A standardised concept for a solar thermal system with significantly reduced costs compared to conventional solar thermal systems is demonstrated with five different field systems. The cost reduction is achieved through standardisation of the system, the use of drainback, a simple solar buffer tank and low-cost components such as pre-insulated plastic pipes. The system concept is optimised for retrofitting hot water generation in multi-family houses. For this P+D project, findings from previous research projects are being implemented and the system concept is being brought towards market maturity.