Would work for low power but not low volt, I think. I don't think the caps will build volts. You need to configure the right resistor on the collector of the 3906 so it doesn't fire until you have over battery voltage. Similar to the old battery charging from antenna set-ups from the depression era, but they had high voltage low power. They would charge a cap and when it was high enough would jump a spark gap through the battery for a pulse charge. Or stepped down through a Model A coil. I think to harvest the low volts you would need a way to step them up before accumulating. How about a BIG switch panel to change your parallel connections to series for the night?