An assessment of high distributed PV generation on eThekwini electricity distribution network.

Abstract

Small-scale Distributed Photovoltaic Generation (DPVG) continues to grow with increasing operational challenges for electricity utilities and Distribution Network (DN) operators. In Low Voltage (LV) DNs, there are well researched potential issues that arise with high Photovoltaic (PV) penetration. These include: feeder voltage rise, voltage fluctuations and reverse power flow. Among these, the most important issue is voltage rise at the LV distribution feeder. In a broader perspective, to this point in time, there has not been more detailed research on small-scale DPVG interconnections in the LV networks in South Africa (SA) and in the KwaZulu-Natal (KZN) region. There is a great need for research in this field for ensuring network efficiency, reliability and future regulatory standards. Other network systems have been studied around the world were conditions, environment, network characteristics and electricity customer loads will be different; e.g in the North-West of England, Germany, and Queensland, Australia. Hence, the main objective of this research study is to analyze the mentioned problems, identify and test the appropriate mitigation solutions, in the event of high DPVG. This study was carried out on a typical SAn LV DN model, which represents an existing housing development estate at eThekwini Municipality. Consequently the aim is to identify solutions suitable for networks in SAn or of similar architect and characteristics. As a result, a specific application is undertaken at the KZN region, which is also representative of network characteristics of SAn networks. A voltage rise, voltage fluctuation and network power loss issues were analyzed at different PV penetration levels and varying customer loads. An innovative approach of utilization of a standard central On-Load-Tap-Change (Off-LTC) transformer for voltage regulation with high DPVG was tested. Usage of this technique has not been reported in the literature to date. National standards in SA were used as a basic guide in this study and stated the possibility of grid voltage control of distributed PV inverters. Assessment of the typical LV network showed that there is indeed voltage rise and hence possible voltage fluctuation, when PV system output power varies. The Off-LTC transformer was able to maintain network voltages within the allowed operational range and reduced the magnitude of voltage rise. This implies that there is a possibility of avoiding expensive upgrades of the existing and widespread Off-LTC transformers technology.