The United States Department of Energy’s solar thermal program is testing an innovative concept for the heliostats used in a solar central-receiver power plant: replacing the familiar glass mirrors with stretched-membrance reflectors. Because of their simplicity and lighter weight, heliostats using membrane reflectors have the potential to cost significantly less than glass-mirror heliostats. To assess the optical performance of these new heliostats, a 50m2 prototype mirror module, representative of a commercial scale design, was built and installed for testing at the Central Receiver Test Facility. The results of the testing program are presented, including the optical performance of the stretched-membrane mirror, the performance of the mirror’s focus control system in windy conditions, the performance of the defocus system, and the durability of the reflective film.

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