|Photovoltaic Power (PV)
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PV or 'solar panels' convert the sun's light directly into direct current electricity. This is different than other forms of solar power like heliostat, passive solar and solar thermal. PV uses semiconductor materials to convert the light into power.
PHOTO - close up of Polysi
PV panels consist of a thin coating (ex 2 micrometers) of a material such as silicon on a backer or 'substrate'. Glass is the most common substrate. An anti-reflective coating on doped silicon deposited on a textured glass traps light in so the silicon can absorb the maximum amount of light.
'Thin Film Solar' describes the use of silicon or other semiconductors deposited onto a substrate using vapor deposition processes. Thin film's advantage is that it can be integrated into many places. Thin film can be built into window tinting, car roofs, building roofs and many other places. Traditional silicon panels are rigid and require dedicated space for setup. Thin-film's disadvantages have been lower efficiency and chemical stability as well as toxicity as some types use poisonous materials.
Types of PV:
Polycrystalline Silicon PV:
The most common and efficient form of PV is polycrystalline solar panels. Silicon crystals can be formed on other substrates like glass. Liquid silicon is deposited on a surface using one seed crystal to start the crystalization of the entire area. This is the most common type of PV panel because it is cheap to produce and yields the highest efficiency.
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Amorphous Silicon PV:
This type of silicon is easier to fabricate than polycrystalline but are not as efficient. Thin films of amorphous silicon are very common in the thin film world. Silicon in this form can be deposited onto plastic, glass or metal.
DIAGRAM thin film
Cadmium-Tellurium and Copper-Indium-Selenium (CdTe and CIS):
First Solar based out of Arizona has achieved some of the best efficiency numbers with CdTe at the time of writing, however crystalline silicon is leaping forward each year and may replace thin film solar.
CdTe solar cells were the first reliable PV cells made, they were used in project Vangaurd, the US's first satellite program. Today CdTe is used in a percent of thin film products. General Electric, RCA, Bell Labs, Hoffman Electronics and Western Electric all developed early PV technology in the 1950s. By 1960 Hoffman Electronics had reached 14% efficiency. PV found extensive use as the space race began, satellites of every kind relied on PV for power.
PV research saw extensive funding from the US government at NREL and the Jet Propulsion Laboratory. By 1979 NASA had build a solar array to power a village in the Papago Indian Reservation in Arizona, this was the first town powered by PV.
More installations around the world (Tunesia, New Mexico, Saudi Arabia) are built. World wide sales of PV reached the hundreds of millions of dollars.
US government money continues to fund much of the PV research at the National Renewable Energy Laboratory.
Private firm First Solar dominates the market and thin film sees new applications. Flexible thin film solar arrays are available for low cost in the consumer market.
Chinese producers take the market by storm dumping low cost PV onto world wide markets. The manufacturing costs were lowered by lack of clean environmental procedures and government subsidies.
Germany invests heavily in solar despite it's poor climate and proves that solar can work on a mass scale.
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The Solar World, Engineering Challenges:
One thing which is certain is that the solar field is changing at an extremely rapid pace and it's all about efficiency numbers. The latest and greatest this month can be eclipsed a few months from now. It is a difficult industry to work in as companies come and go. Engineers constantly are experimenting with new deposition techniques, new materials, new treatments, all in a quest to find the breakthrough efficiency. The other major factor of success is finding a material which will hold up over time. Thin materials exposed to powerful rays and extreme outside temperatures can be broken down by the external factors, they also can break down as the chemicals inside the device react with each other. This engineering challenge is far from easy to solve.
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