Survey and assessment of the impact of embedded generation on the eThekwini electricity distribution grid.

Abstract

Under frequency load shedding, rising electricity tariffs, environmental concerns, reducing costs of renewable energy technology and delays in constructing new power stations has lead consumers and producers alike to explore various energy generation options to reduce their own electricity needs whilst assisting the sector. Embedded Generation (EG), Distributed Energy Resources (DER) or Distributed Generation (DG) is further predicted to play a substantial role in the electrical power system in the near future. Various EG technologies are entering a period of major growth and commercialization. Small scale Embedded Generation (SSEG) projects are quickly becoming a popular sight locally within the city of Durban and numerous projects are been connected to the eThekwini Electricity distribution grids. In these projects, there seems to be a reluctance to couple expensive energy storage technologies to these systems but rather synchronize and utilise the municipal grid as a virtual battery. Whilst the advantages make synchronization to the grid a logical choice, the municipal network architecture and framework was not designed to facilitate this. The municipal mandated core function is to procure electricity from Eskom (the national energy generator), transform it and distribute it to its customers. Power flow is from generation (Eskom), transmission (Eskom) and distribution to the end customer. This includes all technical, regulatory, administrative and legal aspects that have been structured to support this unidirectional power flow. The introduction of DER/DG/EG introduces bi-directional power flow on the existing distribution network. An analysis of the impact of this phenomenon is required as it affects fault level, protection selectivity and sensitivity, network losses, quality of supply, network planning, metering and control of power flow on the existing distribution grid. In order to address and understand the impacts of EG on the existing eThekwini Electricity distribution grid, an investigation was first carried out to identify the drivers and available renewable energy resources in Durban. 5 cases studies were selected based on the investigation which showed that there will be growth and projects in these sectors in Durban. These cases studies were selected to address growth in residential rooftop PV, commercial/industrial rooftop solar PV, PV farm potential on closed landfill sites, wind farm potential at identified sites around the city and landfill gas to electricity projects from existing landfill sites in the city. Accurate models of these sources and their interaction with the grid were then studies. Studies were also carried out on the recently published NRS guidelines for SSEG and the South African Renewable Energy Grid Code to understand how this will provide operational flexibility to the System Operator and assist with mitigating the negative impacts to the distribution network. The 5 case studies provide excellent results and greater understanding of the impacts of increased penetration of EG onto the existing eThekwini Electricity distribution grid. The impacts of increased penetration of EG on the existing eThekwini Electricity distribution network included impacts to the network voltage, fault level rise, losses, power flow, network planning and revenue loss. Based on the results and studies from the case studies methods were then derived to mitigate the impacts of increased penetration of EG on the existing distribution network. The following outcomes and key contributions, were achieved in this research investigation, namely:  An understanding of the drivers of EG in eThekwini Municipality.  Evaluation of the available renewable energy resources within eThekwini Municipality.  The feasibility of residential rooftop solar PV in Durban.  Identified factors affecting residential rooftop solar PV feasibility in Durban.  Assessed the feasibility of municipal landfill gas to electricity EG projects.  Developed and propose methods to improve operational and financial viability of landfill gas to electricity projects in Durban.  Provides results showing the impacts of increasing EG on the eThekwini Municipality distribution network design and performance.  Developed methods to assist and enable distribution network designers when designing distribution networks with increasing EG.  Developed a methodology for selecting EG size on an existing eThekwini Electricity distribution network.  Provide methods to minimise the impacts of preselected size of EG given that the municipality has no control over the size selection which may be dictated by the IPP.  An understanding of the local South African guidelines on small scale EG, and the South African Renewable Energy Grid code requirements.  Provide controllability options to assist manage EG plants on the existing distribution network in eThekwini Municipality. vii  Understand the operation and effects of different EG sources available within eThekwini Municipality. These have been accomplished using the 5 case-studies, modelling and simulation, field tests and measurements; as well as extensive research investigation and analysis.