Abstract

Residential rooftop photovoltaics (PV) systems have great potential to supply part of the growing energy demand. However, its non-dispatchable, fluctuating, and intermittent characteristics may negatively impact the power quality and reliability (PQR) of low voltage (LV) distribution feeders. Large amounts of non-dispatchable PV sources, if integrated in a distributed way, can reverse the power flow in the feeder and lead to overvoltages. In diesel-based autonomous systems with high-penetration of PVs, the reduction in net load can significantly increase the wear and tear on the diesel genset(s). Therefore, connection of only a modest amount of PV is currently allowed at the LV level without a prior impact-assessment study.
This thesis focuses on the detrimental impact of high penetration of PVs on LV systems and on the remedial actions that can be taken to increase PQR and the displacement of fossil fuels in diesel-based autonomous systems. Two scenarios are considered.
First is the possibility of overvoltages in LV grid connected systems during periods of high PV generation and low load. The solutions used in medium-voltage feeders need to be revisited in light of the mostly resistive characteristics of LV feeders. An alternative is to use active power curtailment (APC) techniques. A droop-based APC approach, in which all inverters use the same droop coefficients, is analyzed. However, this strategy results in more APC in the PV inverters located near the end of the feeder than in the ones in the beginning. A new approach is proposed that allows equal sharing of the APC. A one-year simulation study assessed the overvoltage occurrences, the sharing of the burden for overvoltage prevention per house, and the total energy yield of the feeder using a benchmark based on typical parameters of Canadian LV feeders.
The second scenario involves the impact of high-penetration PV systems in diesel-based autonomous LV systems, which are typical of remote communities. The use of APC of PV inverters is discussed, focusing on reducing the frequency variations and ensuring the diesel genset's minimum load, and can improve fuel consumption. This theoretical analysis is validated by simulations. Fuel consumption and yearly energy yields are estimated using statistical information about the load and solar irradiation.