If I might be so bold... if you are considering solar lighting, you should be mindful that batteries are typically not included (nor are decent charge controllers or power inverters) and can make an otherwise great idea rather pricey. But there is some satisfaction in going off grid. One can also have "local" power without extension cords with the right setup. With a timer or two one can automate the whole thing quite easily.
Btw, oil filled electric heaters work great and are a very low risk for fire if installed safely. I use a low amp oil filled heater, plumbed through a thermostat set to only come on below -5.
Last winter, when the temp outside was -35 it was downright cozy in the coop. But then a standby genset becomes a must have item, unless you have a very, very stout solar system... a heater can draw down even the most robust storage setup in very short order.
Edit: sorry for the duplication of the above very sensible responses.
Edit x 2: if you do decide to use lead- acid batteries in a solar setup, I suggest they be kept outside the coop. Off- gassing batteries and electric fans, switches, relays etc can be a substantial explosive hazard -- especially if one is using an old fashioned trickle charger that likely overcharges the battery on a continual basis. Use a "smart" charger instead.
