As long as the sun is out, you always have a source of fire. The energy of the sun, even though it is 93 million miles away, is still enough to light some tinder if focused properly. There are a few things you are going to have to know before you try to start a fire with the sun. This article from Willowhaven Outdoors will set you straight on how to start a solar fire.
8 Solar Fire Starting Tips You Must Know