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This paper investigates effects of voltage unbalance and energy losses due to the connection of rooftop photovoltaic systems in a low voltage distribution system of a housing estate, which has light loads during daytime. The paper presents a case study of a real distribution power system of housing estate in Thailand. Voltage unbalance and energy losses were simulated by using system characteristic and load data from GIS database of PEA with the DIgSILENT Power Factory program. The key findings of our analysis are as follows. Firstly, the number of installable 1-phase rooftop PV systems varies directly with load density. Secondly, the number of installed 1-phase rooftop PV systems can be increased if the installation locations are closer to the transformer. For 3-phase rooftop PV systems, their installations do not have any effects on the voltage unbalance. Furthermore, system energy loss relates to the load density and PV system installation locations in the same way as the voltage unbalance. The key implication of our study is that the installation of 1-phase rooftop PV system should be granted based on a careful consideration of the installation location and the load density.

Voltage drop and energy loss issues in remote areas will degrade the reliability of power system when loads are subsequently increased. This paper aims to design a PV-Battery microgrid system to enhance the performance of the 22 kV radial distribution system of the Sichang island, which is situated remotely in the Gulf of Thailand. The locations and capacities of the PV-Battery microgrid systems were determined based on voltage regulation and limited feeder rating following the Provincial Electricity Authority (PEA) standard and projected energy loss reduction for increasing load demand within the next twenty years. The DigSILENT Power Factory were used for the simulation. From survey and simulation results, these locations are technically suitable for installation. A capacitor bank system should be installed at the end of power-line branch with the suitable sizing of 1.5 MVar. A microgrid PVBattery system should be installed with a PV-array of 1.5 MWp at the cape area and batteries of 1.08 MWh at the PEA operator center, and batteries of 1.44 MWh and 5.28 MWh at the starting point of the island’s distribution line.

High penetration of rooftop photovoltaic systems in a residential low voltage distribution system has to be controlled in order to maintain stable voltage condition. Energy storage systems, such as batteries, can be used to absorb excess energy of photovoltaic systems and to shave peak load during on-peak time. This paper proposes guiding principles for the incorporation of energy storage systems into a residential low voltage distribution system with high penetration of rooftop photovoltaic systems. Real residential distribution system circuits and all parameters from the Geographic Information System database of the Provincial Electricity Authority in Thailand were used for simulation analysis to study the application of energy storage systems for regulating voltage in a range of the nominal voltage by 10 %. Solar radiation data from the PVGIS were used. The voltage results were simulated by using the DIgSILENT Power Factory program. Based on the simulation, it was found that the overvoltage and under voltage protection and energy loss reduction could be achieved by (i) installing small battery systems in households and (ii) installing battery stations within the vicinity of the transformer or the weakest point of the circuit.