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, EstoniaFLEXIBILITY FROM DISTRICT HEATINGTO DECREASE WIND POWER INTEGRATION COSTSJ. Kiviluoma 1 and P. Meibom 21VTT Technical Research Centre of Finland2 Risø DTUABSTRACTVariable power sources (e.g. wind, photovoltaics)increase the value of flexibility in the power system.This paper investigates the benefits of combiningelectric heat boilers, heat pumps, CHP plants and heatstorages in a district heating network when the share ofvariable power increases considerably. The results arebased on scenarios made with a generation planningmodel Balmorel [1]. Balmorel optimises investmentsand operation of heat and power plants, including heatstorages. It uses hourly resolution and enforcestemporal continuity in the use of the heat storages.Scenarios with high amount of wind power wereinvestigated and the paper describes how the increasein variability changes the profitability and operation ofdifferent district heating options in more detail than wasdescribed in the article by Kiviluoma and Meibom [2].Results show that district heating systems could offersignificant and cost-effective flexibility to facilitate theintegration of variable power. Furthermore, thecombination of different technologies offers the largestadvantage. The results imply that, if the share ofvariable power becomes large, heat storages shouldbecome an important part of district heating networks.NOMENCLATUREIndicesi, I Unit, set of unitsI HeatStoHeat storage unitst, T Time steps, set of time stepsa, A Area, set of areasVariablesCPQZParametersc Invc Fixc OperationwhNew capacityPower generationHeat generationCharging of heat storageAnnualized investment costFixed operation and maintenance costsOperation cost function of the unitWeight of time periodHeat demandINTRODUCTIONWind power is projected to be a large contributor tofulfil electricity demand in several countries. This couldtake place due to relatively low cost of wind powerelectricity or policy mechanisms promoting renewableenergy. In any case, power systems with a largefraction of power coming from a variable power sourcewill need to be flexible. Flexibility is used to cope withthe increased variation in residual load (electricitydemand minus variable power production) and with theincreased forecast uncertainty in the residual load. Onthe other hand, lack of flexibility will cause larger costsfrom increased variability and forecast errors.Therefore, it is prudent to investigate the cost optimalconfigurations for the combined power and heatgeneration portfolios.Heat generation could offer significant possibilities forincreasing the flexibility of the power system. Currently,part of the inflexibility of the power system comes fromCHP plants that are operated to serve the heat loadwhile electricity is a side product. Installation of electricresistance heaters next to the CHP units or elsewherein the heat network could break this forced connection.During periods of low power prices, which will becomemore common with high share of wind power, CHPplants could be shut down and heat would be producedwith electricity. The dynamics can be made moreeconomic with the use of heat storages. Further optionis to have heat pumps in the DH network, but they willrequire large amount of full load hours to be profitableand will compete with CHP plants for the operatingspace.In most countries heat demand is in the same order ofmagnitude as electricity demand. For example, in UKthe demand for primary energy due to heat is around40% of total primary energy demand [3]. About 25% ofthe primary energy demand is due to space and nonindustrialwater heating. In the US all kind of heat useaccounts for about 30% of the primary energyconsumption [estimated from 4].Heat is inexpensive to store compared to electricity.Electricity storage has been seriously considered toalleviate the variability of wind power [5-6]. Therefore, itis apparent that the use of heat storages should alsoreceive serious consideration in the current context.Some work has been done [7-9], but not considering193