This is a new and interesting idea for low cost, high temperature solar collectors.
The summary from Jeroen's thesis:
Rotating solar boilers are a new type of solar collector. The boilers consist of two concentric tubes. The inner tube absorbs sunlight and boils water. This tube is called the absorber. The outer transparent tube is filled with air and called the cover. The boilers rotate at 60 rpm to completely prevent convection in the insulating air layer in between the tubes.
Three prototypes were built using different materials of construction. Absorbers made of painted galvanized steel and sputtered copper were evaluated experimentally. The sputtered coating proved to be superior to the paint.
The boilers typically produced 1 kW of steam at 100oC. The efficiencies of the different boilers were measured. A model was developed to predict their performance. The model predicts an efficiency of 68%. For the most advanced prototype the maximum experimental efficiency with reflectors was 46%. The discrepancy between these values may be due to fouling of the selective surface, misalignment of the reflectors or the error in measurement of steam production.
This prototype was fitted with a clean absorber and measurements without reflectors were taken. The model then predicts an efficiency of 62%. An experimental efficiency of 61% was measured.
Economical analyses were performed as well. These analyses showed that any solar boiler should be very lightweight in order to reduce material cost. The rotating solar boiler can be lighter and cheaper than conventional flat plate collectors and evacuated tube collectors.
In the chapter on future work a completely inflatable rotating solar boiler is proposed.
This boiler can have a pay back time of less than 1 year.