Impact of shading heaviness on voltage, current and power of the solar photovoltaic string

The short-term power output variability of solar photovoltaic (PV) systems caused by passing clouds is becoming a major concern for grid operators. As the penetration of utility-scale PV systems boosts, the rapid power fluctuations greatly challenge the grid's transient stability. A photo voltaic system is greatly vulnerable to Partial Shading. The performance analysis of PV systems clearly suggests that the maximum power of partially shaded PV systems is inversely proportional to the heaviness of shading. However, some literatures are not of the same opinion; for them, the maximum power of a partially shaded system is invulnerable to shading heaviness, often at certain critical points. According to research on the P-V characteristic curve under various numbers of shaded modules and shading levels, the irradiance of the shaded modules reaches a certain turning point or critical point. The PV array becomes insensitive to high-level shading, categorically for the series topology. This paper presents an experimental results of performance parameters with varying shading heaviness. The experiment is performed on a Photovoltaics string of series connected modules, a 119KW grid-connected rooftop solar power plant using the Power Quality analyser for continuous recording of various parameters under changing shading heaviness. The degree or heaviness of shading decides the critical point. The critical point can vary based on the number of the shaded modules.