HOT|COOL NO.1/2016 "COP21"



By Dr. Volker Kienzlen, Managing Director of KEA, Climate Protection and Energy Agency for Baden-Württemberg

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Opportunities Use of renewable energy and excess heat

District heatingsystemsarekeyelementsof the„Energiewende” – not only in Germany. They are perfect links between the market for electricity and the market for thermal energy. They allow to use renewable energies the best possible way. To date, district heating systems in Baden-Württemberg see by far too few implementations, despite ecological and economical advantages. We recommend a stronger engagement for district heating systems. Importance of thermal energy The public discussion of the „Energiewende“ in Germany is focusing on the electricity market while the importance of thermal energy is often neglected. In Baden-Württemberg, 33 % of the CO2-emissions are caused by heating systems. Furthermore, we see a growing link between electricity and thermal energy: cogeneration and heatpumps are links between the two systems that have to be integrated properly. Thus, we have to consider a combined electricity/heat system that fits the requirements defined by the Paris climate targets. Baden-Württemberg‘s climate protection law aims at reducing the CO2-emissions by 2050 by 90 %. The energy consumption shall be halved and 80 % of the remaining demand shall be supplied by 80 % renewables leading to the anticipated 90 % CO2-reduction. District heating using cogeneration, waste heat or heat from renewable energy sources can become an important part of the „Energiewende“. To date, district heating is not a top priority for municipalities and utilities in Germany. The growth rate of the grids is - despite attractive funding - too slow. District heating supplies 10 % of the final energy for heating in Baden-Württemberg, a level nearly constant for years.

Energy carriers like wood from rural conservation, straw or excess heat from industry are economical and clean options only for big systems. Filters for flue gas are economical for boilers well above 100 kWth. We expect that wood or straw based systems become a reliable option for cogeneration starting at 1 MWth. The Danish example proves that solar thermal systems can play a significant role for the future heat supply. But each collector field has to cover several 1,000 m² to be able to supply heat at a competitive price. With a growing renewable fraction, large storage systems will play an increasing role. To exploit hydrothermal energy accessible in the south of Germany, district heating is the most efficient option. The temperature of the hot water hardly exceeds 140°C, so the efficiency of electricity generation is poor: Hot water has to be used for heating. Power-to-gas-systems can be considered as a heat source, if this technology will play a role for the long time storage of renewable energy. Many manufacturing processes yield excess heat. Often the temperature level does not allow the use in the enterprise itself. District heating systems carry this heat to suitable heat sinks. Industrial excess heat should be combined with backup- systems to avoid being dependent on a single heat source. A key argument for district heating systems is the flexibility concerning energy sources: it is much easier to switch energy sources depending on the actual market situation compared to small decentralized systems.

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