Each cell follows the single-diode model, solved here for voltage V at a given current I via Newton–Raphson:
I = I_L − I₀(e^(V/nV_T) − 1) − V/R_sh
I_L ∝ irradiance G (fully shaded ⇒ I_L ≈ 0, partially shaded ⇒ I_L scaled down)
Cells in a string are wired in series, so the same current I flows through every cell — the operating current you set with the slider is exactly that shared current, and each cell's voltage is found by solving where that constant-I line crosses its own I-V curve (the chart below draws the whole string's I-V curve this way, sweeping I and re-solving every cell at each point). When a shaded cell's I_L drops below the string current, it can't supply I by generating power, so it is driven into reverse bias (negative V) to force the deficit through its own shunt resistance R_sh. Since P = I·V, a reverse-biased cell doesn't generate — it dissipates power as heat, shown here as a red glow, which is exactly how field "hotspots" that crack cell glass form.
A bypass diode wired antiparallel across a row turns on once that row's voltage drops below about −0.5 V and diverts the string current around it instead of through the shaded cells. This caps the reverse voltage (and the heat) each cell must absorb, at the cost of losing that row's power contribution entirely.
- Click a cell — cycles it through unshaded → 50% shaded → fully shaded (I_L → 0).
- Bypass diodes — toggle the three per-row protection diodes on/off.
- Irradiance — sets I_L for every unshaded cell.
- String current — the operating point (set by the external load); push it past a shaded cell's I_L to force reverse bias.
- Chart below the grid — the string's real computed I-V curve for the current shading pattern, with the live operating point marked.
Approximation: reverse-region avalanche breakdown is modeled as a soft drop in R_sh below about −14 V rather than a full breakdown curve — enough to show the physical mechanism without needing manufacturer breakdown data.