Annual Report 2006 - Plataforma Solar de Almería

PLATAFORMA SOLAR DE ALMERÍA
Motivation: At the present time a wide variety of solar hot water collectors are
available. Although some of their characteristics are different, all of them
have in common a working temperature clearly below 175ºC. The selective
coatings usually used for these collectors at present are economically manufactured,
although their optical and thermal properties are not excellent. Improving
the quality of these coatings and their optical properties is of great
commercial interest if it can be achieved without significantly raising the cost
of manufacture. CIEMAT-PSA has long experience in the field of selective
coatings for solar absorbers manufactured using the Sol-gel technique. This
experience can be applied to the development of solar absorbers with better
properties than those currently used in low-temperature solar collectors without
prohibitively raising the cost. Solar collectors with a better selective coating
without increasing the price will no doubt rank well on the market.
Purposes: Develop an advanced solar collector absorber with a working temperature
below 200ºC manufactured using the Sol-gel technique, which is
industrially competitive with currently available low-temperature coatings.
Achievements in 2006: Although a good advanced coating had already been
achieved in 2005, its quality/cost ratio was not good enough for commercial
applications. Therefore, work done by CIEMAT-PSA on this project in 2006
concentrated mainly on improving the properties of this coating.
A strong effort was devoted to optimizing Cu-Mn spinel deposition, which is
the basis of the new absorbent coating developed by CIEMAT-PSA for industrial
manufacture. It was attempted to improve coating homogeneity to avoid
pore formation by optimizing the substrate cleaning method and solution
composition, particularly, the concentration of additives.
Increased additive concentration in the solution composition used for
manufacturing the new coating was observed to improve the homogeneity of
the films by reducing the amount of undesirable pores formed. The Cu-Mn
spinel precursor solution was also optimized, increasing the extraction speed
up to 45 cm/min and the SiO 2 anti-reflective layer to 23 cm/min, with a mean
solar absorptance of 0.940 and emissivity at 100ºC of about 0.06-0.08.
Accelerated aging tests were performed in a weathering chamber to evaluate
the durability of the new coating following the IEA Solar Heating and Cooling
Program Task X procedures (Standard ISO/DIS 12952), which include
temperature (thermal treatment at 250ºC for 200 hours) and humidity
(treatment in 40ºC condensation for 600 hours) requirements. The performance
coefficient for the AR layer with Cu-Mn spinels was less than 0.05, and
was therefore validated by the standard’s criteria.
Publications: [3.2] - [3.3]
3.2.5 FASOL
Design and development of a parabolic-trough thermal collector
for process heat
Participants: CIEMAT and, and occasionally, SMBs
Contact:
Esther Rojas, esther.rojas@ciemat.es
Funding: 225 000€
Background: Several projects financed by the European Commission (POSHIP,
PROCESOL I and II) have shown the enormous potential for solar thermal
energy in industrial processes requiring temperatures from 60ºC to 300ºC.
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