I'm not wishing to put a damper on things, but we have solar panels on our roof and in the Winter, they generate hardly any electricity. Whereas in the Summer, 2KwH panels will generate 1.5KwH per hour for around 10-hours, in the Winter, they often only produce 1KwH over the course of the entire day. As this Summer has been particularly cloudy and wet, we've had days in the Summer where hardly any electricity was produced. What I'm trying to say is, you may find that the solar panel doesn't generate sufficiently to power your lamp, especially in Winter when there's only a few hours of strong enough light at lunchtime (unless it's overcast).
If you the lamp is an LED lamp, you may be okay as they use hardly any electricity. You may wish to try a battery powered bulb as a back-up.