I agree with bobbi-j. You don't need any heat or light there. Dry and out of the wind are key. Birds easily handle sub-freezing temps, they come with their very own down coat!
Chickens have been around a lot longer than electricity!
Depending on what breeds you have they should be fine. Many of the American breeds--rocks, reds, delawares, etc were bred in harsh New England weather with no supplemental heat. That was part of what they were bred for, to withstand the...