Simple Circuit: 2 LEDs in Parallel with solar cell
3V is low enough that the resistance of the diodes is enough limit the current so they won't blow up immediately, but controlling the current is always a good idea. The voltage is so low, a simple current driver may be a better than a resistor:







simulate this circuit &ndash; Schematic created using CircuitLab

The current trough the transistor (Ice) will be about 100x the current through the base (Ib). Keep in mind this about 0.7V across the base and emitter of the transistor, if you wanted to calculate a new R1, and the gain will increase (and try to drive more current) if you leave it in the sun. You just make R1 bigger if that's an issue.