Solar energy has become essential alternatives for the conversion and production of energy to replace fossil fuels particularly from the current energy and geopolitical crisis by using different solar collector. Black coated steel are used in a thermal solar collector as heat-absorbing materials to convert solar radiation into heat. It constitutes one of the most important parameters of the thermal collector conversion. In order to obtain better performance; the absorber material systems consist of a particular coating to obtain the best selectivity ratio, so solar absorption factor/infrared emission factor ratio by improving some properties such as the solar absorption factor α (or absorptivity) and the emission factor ε (or emissivity). To study the influence of paint surface quality and roughness on thermal performance, a series of experimental tests were carried out on a prototype of a flat air solar collector designed at the renewable energy research center in Adrar (Algeria). Mathematical models were introduced to estimate the hourly diffuse solar fraction to improve the predictability of solar resources at the same site. The results showed that the surface characteristics of the absorber material such as reflectivity, color, and roughness and conversion temperature exert an influence on the absorption properties of the infrared radiation absorbed or emitted and therefore the heat emitted. The absorber surface having a black cover and a rough surface presents better absorption characteristics compared to a clear cover and a smooth surface. In rough surface, a photon that is reflected is likely to need several reflections before escaping. Thus, the likelihood of it being absorbed increases. Roughness therefore leads to a decrease in surface reflectivity.

surface quality; roughness; back coated steel; heat transfer; solar collector prototype; modelization