Follow the power. Compare the paths.

Simplified teaching model: at full sunlight, the maximum power point is 6.2 V / the selected 10W or 12W panel rating. Battery voltage is fixed at 4.0 V, assumed MPPT conversion efficiency is 92%, and the lamp draws 0.4 W. In the direct-connection model, sunlight produces a 4.5 V panel operating point, a 4.0 V battery reference, and a fixed 0.5 V drop across the current-limiting resistor. Current comes from the I–V teaching curve on this page. Resistor loss = 0.5 V × current; output power = 4.0 V × current. The fixed 0.5 V drop is a chosen demonstration condition. In a real fixed resistor, voltage drop changes with current. These are simulated curves, not measurements. The smooth I–V / P–V model is calibrated to a 6.2 V MPP at the selected panel rating and a 7.8 V open-circuit voltage. Sunlight only scales current; temperature effects and low-light voltage changes are not modeled. The illustrated Zener voltage is 4.2 V. This is a teaching diagram, not a complete lithium-ion charging circuit. Pipe width represents voltage, moving particles show current direction, and the inductor glow represents stored energy. Switching is deliberately slowed down. Capacitor fill level illustrates energy buffering, not actual voltage ripple. The initial fill-to-full sequence is a step-by-step teaching aid; it does not mean a real chip must fully charge the capacitor during every switching cycle. This demo does not simulate a specific chip’s control algorithm, charge termination, or protection circuits. In darkness, reverse-current blocking is assumed and the battery powers the lamp.