A Heliostat is a device that tracks the movement of the sun. It is typically used to orient a mirror, throughout the day, to reflect sunlight in a consistent direction. When coupled together in sufficient quantities, the reflected sunlight from the heliostats can generate an enormous amount of heat if all are oriented towards the same target. It was originally developed as an instrument for use in surveying, allowing the accurate observation of a known point from a distance.

Heliostats have been used for sunlight-powered interior lighting, solar observatories, and solar power generation.

The simplest heliostat devices use a clockwork mechanism to turn the mirror in synchronisation with the rotation of the Earth. More complex devices need to compensate for the changing elevation of the Sun throughout a Solar year. Even more advanced heliostats track the sun directly by sensing its position throughout the day.

Use in power production

Using the experience from the earlier U.S. 10MWe experimental solar power plants (Solar One and Solar Two in Barstow, CA), the Solar Tres project in Spain is building a 15MW solar power plant with a 16 hour, 600 MWh thermal power storage system based on molten salt (sodium).

Use in interior lighting

The heliostat reflects the sunlight onto the transmission system. This is typically a set of mirrors that direct the reflected sunlight into the building. Fiber optic cabling has also been used as a transfer mechanism. Various forms of commercial products have been designed for the point of termination (the "light bulb").

Calculating the position of the sun in an "open loop" heliostat

Main article: Sun, Calculating the position of the Sun

Since the path of the sun across the sky varies through the year, a completely automatic heliostat must be guided by continuous calculations. The National Renewable Energy Laboratory has released its Solar Position Algorithm (SPA) with complete documentation.

See Also

Solar Power

External Links

• Field of 63 heliostats at the Odeillo Solar Furnace
• Solar Furnaces at Odeillo
• A large field of heliostats were used at the Solar One and Solar Two experimental solar power plant in Barstow, CA. Includes video.
• The Solar Tres project.