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.