A novel design for a cheap high temperature solar collector: The rotating solar boiler

In this work a novel type of high temperature solar collector is designed: the rotating solar boiler. This rotating solar boiler consists of two concentric tubes. The inner tube, called absorber, absorbs sunlight and boils water. The outer transparent tube, called cover, is filled with air. The boiler rotates to completely prevent convection in the insulating air layer in between the tubes. In this way, the heat loss is reduced considerably resulting in a solar collector that is more efficient than conventional flat plate solar collectors. The prototype built measured 1.20 m length and 0.50 m diameter (illuminated area is 0.60 m2) for the copper absorber with high performance sputtered coating. The cover with a diameter of 0.90 m was made of transparent polyvinylchloride film. The rotation speed was 60 rpm. The efficiency was 61% and the boiler delivered 0.34 kW of 100°C steam at an ambient temperature of 7°C. A model was developed to predict the performance of the prototype. The model predicts an efficiency of 62%, which is in agreement with the measured experimental efficiency. An economical analysis was performed as well. The rotating solar boiler is much cheaper than conventional evacuated tube collectors, especially because the rotating solar boiler is lightweight.