Thinking of adding solar power to coop

[Parront]

So if I were just to use that setup for the coop lighting (about 3hrs a day) it would be fine?

I think that would be fine for just 3 hrs of 40 watts. Small battery, 12 volt light from a car tail light would be enough, you would save watts. You need it bright enough to read by, is all. Think dawn. The less you draw down the battery, the longer it will last.