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

The paper presents a cradle-to-grave life cycle assessment for two domestic solar hot water systems. The first consists of polypropylene unglazed solar panels coupled with a 300-l storage tank; the second one consists of a traditional system with glazed solar panels coupled with a thermal storage of the same volume. Life cycle assessment was conducted according to the Eco-Indicator 99 methodology, Egalitarian Approach, yielding 49.7 and 18.3 eco-indicator points for the glazed and unglazed panels systems, respectively. In addition, for each domestic solar hot water system, the energy, CO2 and economic payback times were calculated. In order to take into account the influence of local climate on the solar panels yield evaluate, the systems performance was simulated for three different locations: Rome, Madrid and Munich. The payback times were evaluated with respect to both natural gas and electrical boilers. The Energy Payback Time of the unglazed panel system ranges between 2 and 5months, that of the glazed panel between 5 and 12months. The CO2 Payback Time of the unglazed panel system ranges between 1 and 2months, that of the glazed panel between 12 and 30months. 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