Electronics/History/Chapter 4

Frequency Spectrum

Beam power

Microwaves can be used to transmit power over long distances,

and post-World War II research was done to examine possibilities. NASA worked in the 1970s and early 1980s to research the possibilities of using Solar Power Satellite (SPS) systems with large solar arrays that would beam power down to the Earth's survace via microwaves.

Van allen radiation belt

The presence of a radiation belt had been theorized prior to the Space Age and the belt's presence was confirmed by the Explorer I on January 31, 1958 and Explorer III missions, under Doctor James van Allen. The trapped radiation was first mapped out by Explorer IV and Pioneer III.

FM

New technology was added to FM radio in the early 1960s to allow FM stereo transmissions, where the frequency modulated radio signal is used to carry stereophonic sound, using the pilot-tone multiplex system.

UHF

On December 29, 1949 KC2XAK of Bridgeport, Connecticut became the first UHF television station to operate on a regular daily schedule.

In Britain, UHF television began with the launch of BBC TWO in 1964. BBC ONE and ITV soon followed, and colour was introduced on UHF only in 1967 - 1969. Today all British terrestrial television channels (both analog and digital) are on UHF.

FCC

The Federal Communications Commission (FCC) is an independent United States government agency, created, directed, and empowered by Congressional statute.

The FCC was established by the Communications Act of 1934 as the successor to the Federal Radio Commission and is charged with regulating all non-Federal Government use of the radio spectrum (including radio and television broadcasting), and all interstate telecommunications (wire, satellite and cable) as well as all international communications that originate or terminate in the United States. The FCC took over wire communication regulation from the Interstate Commerce Commission. The FCC's jurisdiction covers the 50 states, the District of Columbia, and U.S. possessions.

Table of contents [showhide] 1 Organization 2 History 2.1 Report on Chain Broadcasting 2.2 Allocation of television stations 3 Regulatory powers 4 External links

Organization The FCC is directed by five Commissioners appointed by the President and confirmed by the Senate for 5-year terms, except when filling an unexpired term. The President designates one of the Commissioners to serve as Chairperson. Only three Commissioners may be members of the same political party. None of them can have a financial interest in any Commission-related business.

As the chief executive officer of the Commission, the Chairman delegates management and administrative responsibility to the Managing Director. The Commissioners supervise all FCC activities, delegating responsibilities to staff units and Bureaus. The current FCC Chairman is Michael Powell, son of Secretary of State Colin Powell. The other four current Commissioners are Kathleen Abernathy, Michael Copps, Kevin Martin, and Jonathon Adelstein.

History Report on Chain Broadcasting In 1940 the Federal Communications Commission issued the "Report on Chain Broadcasting." The major point in the report was the breakup of NBC (See American Broadcasting Company), but there were two other important points. One was network option time, the culprit here being CBS. The report limited the amount of time during the day, and what times the networks may broadcast. Previously a network could demand any time it wanted from an affiliate. The second concerned artist bureaus. The networks served as both agents and employees of artists, which was a conflict of interest the report rectified.

Allocation of television stations The Federal Communications Commission assigned television the Very High Frequency, VHF, band and gave TV channels 1-13. The 13 channels could only accommodate 400 stations nationwide and could not accommodate color in its state of technology in the early 1940s. So in 1944 CBS proposed to convert all of television to the Ultra High Frequency band, UHF, which would have solved the frequency and color problem. There was only one flaw in the CBS proposal, everyone else disagreed. In 1945 and 1946 the Federal Communications Commission held hearings on the CBS plan. RCA said CBS wouldn't have its color system ready for 5-10 years. CBS claimed it would be ready by the middle of 1947. CBS also gave a demonstration with a very high quality picture. In October of 1946 RCA presented a color system of inferior quality which was partially compatible with the present VHF black and white system. In March 1947 the Federal Communications Commission said CBS would not be ready, and ordered a contiuation of the present system. RCA promised its electric color system would be fully compatible within five years, in 1947 an adaptor was required to see color programs in black and white on a black and white set.

In 1945 the Federal Communications Commission moved FM radio to a higher frequency. The Federal Communications Commission also allowed simulcasting of AM programs on FM stations. Regardless of these two disadvantages, CBS placed its bets on FM and gave up some TV applications. CBS had thought TV would be moved according to its plan and thus delayed. Unfortunately for CBS, FM was not a big moneymaker and TV was. That year the Federal Communications Commission set 150 miles as the minimum distance between TV stations on the same channel.

There was interference between TV stations in 1948 so the Federal Communications Commission froze the processing of new applications for TV stations. On September 30, 1948, the day of the freeze, there were thirty-seven stations in twenty-two cities and eighty-six more were approved. Another three hundred and three applications were sent in and not approved. After all the approved stations were constructed, or weren't, the distribution was as follows: New York and Los Angeles, seven each; twenty-four other cities had two or more stations; most cities had only one including Houston, Kansas City, Milwaukee, Pittsburgh, and St. Louis. A total of just sixty-four cities had television during the freeze, and only one-hundred-eight stations were around. The freeze was for six months only, initially, and was just for studying interference problems. Because of the Korean Police Action, the freeze wound up being three and one half years. During the freeze, the interference problem was solved and the Federal Communications Commission made a decision on color TV and UHF. In October of 1950 the Federal Communications Commission made a pro-CBS color decision for the first time. The previous RCA decisions were made while Charles Denny was chairman. He later resigned in 1947 to become an RCA vice president and general consel. The decision approved CBS' mechanical spinning wheel color TV system, now able to be used on VHF, but still not compatible with black-and-white sets.

RCA, with a new compatible system that was of comparable quality to CBS' according to TV critics, appealed all the way to the U.S. Supreme Court and lost in May, 1951, but its legal action did succeed in toppling CBS' color TV system, as during the legal battle, many more black-and-white television sets were sold. When CBS did finally start broadcasting using its color TV system in mid-1951, most American television viewers already had black-and-white receivers that were incompatible with CBS' color system. In October of 1951 CBS was ordered to stop work on color TV by the National Production Authority, supposedly to help the situation in Korea. The Authority was headed by a lieutenant of William Paley, the head of CBS.

The Federal Communications Commission, under chairman Wayne Coy, issued its Sixth Report and Order in early 1952. It established seventy UHF channels (14-83) providing 1400 new potential stations. It also set aside 242 stations for education, most of them in the UHF band. The Commission also added 220 more VHF stations. VHF was reduced to 12 channels with channel 1 being given over to other uses and channels 2-12 being used solely for TV, this to reduced interference. This ended the freeze. In March of 1953 the House Committee on Interstate and Foreign Commerce held hearings on color TV. RCA and the National Television Systems Committee, NTSC, presented the RCA system. The NTSC consisted of all of the major television manufacturers at the time. On March 25, CBS president Frank Stanton conceded it would be "economically foolish" to pursue its color system and in effect CBS lost.

December 17, 1953 the Federal Communications Commission reversed its decision on color and approved the RCA system. Ironically, color didn't sell well. In the first six months of 1954 only 8,000 sets were sold, there were 23,000,000 black and white sets. Westinghouse made a big, national push and sold thirty sets nationwide. The sets were big, expensive and didn't include UHF.

