Investigation of new integrated solar thermal absorbers by means of a 2-D model

Both cost reduction and flexibility of shape are two important challenges for solar thermal collectors. Classical fin-and-tube absorbers of copper and/or aluminum produced in a welding or soldering process have low cost reduction potential. New sheet metal forming processes like roll-bonding, hydroforming or deep-drawing are promising and in the focus of several projects of Fraunhofer ISE [1, 2, 3]. A new approach of Fraunhofer ISE is to develop multifunctional solar collectors based on an Ultra High Performance Concrete (UHPC). The aim of this approach is to obtain flexible, cost-effective and sustainable collectors which can be integrated into building façades. New manufacturing methods and materials require new integrated absorber designs and adapted analytical models. Using 1-D absorber models [4] it could be shown that in case of UHPC its low thermal conductivity and the resulting low collector efficiency factor F' can be overcompensated by adapting the absorber design. However, this simplified model does not consider 2-D heat transport effects. Therefore a 2-D model was set up using the numerical program OpenFoam®. Simulating F' of the classical absorber designs the model shows very good correspondence with the 1-D model and can now be used to calculate F' also for more complex absorber structures. In the future the model can be extended to investigate also the fluid characteristics depending on channel cross-sections.