Renewable energies in district heating : integration of Power-to-Heat

Abstract

The ambitious goals set by the German government throughout the “Energiewende” and thereafter focus more and more on the heating sector in Germany. While the conversion of the electricity generation and electricity grids keeps pushing forward with more renewable electricity from wind farms and photovoltaics, the heating sector is still only slowly keeping up. Electricity generation in Germany from renewable energies has developed so fast that the necessary restructuring of the infrastructure in order to distribute the electricity where it is needed most is not finished and will continue to take time. Meanwhile solutions have to be found to cope with the developmental disparity between restructuring of the energy generation and the energy distribution in Germany. Power-to-heat provides a possibility to enlarge the amount of renewable energies within the heating sector with otherwise wasted renewable energy while at the same time helps to remediate bottlenecks in the transmission and distribution grids. The usage of the technology could also help dampen the EEG surcharge when used during times of negative prices on the electricity exchange. The aforementioned disparity between the energy generation and the energy distribution is specifically critical in northern Germany. This is due to the large amounts of renewable energy generation (mostly wind energy generation) in the area combined with the distance to the areas in Germany where most of the energy is consumed (mostly western and southern Germany). Therefore the bolting of electricity loads is the regular case in northern Germany and the amount of load management interventions will only increase in the next years and decades. These increasing amounts of otherwise unused renewable energy loads are predestined for the conversion to heat in Power-to-Heat facilities. Hamburg is especially important for the integration of Power-to-Heat because it provides the necessary heat load in order to use the generated heat. The existence of a well-developed district heating grid is another prerequisite for the successful integration of the technology on a large-scale basis. Small Power-to-heat facilities in the industry, or for the provision of negative control energy, are already existent and in business. The integration into large-scale district heating grids proves to be the biggest challenge for the technology as these district heating grids are usually not prepared (or willing) to integrate additional heat. Technical reasons are often mentioned because district 5 heating grids are usually developed for a certain load structure and would need to be adjusted in order to incorporate additional heat loads. Adding heat to a district heating network usually entails that existing heat generation (mostly conventional heat sources like gas or coal) needs to be substituted which is generally not in the interest of grid operators or proves legally difficult as contracts for the existing heat generation exist.