The problem was that UHF stations would not be successful unless people had UHF tuners, and people would not voluntarily pay for UHF tuners unless there were UHF broadcasters. Of the 165 UHF stations that went on the air between 1952 and 1959, 55% went off the air. Of the UHF stations on the air, 75% were losing money. UHF's problems were the following:(1) technical inequality of UHF stations as compared with VHF stations; (2) intermixture of UHF and VHF stations in the same market and the millions of VHF only receivers; (3) the lack of confidence in the capabilities of and the need for UHF television. Suggestions of de-intermixture (making some cities VHF only and other cities UHF only) were not adopted, because most existing sets did not have UHF capability. Ultimately the FCC required all TV sets to have UHF tuners. However over four decades later, UHF is still considered inferior to VHF, despite cable television, and ratings on VHF channels are generally higher than on UHF channels.

The allocation between VHF and UHF in the 1950s, and the lack of UHF tuners is entirely analogous to the dilemma facing digital television of high definition television fifty years later.

Regulatory powers The Federal Communications Commission has one major regulatory weapon, revoking licenses, but short of that has little leverage over broadcast stations. It is reluctant to do this since it operates in a near vacuum of information on most of the tens of thousands of stations whose licences are renewed every three years. Broadcast licenses are supposed to be renewed if the station met the "public interest, convenience, or necessity." The Federal Communications Commission rarely checked except for some outstanding reason, burden of proof would be on the compaintant. Fewer than 1% of station renewals are not immediately granted, and only a small fraction of those are actually denied.

Note: Similar authority for regulation of Federal Government telecommunications is vested in the National Telecommunications and Information Administration (NTIA).

Source: from Federal Standard 1037C

See also: concentration of media ownership, Fairness Doctrine, frequency assignment, open spectrum

Magnetron

There was an urgent need during radar development in World War II for a microwave generator that worked in shorter wavelengths - around 10cm rather than 150cm - available from generators of the time. In 1940, at Birmingham University in the UK, John Randall and Harry Boot produced a working prototype of the cavity magnetron, and soon managed to increase its power output 100-fold. In August 1941, the first production model was shipped to the United States.

FM

FM radio is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation to provide high-fidelity broadcast radio sound.

W1XOJ was the first FM radio station, granted a construction permit by the FCC in 1937. On January 5, 1940 FM radio was demonstrated to the FCC for the first time. FM radio was assigned the 42 to 50 MHz band of the spectrum in 1940.

After World War II, the FCC moved FM to the frequencies between 88 and 106 MHz on June 27, 1945, making all prewar FM radios worthless. This action severely set back the public confidence in, and hence the development of, FM radio. On March 1, 1945 W47NV began operations in Nashville, Tennessee becoming the first modern commercial FM radio station.

TV

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From Wikipedia, the free encyclopedia.

Television is a telecommunication system for broadcasting and receiving moving pictures and sound over a distance. The term has come to refer to all the aspects of television programming and transmission as well. The televisual has become synonymous with postmodern culture. The word television is a hybrid word, coming from both Greek and Latin. "Tele-" is Greek for "far", while "-vision" is from the Latin "visio", meaning "vision" or "sight".

Table of contents [showhide] 1 History 2 TV standards 3 TV aspect ratio 4 Aspect ratio incompatibility 5 New developments 6 TV sets 7 Advertising 8 US networks 9 European networks 10 Colloquial names 11 Related articles 11.1 External links 11.2 See also: 12 Further Reading 12.1 TV as social pathogen, opiate, mass mind control, etc.

History Paul Gottlieb Nipkow proposed and patented the first electromechanical television system in 1884.

A. A. Campbell Swinton wrote a letter to Nature on the 18th June 1908 describing his concept of electronic television using the cathode ray tube invented by Karl Ferdinand Braun. He lectured on the subject in 1911 and displayed circuit diagrams.

A semi-mechanical analogue television system was first demonstrated in London in February 1924 by John Logie Baird and a moving picture by Baird on October 30, 1925. The first long distance public television broadcast was from Washington, DC to New York City and occurred on April 7, 1927. The image shown was of then Commerce Secretary Herbert Hoover. A fully electronic system was demonstrated by Philo Taylor Farnsworth in the autumn of 1927. The first analogue service was WGY, Schenectady, New York inaugurated on May 11, 1928. The first British Television Play, "The Man with the Flower in his Mouth", was transmitted in July 1930. CBS's New York City station began broadcasting the first regular seven days a week television schedule in the U. S. on July 21, 1931. The first broadcast included Mayor James J. Walker, Kate Smith, and George Gershwin. The first all-electronic television service was started in Los Angeles, CA by Don Lee Broadcasting. Their start date was December 23, 1931 on W6XAO - later KTSL. Los Angeles was the only major U. S. city that avoided the false start with mechanical television.

In 1932 the BBC launched a service using Baird's 30-line system and these transmissions continued until 11th September 1935. On November 2, 1936 the BBC began broadcasting a dual-system service, alternating on a weekly basis between Marconi-EMI's high-resolution (405 lines per picture) service and Baird's improved 240-line standard from Alexandra Palace in London. Six months later, the corporation decided that Marconi-EMI's electronic picture gave the superior picture, and adopted that as their standard. This service is described as "the world's first regular high-definition public television service", since a regular television service had been broadcast earlier on a 180-line standard in Germany. The outbreak of the Second World War caused the service to be suspended. TV transmissions only resumed from Alexandra Palace in 1946.

The first live transcontinental television broadcast took place in San Francisco, California from the Japanese Peace Treaty Conference on September 4, 1955.

Programming is broadcast on television stations (sometimes called channels). At first, terrestrial broadcasting was the only way television could be distributed. Because bandwidth was limited, government regulation was normal. In the US, the Federal Communications Commission allowed stations to broadcast advertisements, but insisted on public service programming commitments as a requirement for a license. By contrast, the United Kingdom chose a different route, imposing a television licence fee (effectively a tax) to fund the BBC, which had public service as part of its Crown Charter. Development of cable and satellite means of distribution in the 1970s pushed businessmen to target channels towards a certain audience, and enabled the rise of subscription-based television channels, such as HBO and Sky. Practically every country in the world now has developed at least one television channel. Television has grown up all over the world, enabling every country to share aspects of their culture and society with others.

TV standards See broadcast television systems.

There many means of distributing television broadcasts, including both analogue and digital versions of:

   * Terrestrial television
   * Satellite television
   * Cable television
   * MMDS (Wireless cable)

TV aspect ratio All of these early TV systems shared the same aspect ratio of 4:3 which was chosen to match the Academy Ratio used in cinema films at the time. This ratio was also square enough to be conveniently viewed on round Cathode Ray Tubes (CRTs), which were all that could be produced given the manufacturing technology of the time -- today's CRT technology allows the manufacture of much wider tubes. However, due to the negative heavy metal health effects associated with disposal of CRTs in landfills, and the space-saving attributes of flat screen technologies that lack the aspect ratio limitations of CRTs, CRTs are slowly becoming obsolete.

In the 1950s movie studios moved towards wide screen aspect ratios such as Cinerama in an effort to distance their product from television.

