 Photovoltaics, or PV for short, is a solar power technology that uses solar cells or solar photovoltaic arrays to convert light from the sun directly into electricity. Photovoltaics is also the field of study relating to this technology and there are many research institutes devoted to work on photovoltaics.
History of Solar Electricity
- Henry Bequerel discovered the photovoltaic effect
- 1950s Bell Labs develops the first commercially viable solar cell
- 1970s First practical solar cells were produced (cost 100$/W)
The first conventional PV cells were produced in the late 1950s, and throughout the 1960s were principally used to provide electrical power for earth-orbiting satellites. By the 1970s, improvements in the manufacturing, performance and quality of PV modules helped to reduce costs and opened up a number of opportunities for powering remote terrestrial applications, including battery charging for navigational aids, signals, telecommunications equipment and other critical low power needs.
Following the energy crisis of the 1970s, significant efforts shifted to the development of PV power systems for residential and commercial uses both for stand-alone, remote power, as well as, for utility-connected applications. In the 1980s, PV became a popular power source for some consumer electronic devices, including calculators, watches, radios, lanterns and other small battery charging applications.
Solar cells produce direct current electricity from light, which can be used to power equipment or to recharge a battery. The first practical application of photovoltaics was to power orbiting satellites and other spacecraft and pocket calculators, but today the majority of photovoltaic modules are used for grid connected power generation. In this case an inverter is required to convert the DC to AC.
Cells require protection from the environment and are packaged usually behind a glass sheet. When more power is required than a single cell can deliver, cells are electrically connected together to form photovoltaic modules, or solar panels, A single module is enough to power an emergency telephone, but for a house or a power plant the modules must be arranged in arrays.
A Photovoltaic cell |
Crystalline or polycrystalline silicon has been the most widely used materials technology for the PV industry. Conventional silicon solar modules are fabricated in a step-and-repeat, batch process from small LAYERS of single crystal or polycrystalline silicon semiconductor materials.
Amorphous silicon (a-Si) alloy thin film technology offers an interesting opportunity to reduce materials cost of the solar cells. Because a-Si alloy absorbs light more efficiently than its crystalline counterpart, the a-Si solar cell thickness can be 100 times less than that of conventional cells, thereby significantly reducing materials cost. By utilizing a flexible, stainless steel substrate and polymer-based encapsulates, PV products utilizing this technology can be very lightweight, flexible and durable. The cell is deposited using a vapor-deposition process at low temperatures; the energy payback time is therefore much smaller than that for the conventional technology.
Amorphous materials with different light absorption properties can be deposited continuously, one on top of another, to capture the broad solar spectrum more effectively. This increases the energy conversion efficiency of the multi-cell device and improves performance stability. This multi-junction approach has resulted in world record efficiencies for a-Si technology.
In a high-volume manufacturing plant, solar cells are deposited on rolls of stainless steel that are a mile-and-a half long using automated manufacturing machines. The a-Si alloy processor deposits the nine thin-film layers of the triple-junction cell on six rolls of stainless steel at a time. The rolls of solar cell material are processed further for use in a variety of photovoltaic products for different applications ranging from battery charging to large-scale grid-connected systems.
Photovoltaic power capacity is measured as maximum power output under standardized test conditions in "Wp" (watts peak). Actual peak power may exceed this nominal peak power. Solar photovoltaic arrays have a capacity factor of around 19%, which is lower than many other industrial sources of electricity.
Germany was the fastest growing major PV market in the world in 2005. In 2005, 837 MWp of PV were installed. The German PV industry generates over 10,000 jobs in production, distribution and installation. Over 90% of solar PV installations are in grid-tied applications in Germany. The balance is off-grid (or stand alone) systems.
a-Si Alloy Thin Film Technology
|
