Primary reflectors

The primary reflectors are thin, back-silvered glass attached to an ultralightweight steel truss. The glass is supported to withstand an 80 mph wind. The starting point for manufacture is an 11-foot square of flat window glass (float glass), fire-polished on both front and back sides. The glass is molded into an exact paraboloid by a process developed by the Steward Observatory Mirror Lab at the University of Arizona. Once cooled, a reflective film of silver is applied to the back.

The longevity of back-silvered glass reflectors has been proven in solar thermal trough reflectors in the Mojave desert. After 20 years of exposure to the sun, these retain their original high reflectivity of 93.5%. The track record for mechanical stability is excellent, with only 1 in 300 trough reflector panels damaged each year by wind and hail.

The glass shaping process now being implemented at the Mirror Lab as a batch process with one-day turnaround is designed to be scalable to high-speed production. Initially, REhnu will build three duplicate batch facilities to make 3 reflectors/day (2 MW/year). For very high volume production, the shaping and silvering steps will be incorporated into the production line of a dedicated float-glass factory. With a daily output of 700 tons of glass, the factory will yield one reflector every 12 seconds, enough to build six 1 GW farms each year.

Experimental reflectors made at the University of Arizona

Steward Observatory Mirror Lab has developed the manufacturing process and tested it in experimental dishes like this one, 2.5 m in diameter. REhnu’s 3.1 m square reflectors will be made from a single sheet of glass by a similar process.

This hole was melted in ¼” thick steel in 15 seconds at the focus of an experimental 3 m dish reflector.