Solar Chicken Coop

I am building a chicken coop in northern New Mexico, it will be fairly efficient; straw bale walls minimal windows E and W a good sized S facing window, all recycled from a friends remodel.  The winter extremes here are around -10F overnight, the coop should have an R of around 40 depending on how much clay I slap up on the walls, the floor and ceiling are going to be ~30 so the birds should be kept alive through the winter  but I am interested in making them thrive enough to lay through the winter which means light and heat.  I am planning a tiny little solar system to power a ceiling fan for ventilation, and have been thinking about the feasibility and economics of expanding that for my other needs.

Looking around for lighting I think a 2 15W full spectrum florescent tube would address the lighting needs, but heat seems prohibitively expensive.  Solar Air heaters seem to be overkill as the square footage will be well under 200 feet, and ceramic heat emitters would keep it warm but place a 12 hour 75-150W load and require what appears to be substantially more investment in PV panels and batteries.  I think I can whip up a little DIY passive solar air heater scaled down from one described in Mother Earth News (I think) a few months ago, but that wont do much over night.  Any problem solving ideas anyone can share?