Rotationsenergi i framtidenskraftsystem : En fallstudie av Mälarenergis möjligheter att bidra till frekvensstabilitet genom mekanisk och syntetisk rotationsenergi

The transition towards a power system with a higher share of intermittent production, such as wind and solar, leads to a power system with a lower share of synchronously connected machines. This leads to a decrease in available rotational inertia, which challenges the frequency stability of the Nordic synchronous area. This thesis was conducted in collaboration with Mälarenergi AB, with the purpose to evaluate the company’s potential contribution to the system inertia. Two solutions are investigated; the conversion of three decommissioned generators into synchronous compensators and the use of a planned battery system for synthetic inertia. The technical analysis includes calculations of inertia constants, stored rotational energy and active power delivery during frequency disturbances. Two approaches to the conversion are assessed; the full disconnection of the turbine and the de-blading of the turbine. Furthermore, an economic analysis regarding the conversion and operational costs for the synchronous compensators is done. The results show that the decommissioned generators could contribute with a total of between 618 MWs and 1 298 MWs of rotational energy, depending on the turbine configuration. Generator 3 alone accounts for the majority of this contribution, 429 MWs and 900 MWs respectively. Generator 3 is therefore concluded to be the most viable option for conversion. However, the economic analysis indicates that the current market conditions do not justify the investment, since the investment cost is high and there’s currently no remuneration model for rotational energy in the Nordic synchronous area. It could be concluded that Mälarenergi has significant technical potential to support grid frequency stability, but the viability of these contributions depends on the implementation of financial incentives from the Nordic TSOs.