A heliostat is a device that basically consists of an animated mirror of a certain rotational movement and that serves to direct the rays of the Sun in a certain direction, despite the movement of the Earth with respect to the Sun.
In the past, in many optical experiments it was necessary to pass a beam of sunlight reflected by a mirror through a series of instruments carefully installed one after another on a table or horizontal bench. But the Sun has an apparent continuous movement, which describes during its visible daily circulation around the axis of the world one of the small circles of the celestial sphere.
In the days of the spring and autumn equinox, this circle coincides with the celestial equator, as a result of which the cone described by the ray becomes a plane. On the contrary, in summer and winter, during solstices, these circles will be the smallest, and the cones described by the rays, the most acute. In accordance with such movement of the sunbeam during the daytime movement of this luminaire, heliostats were organized. Heliostats are devices in which the clock mechanism rotates the mirror so that the reflected beam of it maintains its original direction for a long time.
How is the design of a heliostat?
The design of a heliostat should be as economical as possible to compete economically with other non-renewable energy sources.
From the initial investment of a solar power plant, the cost of heliostats is between 30 and 50% of the initial capital. For this reason, it is necessary to lower manufacturing costs so that the cost of the kilowatt hour is as competitive as possible to the cost of the electricity generated through the combustion of fossil fuels or nuclear energy. In addition to the cost, the percentage of solar reflectivity and environmental durability are factors that must be taken into account when comparing heliostat designs.
A simple alternative is for the mirror to rotate around a polarly aligned primary axis, driven by a mechanical mechanism, often mechanical, at 15 degrees per hour, compensating for the rotation of the earth with respect to the sun. The mirror is aligned to reflect solar radiation along the same polar axis in the direction of one of the celestial poles.
There is a perpendicular secondary axis that allows the occasional manual adjustment of the mirror to compensate for the change in the sun's decline with the seasons. The unit's clock settings can also be adjusted occasionally to compensate for changes in the time equation.
The target can be located on the same polar axis that is the primary axis of rotation of the mirror, or a second stationary mirror can be used to reflect the light from the polar axis to the target, wherever it is. This type of mounting and mirror unit is often used with solar cookers, such as Scheffler reflectors. For this application, the mirror can be concave, to concentrate sunlight in the cooking vessel.
What applications do heliostats have?
The heliostat is used in various applications for different reasons:
- Solar energy. In the solar thermal plants of the heliostat, it is used to concentrate the sun's rays at a specific point or area where the solar collectors are located.
- Astronomy. In astronomy this mechanism is used to observe the Sun without having to vary the orientation of the observation apparatus.
- Geodesy. In the field of geodesy, the heliostat is used to transmit long-distance light signals.
- In the case of solar thermal energy, the temperature can be increased considerably. In this way it is easier to obtain steam to be able to drive a steam turbine and generate electricity.
- In the case of photovoltaic solar energy, it allows more solar radiation to be concentrated in the same photovoltaic module. In this way it is possible to increase the solar yield.
On the other hand, these advantages must be contrasted with the inconvenience of increasing the investment of the solar installation.