The paper presents the final results of our prototype investigations regarding the performance and reliability of a high efficiency flat plate collector with a gas-filled low-e double-glazing as transparent cover. The measured efficiency of an optimized prototype results in an increase in efficiency of 70 % at a temperature difference of 60 K (G = 500 W/m2) compared to a standard flat plate collector. The effect of additional antireflecting coatings and different gas fillings of the glazing is analyzed by prototype measurements. As the heat losses of the collector are significantly reduced by the low-e glazing, a stagnation temperature of 265 °C was determined at the absorber plate experimentally. The collector components have to withstand these increased temperature loads. Test and assessment methods for the long term stability of the hermetically sealed double-glazing against high temperatures and the combination of temperature and UV-radiation were developed and performed successfully. Further, the reliability of four prototype collectors was confirmed by a one-year outdoor-exposure test. A simplified economic analysis resulted in an optimum operating range for the collector of 80 °C to 110 °C compared to commercially available flat plate and evacuated tube collectors. As the main result of the research project, a new flat plate collector with a significantly increased performance and an experimentally proved reliability was developed up to a prototype status, which can be transferred to industrial production.