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Abstract
5. Summary and Conclusions
The utilization of solar energy as an alternative source of fossil fuels is due to its outstanding characteristics of being renewable and clean energy.
Egypt enjoys a moderate climate with maximum hours of sunshine around the year and highest sunshine intensity. The average peak h/day is the highest worldwide. These merits qualify Egypt to utilize solar energy as friendly environment energy especially in rural areas.
Solar energy can be converted into heat or electricity through photo-thermal devices which are mainly flat plate collectors. For improved performance of these collectors, special black coatings (selective coatings) are used. Efficient selective coatings must exhibit high visible absorptance () and low infrared emittance (). This will increase the absorption of incident solar energy and minimize thermal losses due to re-radiation. Thus, the performance of selective black coatings is governed by / (S) ratio.
Selective absorber surface coatings are categorized into three types: low, medium and high-temperature surfaces according to the surface temperature range of the absorber material. Black nickel, black chrome and black cobalt are the most recognized selective coatings. The coatings are applied on a metal substrate usually of high thermal conductivity such as copper or aluminum. There are varieties of techniques to produce selective black absorber coatings namely: electrodeposition, chemical conversion, metal pigmented alumina, paint coatings, sol–gel process….etc
The performance and life-time of black coatings depend mainly on temperature and humidity. Both of the two factors can cause degradation due to oxidation of metallic species of the deposits. This thesis covers the preparation and optical evaluation of conventional sulfur–bearing black nickel coatings as a basic comparison for the performance of selective absorber surfaces.