Development of a volumetric solar thermal absorber

Thermal collectors are the central part of a solar energy system. Within the collector, the absorber is the most essential component and contributes about 46% to the total costs of a collector. These absorbers are typically based on the sheet-pipe design. Hence, further improvements of the absorber performance are hard to carry out without increasing costs and weight for the collector significantly. Against this background, current absorber designs are investigated and new possibilities are selected, calculated, optimised and experimentally tested. An analysis of former and current absorber designs is carried out. It can be seen, that during the energycrisis more innovative systems were developed, while in recent years the state-of-the-art is based on the sheet-pipe design. A lot of different connections are applied to join the header and riser pipes to the selectively coated absorber sheet. However, weaknesses in manufacturing and operation as well as those regarding efficiency and costs make it hard to improve this design. In an engineering design process the absorber is analysed and together with a requirements list, new approaches have been developed. New absorber materials are suggested as well as absorber design possibilities for fluid and heat conduction. Based on the solutions several concepts are derived, which are evaluated to select the best for further optimisation and experimental testing. In the course of fluid simulation, the chosen concepts are modelled and optimised regarding flow distribution. This approach is novel as former absorber designs lack homogenous flow, or the distribution was optimised experimentally. The simulation results show a more equal flow distribution for the concepts than is the case for the state-of-the-art absorbers. Calculations of the collector efficiency factor show superior values for volumetric absorbers, while typical values are gained for sheet-pipe-absorbers. Infrared, pressure drop and collector efficiency tests confirm the results of simulation and calculation for both the new designs and the state-of-the-art. The developed absorber with corrugated pattern shows a more homogeneous flow distribution and a higher measured collector efficiency factor than typical state-of-the-art absorber.