The switch to digital television systems has been used as an opportunity to change the standard television picture format from the old ratio of 4:3 (1.33:1) to an aspect ratio of 16:9 (1.78:1). This enables TV to get closer to the aspect ratio of modern wide-screen movies, which range from 1.85:1 to 2.35:1. The 16:9 format was first introduced on "widescreen" DVDs. DVD provides two methods for transporting wide-screen content, the better of which uses what is called anamorphic wide-screen format. This format is very similar to the technique used to fit a wide-screen movie frame inside a 1.33:1 35mm film frame. The image is squashed horizontally when recorded, then expanded again when played back. The U.S. ATSC HDTV system uses straight wide-screen format, no image squashing or expanding is used.

There is no technical reason why the introduction of digital TV demands this aspect ratio change, however it has been decided to introduce these changes for marketing reasons.

Aspect ratio incompatibility Displaying a wide-screen original image on a conventional aspect television screen presents a considerable problem since the image must be shown either:

   * in "letterbox" format, with black stripes at the top and bottom
   * with part of the image being cropped, usually the extreme left and right of the image being cut off (or in "pan and scan", parts selected by an operator)
   * with the image horizontally compressed

A conventional aspect image on a wide screen television can be shown:

   * with black vertical bars to the left and right
   * with upper and lower portions of the image cut off
   * with the image horizontally distorted

A common compromise is to shoot or create material at an aspect ratio of 14:9, and to lose some image at each side for 4:3 presentation, and some image at top and bottom for 16:9 presentation.

Horizontal expansion has advantages in situations in which several people are watching the same set; it compensates for watching at an oblique angle.

New developments

   * Digital television (DTV)
   * High Definition TV (HDTV)
   * Pay Per View
   * Web TV
   * programming on-demand.

TV sets The earliest television sets were radios with the addition of a television device consisting of a neon tube with a mechanically spinning disk (the Nipkow disk, invented by Paul Gottlieb Nipkow) that produced a red postage-stamp size image . The first publicly broadcast electronic service was in Germany in March 1935. It had 180 lines of resolution and was only available in 22 public viewing rooms. One of the first major broadcasts involved the 1936 Berlin Olympics. The Germans had a 441 line system in the fall of 1937. (Source: Early Electronic TV)

Television usage skyrocketed after World War II with war-related technological advances and additional disposable income. (1930s TV receivers cost the equivalent of $7000 today (2001) and had little available programming.)

For many years different countries used different technical standards. France initially adopted the German 441 line standard but later upgraded to 819 lines, which gave the highest picture definition of any analogue TV system, approximately four times the resolution of the British 405 line system. Eventually the whole of Europe switched to the 625 line standard, once more following Germany's example. Meanwhile in North America the original 525 line standard was retained.

A television with a VHF "rabbit ears" antenna and a loop UHF antenna. Television in its original and still most popular form involves sending images and sound over radio waves in the VHF and UHF bands, which are received by a receiver (a television set). In this sense, it is an extension of radio. Broadcast television requires an antenna (UK: aerial). This can be an external antenna mounted outside or smaller antennas mounted on or near the television. Typically this is an adjustable dipole antenna called "rabbit ears" for the VHF band and a small loop antenna for the UHF band.

Color television became available on December 30, 1953, backed by the CBS network. The government approved the color broadcast system proposed by CBS, but when RCA came up with a system that made it possible to view color broadcasts in black and white on unmodified old black and white TV sets, CBS dropped their own proposal and used the new one.

European colour television was developed somewhat later, in the 1960s, and was hindered by a continuing division on technical standards. The German PAL system was eventually adopted by West Germany, the UK, Australia, New Zealand, much of Africa, Asia and South America, and most West European countries except France. France produced its own SECAM standard, which was eventually adopted in much of Eastern Europe. Both systems broadcast on UHF frequencies and adopted a higher-definition 625 line system.

Starting in the 1990s, modern television sets diverged into three different trends:

   * standalone TV sets;
   * integrated systems with DVD players and/or VHS VCR capabilities built into the TV set itself (mostly for small size TVs with up to 17" screen, the main idea is to have a complete portable system);
   * component systems with separate big screen video monitor, tuner, audio system which the owner connects the pieces together as a high-end home theater system. This approach appeals to videophiles that prefer components that can be upgraded separately.

There are many kinds of video monitors used in modern TV sets. The most common are direct view CRTs for up to 40" (4:3) and 46" (16:9) diagonally. Most big screen TVs (up to over 100") use projection technology. Three types of projection systems are used in projection TVs: CRT based, LCD based, and reflective imaging chip based. Modern advances have brought flat screens to TV that use active matrix LCD or plasma display technology. Flat panel displays are as little as 4" thick and can be hung on a wall like a picture. They are extremely attractive and space-saving but they remain expensive.

Nowadays some TVs include a port to connect peripherals to it or to connect the set to an A/V home network (HAVI), like LG RZ-17LZ10 that includes a USB port, where one can connect a mouse, keyboard and so on (for WebTV, now branded MSN TV).

Even for simple video, there are five standard ways to connect a device. These are as follows:

   * Component Video- three separate connectors, with one brightness channel and two color channels (hue and saturation), and is usually referred to as Y, B-Y, R-Y, or Y Pr Pb. This provides for high quality pictures and is usually used inside professional studios. However, it is being used more in home theater for DVDs and high end sources. Audio is not carried on this cable.

   * SCART - A large 21 pin connector that may carry Composite video, S-Video or, for better quality, separate red, green and blue (RGB) signals and two-channel sound, along with a number of control signals. This system is standard in Europe but rarely found elsewhere.

   * S-Video - two separate channels, one carrying brightness, the other carrying color. Also referred to as Y/C video. Provides most of the benefit of component video, with slightly less color fidelity. Use started in the 1980s for S-VHS, Hi-8, and early DVD players to relay high quality video. Audio is not carried on this cable.

   * Composite video - The most common form of connecting external devices, putting all the video information into one stream. Most televisions provide this option with a yellow RCA jack. Audio is not carried on this cable.

   * Coaxial or RF (coaxial cable) - All audio channels and picture components are transmitted through one wire and modulated on a radio frequency. Most TVs manufactured during the past 15-20 years accept coaxial connection, and the video is typically "tuned" on channel 3 or 4. This is the type of cable usually used for cable television.

Advertising From the earliest days of the medium, television has been used as a vehicle for advertising. Since their inception in the USA in the late 1940s, TV commercials have become far and away the most effective, most pervasive, and most popular method of selling products of all sorts. US advertising rates are determined primarily by Nielsen Ratings

US networks In the US, the three original commercial television networks (ABC, CBS, and NBC) provide prime-time programs for their affiliate stations to air from 8pm-11pm Monday-Saturday and 7pm-11pm on Sunday. (7pm to 10pm, 6pm to 10pm respectively in the Central and Mountain time zones). Most stations procure other programming, often syndicated, off prime time. The FOX Network does not provide programming for the last hour of prime time; as a result, many FOX affiliates air a local news program at that time. Three newer broadcasting networks, The WB, PAX, and UPN, also do not provide the same amount of network programming as so-called traditional networks.

