Comparative measurements and theoretical modelling of single- and double-stage heat pipe coupled solar cooking systems for high temperatures

The measured and calculated properties of three collector-based solar cooking systems are described. Two of them have a direct single-stage heat-pipe coupling between collector and oven plate. The first one is heated by a flat-plate collector with 2.33 m 2 aperture area, while the second system is heated by one module of a Sydney vacuum-tube collector with 1.085 m 2 of aperture area. The third system with a double-stage thermal coupling is heated by two Sydney modules. Extensive outdoor measurements were conducted in Marburg (latitude 50.8° N) proving the operational stability of the different heat pipe systems even on days with rapidly varying irradiance. On clear days the shortest heat-up times from 40 to 99.5°C for 5 kg water were 36, 32 and 17 min corresponding to an average thermal power of 580, 653 and 1220 W for the three systems, respectively.