Thermal storage valuation in Gothenburg district heating system

Examensarbete för masterexamen
Master's Thesis
Sustainable energy systems (MPSES), MSc
Håkansson, Pontus
Johansson, Ludvig
Göteborg Energi has invested in an accumulator tank for their district heating system in Rya. This accumulator tank needs further investigation about cost-efficiency and best usage. The study’s goal is to investigate the profitability of the installed accumulator tank and see if future accumulator tank investment is a profitable solution. The district heating network is divided into different nodes which are connected by water pipes, and different plants/units are found at different nodes. The units have different fuels, start times, start costs, efficiencies, and limitations which makes these units more or less expensive to run. In this work, the combined heat and power (CHP) plants have decided to have a restricted minimum load, and the rest of the units have a flexible load. The different generation units are heat-only boilers (HOB), CHPs, and heat pumps (HP). The method was set up to calculate the minimum annual cost of generation in three different cases with different input values. These cases are 2019, 2030, and 2030 new investments where the differences are that 2019 is the current system and is modeled with an accumulator tank and without. The 2030 case is based on Göteborg Energi’s prognosis of how the new installment of units will look in 2030. Here the comparison was made between the current accumulator installed and the possibility of new accumulator investments in the system. The last case was like the 2030 case, but instead of the 2030 prognosis of installed units, the model invested in three categories of plants (HOB, HP, and CHP), where the units still in service from 2019 remained. A sensitivity analysis was also made in all these cases where the fuel prices were varied. The 2019 case showed a saving of 1.55 MAC, and in both cases, investments in new accumulator tanks were made, especially in nodes 5 and 6, which are in the north and eastern districts of Gothenburg. The sensitivity also showed that accumulator tanks are profitable even though bigger fuel price fluctuations occur. One important discovery in the study was that bottlenecks were decreased with the help of accumulator tanks. In contrast, plants further up the merit order decreased production when more accumulator tanks were available. Also, electricity-dependent heat generation units have good integration with this kind of thermal storage because of the higher use of heat pumps and CHPs when accumulator tank capacity increases. One of the study’s conclusions is that the current accumulator tank is profitable and has a payback of approximately 11 years, and investing in more accumulator tanks would decrease the cost of the district heating system.
Accumulator tank , Thermal energy storage , District heating system , Node division , Bottlenecks
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