The Role of the High Voltage Power Level in Future Power Systems and Their Modelling

The electricity system in Germany is increasingly dominated by renewable decentralised power plants. This contribution focuses on the role of the high voltage level in Germany's current and future electricity system. Two approaches have been developed in order to compare the consideration of the high voltage (110 kV) level to the disregard of it. This disregard was accomplished by applying a Dijkstra algorithm to the high voltage level allocating the decentralised power plants to the nearest extra high voltage buses. In general a k-means network clustering algorithm was applied to reduce computational effort while still allowing the consideration of the grid topology and its restrictions in an abstract way. The comparison of the two alternative modelling approaches showed that with increasing shares of renewable energy connected to the distribution grid, the relevance of the high voltage level rises. Neglecting this voltage level led to an overestimation of the economic system efficiency by 5 to 7 %. The consideration of the high voltage level introduced additional grid restrictions, which exceeded the effect of increased transmission capacities (enabling transit flows). Consequently an economically less optimal power dispatch was discovered, which is characterised by higher shares of conventional generation. When storage expansion was optimised, it became evident that the application of high voltage grid restrictions led to lower storage investments.