- BC modules record 12.9% power loss under single cell shading compared with 33.9% for TOPCon.
- BC technology delays bypass diode activation, improving output under mild shading conditions.
- Performance gap disappears under heavy shading, with both technologies losing about 50% output.
A new comparative study titled ‘A comparative study on the performance of BC and TOPCon modules under partial shading conditions,’ has found that back contact (BC) solar modules outperform TOPCon modules under partial shading conditions, offering important insights for project developers operating in environments prone to shading.
Partial shading remains a major challenge for photovoltaic systems, particularly in regions where installations are exposed to trees, buildings, dust, or debris. These factors can cause current mismatch, hotspot formation, and long term reliability issues, ultimately reducing energy yield and system lifespan.
The research evaluated the performance of back contact and tunnel oxide passivated contact modules across six shading scenarios, including patterns that simulate real world conditions such as bird droppings, fallen leaves, and narrow linear shadows. The findings show that module architecture and cell characteristics play a critical role in how systems respond to shading.
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Under single cell shading, back contact modules demonstrated a clear advantage, with power losses limited to 12.9%, compared with 33.9% for TOPCon modules. This improved performance is linked to the lower breakdown voltage of back contact cells, which allows them to better tolerate reverse bias conditions and delay the activation of bypass diodes.
The study also quantified the threshold at which bypass diodes activate. In the tested 66 cell module, at least 2.6 series connected cells needed to be shaded before bypass activation occurred in back contact modules. In contrast, TOPCon modules required more than 90% shading of a single cell to trigger the same response, leading to earlier and more significant power losses.
Under mild shading conditions, defined as three or fewer shaded cells distributed across different substrings, back contact modules consistently delivered higher output. This makes them particularly suitable for installations where intermittent or uneven shading is expected.
However, the advantage diminishes as shading severity increases. When four or more cells are shaded, both technologies show similar performance, with power losses approaching 50%. In these scenarios, the shaded string effectively stops generating electricity, and only the unshaded portion of the module contributes to output.
The findings highlight a clear performance threshold between mild and severe shading conditions, providing practical guidance for system design and technology selection. For solar projects in Africa and other regions with complex shading environments, the choice between module technologies could have a measurable impact on energy yield and long term reliability.
By quantifying how different module types respond to realistic shading patterns, the study offers developers and EPCs a more precise basis for optimising photovoltaic system performance in challenging operating conditions.
Author: Bryan Groenendaal