European networks In much of Europe television broadcasting has historically been state dominated, rather than commercially organised, although commercial stations have grown in number recently. In the United Kingdom, the major state broadcaster is the BBC (British Broadcasting Corporation), commercial broadcasters include ITV (Independent Television), Channel 4 and Channel 5, as well as the satellite broadcaster British Sky Broadcasting. Other leading European networks include RAI (Italy), Télévision Française (France), ARD (Germany), RTÉ (Ireland), and satellite broadcaster RTL (Radio Télévision Luxembourg). Euronews is a pan-European news station, broadcasting both by satellite and terrestrially (timesharing on State TV networks) to most of the continent. Broadcast in several languages (English, French, German, Spanish, Russian, etc.) it draws on contributions from State broadcasters and the ITN news network.

Colloquial names

   * Telly
   * The Tube/Boob Tube
   * The Goggle Box
   * The Cyclops
   * Idiot Box

Renewable energy

From Wikipedia, the free encyclopedia.

Renewable energy is energy from a source which can be managed so that it is not subject to depletion in a human timescale . Sources include the sun's rays, wind, waves, rivers, tides, biomass, and geothermal. Renewable energy does not include energy sources which are dependent upon limited resources, such as fossil fuels and nuclear fission power.

Table of contents [showhide] 1 General Information 2 Pros and cons of renewable energy 3 Renewable energy history 3.1 Wood 3.2 Animal Traction 3.3 Water Power 3.4 Wind Power 3.5 Solar power 3.6 The renewable energy movement 4 Renewable Energy Today 5 Modern sources of renewable energy 5.1 Smaller-scale sources 5.2 Renewables as solar energy 5.3 Solar energy per se 5.3.1 Solar electrical energy 5.3.2 System problems with solar electric 5.3.3 Solar thermal electric energy 5.3.4 Solar thermal energy 5.3.4.1 Solar water heating 5.3.4.2 Solar heat pumps 5.3.4.3 Solar ovens 5.4 Wind Energy 5.5 Geothermal Energy 5.6 Water power 5.6.1 Electrokinetic energy 5.6.2 Hydroelectric Energy 5.6.3 Tidal power 5.6.4 Tidal stream power 5.6.5 Wave power 5.6.6 OTEC 5.7 Biomass 5.7.1 Liquid biofuel 5.7.2 Solid biomass 5.7.3 Biogas 6 Renewable energy storage systems 6.1 Hydrogen fuel cells 6.2 Other renewable energy storage systems 6.2.1 Pumped water storage 6.2.2 Battery storage 6.2.3 Electrical grid storage 7 Renewable energy use by nation 8 Renewable energy controversies 8.1 The funding dilemma 8.2 Centralization versus decentralization 8.3 The nuclear "renewable" claim 9 References

General Information Most renewable forms of energy, other than geothermal, are in fact stored solar energy. Water power and wind power represent very short-term solar storage, while biomass represents slightly longer-term storage, but still on a very human time-scale, and so renewable within that human time-scale. Fossil fuels, on the other hand, while still stored solar energy, have taken millions of years to form, and so do not meet the definition of renewable.

Renewable energy resources may be used directly as energy sources, or used to create other forms of energy for use. Examples of direct use are solar ovens, geothermal heat pumps, and mechanical windmills. Examples of indirect use in creating other energy sources are electricity generation through wind generators or photovoltaic cells, or production of fuels such as ethanol from biomass (see alcohol as a fuel).

Pros and cons of renewable energy Renewable energy sources are fundamentally different from fossil fuel or nuclear power plants because of their widespread occurrence and abundance - the sun will 'power' these 'powerplants' (meaning sunlight, the wind, flowing water, etc.) for the next 4 billion years. Some renewable sources do not emit any additional carbon dioxide and do not introduce any new risks such as nuclear waste. In fact, one renewable energy source, wood, actively sequesters carbon dioxide while growing.

A visible disadvantage of renewables is their visual impact on local environments. Some people dislike the aesthetics of wind turbines or bring up nature conservation issues when it comes to large solar-electric installations outside of cities. Some people try to utilize these renewable technologies in an efficient and aesthetically pleasing way: fixed solar collectors can double as noise barriers along highways, roof-tops are available already and could even be replaced totally by solar collectors, etc.

Some renewable energy capture systems entail unique environmental problems. For instance, wind turbines can be hazardous to flying birds, while hydroelectric dams can create barriers for migrating fish ? a serious problem in the Pacific Northwest that has decimated the numbers of many salmon populations.

Another inherent difficulty with renewables is their variable and diffuse nature (with the exception being geothermal energy, which is however only accessible where the Earth's crust is thin, such as near hot springs and natural geysers). Since renewable energy sources are providing relatively low-intensity energy, the new kinds of "power plants" needed to convert the sources into usable energy need to be distributed over large areas. To make the phrases 'low-intensity' and 'large area' easier to understand, note that in order to produce 1000 kWh of electricity per month (a typical per-month-per-capita consumption of electricity in Western countries), a home owner in cloudy Europe needs to use ten square meters of solar panels. Systematic electrical generation requires reliable overlapping sources or some means of storage on a reasonable scale (pumped-storage hydro systems, batteries, future hydrogen fuel cells, etc.). So, because of currently-expensive energy storage systems, a small stand-alone system is only economic in rare cases.

If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems would no longer be the main distributors of electrical energy but would operate to balance the electricity needs of local communities. Those with surplus energy would sell to areas needing "top ups".

Renewable energy history The original energy source for all human activity was the sun via growing plants. Solar energy's main human application throughout most of history has thus been in agriculture and forestry, via photosynthesis.

Wood Firewood was the earliest manipulated energy source in human history, being used as a thermal energy source through burning, and it is still important in this context today. Burning wood was important for both cooking and providing heat, enabling human presence in cold climates. Special types of wood cooking, food dehydration and smoke curing, also enabled human societies to safely store perishable foodstuffs through the year. Eventually, it was discovered that partial combustion in the relative absence of oxygen could produce charcoal, which provided a hotter and more compact and portable energy source. However, this was not a more efficient energy source, because it required a large input in wood to create the charcoal.

Animal Traction Motive power for vehicles and mechanical devices was originally produced through animal traction. Animals such as horses and oxen not only provided transportation but also powered mills. Animals are still extensively in use in many parts of the world for these purposes.

Water Power Animal power for mills was eventually supplanted by water power, the power of falling water in rivers, wherever it was exploitable. Direct use of water power for mechanical purposes is today fairly uncommon, but still in use.

Originally, water power through (hydroelectricity) was the most important source of electrical generation throughout society, and is still an important source today. Throughout most of the history of human technology, hydroelectricity has been the only renewable source of electricity generation significantly tapped for the generation of electricity.

Wind Power Wind power has been used for several hundred years. It was originally used via large sail-blade windmills with slow-moving blades, such as those seen in the Netherlands and mentioned in Don Quixote. These large mills usually either pumped water or powered small mills. Newer windmills featured smaller, faster-turning, more compact units with more blades, such as those seen throughout the Great Plains. These were mostly used for pumping water from wells. Recent years have seen the rapid development of wind generation farms by mainstream power companies, using a new generation of large, high wind turbines with two or three immense and relatively slow-moving blades.

