The heliostat (from ancient Greek ἥλιος helios “sun” and στατός statós “standing, adjusted”) is a device with a mirror that always reflects sunlight to the same, fixed point regardless of the change in the sun's position in the sky.
The earliest mention of the heliostat, probably not by the inventor, is in a book by the Dutch physicist Willem Jacob 's Gravesande from 1742 . Before him, the Italian Giovanni Alonso Borelli (1608–1679) described such a mechanism in an unpublished manuscript. The heliostat was rotated by clockwork. Later the device was u. a. further developed by the French physicist Jean Thiébault Silbermann .
Around 1865, Léon Foucault developed an improved heliostat that could be used for a larger angle range for sky observation. His fixed large system called Sidérostat , equipped with a mirror of the highest quality at the time, reduced costs and technical difficulties, v. a. for equatorial mounts .
With heliostats and siderostats, the image rotates around a point in the projection plane (see image field rotation ). In order to eliminate this disadvantage, too, the coelostats were developed, which are an important part of solar observation instruments, especially in large solar telescopes .
At first, the radiation energy was used in particular in optical laboratories that investigate the composition of sunlight. For this purpose, the heliostat was placed outside the test room in order to introduce rays of light into the room. If the laboratory is on a higher floor, a ledge is built for the installation of the heliostat.
Heliostats have recently been used in so-called solar tower power plants, in which hundreds of computer-controlled heliostats concentrate their light on an absorber housed in a tower top. The concentration factor of the radiation reaches values of 1000 and more. With its help, the radiation is converted into heat, which is dissipated in order to then drive a generator by means of steam generation via a conventional turbine .
Heliostats can also be used for lighting purposes. The light is directed onto parts of the building, light shafts or vehicle tunnels that are otherwise in the dark. A total of four heliostats are used on the Italian A6 motorway near the village of Painissolo to illuminate short tunnel sections. On the roof of the Nord / LB administration building in Hanover, numerous heliostats ensure that offices facing away from the sun receive more daylight. Heliostats are increasingly being used to artificially illuminate places with sunlight that are not exposed to direct sunlight in the winter months due to their valley location. Such a mirror has been in operation in Viganella, Piedmont, since 2006 . In 2013 a similar system was set up in Rjukan , Norway .
Heliostats were also used as a light source for light microscopic applications with high brightness requirements, before sufficiently strong artificial light sources were available from the 20th century.
- Chapter 4.1.1 Heliostats. In: M. Mohr, P. Svoboda, H. Unger: Practice of solar thermal power plants. Springer, Berlin / Heidelberg 1999, ISBN 978-3-642-63616-5 , pp. 122-135.
- Kaltschmitt, Streicher, Wiese (eds.): Renewable energies: system technology, economic efficiency, environmental aspects. Springer-Vieweg, 5th edition from 2014, ISBN 978-3-642-03248-6 :
- Heliostat. Pp. 294-296.
- Heliostat fields. Pp. 296-299.
- H. Weik: Expert Praxislexikon: Solar energy and solar technologies. 2nd revised edition from 2006, expert Verlag, ISBN 978-3-8169-2538-5 :
- Heliostat. P. 132.
- Heliostat fields. P. 132.
- Description on Lumena.ch
- further information on heliostats
- Do-it-yourself projects for heliostats
- The German Museum of Technology in Berlin uses heliostats for lighting and in the attached Science Center Spectrum for experiments on the subject of light and vision
- Pieter van der Star: Daniel Gabriel Fahrenheit's Letters to Leibniz and Boerhaave. Leiden 1983, p. 7.
- Thomas B. Greenslade, Jr .: Heliostats. Retrieved February 11, 2008 .
- heliostat de Silbermann. (No longer available online.) École polytechnique , formerly in the original ; Retrieved May 8, 2008 (French). ( Page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
- Wolf, C .: Description du sidérostat de L. Foucault. (No longer available online.) Annales scientifiques de l'École Normale Supérieure Sér. 2, 1 (1872), p. 51-84, archived from the original on June 6, 2014 ; Retrieved May 10, 2008 (French). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- Henri Chamoux: Inventaire des instruments scientifiques anciens dans les établissements publics - Héliostat de Silbermann. Laboratoire de recherche historique Rhône-Alpes, accessed on June 23, 2014 (French).
- Martina Flamme-Jasper: NORD / LB Hanover - Behnisch, Behnisch & Partner. Hatje Cantz, Ostfildern-Ruit, 2002. ISBN 3-7757-1231-3 . Pp. 72-79.
- Heliostats: Norwegian community diverts sunlight . Spiegel Online . July 1, 2013. Retrieved July 18, 2013.