Back-contact’s advertised shading advantage has practical limits. Research comparing it with TOPCon modules shows where that advantage ends and why installers should consider the size and pattern of shadows alongside everyday energy yield.
The advantages of back-contact (BC) technology under partial shading have been widely advertised. For project developers and installers, however, the key question is whether that advantage applies to the shading patterns they actually encounter. In the configuration tested in a 2026 study, BC’s advantage ended when four or more cells were shaded across different substrings within one string. A chimney casting a broad shadow across a rooftop, a vent pipe shading several cells, a tree branch stretching across a module or one PV row shading another can affect multiple cells. These practical shading patterns need to be considered before assuming that BC will deliver a meaningful advantage over tunnel oxide passivated contact (TOPCon).
For some years now, BC modules have been marketed as particularly suitable for partially shaded roofs. The technical basis is solid: BC cells can continue to conduct electricity under certain shading conditions, which delays the activation of the module’s bypass diodes and reduces power losses due to light, local shading.
A peer-reviewed study by scientists from Trinasolar’s State Key Laboratory of Photovoltaic Science and Technology (SKL) and Nanchang University examined the limits of that advantage. The researchers compared complete BC and TOPCon modules under progressively larger shaded areas, as well as under row-to-row shading typical of ground-mounted systems. A separate 2026 study by Liu et al. examined more complex shading patterns, including shading across different substrings within one string.