Optical durability testing of candidate solar mirrors Page: 4 of 61
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Optical Durability Testing of Candidate Solar Mirrors
Gary Jorgensen, Cheryl Kennedy, David King, Kent Terwilliger
Durability testing of a variety of candidate solar reflector materials at outdoor test sites and in
laboratory accelerated weathering chambers is the main activity within the Advanced Materials task
of the Concentrated Solar Power (CSP) Program. Outdoor exposure testing (OET) at up to eight
outdoor, worldwide exposure sites has been underway for several years. This includes collaboration
under the auspices of the International Energy Agency (IEA) Solar Power and Chemical Energy
Systems (SolarPACES) agreement. Outdoor sites are fully instrumented in terms of monitoring
meteorological conditions and solar irradiance. Candidate materials are optically characterized prior
to being subjected to exposure in real and simulated weathering environments. Optical durability is
quantified by periodically re-measuring hemispherical and specular reflectance as a function of
exposure time. By closely monitoring the site- and time-dependent environmental stress conditions
experienced by the material samples, site-dependent loss of performance may be quantified. In
addition, accelerated exposure testing (AET) of these materials in parallel under laboratory-controlled
conditions may permit correlating the outdoor results with AET, and subsequently predicting service
lifetimes. Test results to date for a large number of candidate solar reflector materials are presented in
this report. Acronyms are defined in Table 1.
Based upon OET and AET results to date, conclusions can be drawn about the optical durability of
the candidate reflector materials. The optical durability of thin glass (from Naugatuck, Schlaich,
Bergermann und Partner, or Steinmuller), thick glass (from ATS or Flagsol), and two metallized
polymers (SA-85, ECP-305+) can be characterized as excellent. The all-polymeric construction,
several of the aluminized reflectors (Alanod's improved product, materials from Metalloxyd), and
a metallized polymer (ECP-305) can be characterized as having intermediate durability and require
further improvement, testing and evaluation, or both. A metallized polymer (SS-95), metallized
fluoropolymers (until specularity can be sufficiently improved), and constructions in which
adhesives are in direct contact with a silver reflective layer can be characterized as poor and do not
warrant further consideration for solar applications. Recently, a number of new promising
constructions have been identified including: several front-surface mirrors under an ongoing
Sun+Lab subcontract and prepared by Sun+Lab staff, a new all-polymeric construction using
improved interlayer resins and incorporating UV screens; a newly available commercial solar
reflector material called SolarBrite 95; and a novel commercial laminate construction co-invented
by Sun+ Lab staff and industry collaborators.
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Jorgensen, G.; Kennedy, C.; King, D. & Terwilliger, K. Optical durability testing of candidate solar mirrors, report, March 24, 2000; Golden, Colorado. (digital.library.unt.edu/ark:/67531/metadc711115/m1/4/: accessed January 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.