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Background: In this study, a general model of a hybrid off-grid energy system is developed, which can be adjusted to reflect real conditions in order to achieve economical and ecological optimisation of off-grid energy systems.

This paper assesses and compares existing and new technologies for space heating in Germany (e.g., heat pumps, and solar thermal and wood pellet systems) in terms of their environmental impacts. The various technologies were analyzed within the context of the new German legislation. The assessment was carried out on three levels: 1. Global emissions: a life cycle assessment was carried out in order to find the global environmental footprint of the various technologies; 2. Local emissions: the effects of local emissions on human health were analyzed; and 3. Immissions: the immissions were evaluated for the various technologies using a dispersion calculation. A special feature of this study is the substitution of frequently used database emission values by values obtained from field studies and our own measurements. The results show large differences between the different technologies: while electric heat pumps performed quite well in most categories, wood pellet systems performed the best with respect to climate change. The latter, however, are associated with high impacts in other environmental impact categories and on a local scale. The promotion of some technologies (especially systems based on fuel oil, a mixture of fuel oil and rapeseed oil, or a mixture of natural gas and biomethane) by the newly introduced German legislation is doubtful. In terms of the immissions of wood pellet systems, it can be concluded that, even for extremely unfavorable meteorological conditions, the regulatory limits are not exceeded and the heating systems have a negligible influence on the total PM load in the ambient air

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