This simulator models a single crystalline-silicon photovoltaic cell with a temperature-dependent single-diode equivalent circuit — series and shunt resistance included. Change the light source, the external circuit and the operating point, and watch how photon absorption at the junction becomes usable electrical power.
• A real-time 3D cutaway of the silicon junction — cyan spheres for electrons, pink spheres for holes, gold rays for incident photons — with home view, explode-layers, show/hide-photons, auto-rotate and expand-3D scene tools, plus tappable components with anchored callout labels. • Illumination selector: broadband sunlight fixture or a monochromatic light experiment with an adjustable wavelength, so you can probe the silicon band gap directly. • External circuit modes: resistive load, open circuit, short circuit, an ideal voltage-controlled load, and perturb-and-observe MPPT, plus a one-click "set load to MPP resistance" and a "half-light cloud" fixture. • Time controls: run time, step 200 ms, and advance 5 seconds. • A Measurements & trends tab with an I-V characteristic chart (cell curve, load line, operating point and MPP), a P-V characteristic chart, a delivered-power-over-time trend (useful for watching the MPPT search and its oscillation), a photon-energy-versus-band-gap chart for the monochromatic probe, the full equivalent-circuit equation set and stated model conventions. • An equivalent-circuit accounting readout showing how photogenerated current splits into external, diode-recombination and shunt-leakage current, plus I²Rs series loss. • An Experiments & tests tab with 14 guided experiments (sunlit cell, open circuit, short circuit, load matching, MPPT search, cloud passage, hot cell, oblique illumination, uniform obscuration, poor contacts, leakage defect, recombination defect, below-gap photons, wavelength sweep), 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 with references to Sandia PVPMC and Penn State photovoltaics materials.
Absorbed photons above the silicon band gap (1.12 eV) generate electron-hole pairs; the junction field separates them so they can drive an external circuit. The single-diode model expresses terminal current as I = Iph − I0[exp((V+IRs)/(nVT))−1] − (V+IRs)/Rsh, where Iph is photogenerated current, the exponential term is diode recombination current, and the last term is shunt leakage. Series resistance dissipates additional power as I²Rs before current reaches the terminals.
Open circuit forces external current to zero, so despite a healthy Voc no useful power is delivered — a point the diagnostic challenge tests directly. Short circuit forces terminal voltage to zero, so current is high but power is again zero. Only an intermediate operating point — ideally at the maximum-power point — delivers useful terminal power, which is why the resistive-load, voltage-controlled and MPPT modes exist alongside the two null cases.
The I-V chart plots the cell's characteristic curve in mint, the resistive load line in amber, the live operating point in white, and the maximum-power point in violet; the P-V chart shows the same operating point against available power. The photon-energy chart applies E = 1239.84/wavelength(nm) so you can see directly why a 1300 nm photon (below the 1.12 eV gap) produces no photocurrent in this model.
This is a teaching model: broadband current is calibrated to an illustrative 9.5 A reference cell rather than an integrated solar spectrum, the monochromatic experiment uses an illustrative energy-dependent external quantum efficiency rather than measured EQE, junction fields and carrier trajectories are conceptual (not a Poisson/drift-diffusion solution), and temperature is prescribed rather than calculated from a heat balance. The ideal MPPT load controls terminal voltage without converter loss or switching dynamics.
Open circuit forces external current to zero, so despite the cell reading close to its normal open-circuit voltage, power (P = VI) is zero because no current flows. The simulator's diagnostic challenge is built around this exact scenario.
It repeatedly nudges the operating voltage and checks whether delivered power rose or fell, reversing direction on a fall. Advance time (e.g. 5 second steps) to watch the tracker approach the maximum-power point and settle into a small oscillation around it, exactly as the delivered-power-over-time chart shows.
Photon energy is E = 1239.84/wavelength(nm). At 1300 nm that is below the simplified silicon band gap of 1.12 eV used in the model, so the photon cannot create an electron-hole pair and the monochromatic experiment shows zero short-circuit current for that wavelength.
It is a single-cell single-diode model with prescribed (not calculated) temperature, an illustrative reference photocurrent rather than an integrated solar spectrum, and an illustrative quantum-efficiency curve rather than measured EQE. Junction fields and carrier animations are conceptual, and the ideal MPPT load excludes converter loss and switching dynamics.