Solar Energy We are using energy from the beginning of man life in earth. We owe our life to sun. That is why all religions worship the sun one way or another. Our sun is just one of billions stars in universe. Without sun’s energy, there wasn’t any form of life on earth. Plants, animals and all imaginable live beings do depend to sun. Even other forms of energy available in our planet are somehow are derived from solar energy. Just thinking about fossil fuels, as you learned earlier, originated from living beings. Most of the universe energy is concentrated in stars. As we learned our sun is one of many starts. Even a nuclear energy has a solar energy because uranium is just one of many by products of stars explosions. Looking around, you will find more usages of sun.    Solar Hot water In sunny areas of the world solar energy could be used effectively to warm our houses. By laying a network of water pipes in front of sunshine, you may get enough hot water to keep you home and pool warm. Such solar water heaters have been used in united state sine 1890. This way tens of thousands of such systems were sold by 1920. By introducing cheap oil and natural gas this system lost its market but again as a pollution consideration, its popularity is coming back. Only in California, half a million of solar-heaters have been used.    Solar Thermal Electricity By using lens and curved mirrors, the rays of sun light can focus and heat up the water pipes to a boiling point. The resulted steam then can be used for turning a turbine for electricity generation purposes. In a solar power plant rows of solar mirrors are needed to provide enough energy. A sample of such a power plant provides electricity of 350.000 homes. By using a hybrid technology the problem of not availability of solar energy at night time and cloudy days is solved. It means that during mentioned periods, complement fuel fossil power plants will provide the electricity. In a better design, a turning tower equipped too many mirror turn according to sun position. An experimental power plant like this is built in California. Another under construction will make enough electricity for about 10.000 homes.    Solar Cell or Photovoltaic Energy Sunlight can be changed to electricity in a device called solar cell. This kind of cells is found in many small appliances and the most usefulness of it is in satellites. Striking usefulness of it is in satellites. Striking light on a crystal of silicon or germanium, frees electrons to move around. By suing dissimilar crystals, removed electrons make an in balance distribution of charges around the junction joining by a wire, a current of electricity between the two side occurs. A solar battery is a combination of many PV cells, arranged in modules and arrays. Some of the arrays, by setting on a tracking device can follow the sun all day long. This way it is possible to have a direct use of solar energy. By storing its energy, it can be used at night. Isolated areas, road side billboards and emergency road side cellular telephones can exploit such a property. Cars can also power up by PV cells. There are now some experimental models of these kinds of cars. Satellites with no access to conventional energy, utilize this sort of energy.