Solar power Solar power as a direct energy source has been not been captured by mechanical systems until recent human history, but was captured as an energy source through architecture in certain societies for many centuries. Not until the twentieth century was direct solar input extensively explored via more carefully planned architecture (passive solar) or via heat capture in mechanical systems (active solar) or electrical conversion (photovoltaic). Increasingly today the sun is harnessed for heat and electricity.

The renewable energy movement Renewable energy as an issue was virtually unheard-of before the middle of the twentieth century. There were experimentations with passive solar energy, including daylighting, in the early part of the twentieth century, but little beyond what had actually been practiced as a matter of course in some locales for hundreds of years. The renewable energy movement gained awareness, credence and strength with the great burgeoning of interest in environmental affairs in the mid-1900s, which in turn was largely due to Rachel Carson's ?'Silent Spring'?.

The first US politician to focus significantly on solar energy was Jimmy Carter, in response to the long term consequences of the 1973 energy crisis. No president since has paid much attention to renewable energy.

Renewable Energy Today Around 80% of energy requirements are focused around heating or cooling buildings and powering the vehicles that ensure mobility (cars, trains, airplanes). This is the core of society's energy requirements. However, most uses of renewable power focus on electricity generation.

Geothermal heat pumps (also called ground-source heat pumps) are a means of extracting heat in the winter or cold in the summer from the earth to heat or cool buildings.

Modern sources of renewable energy There are several types of renewable energy, including the following:

   * Solar power.
   * Wind power.
   * Geothermal energy.
   * Electrokinetic energy.
   * Hydroelectricity.
   * Biomatter, including Biogas Energy.

Smaller-scale sources Of course there are some smaller-scale applications as well:

   * Piezo electric crystals embedded in the sole of a shoe can yield a small amount of energy with each step. Vibration from engines can stimulate piezo electric crystals.
   * Some watches are already powered by movement of the arm.
   * Special antennae can collect energy from stray radiowaves or even light (EM radiation).

Renewables as solar energy Most renewable energy sources can trace their roots to solar energy, with the exception of geothermal and tidal power. For example, wind is caused by the sun heating the earth unevenly. Hot air is less dense, so it rises, causing cooler air to move in to replace it. Hydroelectric power can be ultimately traced to the sun too. When the sun evaporates water in the ocean, the vapor forms clouds which later fall on mountains as rain which is routed through turbines to generate electricity. The transformation goes from solar energy to potential energy to kinetic energy to electric energy.

Solar energy per se Since most renewable energy is "Solar Energy" this term is slightly confusing and used in two different ways: firstly as a synonym for "renewable energies" as a whole (like in the political slogan "Solar not nuclear") and secondly for the energy that is directly collected from solar radiation. In this section it is used in the latter category.

There are actually two separate approaches to solar energy, termed active solar and passive solar.

Solar electrical energy For electricity generation, ground-based solar power has serious limitations because of its diffuse and intermittent nature. First, ground-based solar input is interrupted by night and by cloud cover, which means that solar electric generation inevitably has a low capacity factor, typically less than 20%. Also, there is a low intensity of incoming radiation, and converting this to high grade electricity is still relatively inefficient (14% - 18%), though increased efficiency or lower production costs have been the subject of much research over several decades.

Two methods of converting the Sun's radiant energy to electricity are the focus of attention. The better-known method uses sunlight acting on photovoltaic (PV) cells to produce electricity. This has many applications in satellites, small devices and lights, grid-free applications, earthbound signaling and communication equipment, such as remote area telecommunications equipment. Sales of solar PV modules are increasing strongly as their efficiency increases and price diminishes. But the high cost per unit of electricity still rules out most uses.

Several experimental PV power plants mostly of 300 - 500 kW capacity are connected to electricity grids in Europe and the USA. Japan has 150 MWe installed. A large solar PV plant was planned for Crete. In 2001 the world total for PV electricity was less than 1000 MWe with Japan as the world's leading producer. Research continues into ways to make the actual solar collecting cells less expensive and more efficient. Other major research is investigating economic ways to store the energy which is collected from the Sun's rays during the day.

Alternatively, many individuals have installed small-scale PV arrays for domestic consumption. Some, particularly in isolated areas, are totally disconnected from the main power grid, and rely on a surplus of generation capacity combined with batteries and/or a fossil fuel generator to cover periods when the cells are not operating. Others in more settled areas remain connected to the grid, using the grid to obtain electricity when solar cells are not providing power, and selling their surplus back to the grid. This works reasonably well in many climates, as the peak time for energy consumption is on hot, sunny days where air conditioners are running and solar cells produce their maximum power output. Many U.S. states have passed "net metering" laws, requiring electrical utilities to buy the locally-generated electricity for price comparable to that sold to the household. Photovoltaic generation is still considerably more expensive for the consumer than grid electricity unless the usage site is sufficiently isolated, in which case photovoltaics become the less expensive.

System problems with solar electric Frequently renewable electricity sources are disadvantaged by regulation of the electricity supply industry which favors 'traditional' large-scale generators over smaller-scale and more distributed generating sources. If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems would no longer be the main distributors of electrical energy but would operate to balance the electricity needs of local communities. Those with surplus energy would sell to areas needing "top ups". Some Governments and regulators are moving to address this, though much remains to be done. One potential solution is the increased use of active management of electricity transmission and distribution networks.

Solar thermal electric energy The second method for utilizing solar energy is solar thermal. A solar thermal power plant has a system of mirrors to concentrate the sunlight on to an absorber, the resulting heat then being used to drive turbines. The concentrator is usually a long parabolic mirror trough oriented north-south, which tilts, tracking the Sun's path through the day. A black absorber tube is located at the focal point and converts the solar radiation to heat (about 400°C) which is transferred into a fluid such as synthetic oil. The oil can be used to heat buildings or water, or it can be used to drive a conventional turbine and generator. Several such installations in modules of 80 MW are now operating. Each module requires about 50 hectares of land and needs very precise engineering and control. These plants are supplemented by a gas-fired boiler which ensures full-time energy output. The gas generates about a quarter of the overall power output and keeps the system warm overnight. Over 800 MWe capacity worldwide has supplied about 80% of the total solar electricity to the mid-1990s.

One proposal for a solar electrical plant is the solar tower, in which a large area of land would be covered by a greenhouse made of something as simple as transparent foil, with a tall lightweight tower in the centre, which could also be composed largely of foil. The heated air would rush to and up the centre tower, spinning a turbine. A system of water pipes placed throughout the greenhouse would allow the capture of excess thermal energy, to be released throughout the night and thus providing 24-hour power production. A 200 MWe tower is proposed near Mildura, Australia.

Solar thermal energy Solar energy need not be converted to electricity for use. Many of the world's energy needs are simply for heat ? space heating, water heating, process water heating, oven heating, and so forth. The main role of solar energy in the future may be that of direct heating. Much of society's energy need is for heat below 60°C (140°F) - e.g. in hot water systems. A lot more, particularly in industry, is for heat in the range 60 - 110°C. Together these may account for a significant proportion of primary energy use in industrialized nations. The first need can readily be supplied by solar power much of the time in some places, and the second application commercially is probably not far off. Such uses will diminish to some extent both the demand for electricity and the consumption of fossil fuels, particularly if coupled with energy conservation measures such as insulation.

