Thermal performance of flat plate solar collectors with sheet-and-tube and roll-bond absorbers

• Roll-bond solar collectors use an aluminium absorber plate with integrated channels.
• Efficiency measurements on glazed flat plate roll-bond solar collectors are reported.
• A new numerical model of flat plate collectors is presented and validated.
• The effects of absorber coating and channels number are discussed.
• The effect of ambient temperature on thermal efficiency curve is discussed.

A prototype of glazed flat plate solar collector with roll-bond absorber is presented and its performance is experimentally characterized. Differently from common sheet-and-tube collectors, in the present prototype the channels for the liquid are integrated in the roll-bond absorber plate. Measurements of thermal efficiency are reported for two samples of the prototype, one with a black coating on the absorber and the other with a semi-selective coating. Efficiency test runs have been performed in both steady-state and quasi-dynamic conditions, according to the standard EN 12975-2 (EN 12975-2. Thermal solar systems and components – solar collectors – part 2: test methods. Brussels: CEN; 2006). The efficiency measurements are compared with those taken for standard glazed flat plate collectors with sheet-and-tube absorber under the same test conditions. The experimental results show that the roll-bond absorber can provide higher performance. Besides, the thermal efficiency can be further increased and this is shown by means of a numerical model. The model is experimentally validated for standard flat plate collectors with sheet-and-tube absorber and for roll-bond collectors.