You may get some IDEAS and advice from a recent thread.
https://www.backyardchickens.com/threads/advice-needed-water-heater-light-electric-coop-door.1313185/
If you do have a possible access to electricity from the home,,,, it is the easiest option. Not sure how much winter weather you get...
I do not know of an easy way to solve your needs. Your options are to invest in medium size solar panels and with a battery as storage. Use a power converter and a small aquarium heater or equivalent. Not sure how much power your solar panel would produce compared to power requirements of...