Solar water heating Domestic solar hot water systems were once common in Florida until they were displaced by highly-advertised natural gas. Such systems are today common in the hotter areas of Australia, and simply consist of a network of dark-colored pipes running beneath a window of heat-trapping glass. They typically have a backup electric or gas heating unit for cloudy days. Such systems can actually be justified purely on economic grounds, particularly in some remoter areas of Australia where electricity is expensive.

Solar heat pumps With adequate insulation, heat pumps utilizing the conventional refrigeration cycle can be used to warm and cool buildings, with very little energy input other than energy needed to run a compressor. Eventually, up to ten percent of the total primary energy need in industrialized countries may be supplied by direct solar thermal techniques, and to some extent this will substitute for base-load electrical energy.

Solar ovens Large scale solar thermal powerplants, as mentioned before, can be used to heat buildings, but on a smaller scale solar ovens can be used on sunny days. Such an oven or solar furnace uses mirrors or a large lens to focus the Sun's rays onto a baking tray or black pot which heats up as it would in a standard oven.

Wind Energy Wind turbines have been used for household electricity generation in conjunction with battery storage over many decades in remote areas. Generator units of more than 1 MWe are now functioning in several countries. The power output is a function of the cube of the wind speed, so such turbines require a wind in the range 3 to 25 m/s (11 - 90 km/h), and in practice relatively few land areas have significant prevailing winds. Like solar, wind power requires alternative power sources to cope with calmer periods.

There are now many thousands of wind turbines operating in various parts of the world, with utility companies having a total capacity of over 39,000 MWe of which Europe accounts for 75% (ultimo 2003). Additional windpower is generated by private windmills both on-grid and off-grid. Germany is the leading producer of wind generated electricity with over 14,600 MWe in 2003. In 2003 the U.S.A. produced over 6,300 Mwe of wind energy, second only to Germany.

New wind farms and offshore wind parks are being planned and built all over the world. This has been the most rapidly-growing means of electricity generation at the turn of the 21st century and provides a complement to large-scale base-load power stations. Denmark generates over 10% of its electricity with windturbines, whereas windturbines account for 0.4% of the total electricity production on a global scale (ultimo 2002). The most economical and practical size of commercial wind turbines seems to be around 600 kWe to 1 MWe, grouped into large wind farms. Most turbines operate at about 25% load factor over the course of a year, but some reach 35%.

Geothermal Energy Where hot underground steam or water can be tapped and brought to the surface it may be used to generate electricity. Such geothermal power sources have potential in certain parts of the world such as New Zealand, United States, Philippines and Italy. The two most prominent areas for this in the United States are in the Yellowstone basin and in northern California. Iceland produced 170 MWe geothermal power and heated 86% of all houses in the year 2000. Some 8000 MWe of capacity is operating over all.

There are also prospects in certain other areas for pumping water underground to very hot regions of the Earth's crust and using the steam thus produced for electricity generation. An Australian startup company, Geodynamics, proposes to build a commercial plant in the Cooper Basin region of South Australia using this technology by 2004.

Water power Energy inherent in water can be harnessed and used, in the forms of kinetic energy or temperature differences.

Electrokinetic energy This type of energy harnesses what happens to water when it is pumped through tiny channels. See electrokinetics (water).

Hydroelectric Energy Hydroelectric energy produces essentially no carbon dioxide, in contrast to burning fossil fuels or gas, and so is not a significant contributor to global warming. Hydroelectric power from potential energy of rivers, now supplies about 715,000 MWe or 19% of world electricity. Apart from a few countries with an abundance of it, hydro capacity is normally applied to peak-load demand, because it is so readily stopped and started. It is not a major option for the future in the developed countries because most major sites in these countries having potential for harnessing gravity in this way are either being exploited already or are unavailable for other reasons such as environmental considerations.

The chief advantage of hydrosystems is their capacity to handle seasonal (as well as daily) high peak loads. In practice the utilization of stored water is sometimes complicated by demands for irrigation which may occur out of phase with peak electrical demands.

Tidal power Harnessing the tides in a bay or estuary has been achieved in France (since 1966) and Russia, and could be achieved in certain other areas where there is a large tidal range. The trapped water can be used to turn turbines as it is released through the tidal barrage in either direction. Worldwide this technology appears to have little potential, largely due to environmental constraints.

Tidal stream power A relatively new technology development, tidal stream generators draw energy from underwater currents in much the same way that wind generators are powered by the wind. The much higher density of water means that there is the potential for a single generator to provide significant levels of power. Tidal stream technology is at the very early stages of development though and will require significantly more research before it becomes a significant contributor to electrical generation needs.

Wave power Harnessing power from wave motion is a possibility which might yield much more energy than tides. The feasibility of this has been investigated, particularly in the UK. Generators either coupled to floating devices or turned by air displaced by waves in a hollow concrete structure would produce electricity for delivery to shore. Numerous practical problems have frustrated progress.

OTEC Ocean Thermal Energy Conversion is a relatively unproven technology, though it was first used by the French engineer Jacques Arsene d'Arsonval in 1881. The difference in temperature between water near the surface and deeper water can be as much as 20°C. The warm water is used to make a liquid such as ammonia evaporate, causing it to expand. The expanding gas forces its way through turbines, after which it is condensed using the colder water and the cycle can begin again.

Biomass Biomass, also known as biomatter, can be used directly as fuel or to produce liquid biofuel. Agriculturally produced biomass fuels, such as biodiesel, ethanol and bagasse (a byproduct of sugar cane cultivation) are burned in internal combustion engines or boilers.

Liquid biofuel Liquid biofuel is usually bioalcohols -like methanol and ethanol- or biodiesel. Biodiesel can be used in modern diesel vehicles with little or no modification and can be obtained from waste and crude vegetable and animal oil and fats (lipids). In some areas corn, sugarbeets, cane and grasses are grown specifically to produce ethanol (also known as alcohol) a liquid which can be used in internal combustion engines and fuel cells.

Solid biomass Direct use is usually in the form of combustible solids, either firewood or combustible field crops. Field crops may be grown specifically for combustion or may be used for other purposes, and the processed plant waste then used for combustion. Most sorts of biomatter, including dried manure, can actually be burnt to heat water and to drive turbines. Plants partly use photosynthesis to store solar energy, water and CO2. Sugar cane residue, wheat chaff, corn cobs and other plant matter can be, and is, burnt quite successfully. The process releases no net CO2.

Biogas Animal feces (manure) release methane under the influence of anaerobic bacteria which can also be used to generate electricity. See biogas.

Renewable energy storage systems One of the great problems with renewable energy, as mentioned above, is transporting it in time or space. Since most renewable energy sources are periodic, storage for off-generation times is important, and storage for powering transportation is also a critical issue.

