dc-dc step down converter (used with solar panel?)

they are available on ebay for under $2 adjustable are well within power/voltage range. th question I have is...... the input voltage is supposed to be at least 2v above output, which it is when the sun is out, but when it is going from night to day or visa versa, the input is lower than the output. will this damage the dc-dc step down control board? It doesnt say if they are switching or not? any thoughts on this?

You could use a diode to prevent reverse current.

What are you running with the solar panel? You might check e-bay for buck boost converter (or regulator), then you could keep things going in less sunlight as well.