12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, EstoniaINTEGRATING RENEWABLE ENERGY INTO LARGE-SCALE DISTRICT HEATINGSYSTEMSPeter Begerow, Dr. Stefan HollerMVV Energie AG, Mannheim, GermanyABSTRACTRenewable energy for heating is mostly used in smallsystems for single-family houses. The existing districtheating networks are generally run by large heatingplants or combined heat and power plants fired withfossil fuels.To combine these two systems, a feasibility study wascompleted with a focus on the district heating grid inMannheim, Germany, and with a focus on solar thermalheat. Other renewable energy heat sources,geothermal heat and heat from biomass, are includedfor a comparison.The study focuses on the heat price as a key figure toanalyse the economic feasibility. The technicalfeasibility has been evaluated by using a simulationmodel of a secondary district heating grid, which isoperated on a low flow temperature level of 70 °C andwhich is connected to a central solar thermal energyplant. The paper describes which technical andeconomic framework conditions are necessary forimplementing renewable energy into large-scale districtheating systems. The calculations show that incomparison with other renewable heat sources solarheat has the highest heat costs ranging from7,7 ct/kWh to 14,5 ct/kWh depending on the plant size,the solar fraction and the use of a storage system. Themajor technical problems for integrating solar heat intoa heat grid are the pressure difference between theflow pipe and return pipe and the low temperature theflat plate solar collectors are working with.INTRODUCTIONBased on the protocol of Kyoto and Europeanregulations a high reduction of CO 2 emissions inGermany is necessary. To achieve those goals, anexpansion of renewable energy in the heat market isrequired. In Germany the major aim to reach is a shareof 50 % renewable energy in the heat market by 2050.Furthermore, 50 % of the renewable heat is supposedto be contributed by a heating grid. [13]To achieve these goals, different governmental as wellas local support mechanism and financial subsidies areavailable. If the heat production is combined with anelectricity production, the major financial support isbased on the EEG (German law for renewable energy).If the used technology just produces heat, a financialaid from the BAFA (Federal Office of Economics andExport Control, Germany) or KfW (bank under controlof the Federal Republic, Germany) is possible. Thereare different regulations which have to be fulfilled bythe project in order to be eligible for those subsidies [8].Main criteria are the size and type of the investor andplanner, the type of technology and the size of the heatplant and of the storage tank.Previous studies [2], [12], [16], [18] showed that solarthermal energy is mostly used in single-family housesand smaller heating grids combined with seasonal heatstorage systems. Those systems are still indevelopment and need financial support to be realized.Most of these heating grids run with a lower flowtemperature and use either fossil fuels or heat frombiomass for an auxiliary heat generation. The largestsolar thermal district heat system in Germany is locatedin Crailsheim. It covers an area of approx. 7300 m² ofsolar collectors with two buffer tanks with a combinedvolume of about 500 m³ as thermal storage. In additiona seasonal geothermal storage has been built whichwill cover 50 % of the heat demand for about 2000residents. This research project has heat productioncosts without any financial support of about 19 ct/kWh.This sum will be reduced depending on the possiblesubsidies. [12] Reported technical difficulties weremostly in the thermal storage technology. There werelittle problems with the collectors as common flat platecollectors were used which are commercially availableand used in large numbers in smaller systems.The project in Crailsheim has shown the technicalfeasibility of a system with a seasonal thermal storage,but it also shows that considerable costs are involved.Furthermore, if a single-family house will install aseasonal storage to get a solar fraction above 50 %, itneeds more than 10 m³ of hot water storage(depending on the building type and planned solarfraction). However, in common buildings there isn‘tenough room for that size of storage [17]. Those twoaspects show that the use of a heating grid couldsignificantly reduce the costs of the solar thermalsystems and could save space otherwise necessary fora storage tank.The paper will give an overview of how the expansionof renewable energy in the heat market will be possible132