Heliostat: history, operation and uses

You know when as a child you played with mirrors or other reflective surfaces to direct the sun's rays into someone's eyes? What rascals! Well, in those circumstances you were taking advantage of the principle on which aheliostat.

UpWikipediawe read that the first mention to aheliostatdates back to 1742 in a work by the Dutch physicist Willem's Gravesande but in reality the invention ofheliostatit has deeper roots, dates back to about a century earlier and is entirely Italian. The device was invented byGiovanni Alfonso Borelli, mathematician and astronomer born in Naples in January 1608.

L'heliostatit is constituted, in its essential part, by a mirror which is rotated on an axis parallel to the terrestrial one with an angular velocity equal to half the apparent one of the sun; the rotary motion occurs by means of a clockwork movement.

The mirror, which has the purpose of directing the sun's rays, is not rigidly fixed to the rotation axis but is connected in such a way as to allow different movements thanks to which it is possible to "intercept" the light beam to be projected.

The various models of heliostat they differ mostly in this connection system (between mirror and axis) or in the shape of the mirror. Given its function, it can be said that theheliostatis the oldest form ofsolar tracker.

How is the heliostat used?

The heliostat is used in various sectors:
-it is very useful in solar physics, since it is not always possible to equatorially mount demanding instruments such as the telescopes themselves. L'heliostatit is an essential part of tower telescopes, in which the image of the star must always be observed in the mirror of the heliostat.


-it is fundamental in the sector of renewable energies, in photovoltaic systems it is used assolar tracker. In the asolar thermaltheheliostatsthey continuously reflect sunlight to heat a collector, in fact thermal solar power plants can be considered gods heliostatic fields(fields of heliostats). Again, in France (in the Eastern Pyrenees) a system ofheliostatsto heat a "Solar oven" that reaches the incredible temperature of 3,500 ° C (solar furnaces of Odeillo).

-in the sector ofgreen building, especially in thebioclimatic architecture, theheliostatsthey can be used to reflect the light intensity on the north facade of the house. An excellent strategy for heating the house in winter so as to achieve the ambitious model of thepassive house.

Minor projects use the principle ofheliostatfor the construction of mobile kitchens: the sun as a natural cooking method, is an exampleLapin Kulta Solar Kitchen.

In the residential setting, aheliostatit can be used to increase the power of the domestic photovoltaic system for the production of electricity orsolar thermal panel for the production of domestic hot water and to heat the home.


Considering the complexity of the projects (heliostatic fields, solar towers, solar furnaces…), manyheliostatsthey are not guided by a random mechanical motion or by the mechanism of a watch but are controlled by sensors or, now more commonly, by software developed ad hoc. Generally, all the mirrors that make up the heliostat fields of a solar-thermal power plant are managed by a single computer.

The surface of the mirror must be chosen according to the uses for which it is to be used: generally it is a metal surface (silver) or even a common mirror when you want to use theheliostat only as an intense source of light.

In the photo above, the ambitious Californian "Solar Two" project, a solar-thermal field where each heliostatic mirror reflects the sunlight continuously on the receiver placed on the tower.


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