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A device with a flat mirror that reflects sunlight onto a specific target, and rotates during the day to compensate for the sun’s movement across the sky. The movement of the heliostat is usually controlled by a computer. It is used in a central tower solar power plant, where an array of heliostats reflects the sun’s rays onto an absorber on a tall column to achieve very high temperatures. The heliostat principle can also be used by photovoltaic panels, which follow the sun during the day to increase their efficiency.