Heliostat

The heliostat is a device with a mirror which always reflects the sunlight regardless of the change of the position of the sun in the sky at the same fixed point. The name is made up of Helios (Greek for sun) and stat ( for stable).

A similar, but provided with a telescopic sight instrument is the 1821 developed by Gauss heliotrope to visualize further survey points.

History

The earliest mention of the heliostat, probably not by the inventor, is in a book by the Dutch physicist Willem Jacob ' s Gravensande from the year 1742. Before him the Italian Giovanni Alonso Borelli described ( 1608-1679 ) such a mechanism in an unpublished manuscript. The rotation of the heliostat was carried out by a clockwork .. Later the device was inter alia developed by French physicist Jean Thiébault Silbermann.

Jean Bernard Léon Foucault developed in 1865 by an improved heliostat, which was used for a larger area of the sky. His firm large plant called Siderostat, equipped with a mirror at the time of the highest quality, reduced costs and technical difficulties, especially for equatorial mounts.

In heliostats and siderostats the image rotates in the course of time in the projection plane to a point (see image field rotation). To also remove this drawback, the coelostat have been developed which are an important part of solar observation instruments, particularly with large solar telescopes.

Application

First, the radiation energy was particularly applied in optical laboratories that examine the composition of sunlight. For this, the heliostat was placed outside the experimental room to initiate light rays into the room. If the laboratory is in a higher floor, a projection is built for installation of heliostats.

Heliostats have been used more recently in the so-called solar tower power plants, which concentrate hundreds of computer-controlled heliostats their light on a housed in a spire absorber. The concentration factor of the radiation reaches values ​​of 1000 and more. With his help, the radiation is converted into heat that is dissipated, then drive a generator by means of steam generation through a conventional turbine.

Heliostats can also be used for lighting purposes. The light is directed onto otherwise lying in the dark parts of the building, light wells or vehicle tunnel. Thus, a total of four heliostats on the Italian highway A6 near the village Painissolo are used to light a short tunnel sections. Increasingly heliostats are used to places that experienced in the winter months due to its valley location no direct sunlight, artificially illuminated by sunlight. Since 2006, such a mirror is in the Piedmont Viganella in operation. 2013 a similar plant in Rjukan Norway was established.

As a light source for light microscopic applications with large brightness is required heliostats were also used before sufficiently strong artificial light sources were available from the 20th century.