solar power

solar power                                                                                                                                       

                           Solar power involves using solar cells to convert sunlight into electricity, using sunlight hitting solar thermal panels to convert sunlight to heat water or air, using sunlight hitting a parabolic mirror to heat water (producing steam), or using sunlight entering windows for passive solar heating of a building. It would be advantageous to place solar panels in the regions of highest solar radiation[44]. In the Phoenix, Arizona area, for example, the average annual solar radiation is 5.7 kW·h/(m²·day),[45] or 2.1 MW·h/(m²·yr). Electricity demand in the continental U.S. is 3.7×1012 kW·h per year. Thus, at 20% efficiency, an area of approximately 3500 square miles (3% of Arizona's land area) would need to be covered with solar panels to replace all current electricity production in the US with solar power. The average solar radiation in the United States is 4.8 kW·h/(m²·day),[46] but reaches 8–9 kWh/m²/day in parts of the Southwest.

China is increasing worldwide silicon wafer capacity for photovoltaics to 2,000 metric tons by July 2008, and over 6,000 metric tons by the end of 2010.[47] Significant international investment capital is flowing into China to support this opportunity. China is building large subsidized off-the-grid solar-powered cities in Huangbaiyu and Dongtan Eco City

1.solar cell
                                                                     

                                                                                                                                                              A solar cell is a device that converts the energy of sunlight directly into electricity by the photovoltaic effect. Sometimes the term solar cell is reserved for devices intended specifically to capture energy from sunlight such as solar panels and solar cells, while the term photovoltaic cell is used when the light source is unspecified. Assemblies of cells are used to make solar panels, solar modules, or photovoltaic arrays. Photovoltaics is the field of technology and research related to the application of solar cells in producing electricity for practical use. The energy generated this way is an example of solar energy.
  
2.Solar water heating

             where heat from the Sun is used to heat water in glass panels on your roof.

             This means you don't need to use so much gas or electricity to heat your water at home.
Water is pumped through pipes in the panel. The pipes are painted black, so they get hotter when the Sun shines on them. The water is pumped in at the bottom so that convection helps the flow of hot water out of the top.
             This helps out your central heating system, and cuts your fuel bills. However, with the basic type of panel shown in the diagram you must drain the water out to stop the panels freezing in the winter. Some manufacturers have systems that do this automatically.
             Solar water heating is easily worthwhile in places like California and Australia, where you get lots of sunshine. Mind you, as technology improves it's becoming worthwhile in the UK.

Here's a more advanced type of solar water heating panel :-

            The suppliers claim that in the UK it can supply 90% of a typical home's hot water needs from April to November.
            This "Thermomax" panel is made of a set of glass tubes. Each contains a metal plate with a blue-ish coating to help it absorb solar energy from IR to UV, so that even in diffuse sunlight you get a decent output. The air has been removed from the glass tubes to reduce heat loss, rather like a thermos flask.
            Up the back of the metal plate is a "heat pipe", which looks like a copper rod but contains a liquid that transfers heat very quickly to the top of the glass tube. A water pipe runs across the top of the whole thing and picks up the heat from the tubes.