Large-scale renewable energy integration within energy-efficient urban areas: results from three German case studies

Cities consume the vast majority of global energy and, therefore, are major contributors of worldwide CO2 and greenhouse gas emissions. Energy use is chiefly driven by how electricity is produced, how energy is utilized within buildings and how people and materials are moved around a city. Thus, many cities today are committed to increasing the energy efficiency of buildings and the fraction of renewables in energy budgets. However, quantitative data on energy performance and costs are rarely available, making it difficult for cities to effectively evaluate which energy-saving concepts work today and which will work best in the future. This article contributes to the analysis of urban energy performance through a detailed study of three urban case studies. The German case studies cover a medium-sized city (Ludwigsburg) and two city quarters under development (Munich) as well as a recently built (Ostfildern). Although in all cases, solar technologies have the highest potential for decentral renewable supply, the main renewable sources used are biomass and deep geothermal energy, the main reason being today's cost-effectiveness. The Munich case study showed that deep geothermal energy can produce renewable heat at less cost and emissions than biomass or conventional fuels, but there is no renewable contribution to the electricity demand. The 350 ha development will rely on large-scale photovoltaic (PV) integration for a renewable electricity contribution. In the low energy building quarter of Ostfildern, a biomass cogeneration plant covers 80% of the heating and 35% of the electricity consumption. Another 45% of the electricity consumption could be theoretically covered by rooftop PV. The monitoring results show that even on a city quarter scale, it is very difficult to achieve a 100% renewable supply of heating and electricity, if the consumption levels stay at current levels.