Solutions to Power Quality Issues in Rooftop Solar Photovoltaic Systems

Power quality issues are becoming more common as rooftop solar photovoltaic (PV) systems are integrated with low voltage (LV) distribution grids. While these systems provide sustainable energy, they also present several power quality challenges.

Common issues include voltage fluctuations, harmonic distortion, voltage imbalance, and DC injection. These issues can affect not only the solar system itself, but the entire grid, leading to equipment damage, energy inefficiency, and grid instability.

Voltage Flicker

Voltage flicker is one of the most noticeable power quality issues in solar PV systems. It occurs when the output of the solar inverter fluctuates, usually due to changes in sunlight intensity, cloud cover, or shadows. These rapid voltage changes can cause lights to appear to flicker noticeably, causing discomfort to consumers or even damage sensitive electrical equipment.

For rooftop solar installations connected to the LV distribution grid, voltage flicker can be exacerbated by the variability of solar power generation. Solar panels produce varying amounts of electricity throughout the day, depending on weather, time of day, and environmental factors. Without proper regulation, this can result in large voltage fluctuations. This problem can be exacerbated when multiple rooftop solar systems are located close to each other, causing them to move.

Voltage Imbalance

Voltage imbalance is another common problem caused by rooftop solar systems. Many solar systems are single-phase, meaning they only feed power to one phase of the three-phase distribution grid. When many single-phase solar systems are connected to the LV grid, they cause voltage imbalances between the phases. This can lead to overheating, equipment damage, reduced efficiency, and even system failure.

Voltage imbalance is particularly common in areas with high solar adoption. It can stress transformers, shorten their lifespan, and lead to possible unexpected downtime. These issues are a concern for both residential and industrial users.

Harmonics and DC Injection

The operation of solar inverters can introduce harmonics into the grid. Harmonics are high-frequency currents that distort the smooth sinusoidal waveform of the grid, resulting in harmonic distortion. These distortions occur due to the switching operations of the inverter power electronics. Harmonics can damage sensitive electrical equipment, reduce grid efficiency, and increase wear and tear on components such as transformers and motors.

DC injection is another potential problem. Some solar inverters, especially those without an isolation transformer, can inject DC into the grid. This DC injection can cause major problems, such as transformer overheating and damage to grid infrastructure. DC current in an AC system can cause transformer saturation, which reduces efficiency and eventually causes failure.