Well, to start. Solar Energy for heat. You can do it a few ways.
1. solar energy pretty much becomes heat as it strikes the earth. so the most direct route, but not necessarily the cheapest is simply to capture that heat and store it. This generally requires some way to circulate a fluid through a collector panel and then transfer that heat to a holding tank (Even a well insulated hot water heater can serve) so related costs are all the materials for the collector panel which usually includes a copper sheet (Expensive) and lots of copper tubing (again expensive). A pump and the storage tank/pit, or whatever and the related expense of insulating that storage tank. the hardest part of a system like this is calculating just how big it needs to be but most people that do find out they can be surprisingly small if built well.
2. convert light to electricity and then store that for later use through an electric heater. Usually a much more straight forward and understandable way. the least efficient but the energy is free and otherwise always completely wasted. But can still be a little pricey when you start shopping for batteries and such for storing electricity.
3. Passive solar. this is probably the most acceptable method of harvesting Solar heat of them all. It require no pumps, tubes, expensive copper panels and what not. Additional costs are general minimal. But as a general rule in order to have it you have to either include it in something before it is built or be willing to rebuild to add it. One of the simplest forms of passive solar heat is south facing windows. But they can and do get far more complicated, creative and effective. In a nut shell passive solar heat is simply anything that allows your coop to warm up when the sun shines yet keeps it that way all the time the sun is not shining. As a rule they need to be designed by an engineer. they take into account conditions that are specific to your location such as mean sun hours and average temperatures, wind conditions and many other factors. But when they work they work. I know of one system that kept a house heated for 30 days of cloudy days and still was no where near running out of energy. And that was at constant sub freezing temperatures outside. and in this case the system is it not only cheap, it can be outright free. a coop with a south facing window with a 30 gal drum of water setting so the sun shines on it all day will then release that heat all night. sort of an example of how it could work and work cheap.
