as they can improve performance of PV-solar panels drastically.[87]
Thermoelectric, or "thermovoltaic" devices convert a temperature difference between dissimilar materials into an electric current. First proposed as a method to store solar energy by solar pioneer Mouchout in the 1800s,[88] thermoelectrics reemerged in the Soviet Union during the 1930s. Under the direction of Soviet scientist Abram Ioffe a concentrating system was used to thermoelectrically generate power for a 1 hp engine.[89] Thermogenerators were later used in the US space program as an energy conversion technology for powering deep space missions such as Cassini, Galileo and Viking. Research in this area is focused on raising the efficiency of these devices from 7–8% to 15–20%.[90]
Space-based solar power is a theoretical design for the collection of solar power in space, for use on Earth. SBSP differs from the usual method of solar power collection in that the solar panels used to collect the energy would reside on a satellite in orbit, often referred to as a solar power satellite (SPS), rather than on Earth's surface. In space, collection of the Sun's energy is unaffected by the day/night cycle, weather, seasons, or the filtering effect of Earth's atmospheric gases. Average solar energy per unit area outside Earth's atmosphere is on the order of ten times that available on Earth's surface. However, there is no shortage of energy reaching the surface. The amount of solar energy reaching the surface of the planet each year is about twice the amount of energy that will be obtained forever from coal, oil, natural gas, and mined Uranium, combined, even using breeder reactors.[91]