Life cycle assessment and energy-CO2-economic payback analyses of renewable domestic hot water systems with unglazed and glazed solar thermal panels

The economic payback time, if compared with natural gas boiler, is in the range 9-11 years/8-13 years for the system with unglazed/glazed panels, respectively; if compared with the electrical boiler, it is in the range of 3-4 years for the system with unglazed panels and 4 years for that with glazed panels. The different national costs of natural gas and/or electricity play an important role in the economic payback times. Indeed, in Munich, the smaller energy savings achieved with the renewable systems are offset by the higher costs of these commodities.