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This thesis investigates how the operation of Turbine 6 at Mälarenergi has changed after a large underground hot-water storage system was put into operation. The storage makes it possible to store heat when the demand is low and use it later, which reduces the need to adjust the turbine’s load in real time.

The purpose of the study is to examine how the turbine’s operating patterns, average output, efficiency, and role in the electricity and reserve markets have been affected by the introduction of the heat storage system.

The work is based on a comparison of operating data from before and after the storage was activated. The analysis includes start and stop frequency, electricity and heat production, efficiency, and how much of the available energy was not used.

The results show that the turbine now runs more steadily and needs fewer starts and stops. Both electric and heat output have increased, and the turbine’s efficiency has improved. The amount of unused energy has also decreased, which means the turbine is used more effectively.

Overall, the study shows that the heat storage has made the system more flexible and efficient. Turbine 6 can operate closer to its optimal load, while Mälarenergi gains better opportunities to adjust production according to changes in electricity prices and heat demand.