The Series Connection Problem
Solar cells within a module are wired in series to build up voltage. A typical 60-cell module produces about 30-40 volts by summing each cell's ~0.6 V contribution. But series connection means the same current must flow through every cell. If one cell generates less current due to shading, it restricts the entire string. A single leaf, bird dropping, or chimney shadow can reduce a module's output far more than the shaded area fraction would suggest.
Bypass Diodes to the Rescue
Every modern solar module contains 2-6 bypass diodes, each protecting a group of cells. When shading reduces a cell group's output, the bypass diode activates and routes the string current around the affected group. The module loses that group's voltage contribution but the remaining groups continue operating normally. A 60-cell module with 3 bypass diodes loses at most one-third of its output from localized shading, instead of 70-90% without protection.
Hotspots and Cell Damage
Without bypass diodes, a shaded cell is forced into reverse bias by the rest of the string. It absorbs power instead of generating it, and the dissipated energy can heat the cell above 150°C. This creates visible brown spots (hotspots), degrades the EVA encapsulant, and can crack cell interconnects. Thermal imaging of older panels without adequate bypass protection often reveals these damage patterns, especially under trees or near roof obstructions.
Quantifying the Impact
This simulation visualizes a solar module as a grid of cells, letting you shade individual cells and toggle bypass diode protection on and off. Watch how power output collapses without diodes when even a few cells are shaded, then see the protective effect when diodes are enabled. The power loss readout quantifies the difference, making the engineering case for bypass diode design immediately visible.