Maybe this isn’t a new idea, but I came up with a way to keep my hive warmer during the winter.
Since the sun never shines on the north side of a hive, I put a piece of reflective foam board (I think it is called silverboard) about 10 inches away from the north side of my hive at an angle that reflects sunlight onto the hive wall. The reflection definitely heats up that side, and you can feel the heat by with your hand. It actually gets as warm as the sides being directly hit by the sun.
(I also tape black-painted styrofoam onto my hive during the winter; and then tape black plastic garbage bags over the styrofoam. The black bags absorb heat, and the air pocket created by the bags over the styrofoam gets pretty warm.)
Hope this helps some cold-weather beekeepers.