Virtual power lines in the future Swedish power system

Abstract: The transition towards renewable energy and electrification is expected to accelerate in the coming decades. This change is being studied by several actors, in Sweden most notably by Svenska kraft- nät, the Swedish TSO. They have recently constructed four different scenarios, two of which explore a future with a doubling of electricity consumption from year 2022 to year 2045. These two scenarios have been studied in this thesis work in the context of challenges in the underlying power system. There is currently a lack of transmission capacity between the Swedish bidding zones, which could worsen if the electrical power usage doubles in the future. Building new power grid infrastructure is a slow pro- cess, where new transmission lines can take 10-12 years to complete. A rapidly growing demand for electricity combined with long lead times to reinforce an already strained system is problematic since it slows down the rate of the electrification of society and increases electricity prices. One part of a possible solution to this dilemma is virtual power lines. These grid connected battery energy storage systems can reinforce already existing infrastructure by increasing power transmission capacities. Virtual power lines use battery storages which work in pairs where the demand side storage discharges during hours of congestion in the transmission system, at the same time as the supply side storage charges, thus virtually increasing the power transfer capacity. During low load hours in the transmission system, the supply side storage recharges the demand side storage. The main objective of this thesis work is to examine if virtual power lines can be a part of the solu- tion to the lack of transfer capacity across the Swedish bidding zone borders. This is done through simulations in PowerFactory in an updated version of the Nordic44 network model depicting the Nordic synchronous area in year 2045. The control of the virtual power lines, ie the decision of when the virtual power lines should charge or discharge is also modeled through conditional logic in a Python script. The results of the simulations show that virtual power lines can benefit the Swedish transmission system. It is also concluded that virtual power lines should not be the only solution to reduce congestion in the grid, as the battery energy storage systems in the virtual power lines would in some cases need to be 100 000 MWh or more. A common result for both studied scenarios was that bidding zone border 1 in the north of Sweden would benefit the most from a virtual power line, with reductions in the number of overloaded hours of around 50% in some cases and a reduction in MWh overload of around 40%. When studying cases with delayed reinforcement projects in the power grid, virtual power lines could in some cases reduce both the number of overloaded hours as well as MWh overload with over 80%. These results were acquired using virtual power lines with energy ratings of 1 000-10 000 MWh. Additionally, factors that should be considered when dimensioning virtual power lines include how much of the overload energy that needs to be covered as well as utilization time.