Impact of LV connected DER steerability on HV and MV networks

Abstract

Climate change results in governments making policies for more renewable electricity generation. At the same time, electricity prices are rising. These factors result in an increasing number of photovoltaic (PV) systems being installed and connected to the low voltage (LV) grid. More than half of the areas in The Netherlands have capacity issues related to distributed power generation, which can be solved by reinforcing the electricity grid or reducing the combined power being fed into the grid. This thesis aims at investigating the possibilities and effect of reducing PV power put into the grid.

Grid reinforcement can not happen instantly and requires a considerable investment while currently not enough skilled labourers are available. Together with this labour shortage and time delay, a large cost is associated with this action. Another factor is the eventual over generation from distributed energy resources (DER’s) reducing power grid stability. All these considerations provide the basis for research into the possibilities of LV PV curtailment. There is a significant amount of research on the effects of curtailment, however this research mainly focuses on the LV effects or looks at not technically feasible curtailment options.

The current overloaded grid can be solved by different ways of curtailing LV PV alongside medium voltage (MV) and high voltage (HV) curtailment. Different options result in more curtailed energy correlated with lower grid loading or less curtailed energy but more residual network loading. The current German-implemented method sets a power limit of 70% of the installed power for small PV systems and requires a gradual curtailment possibility for larger systems. This approach has proven to provide a good trade-off between loading reduction and generation losses for now. Other curtailment may be more effective in the future. Therefore the research question of this thesis is How will LV connected PV curtailment affect the loading of the MV and HV network?.

In order to determine the impact of different curtailment methods a simulation based approach was chosen. Further on in this thesis the generation of power consumption and generation data will be discussed, as well as the implemented and explored curtailment methods. The selected networks are based on the amount of LV PV present together with the network capacity relative to the total amount of installed PV generation.

At the moment MV to LV transformers are the main bottleneck, which can only be solved by installing larger transformers or curtailing LV connections. When analysing all other assets an optimisation approach reduces grid loading the most, however this is far from necessary. In order to keep MV cable loading and HV to MV transformer loading within limits any form of curtailment is functional, even curtailment methods which do not impact LV connections.

The main takeaways from this thesis are that curtailment will become necessary in the coming years. Combined with the fact that LV curtailment has to be implemented within 10 years in order to avoid overloading the MV to LV transformers.

All in all a system wide approach is preferred, as this reduces loading with minimal energy curtailment. This can be achieved with an optimisation approach or propagating rules associated to the maximally loaded asset. Considerations, which should be explored further, are the financial impact, social impact of curtailment and complexity of the system. As these impact customers both directly and indirectly.