A parabolic-trough collector for cleaner industrial process heat

Despite its huge potential for increasing sustainability, the use of solar energy in industry is still scarce. Many industrial thermal demands range from 120 to 250 °C, which are difficult to supply using solar energy because of the lack of specific solar thermal conversion devices. Parabolic-trough collectors (PTCs) suitable for these applications should be small due to space constraints. This study addressed the specific design of a small-sized industrial PTC with a flat transparent cover in the aperture plane. The cover is critical to the success of this technology in industrial environments, because it ensures protection of the rest of the collector components, which may have very poor durability. The cover also increases rigidity and makes cleaning easier. Three different PTCs with the same basic geometry were analysed by numerical simulation. Two of them had glass receiver tube covers, one with an additional flat cover in the aperture plane and the other one without it. The third one had an uncovered receiver but a flat cover in the aperture plane. Simulations showed that the collector design with a flat glass aperture cover only has the highest thermal losses. The design with both flat glass aperture and tube covers has lower thermal losses than the one with a glass tube cover only. However, optical-geometric efficiency is inferior and, as a result, overall efficiency is slightly lower. In addition, thermal insulation on the reflector back is not recommended.