Abstract
Abstract To enable large-scale integration of offshore wind over the next decades, offshore grid solutions based on DC technology are being proposed and developed. This paper addresses the challenges of modelling the future power system with DC grids coupled to AC grids for long-term transmission grid planning purposes. It presents an approach for assessment of coupled offshore and onshore grid development solutions using 1) an open power system data set, 2) a power market simulation model (PowerGAMA) and 3) a hybrid AC/DC security-constrained optimal power flow (SCOPF) model. An open, aggregated grid model of the transmission system in the Nordic synchronous area is supplemented by assumed changes towards 2040. The advantages of this open data set is its derivation from open data sources in a traceable and reproducible manner. The PowerGAMA model uses the data set as input to generate representative operating states for the hydropower-dominated Nordic power system. First, the data set is validated through an hour-by-hour model simulation for the year 2024, using historical data on power flows, generation mix, and hydropower reservoir utilisation. Then simulated operating states for 2040 are used as input to a SCOPF model that more accurately captures the interactions between the AC grid and DC grid and more realistic restrictions on the power flow due to security constraints. The results show that the operational strategy associated with the security constraints is the main driver of operational costs. This demonstrates the value of an integrated approach to assess coupled offshore and onshore grid development solutions.