The Impact of Shading on PV Panel Electricity Production in Series Connections

Introduction

When it comes to maximizing solar panel efficiency in a series connection, shading can significantly impact electricity production. This article explores the effects of partial and total shading, drawing upon practical examples from an off-grid solar system to provide a clear understanding of this phenomenon.

Theoretical Understanding of Series Connections

In a series connection of photovoltaic (PV) panels, the current generated by each panel is the same throughout the series. The voltage, however, adds up across all the panels. Therefore, ensuring consistent voltage output is crucial for the overall system performance.

However, a single panel in the series being shaded can affect the entire string. This is because the shaded panel will reduce the overall current output, which in turn affects the entire series. Understanding the extent of this impact is key for optimizing solar installations.

Practical Observations from an Off-Grid Solar System

I live off-grid with a solar system, and recently conducted an experiment to observe the impact of shading on my PV panels. The system consists of four panels, three of which are connected in series and supply power to a 12V battery bank. The fourth panel is dedicated to running a water pump.

During an experiment, I placed my work shirt over two strings of the series-connected panels to simulate partial shading. Here are the results:

Partial Shading Experiment

Before shading:

Array Voltage: 75.9V Current: 36.2A

After covering two strings with my shirt:

Array Voltage: 61.5V Current: 29.7A

While the current dropped, the voltage also showed a significant decrease. However, the system still managed to supply a substantial amount of power with 29.7A into the battery bank.

Total Shading Experiment

For a more severe test, I covered the entire panel with my shirt:

Array Voltage: 44.1V Current: 24.9A

The results were more noticeable, with both voltage and current decreasing significantly. Despite the shade covering all three series panels, the system still managed to deliver a measurable amount of current, indicating the resilience of the system to partial shading.

My observation showed that a total of 11 cells (4 cells completely covered and 7 cells partially or half-covered) were enough to substantially reduce the current and voltage output, but not to completely shut down the system.

Conclusion

Shading can have a noticeable impact on the efficiency of PV panels connected in series, but the extent of this impact depends on the extent and distribution of the shading. While full shading can cause significant drops in power output, partial shading can still maintain a considerable level of electricity production.

Understanding and managing shading is critical for optimizing the performance of solar systems, especially in partial-shade environments. Regular maintenance and monitoring can help in identifying and mitigating the effects of shading on your solar panels.