you need a
4V solar panel from ebay
1 schottky diode 1n5817
1 rechargeable battery 3,7V lipo or 3 ni-mh
how it works?
The solar panel in a sunny day charge the battery through a diode, and block a night current from battery to panel of some mA, this is also the maximal current flowing in the led in the night because the panel is used also as a sensor, in the night his voltage drop to about 0V and its resistance in the night allow current to flow from battery to the led and it light up without burning, the current dipends on your panel type but it's about 7mA.
For more power light you could use the other schematic and add a pnp transistor like bc369 and light up 3 or more leds each with its resistance if necessary, the resistance is calculated by (Vbatt-Vled)/Current led Volt/mA=kohm, you should use the same power for light and for solar panel.
Remember lipo batteries should not drop under 3V each cell so when the battery is low it can't light the led and lose other current, ni-mh batteries are not affect by this problem.
I hope you like it, have fun! :)
more info to my site http://elettroportale.altervista.org/Lampadagiardino.html