Hosting Capacity Methods Considering Complementarity between Solar and Wind Power : A Case Study on a Swedish Regional Grid

Sammanfattning: The demand for electrical power is growing due to factors such as population growth, urbanisation, and the transition from fossil fuels to renewable energy sources. To be able to keep up with the changes in electricity demand, the Swedish power grid must connect more renewable power generation, but also  increase its transmission capacity. Traditionally, power grids are expanded to increase the transmission capacity which requires a lot of time and investments. In order not to hinder the electrification of society, it is important to adequately estimate the current transmission capacity and plan the expansions accordingly. In the past, the generation of electrical power was primarily based on dispatchable energy sources, and the planning of new connections to the grid was assessed according to the stable and controllable nature of the electricity supply. However, renewable sources like solar and wind power are affected by weather variations. Therefore, the traditional methods of planning the power grid are no longer sufficient. Instead, there is a need to develop and implement new methods that account for the variable nature of renewable energy sources, and also the possible complementarity between different renewable power sources. This can possibly allow more connection of renewable power generation to the grid, without the need of expanding it. The aim of this thesis is to investigate two different methods for analysing how much renewable power generation that can be connected to the power grid, so-called hosting capacity methods. The first method is a deterministic method which is traditionally used in power system analyses since it is a fast, simple and conservative method. This method does neither consider the intermittent nature of solar and wind power, nor any complementarity. The second method is a time series method which considers the complementarity and intermittency of solar and wind power but requires much data. The methods are compared in regards to assessed hosting capacities, risks and reliability of results. The study is performed on a regional grid case in the middle of Sweden. Solar and wind power plants with different capacities are modeled at ten buses in the power grid. The power grid is analysed in PSS/E with loading of lines and voltage levels determining the assessed hosting capacities. A correlation map presenting the temporal correlations of solar and wind power over the grid case area is also created in order to evaluate the complementarity in the area and its possible effects on the assessed hosting capacities.  The results show that the time series method is more reliable than the deterministic method. This is due to the difficulties in identifying accurate worst case hours that are used for the deterministic method. The time series method is also preferred as it considers complementarity between solar and wind power. However, the correlation map argues that the grid case area has weakly positive correlations, meaning low complementarity between solar and wind power. This suggests that the differences in hosting capacity between the two methods are more likely dependent on the temporal variations in existing load and power generation. The differences in assessed hosting capacity between the ten buses in the power grid are probably not due to the local complementarity either, but rather the structural differences of the grid in terms of components, local loads and existing power generation.