District heating networks are commonly addressed in the literature as one of the most effective solutions for decreasing the greenhouse gas emissions from the building sector. These systems require high investments which are returned through the heat sales. Due to the changed climate conditions and building renovation policies, heat demand in the future could decrease, prolonging the investment return period. The main scope of this paper is to assess the feasibility of using the heat demand

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... door temperature function for heat demand forecast. The district of Alvalade, located in Lisbon (Portugal), was used as a case study. The district is consisted of 665 buildings that vary in both construction period and typology. Three weather scenarios (low, medium, high) and three district renovation scenarios were developed (shallow, intermediate, deep). To estimate the error, obtained heat demand values were compared with results from a dynamic heat demand model, previously developed and validated by the authors. The results showed that when only weather change is considered, the margin of error could be acceptable for some applications (the error in annual demand was lower than 20% for all weather scenarios considered). However, after introducing renovation scenarios, the error value increased up to 59.5% (depending on the weather and renovation scenarios combination considered). The value of slope coefficient increased on average within the range of 3.8% up to 8% per decade, that corresponds to the decrease in the number of heating hours of 22-139h during the heating season (depending on the combination of weather and renovation scenarios considered). On the other hand, function intercept increased for 7.8-12.7% per decade (depending on the coupled scenarios). The values suggested could be used to modify the function parameters for the scenarios considered, and improve the accuracy of heat demand estimations. Abstract The increasing penetration of renewable energies will make new storage technologies indispensable in the future. Power-to-Gas (PtG) is one long-term storage technology that exploits the existing gas infrastructure. However, this technology faces technical, economic, environmental challenges and questions. This contribution presents the final results of a large research project, which attempted to address and provide answers to some of these questions for Baden-Württemberg (south west Germany). Three energy scenarios out to 2040 were defined, one oriented towards the Integrated Energy and Climate Protection Concept of the Federal State Government and two alternatives. Timely-resolved load profiles for gas and electricity for 2015, 2020, 2030 and 2040 have been generated at the level of individual municipalities. The profiles include residential and industrial electrical load, gas required for heating (conventional and current-controlled CHP), as well as gas and electricity demand for mobility. The installation of rooftop PV-plants and wind power plants is projected based on bottom up cost-potential analyses which account for some social acceptance barriers. Residential load profiles are derived for each municipality. In times with negative residual load, the PtG technology could be used to convert electricity into hydrogen or methane. The detailed analysis of four structurally-different model regions delivered quite different results. While in large cities, no negative residual load is likely due to the continuously high demand and strong networks, rural areas with high potentials for renewables could encounter several thousand hours of negative residual load. A cost-effective operation of PtG would only be possible under favorable conditions, including high full load hours, a strong reduction in costs and a technical improvement of efficiency. Whilst these conditions are not expected to appear in the short to mid-term but may occur in the long term in energy systems with very high shares of renewable energy sources.