Hydrogen fuel cells Hydrogen as a fuel has been touted lately as a solution in our energy dilemmas. However, the idea that hydrogen is a renewable energy source is a misunderstanding. Hydrogen is not an energy source, but a portable energy storage method, because it must be manufactured by other energy sources in order to be used. However, as a storage medium, it may be a significant factor in using renewable energies. It is widely seen as a possible fuel for hydrogen cars, if certain problems can be overcome economically. It may be used in conventional internal combustion engines, or in fuel cells which convert chemical energy directly to electricity without flames, in the same way the human body burns fuel. Making hydrogen requires either reforming natural gas (methane) with steam, or, for a renewable and more ecologic source, the electrolysis of water into hydrogen and oxygen. The former process has carbon dioxide as a by-product, which exacerbates (or at least does not improve) greenhouse gas emissions relative to present technology. With electrolysis, the greenhouse burden depends on the source of the power, and both intermittent renewables and nuclear energy are considered here.

With intermittent renewables such as solar and wind, matching the output to grid demand is very difficult, and beyond about 20% of the total supply, apparently impossible. But if these sources are used for electricity to make hydrogen, then they can be utilized fully whenever they are available, opportunistically. Broadly speaking it does not matter when they cut in or out, the hydrogen is simply stored and used as required.

Nuclear advocates note that using nuclear power to manufacture hydrogen would help solve plant inefficiencies. Here the plant would be run continuously at full capacity, with perhaps all the output being supplied to the grid in peak periods and any not needed to meet civil demand being used to make hydrogen at other times. This would mean far better efficiency for the nuclear power plants.

About 50 kWh (1/144,000 J) is required to produce a kilogram of hydrogen by electrolysis, so the cost of the electricity clearly is crucial.

Other renewable energy storage systems Sun, wind, tides and waves cannot be controlled to provide directly either reliably continuous base-load power, because of their periodic natures, or peak-load power when it is needed. In practical terms, without proper energy storage methods these sources are therefore limited to some twenty percent of the capacity of an electricity grid, and cannot directly be applied as economic substitutes for fossil fuels or nuclear power, however important they may become in particular areas with favorable conditions. If there were some way that large amounts of electricity from intermittent producers such as solar and wind could be stored efficiently, the contribution of these technologies to supplying base-load energy demand would be much greater.

Pumped water storage Already in some places pumped storage is used to even out the daily generating load by pumping water to a high storage dam during off-peak hours and weekends, using the excess base-load capacity from coal or nuclear sources. During peak hours this water can be used for hydroelectric generation. However, relatively few places have the scope for pumped storage dams close to where the power is needed.

Battery storage Many "off-the-grid" domestic systems rely on battery storage, but means of storing large amounts of electricity as such in giant batteries or by other means have not yet been put to general use. Batteries are generally expensive, have maintenance problems, and have limited lifespans. One possible technology for large-scale storage exists: large-scale flow batteries.

Electrical grid storage One of the most important storage methods advocated by the renewable energy community is to rethink the whole way that we look at power supply, in its 24-hour, 7-day cycle, using peak load equipment simply to meet the daily peaks. Solar electric generation is a daylight process, whereas most homes have their peak energy requirements at night. Domestic solar generation can thus feed electricity into the grid during grid peaking times during the day, and domestic systems can then draw power from the grid during the night when overall grid loads are down. This results in using the power grid as a domestic energy storage system, and relies on ?'net metering'?, where electrical companies can only charge for the amount of electricity used in the home that is in excess of the electricity generated and fed back into the grid. Many states now have net metering laws.

Today's peak-load equipment could also be used to some extent to provide infill capacity in a system relying heavily on renewables. The peak capacity would complement large-scale solar thermal and wind generation, providing power when they were unable to. Improved ability to predict the intermittent availability of wind enables better use of this resource. In Germany it is now possible to predict wind generation output with 90% certainty 24 hours ahead. This means that it is possible to deploy other plants more effectively so that the economic value of that wind contribution is greatly increased.

Renewable energy use by nation Iceland is a world leader in renewable energy due to its abundant hydro- and geothermal energy sources. Over 99% of the country's electricity is from renewable sources and most of its urban household heating is geothermal. Israel is also notable as much of its household hot water is heated by solar means. These countries' successes are at least partly based on their geographical advantages.

Leading countries by renewable electricity production, (2000) Hydro Geothermal Wind PV Solar 1. Canada U.S. Germany Japan 2. U.S. Philippines U.S. Germany 3. Brazil Italy Spain U.S. 4. China Mexico Denmark India 5. Russia Indonesia India Australia

Share of the total power consumption in EU-countries that are renewable.

< td> 5,73 < td> 7,54 < td> 5,19

1985  1990  1991  1992  1993  1994

EUR-15 5,61 5,13 4,92 5,16 5,28 5,37 Belgium 1,04 1,01 1,01 0,96 0,84 0,80 Denmark 4,48 6,32 6,38 6,80 7,03 6,49 Germany 2,09 2,06 1,61 1,73 1,75 1,79 Greece 8,77 7,14 7,63 7,13 7,33 7,16 Spain 8,83 6,70 6,56 6,49 6,50 France 7,24 6,34 6,75 7,32 7,98 Ireland 1,75 1,65 1,68 1,59 1,59 1,63 Italy 5,60 4,64 5,16 5,34 5,50 Luxembourg 1,28 1,21 1,14 1,26 1,21 1,34 The Netherlands 1,36 1,35 1,35 1,37 1,38 1,43 Austria 24,23 22,81 20,99 23,39 24,23 23,71 Portugal 25,07 17,45 17,03 13,88 15,98 16,61 Finland 18,29 16,71 17,02 18,10 18,48 18,28 Sweden 24,36 24,86 22,98 26,53 27,31 24,04 United Kingdom 0,47 0,49 0,48 0,56 0,54 0,65 Table from [1]

Renewable energy controversies As with anything, even renewable energy generates controversies.

The funding dilemma Research and development in renewable energies has been severely hampered by only receiving a tiny fraction of energy R&D budgets, with conventional energy sources getting the lion's share.

Centralization versus decentralization Frequently renewable electricity sources will be disadvantaged by regulation of the electricity supply industry which favors 'traditional' large-scale generators over smaller-scale and more distributed generating sources. If renewable and distributed generation were to become widespread, electric power transmission and electricity distribution systems would no longer be the main distributors of electrical energy but would operate to balance the electricity needs of local communities. Those with surplus energy would sell to areas needing "top ups". Some Governments and regulators are moving to address this, though much remains to be done. One potential solution is the increased use of active management of electricity transmission and distribution networks.

The nuclear "renewable" claim Some nuclear advocates claim that nuclear energy should be regarded as renewable energy. Arguments they put forward include:

   * The view that nuclear energy does not contribute to global warming (although evaporative cooling has a minor effect by introducing additional water vapor into the atmosphere, along with the heat production of the process).
   * Fast breeder reactors can produce more fuel than they consume.
   * The view that uranium and thorium, being radioactive, are not theoretically long-term resources.
   * The view that nuclear waste, since it will eventually become less radioactive than the original ore bodies, is not theoretically a long-term problem.

