HYDRA RoS: Large-Scale Production of a Vacuum Tube Collector With an Innovative Hydraulic Design - Robust Manufacturing Process by Rotary Draw Bending and Induction Brazing

Solar thermal systems, especially in district heating networks, are crucial to achieving climate neutrality in Germany's heat supply by 2045. The joint project HYDRA RoS, funded by the Federal Ministry for Economic Affairs and Climate Protection (Germany), focuses on the development of high-efficiency solar thermal collector concepts for series production with the aim of optimising material and energy use, field hydraulics and control technology. A key component of the project is the use of vacuum tube collectors with CPC (Compound Parabolic Concentrator) reflectors, such as those of Ritter XL Solar. These collectors have proven to deliver high heat yields and can easily reach temperatures of up to 120 °C. The project introduced a new hydraulic register design for these vacuum tube collectors, which improved efficiency and enabled new field interconnection options. However, the new design presented some manufacturing challenges. Finite Element Analysis (FEA) was used to improve the rotary draw bending process and minimise cross-section reductions. Experiments and studies were carried out to achieve a leak-proof connection between the drum connector and the tubes. Computational Fluid Dynamics (CFD) simulations were used to model thermal and fluid dynamic behaviour to guide design optimisation. Prototype collectors were fabricated and tested under controlled conditions to assess their hydraulic and thermal performance. The results show that the new design achieves a significant lower hydraulic loss with the same or a little bit higher thermal efficiencies comparable to the current Ritter XL collector series, while significantly simplifying the manufacturing process.