The vacuum significantly reduces convective heat loss

The vacuum significantly reduces convective heat loss. A fluid (also called heat transfer fluid) passes through the
receiver and becomes very hot. Common fluids are synthetic oil, molten salt and pressurized steam. The fluid
containing the heat is transported to a heat engine where about a third of the heat is converted to electricity. Full-
scale parabolic trough systems consist of many such troughs laid out in parallel over a large area of land. Since 1985
a solar thermal system using this principle has been in full operation in California in the United States. It is called
the Solar Energy Generating Systems (SEGS) system. Other CSP designs lack this kind of long experience and
therefore it can currently be said that the parabolic trough design is the most thoroughly proven CSP technology.

Parabolic dish
Solar Parabolic dish
With a parabolic dish collector, one or more parabolic dishes concentrate solar energy at a single focal point, similar
to the way a reflecting telescope focuses starlight, or a dish antenna focuses radio waves. This geometry may be
used in solar furnaces and solar power plants. The shape of a parabola means that incoming light rays which are
parallel to the dish's axis will be reflected toward the focus, no matter where on the dish they arrive. Light from the
sun arrives at the Earth's surface almost completely parallel, and the dish is aligned with its axis pointing at the sun,
allowing almost all incoming radiation to be reflected towards the focal point of the dish. Most losses in such
collectors are due to imperfections in the parabolic shape and imperfect reflection. Losses due to atmospheric
scattering are generally minimal. However, on a hazy or foggy day, light is diffused in all directions through the
atmosphere, which significantly reduces the efficiency of a parabolic dish. In dish stirling power plant designs, a
stirling engine coupled to a dynamo, is placed at the focus of the dish. This absorbs the energy focused onto it and
converts it into electricity.
Power tower
A power tower is a large tower surrounded by tracking mirrors called heliostats . These mirrors align themselves and
focus sunlight on the receiver at the top of tower, collected heat is transferred to a power station below. This design
reaches very high temperatures. High temperatures are suitable for electricity generation using conventional
methods like steam turbine or a direct high temperature chemical reaction such as liquid salt. By concentrating
sunlight, current systems can get better efficiency than simple solar cells. A larger area can be covered by using
relatively inexpensive mirrors rather than using expensive solar cells . Concentrated light can be redirected to a

suitable location via optical fiber cable for such uses as illuminating buildings. Heat storage for power production
during cloudy and overnight conditions can be accomplished, often by underground tank storage of heated fluids.