A quick calculation gave the answer as 470 000 seconds, or about five days. Not too bad: if we use the capacitor for energy storage in a solar-powered lamp we can probably allow a couple more microamps of current and still have the lamp on throughout the night and day. All we need to add is a suitable solar panel. The figure shows the circuit diagram of our (in every sense) green solar lamp.
By Burkhard Kainka (Germany, Elektor)