Photovoltaics (PV) is a method of  generating electrical power by converting solar radiation into direct current electricity using  semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs dolar panels composed of a number of solar cells containing a photovoltaic material. Materials presently used for photovoltaics include monocrystalline silicon, polycrystalline silicon, amorphous silicone, cadmium telluride,and copper indium gallium selenide/sulfide. Due to the growing demand for renewable energy sources, the manufacturing of solar cells and photovoltaik arrays has advanced considerably in recent years.

Solar photovoltaics is growing rapidly, albeit from a small base, to a total global capacity of 40,000 MW at the end of 2010. More than 100 countries use solar PV. Installations may be ground-mounted (and sometimes integrated with farming and grazing) or built into the roof or walls of a building ( building-intergrated-photovoltaics).

Driven by advances in technology and increases in manufacturing scale and sophistication, the cost of photovoltaics has declined steadily since the first solar cells were manufactured. Net metering and financial incentives, such as preferential feed-in tariffs for solar-generated electricity, have supported solar PV installations in many countries.

Current developments

Photovoltaic panels based on crystalline silicon modules are encountering competition in the market by panels that employ thin-film solar cells (CdTe, CIGS, amorphous Si, microcrystalline Si), which had been rapidly evolving and are expected to account for 31 percent of the global installed power by 2013. Howethun ver, precipitous drops in prices for polysilicon and their panels in late 2011 have caused some thin-film makers to exit the market and severely squeezing profits at others. Other developments include casting wafers instead of sawing, concentrator modules, Silver cells, and continuos printing processes. Due to economies of scale solar panels get less costly as people use and buy more — as manufacturers increase production to meet demand, the cost and price is expected to drop in the years to come. By early 2006, the average cost per installed watt for a residential sized system was about USD 7.50 to USD 9.50, including panels, inverters, mounts, and electrical items.

In 2006 investors began offering free solar panel installation in return for a 25 year contract, or Power Purchase Agreement , to purchase electricity at a fixed price, normally set at or below current electric rates. A 2008 report predicted that over 90% of commercial photovoltaics installed in the United States would be installed using a power purchase agreement by 2009. An innovative financeing arrangement in Berkeley, California, funded by grants from the United States Environmental Protection Agency and the Bay Area Air Quality Managment , lends money to a homeowner for solar system, to be repaid via an additional tax assessment on the property which remains in place for 20 years. This allows installation of the solar system at relatively little up-front cost to the property owner.

The  San Jose -based company Sunpower produces cells that have an energy conversion ratio of 19.5%, well above the market average of 12–18%. The most efficient solar cell so far is a multi-junction concentrator solar cell with an efficiency of 43.5% produced by the National Renewable Energy Laboratory in April 2011. The highest efficiencies achieved without concentration include Sharp Corporation at 35.8% using a proprietary triple-junction manufacturing technology in 2009, and Boeing Spectrolab (40.7% also using a triple-layer design). A March 2010 experimental demonstration of a design by a Caltech group led by Harry Atwater which has an absorption efficiency of 85% in sunlight and 95% at certain wavelengths is claimed to have near perfect quantum efficiency. However, absorption efficiency should not be confused with the sunlight-to-electricity conversion efficiency.

The new European Photovoltaic Industry Association (EPIA) report predicts a promising future for photovoltaics. "The future of the PV market remains bright in the EU and the rest of the world," the report said. "Uncertain times are causing governments everywhere to rethink the future of their energy mix, creating new opportunities for a competitive, safe and reliable electricity source such as PV." By 2015, between 131 and 196 gigawatts (GW) of photovoltaic systems could be installed around the globe. (Until now, only 40 GW have been installed.)