Annual Report 2006 - Plataforma Solar de Almería

CONCENTRATING SOLAR SYSTEMS UNIT
bility of the films, a method has been developed for replacing the hydrophilic
–OH groups on the surface with Si-CH 3 groups, which makes hydrophobic
films water-resistant while conserving excellent optical properties.
Accelerated aging studies in a weathering chamber done at the PSA demonstrate
the effectiveness of the process, finding variations in solar transmittance
of less than 0.8% after 1500 hours at 40ºC and 100% relative humidity
while there was more than a 3% drop in transmittance in the untreated antireflective
films after 200 hours of testing.
High-temperature selective absorbers
In 2006, the optical properties and thermal durability of the hightemperature
selective absorber were optimized. Solar absorptance of 0.96
and thermal emissivity at 500ºC of 0.14 were achieved.
No optical or layer-adherence degradation was found in the coating deposited
on AISI 304 stainless steel after a two-month thermal durability test in a
furnace at 500ºC air temperature.
A pre-industrial procedure for manufacture of the absorber is being developed
and it has been observed that better optical properties and more homogeneity
are achieved if the films are dried at a certain temperature for a few
seconds while the precursor solution sample is being extracted.
To date, the maximum size of flat samples prepared has been
100x100 mm. These samples have had excellent homogeneity and optical
properties. Next year, tubes of different diameters up to 500 mm long will be
coated.
Transmittance (%)
100
90
80
70
60
Publications: [3.1]
Borosilicate glass substrate Ts:0,917
AR film as deposited Ts:0,962
AR film after condensation test 1500 h. Ts: 0,955
500 1000 1500 2000 2500
λ (nm)
Hemispherical Reflectance
100
90
80
70
60
50
40
30
20
10
0
250 500 750 1000 1250 1500 1750 2000 2250 2500
Wavelength (nm)
Figure 3.3 Glass transmittance with and
without the AR film, before and
after 1500 h in weathering
chamber
Figure 3.4
Hemispherical reflectance of the
high-temperature absorbers
3.2.4 Advanced low-temperature absorber coatings
Participants: CIEMAT-PSA, WAGNER Solar
Contact: Angel Morales, angel.morales@ciemat.es
Total Budget: 161 500 €.
Duration: March, 2005 - June, 2008
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