What is Photovoltaic
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, 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. There is a smaller market for off grid power for remote dwellings, roadside emergency telephones, remote sensing, and cathodic protection of pipelines.
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. Although the selling price of modules is still too high to compete with grid electricity in most places, significant financial incentives in Japan and then Germany triggered a huge growth in demand, followed quickly by production.
Perhaps not unexpectedly, a significant market has emerged in urban or grid-proximate locations for solar-power-charged storage-battery based solutions. These are deployed as stand-by systems in energy deficient countries like India and as supplementary systems in developed markets. In a vast majority of situations such solutions make neither economic nor environmental sense, any green credentials being largely offset by the lead-acid storage systems typically deployed.