Resources Center Solar Technologies
Solar Technologies |
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There are two main technologies for converting sunlight into electrical energy – Photovoltaic and Thermal. Within these two branches of technologies there is a variety of technologies that differ in the way sunlight is captured or the materials used to convert the sunlight to electrical energy. PhotovoltaicThe photovoltaic technology is based on the photoelectric effect that was discovered by Albert Einstein in 1905 and for which he was awarded the Nobel Prize in physics. The PE effect is a phenomenon where photons (light) hitting a matter cause this matter to emit electrons (electric energy). Photovoltaic panels are made from materials that are optimized to take advantage of the PE effect and directly convert solar energy into electrical energy. This animation explains how solar PV work.There are several photovoltaic technologies. The variation is in the type of materials used and in the way sunlight is captured. Crystalline Silicon - This is the most common PV (and solar) technology. Panels made from crystalline silicon (c-Si) have been around for decades. These panels are made from silicon, an abundant material that is also used in the semi-conductor industry. C-Si converts solar energy into electrical energy at a rate of 14%-20% at the cell level. The variation depends, among other things, on the quality of silicon. The higher quality silicon, which is called mono crystalline silicon, has higher conversion efficiency than  poly or multi c-Si but it is also more costly. The benefits of c-Si is that it is a wide spread technology with known performance history and benchmarks. C-Si had more than 87% market share in 2007 and is expected to be the dominant technology in the next 5 years. While silicon is an abundant material, still the active material and related process constitute a significant portion of the PV system cost (around 33%). Therefore, other technologies try to minimize the amount of active material. There two basic approaches:
Thin Film - Panels manufactured with this technology use a thin layer of active semi-conductor material deposited on a relatively cheap substrate material. There is a variety of materials that are used as the active material in thin film panels. The most prevalent technology uses Cadmium Telluride (CdTe) as the active material. Other approaches use Amorphous Silicon (a-Si) or Copper Indium Gallium Selenide (CIGS) as the active material. Thin film panels have the potential of lower cost than c-Si panels, but they also suffer from lower efficiencies (5%-11%), and thus, require more surface area compared to c-Si. Thin-film technologies have less performance history, and thus, are probably more risky in terms of reliability. Thermal
Solar thermal technologies use sunlight to heat some sort of liquid – oil or water – thereby creating steam that powers a turbine that generates electricity. Because solar thermal systems need to generate heat they all use concentration technologies to focus the light and reach high temperatures. For that reason the common name for this technology is concentrated solar power of CSP. There are 3 main concentration approaches: Parabolic Trough, Tower and Dish
Parabolic trough is the most common CSP technology. Early installations in California date back to the 1980s and are still in operation today.
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