Antireflection pyrex envelopes for parabolic solar collectors

Technical Report · Sat Jan 01 04:00:00 EST 1983

OSTI ID:6345929

McCollister, H L; Pettit, R B

Parabolic trough solar collectors utilize glass envelopes around the receiver tube in order to reduce thermal losses. Antireflective (AR) coatings applied to the envelope can potentially increase the solar transmittance by 0.07. An excellent AR surface can be formed on Pyrex (Corning Code 7740 glass) by first heat treating the glass to cause a compositional phase separation. After heat treating, a surface layer is removed using a pre-etch solution of aqueous ammonium bifluoride. Finally the AR layer is formed by etching in a solution containing hydrofluorosilic and ammonium bifluoride acid. Processing parameters studied included the phase separation temperature and heat treatment time, the pre-etch time, and the etching bath temperature and time. AR-coated samples with solar transmittance values >0.97, as compared to a value of 0.91 in untreated samples, were obtained for a range of heat treatment temperatures from 560 to 630/sup 0/C. The phase separation time and temperature interact so that at 630/sup 0/C short times are required (3 hours) while at 560/sup 0/C longer times are necessary (24 hours). Optimum values for the other processing parameters are 12 to 18 minutes in the pre-etching bath, and 5 to 10 minutes in the film forming bath when maintained between 35 and 45/sup 0/C. Application of this process to full scale 3 m long x 6 cm diameter Pyrex envelopes was successful in producing solar transmittance values greater than or equal to 0.97.

• Research Organization: Sandia National Labs., Albuquerque, NM (USA)
• DOE Contract Number: AC04-76DP00789
• OSTI ID: 6345929
• Report Number(s): SAND-82-1970C; CONF-830405-18; ON: DE83008183
• Country of Publication: United States
• Language: English

Related Subjects

14 SOLAR ENERGY
141000* -- Solar Collectors & Concentrators
ANTIREFLECTION COATINGS
BOROSILICATE GLASS
COATINGS
CONCENTRATING COLLECTORS
DATA
EQUIPMENT
ETCHING
EXPERIMENTAL DATA
GLASS
HEAT TREATMENTS
INFORMATION
LIGHT TRANSMISSION
NUMERICAL DATA
OPTICAL PROPERTIES
OPTIMIZATION
PARABOLIC COLLECTORS
PARABOLIC TROUGH COLLECTORS
PHYSICAL PROPERTIES
PYREX
SOLAR COLLECTORS
SOLAR EQUIPMENT
SOLAR RECEIVERS
SPECTRAL REFLECTANCE
SURFACE FINISHING
TUBES