, Curve . When the voltage reaches zero, the cell delivers its maximum current -- which is about 9 amps for my BP panel in full-on sunlight and less when it’s twilight or overcast . Because the cells in a panel and the panels in a string are wired in series, the amperage of one determines the amperage of all. If you need more current, you have to wire strings of panels in parallel. My solar array consists of two 12-panel strings, doubling the current.
Because power equals volts times amps, a panel doesn’t do a whole lot of good if it generates 30 volts at 0 amps or 9 amps at 0 volts. In between these extremes, it produces useful power, and there’s a sweet spot in the middle where the power is maximized -- for my panels, 8.16 amps at 24.5 volts, giving 200 watts of power. If you hit this sweet spot and point this panel straight at the sun, it will convert 16 percent of the incoming solar energy to electricity. When most people talk about efficiency, this is the number they’re referring to, but it presumes you've hit the sweet spot, and that's easier said than done.