Techno-economic analysis of combined heat pump and PV systems in Austria

Sammanfattning: With the increasing amount of buildings that are being renovated in Austria, the potential of replacing conventional heating systems with heat pumps increases and thus CO2 emissions could be reduced. Several companies therefore focus on installing combined heat pump and PV systems. The installation of heat pumps and PV systems are being subsidized in Austria with different schemes for every state. The subsidy programs could therefore be clearer and more constant, like the Swedish heat pump subsidies of the last decades. Heat pumps currently cover the heating of over 10% of the gross floor area of single-family houses in Austria. For multifamily houses less than 5% of the gross floor area is heated with heat pumps. The research goal has been to analyze the sensitivity of the net present value (NPV), benefit cost ratio (BCR) and internal rate of return (IRR) on different input parameters for the replacement of a conventional heating system in a multifamily house, by a heat pump combined with a PV system. This way it could be researched what parameters would have most influence on the profitability of a combined heat pump and PV system. A case study has therefore been performed on the replacement of a gas heating system by an ambient air/water heat pump and a borehole ground source heat pump combined with a PV system in a multifamily house in Vienna. A model has been developed with Excel to perform this analysis uses the building space heating demand generated from a simulation tool created internally by AIT: The Building Model Generator. The model calculates the annual energy demand of a multifamily building in Vienna, which leads to the annual costs and benefits with respect to the conventional gas heating system. This model has been validated by a model created with the Polysun software. The results of the analysis showed that installing a combined heat pump and PV system to replace a gas heating system in a multifamily house would improve the NPV in comparison to installing the heat pump or PV system separately. The BCR is greater than one for both the combined air/water heat pump and PV system (AW HP+PV) and the combined ground source heat pump and PV system (GS HP+PV) for the currently used input. Subsidies currently have a large influence on the NPV and payback time of the installment of these combined systems, especially for the GS HP+PV due to the high investment subsidies for this type of heat pump in Vienna. The sensitivity analysis shows that the bigger the PV area of these combined systems, the higher the BCR, but this BCR increase flattens out for increasing PV areas. The investment costs have a large influence: if these would decrease somehow by 50%, the BCR would double. The large influence of the investment costs is shown by the sensitivity analysis on the assumptions for the heat pump investment costs as well. The electricity price has a larger influence on the BCR than the feed-in tariff does. When the electricity price decreases, the BCR increases. It could be concluded from the sensitivity analysis that the gas price has the largest influence however. Because of this high dependency on the gas price, a gas price increase could even make subsidies redundant. Increasing the gas price could thus be the quickest way to stimulate the sales of combined heat pump and PV systems, which could lead to a decrease of approximately 45%-60% of the total CO2 emissions for every multifamily house where these combined heat pump and PV systems are installed. In the future the Excel model could be included in the Building Model Generator. With only a few input parameters it would then be possible to evaluate the replacement of a heating system with another heating system in different building types for the whole of Austria where there are various subsidy schemes.