This viewpoint is strongly rejected by most renewable energy advocates. The fact that nuclear power uses a depleting resource (uranium or thorium), that the half-life of uranium 238 is 4.5 billion years, and that the decay of the waste to a safe level may take three thousand years or longer (depending on the technology used) means that it cannot be included in such a classification. Breeder reactors consume uranium or thorium to produce fissile fuel, so this particular argument is a simple misunderstanding of the basic processes involved. Similar arguments can also be applied against proposed nuclear fusion power stations using deuterium and tritium, the latter bred from lithium, as fuel.

References

   * U.S. Energy Information Administration provides lots of statistics and information on the industry.
   * Boyle, G. (ed.), Renewable Energy: Power for a Sustainable Future. Open University, UK, 1996.

Solar power

From Wikipedia, the free encyclopedia.

Solar power has become of increasing interest as other finite power sources such as fossil fuels and hydroelectric power become both more scarce and expensive (in both fiscal and environmental terms). As the earth orbits the sun it receives 1,410 W / m2 as measured upon a surface kept normal (at a right angle) to the sun. Of this approximately 19% of the energy is absorbed by the atmosphere, while clouds reflect 35% of the total energy upon average.

After passing through the Earth's atmosphere most of the sun's energy is in the form of visible and ultraviolet light. Plant's use solar energy to create chemical energy through photosynthesis. We use this energy when we burn wood or fossil fuels. There have been experiments to create fuel by absorbing sunlight in a chemical reaction in a way similar to photosynthesis without using living organisms.

Most solar energy used today is converted into heat or electricity.

Types of solar power

Methods of solar energy have been classified using the terms direct, indirect, passive and active.

Direct solar energy involves only one transformation into a usable form. Examples:

   * Sunlight hits a photovoltaic cell creating electricity. (Photovoltaics are classified as direct despite the fact that the electricity is usually converted to another form of energy such as light or mechanical energy before becoming useful.)
   * Sunlight hits a dark surface and the surface warms when the light is converted to heat by interacting with matter. The heat is used to heat a room or water.

Indirect solar energy involves more than one transformation to reach a usable form. Example:

   * systems to close insulating shutters or move shades. Passive solar systems are considered direct systems although sometimes they involve convective flow which technically is a conversion of heat into mechanical energy.

Active solar energy refers to systems that use electrical, mechanical or chemical mechanisms to increase the effectiveness of the collection system. Indirect collection systems are almost always active systems.

Solar design is the use of architectural features to replace the use of electricity and fossil fuels with the use of solar energy and decrease the energy needed in a home or building with insulation and efficient lighting and appliances.

Architectural features used in solar design:

   * South facing windows with insulated glazing that has high ultraviolet transmittance.
   * Thermal masses.
   * Insulating shutters for windows to be closed at night and on overcast days.
   * Fixed awnings positioned to create shade in the summer and exposure to the sun in the winter.
   * Movable awnings to be repositioned seasonally.
   * A well insulated and sealed building envelope.
   * Exhaust fans in high humidity areas.
   * Passive or active warm air solar panels.
   * Passive or active Trombe walls.
   * Active solar panels using water or antifreeze solutions.
   * Passive solar panels for preheating potable water.
   * Photovoltaic systems to provide electricity.
   * Windmills to provide electricity.

Solar hot water systems are quite common in some countries where a small flat panel collector is mounted on the roof and able to meet most of a household's hot water needs. Cheaper flat panel collectors are also often used to heat swimming pools, thereby extending their swimming seasons.

Solar cooking is helping in many developing countries, both reducing the demands for local firewood and maintaining a cleaner environment for the cooks. The first known record of a western solar oven is attributed to Horace de Saussure, a Swiss naturalist experimenting as early as 1767. A solar box cooker traps the sun's power in an insulated box; these have been successfully used for cooking, pasteurization and fruit canning.

Solar cells (also referred to as photovoltaic cells) are devices or banks of devices that use the photoelectric effect of semiconductors to generate electricity directly from the sunlight. As their manufacturing costs have remained high during the twentieth century their use has been limited to very low power devices such as calculators with LCD displays or to generate electricity for isolated locations which could afford the technology. The most important use to date has been to power orbiting satellites and other spacecraft. As manufacturing costs decreased in the last decade of the twentieth century solar power has become cost effective for many remote low power applications such as roadside emergency telephones, remote sensing, and limited "off grid" home power applications.

Solar power plants generally use reflectors to concentrate sunlight into a heat absorber.

   * Heliostat mirror power plants focus the sun's rays upon a collector tower. The vast amount of energy is generally transported from the tower and stored by use of a high temperature fluid. Liquid sodium is often used as the transport and storage fluid. The energy is then extracted as needed by such means as heating water for use in stream turbines.
   * Trough concentrators have been used successfully in the State of California (in the U.S.) to generate 350MW of power in the past two decades. The parabolic troughs can increase the amount of solar radiation striking the tubes up to 30 or 60 times, where synthetic oil is heated to 390°C. The oil is then pumped into a generating station and used to power a steam turbine.
   * Parabolic reflectors are most often used with a stirling engine or similar device at its focus. As the single parabolic reflector achieves a greater focusing accuracy than any larger bank of mirrors can achieve, the focus is used to achieve a higher temperature which in turn allows a very efficient conversion of heat into mechanical power to drive a electrical generator. Parabolic reflectors can also be used to generate steam to power turbines to generate electricity.

Applying Solar Power

Deployment of solar power depends largely upon local conditions and requirements, for example while certain European or U.S. states could benefit from a public hot water utility, such systems would be both impractical and counter-productive in countries like Australia or states like New Mexico. As all industrialised nations share a need for electricity, it is clear that solar power will increasingly be used to supplying a cheap, reliable electricity supply.

Many other types of power generation are indirectly solar-powered. Plants use photosynthesis to convert solar energy to chemical energy, which can later be burned as fuel to generate electricity; oil and coal originated as plants. Hydroelectric dams and wind turbines are indirectly powered by the sun.

In some areas of the U.S., solar electric systems are already competitive with utility systems. The basic cost advantage is that the home-owner does not pay income tax on electric power that is not purchased. As of 2002, there is a list of technical conditions: There must be many sunny days. The systems must sell power to the grid, avoiding battery costs. The solar systems must be inexpensively mass-purchased, which usually means they must be installed at the time of construction. Finally, the region must have high power prices. For example, Southern California has about 260 sunny days a year, making it an excellent venue. It yields about 9%/yr returns of investment when systems are installed at $9/watt (not cheap, but feasible), and utility prices are at $0.095 per kilowatt-hour (the current base rate). On grid solar power can be especially feasible when combined with time-of-use net metering, since the time maximum production is largely coincident with the time of highest pricing.

For a stand-alone system some means must be employed to store the collected energy for use during hours of darkness or cloud cover - either as electrochemically in batteries, or in some other form such as hydrogen (produced by electrolysis of water), flywheels in vacuum, or superconductors. Storage always has an extra stage of energy conversion, with consequent energy losses, greatly increasing capital costs.

Several experimental photovoltaic (PV) power plants of 300 - 500 kW capacity are connected to electricity grids in Europe and the U.S. Japan has 150 MWe installed. A large solar PV plant is planned for the island of Crete. Research continues into ways to make the actual solar collecting cells less expensive and more efficient. Other major research is investigating economic ways to store the energy which is collected from the sun's rays during the day.