The Earth is bombarded by about 174 petawatts (one quadrillion seventy four trillion watts) of solar power. Solar radiation hits our homes, businesses, and the Earth’s surface whether we use it or not. It can be harnessed by homeowners to power individual appliances, or by power suppliers to supplement public power generation.

Experimental solar power plants have been built in the United States and many other countries. Most of these power plants work using mirrors to focus solar radiation from a large area onto a tower, boiling water in the tower which is used to spin a turbine generator, or use mirrors shaped into paraboloids or parabolic cylinders onto energy collection devices located at the mirrors' foci. Other solar power plants utilize photovoltaic cells. These devices convert radiation directly into electricity through the ejection of electrons from atoms within the cells as they absorb energy (the photovoltaic effect).

While experimental solar power plants have been built and are generating power, there are many problems with large-scale solar power generation. Their cost per watt of power is three times that of conventional power plants, but that cost will fall as technology advances and cheaper ways to harness solar power are created. Solar energy is an intermittent power source: solar energy collection is impossible during night time and hampered by cloud cover.

Solar energy is used to power specialty devices. Many calculators today are completely powered by photovoltaic cells, and many spacecraft and planetary probes are powered exclusively by the same technology. Experimental solar powered cars have also been built, although since the maximum energy absorption of a solar cell is limited by its area, solar powered cars are limited to low speeds and unusual shapes. Solar power may benefit transportation if used in electrolysis to produce hydrogen for fuel cells.

Solar energy usage has been very successful in the private sector. Homeowners have found that a solar powered water heater costs them less in the long run than a conventional water heater, and may use solar panels to power other devices in their homes. The limitations homeowners face in solar energy utilization are due to the high initial investment of solar cell installation and space. Geographical factors such as climate and latitude must also be considered. A solar power system will absorb less energy at a higher latitude and in areas more frequently covered by clouds.

The most common type of solar energy capturing device homeowners use is the photovoltaic cell. These cells are usually installed on the roofs of houses, and convert radiation directly into electricity. Photovoltaic cells are useful for powering any electrical appliance, and may even be used to at least partially power a home electrolysis system to produce pure hydrogen for fuel cell vehicles.

A mirror that focuses radiation onto a sample of water could be used to heat water for bathing, dish washing, and clothes washing. Radiation absorption devices can also replace or supplement electrical air heaters.

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