Ah the Mojave. I might have to hit you up for advice one day! The work shed is a much more feasible problem. Look up Trombe wall. A retrofitted south facing wall would have the building nice and warm in no time and with minimal cost to the wallet. Or if growing food is your thing, a sunroom with considerations on the varying angle of the sun throughout the seasons (to not overheat in the summer) https://en.m.wikipedia.org/wiki/Passive_solar_building_design would be a simple addition to heat the room and be a way to have a head start on plants like tomatoes. I've seen a simple polycarbonate or fiberglass lean to on the side of a garden shed in Mariposa that was plenty warm even in winter and was chock full of seedlings and young plants. The resources are a great place to start, just start with insolation and the rest is just dimensional analysis until you get the value you are looking for. Another resource is this exceptionally detailed book which is beyond your application but would be the go to place for the various solar concepts and theories. https://www.amazon.com/Principles-Solar-Engineering-Second-Goswami/dp/1560327146