Parabolic trough concentrators for low enthalpy processes

Five parabolic trough concentrating solar collectors were designed, constructed, evaluated, and operated in order to generate hot water and low-enthalpy steam. Three of them were designed with a rim angle of 90° and the other two have a rim angle of 45°. All of them were designed with a solar collector area close to 2.6 m2 and a concentration ratio close to 14. The purpose of the size of both designs is to provide modular solar collectors that can be operated in a serial or parallel arrangement depending on the thermodynamic availability that is required. All elements of both designs are made of aluminium with the aim of having a light but robust structure that has good resistance to outdoor conditions. In the construction of both collectors there is no need for sophisticated machinery or skilled labour and during the assembly only hand tools are required. The design of both collectors considers unshielded receivers and without glass cover in order to reduce manufacturing and transportation costs. A low temperature test for both designs was conducted according to the Standard ASHRAE 93-1986 (RA 91). Thermal and optical analyses were carried out for each collector, and the efficiency curve for each concentrator one was estimated. A peak efficiency of 35% was obtained for solar collectors with a rim angle of 45° and a peak efficiency of 67% was estimated for collectors with a rim angle of 90°. On the other hand, a serial arrangement using the five collectors was assembled and evaluated in order to obtain low-enthalpy steam generation. In preliminary results it was possible to obtain a temperature close to 110 °C with low steam quality. The overall efficiency of the arrangement system was evaluated to be between 25 and 45%. The cost of both designs is close to 170 US$/m2.