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Solar Technology Today
Photovoltaic power can be produced in many ways, with widely varying efficiency and costs. They can be divided into two basic groupings: discrete cell technology and integrated thin film technology.
 

Discrete Cell Technology

Single-crystal silicon
 
Sliced from single-crystal boules of grown silicon, these wafers/cells are now cut as thin as 200 microns. Research cells have reached nearly 24-percent efficiency, with commercial modules of single-crystal cells exceeding 15-percent.

Multicrystalline silicon
Sliced from blocks of cast silicon, these wafers/cells are both less expensive to manufacture and less efficient than single-crystal silicon cells. Research cells approach 18-percent efficiency, and commercial modules approach 14-percent efficiency.

Edge-defined film-fed growth ribbons
Nearly single-crystal silicon ribbons grown from a crucible of molten silicon, drawn by capillary action between the faces of a graphite die.

Dendritic web
A film of single-crystal silicon pulled from a crucible of molten silicon, like a soap bubble, between two crystal dendrites.

Gallium Arsenide (GaAs)
A III-V semiconductor material from which high-efficiency photovoltaic cells are made, often used in concentrator systems and space power systems. Research cell efficiencies greater than 25 percent under 1-sun conditions, and nearly 28 percent under concentrated sunlight. Multijunction cells based on GaAs and related III-V alloys have exceeded 30-percent efficiency.


Integrated Thin Film Technology

Copper Indium Diselenide (CuInSe2, or CIS)
A thin-film polycrystalline material, which has reached a research efficiency of 17.7 percent, delivers the highest completed module efficiency for full sized power modules, reaching over 11 percent.

Amorphous Silicon (a-Si)
Used mostly in consumer products for solar watches and calculators, a-Si technology is also used in building-integrated systems, replacing tinted glass with semi-transparent modules. The primary issue with a-Si technology remains the low efficiency and associated greater requirement for space and higher array installed cost and weight

Cadmium Telluride (CdTe)
A thin-film polycrystalline material, deposited by electrodeposition, spraying, and high-rate evaporation.Small laboratory devices approach 16-percent efficiency, with commercial-sized modules (7200-cm2) measured at 8.34-percent (NREL-measured total-area) efficiency and production modules at approximately 7 percent.

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Advantages of Photovoltaic Power

 

 Siemens Solar panels

Solar panel
From solar panel, the free solar panels
• Ten things you may not know about solar panel •Jump to: navigation, search

A photovoltaic (PV) module that is composed of multiple PV cells. Two or more interconnected PV modules create an array.conservs the energy of THE LIGHT . Electrons from these excited atoms form an electric current, which can be used by external devices. Solar panels were in use over one hundred years ago for water heating in homes. Solar panels can also be made with a specially shaped mirror that concentrates light onto a tube of oil. The oil then heats up, and travels through a vat of water, instantly boiling it. The steam created turns a turbine for power.[1]

Contents [hide]
1 History 
2 How Solar Panels Work 
3 See also 
4 References 



solar panels History
The history of solar panels dates back to 1839, when French physicist Antoine César Becquerel discovered the photovoltaic effect during an experiment involving an electrolytic cell that was made up of two metal electrodes placed in an electrolyte solution. Becquerel discovered that when his device was exposed to light the amount of electricity generated increased.[2]

Then in 1883, the first genuine solar cell was built by Charles Fritts. Fritts' solar cell was formed by coating sheets of selenium with a thin layer of gold.[3]

Between 1883 and 1941 many scientists, inventors and companies experimented with solar energy. During these years Clarence Kemp, a Baltimore inventor patented the first commercial water heater powered from solar energy. In addition, Albert Einstein published his thesis on the photoelectric effect and a few years later received the Nobel Prize in Physics for his research. William Bailey, an employee of the Carnegie Steel Company, invented the first solar collector with copper coils contained in an insulated box.[2]

In 1941, Russell Ohl, an American inventor who worked for Bell Laboratories, patented the first silicon solar cell. Ohl’s new invention led Bell Laboratories to produce the first crystalline silicon solar panel in 1954. This solar cell achieved a 4% return on energy conversion. In the years that followed, other scientists continued to improve on this original solar cell and began to produce solar cells with 6% efficiency.[4]

The first large scale use for solar electrical energy was space satellites. With government backing much of the research the US was able to produce a solar cell with twenty percent efficiency by 1980 and by early 2000 had produced solar cells with 24% efficiency. As of November 2007 two companies, Spectrolab and Emcore Photovoltaics dominate world solar cell production and have the ability to produce cells with 28% efficiency.[4]


solar panels How Solar Panels Work
The basic element of solar panels is pure silicon. When stripped of impurities, silicon makes an ideal neutral platform for transmission of electrons. In silicon’s natural state, it carries four electrons, but has room for eight. Therefore silicon has room for four more electrons. If a silicon atom comes in contact with another silicon atom, each receives the other atom's four electrons. Eight electrons satisfy the atoms' needs, this creates a strong bond, but there is no positive or negative charge. This material is used on the plates of solar panels. Combining silicon with other elements that have a positive or negative charge can also create solar panels.[5]

For example, phosphorus has five electrons to offer to other atoms. If silicon and phosphorus are combined chemically, the results are a stable eight electrons with an additional free electron. The silicon does not need the free electron, but it can not leave because it is bonded to the other phosphorous atom. Therefore, this silicon and phosphorus plate is considered to be negatively charged.[5]

A positive charge must also be created in order for electricity to flow. Combining silicon with an element such as boron, which only has three electrons to offer, creates a positive charge. A silicon and boron plate still has one spot available for another electron. Therefore, the plate has a positive charge. The two plates are sandwiched together to make solar panels, with conductive wires running between them.[5]

Photons bombard the silicon/phosphorus atoms when the negative plates of solar cells are pointed at the sun. Eventually, the 9th electron is knocked off the outer ring. Since the positive silicon/boron plate draws it into the open spot on its own outer band, this electron doesn't remain free for long. As the sun's photons break off more electrons, electricity is then generated. When all of the conductive wires draw the free electrons away from the plates, there is enough electricity to power low amperage motors or other electronics, although the electricity generated by one solar cell is not very impressive by itself. When electrons are not used or lost to the air they are returned to the negative plate and the entire process begins again.[5]


solar panels See also
Battery (electricity) 
Energy economics 
Photovoltaic array 
Photovoltaics in transport 
Renewable energy 
Solar power satellite 
Solar lamp 

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