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The spread of solar cell farms - power plants fueled by the sun and typically found where the sun is plentiful and land is cheap - are evidence of the ever-evolving solar technology. Two forms dominate; photovoltaic (PV) solar farms and solar thermal technology.
PV solar farms have hundreds to thousands of solar panels mounted on large racks, often covering hundreds of acres to produce enough electricity to feed power grids and communities. Solar thermal technology precedes PV, and it works by capturing the suns heat to convert it into electricity. This form uses mirrors to concentrate the sun’s heat into a steam-generating central column that then spins a turbine to make electricity.
Solar Cell Farms Around the World
For example, Pakistani public company Quaid-e-Azam Solar Power (Pvt.) Limited is building the Quaid-e-Azam Solar Power Park, a $130 million project on about 500 acres of land in the Cholistan desert in Punjab, due to open in 2017. The farm is expected to have 5.2 million PV cells that produce as much as 1,000 megawatts of electricity, or enough power for 320,000 households.
Other countries including China and the U.S. are leaders in the solar farm industry, and many American utilities are pioneers in solar. First Solar, Inc. already have more than 10 gigawatts installed worldwide, and Mid American Energy, a subsidiary of Berkshire Hathaway, built the $2.4 billion, 550 megawatt Topaz Solar Farm to sell power to the California utility PG&E.
Materials Used in Solar Cells
Wafer-based crystalline silicon technology is used by the vast majority (over 85%) of installed solar capacity but is considered mature. Cadmium telluride (CdTe) solar cells are the second most common PV source material with advantages of low-cost manufacturing and a conversion efficiency rate of up to 21.5%
Most solar companies are innovators, pushing the technology forward. Other materials being utilized for Solar Cells are discussed below.
Gallium Arsenide Solar Cells
NanoFlex is combining gallium arsenide with a lightweight thin-film form factor to bring down costs and enable off-grid and mobile applications. The company is using gallium arsenide as it has found conversion efficiencies in excess of 40%, which it claims are nearly double those of crystalline silicon.
Organic PV (OPV)
Many researchers in industry and academia, including Solarmer Energy and NanoFlex, are working on OPV cells, where part of the cell is made of an organic material such as a small molecule or polymer. Today most solar cells are made from inorganic semiconductors but there is a belief that by changing the molecules in the organic layers of organic cells they can be tuned to produce desired results. Made from carbon-rich compounds they are considered thin and malleable with different shapes and colors possible.
NanoFlex is also designing OPV for many applications including mobile devices. Its OPV is a series of very thin vapor deposited organic layers sandwiched between two electrodes, a transparent anode (indium tin oxide) and a metallic cathode on top. They work with the University of Southern California and University of Michigan researchers to refine and test its OPV.
Other academic groups are creating new forms of OPV. Researchers at the Kaunas University of Technology (KTU) in Kaunas, Lithuania created perovskite solar cells with carbazole that in tests showed 16.9% effectivity in the conversion of solar energy into electricity.
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Also refining perovskite solar cells are researchers at the Global Research Center for Environment and Energy based on Nanomaterials Science at the National Institute for Materials Science (NIMS) in Ibaraki, Japan. There, researchers testing what they state are lower-cost lead-halide-based perovskite cells produced through low-temperature processes such as spin coating.
In a March 2015 issue of Applied Physics Letters, the researchers described how they constructed the cells by simplifying the structure and using a fabrication technique to eliminate moisture and oxygen. In tests, they found the perovskite solar cell material acted as a semiconductor with ideal diode properties but admit it requires refinement.
Oxford Photovoltaic in Oxford, UK is already commercializing its version of thin-film perovskite solar cells that it can print directly onto silicon solar cells, copper-indium-gallium-selenide, or CIGS, solar cells or glass. The most established alternative to silicon solar cells, CIGS solar cells are already known to achieve solar conversion efficiencies of over 20%. But it is considered second-generation PV technology, while gains with perovskite solar cells are considered new ground.
References and Further Reading