This simulator models an illustrative 60-cell crystalline-silicon module (about 293 W at standard test conditions) built from three series-connected, bypass-diode-protected 20-cell substrings. Change irradiance, cell temperature and substring shading, and trace how the module's full current-voltage characteristic reshapes in response.
• A real-time 3D cutaway of the 60-cell module and its three substrings, with home view, rear/front view toggle, auto-rotate, expand-3D and a transparent rear junction-box cover for inspecting the bypass diodes, plus tappable components with anchored callout labels. • Five operating modes: resistive load, open circuit, short circuit, a voltage-controlled sweep point, and local perturb-and-observe MPPT, plus a global MPP scan, a pin/clear comparison-curve tool and a half-irradiance cloud fixture. • Time controls: run time, step 200 ms, and advance 5 seconds. • A Measurements & trends tab with a panel I-V curve (present curve, pinned comparison, resistive load line, operating point, global maximum), a P-V curve showing how partial shading creates multiple power peaks, a power-response-over-time trend, a per-substring voltage chart (substrings A, B and C, with negative voltage indicating an operating bypass clamp), the full equation set and stated model conventions. • Module and substring measurements showing how the three 20-cell substrings carry the same series current while their voltages add, and how an operating bypass diode clamps its substring to about −0.5 V to let current keep flowing through the others. • An Experiments & tests tab with 14 guided experiments (reference conditions, half irradiance, hot/cold module, open circuit, short circuit, load sweep, local MPPT, substring shade, local-versus-global peak, cloud during tracking, series-resistance defect, shunt-leakage defect, complete substring obscuration), a Verification bench that runs automated model checks, and a diagnostic challenge. • A Learn & assess tab with an 8-question knowledge-check quiz and a written model-scope statement referencing Sandia PVPMC single-diode and electrical-shading materials.
Each substring's cell current follows the same single-diode equation as an individual cell, but shading one substring's cells reduces its available photocurrent below what the other two substrings can pass in series. Rather than force the whole string down to the shaded substring's current, its bypass diode turns on and clamps that substring to about −0.5 V, sacrificing its voltage contribution so the healthier substrings can keep driving current. That clamp event is what produces the visible step in the I-V curve and the second local peak in the P-V curve — a genuinely different mechanism from simply lowering uniform irradiance across the whole module.
Because a local perturb-and-observe tracker only sees local slope information, it can settle at the nearer, weaker peak instead of the true global maximum once a substring is shaded — which is exactly why the simulator provides a separate ideal global MPP scan alongside the local MPPT mode, so you can directly compare what a naive local tracker finds against the true optimum.
Pin a curve at one set of conditions, then change irradiance, temperature or shading and watch the new curve trace against the frozen comparison — negative substring voltage on the sub-chart tells you exactly when and which substring has gone into bypass. The efficiency readout divides delivered power by full-irradiance-times-full-module-area, so it captures the real shading penalty relative to the unobstructed aperture rather than hiding it in a reduced denominator.
This is a teaching model: cell temperature is prescribed rather than ambient, shade is applied uniformly across all 20 cells of substring C only, bypass diodes use an ideal −0.5 V clamp, and the global scan is an ideal instantaneous sweep rather than a simulated commercial inverter search. Individual-cell reverse breakdown, hotspots, diode temperature dependence, real spatial shadow patterns, alternative wiring topologies, capacitance and converter switching dynamics are not modeled.
The module has three series 20-cell substrings, each with its own bypass diode. When shading reduces one substring's available current below what the others can pass, its bypass diode clamps that substring to about −0.5 V so current keeps flowing. That clamp transition produces a visible step in the I-V curve and a second, local peak in the P-V curve.
Local perturb-and-observe tracking only follows local slope information and can settle at the nearer of two power peaks created by substring shading. The simulator includes a separate ideal global MPP scan so you can compare what local tracking finds against the true global maximum directly.
Pin captures the current I-V curve as a frozen gray dashed reference. Change irradiance, temperature or shading afterward and the new mint curve traces alongside the pinned one, making it easy to see exactly how conditions reshaped the characteristic. Clear comparison removes the pinned curve.
Cell temperature is prescribed rather than calculated from ambient conditions, shade is applied uniformly to all of substring C's cells rather than as a real spatial shadow, bypass diodes use an ideal fixed clamp voltage, and the global scan is an ideal instantaneous sweep, not a simulated inverter search algorithm. Reverse breakdown, hotspots and converter switching dynamics are outside scope.