Solar power

Solar power refers to energy harnessed from the sun and converted to heat or electricity for human use.

As of today, the major part of the energy available to mankind derives from the burning of fossil fuels: coal, oil and natural gas. However, because of increased prices, concern over dwindling fossil fuel resources, and protecting the environment from pollution and the consequences of global warming, there has been renewed interest in “alternate energy” sources in the new millennium. Solar power is one of the most promising alternate sources of energy, because it is renewable, in-exhaustible and available in huge quantities.

How it works
There are many different technologies used to extract energy from sunlight.
 * 1) Photoelectric cells  convert sunlight into electricity.
 * 2) Solar panels heat water directly.
 * 3) Stirling engines or steam turbines generate mechanical work from temperature differences. Using parabolic mirrors, temperatures and efficiencies can be increased.
 * 4) Biofuel is essentially sunlight converted into chemical energy with the help of plants' photosynthesis. Like wind and water derived power, this is indirect solar power and not normally referred to as such.

Residential solar power
Roof-top solar panels present the easiest way of providing a house with heat and electricity. Hot water production is economical everywhere where the sun shines occasionally on a suitable roof. Winter heating generally isn't economical as the periods of least sun coincide with the periods of highest power requirement. Electricity production costs more money than does electricity provided by large power plants but is often done because of governmental pay-back schemes and personal motivation.

For heat storage, hot water provides good storage capability for several hours or days depending on the size of the installation. Storage over a year is possible but not economical for individual houses.

Electricity is normally stored in accumulator batteries. With their lifetime of only several years, this is only done if no reliable grid-connection is available. With grid-connected houses, solar electricity is generated as direct current at voltages from about 12 V to 800 V and converted to alternating current at the grid voltage, e.g. 230 V. Surplus is automatically fed into the grid and if more power than provided is required, the difference is taken from the grid.

Solar powered vehicles
Covering a vehicle with solar panels connected to an electric motor is a very easy way to move a vehicle, but there are limitations, especially to the solar surface and hence direct power available. Normally accumulator storage batteries are used so that power is available also during shady or dark parts of the trip and in order to harvest energy also during the time the vehicle is not moving. This also allows fast acceleration and regenerative braking. Solar racing vehicles can be both fast and travel over long distances. Utility solar vehicles are often combined with a human power drive and travel at speeds typical for cycling. No manufacturer has yet provided models which are perfomant, comfortable and cheap at the same time and so they are rarely used apart from racing.

Indirect solar vehicles are very popular, as every electric bicycle can be indirectly powered by a small roof-top solar panel and some manufacturers sell solar energy together with their vehicles. Some people also generate or buy enough solar energy to indirectly power their cars.

Direct solar power is very feasible for marine vehicles because many of the limitations of road vehicles do not apply. In particular extremely low power levels suffice to propel boats at low speeds in calm conditions and displacement boats can carry large amount of heavy storage batteries. Therefore many many solar boats are in use. Some of these are grid-connected when not under way, so that surplus solar energy is fed into the grid.

Direct solar power can be used for air vehicles, but these are very costly, as they must be large and light at the same time.

In model sizes, solar vehicles for land, water, and air are routinely built by hobbyists.

Solar vehicles using thermal power instead of photovoltaic solar cells have been demonstrated but are very rare.