KiminPA
In the Brooder
Please allow me to make a suggestion. If you don't want to be dependent on electricity, how about a cardboard huddle box lined with "space blanket" material? It would reflect back Silkies' body heat to them as they huddle in the box. The whole point really isn't to heat the chicken but to prevent the chicken from losing precious body heat. You would need to glue the fragile material down real well so busy beaks can't rip it up.
You would need to teach the chickens to use the box, but that shouldn't be hard if you toss some meal worms inside.
Great idea. I like that a lot!