I do a lot of work in the garage. In winter its really cold and uncomfortable out there! So, for the longest time I've wanted to heat my garage with solar power. Weather that be hydronic heat or a hot air panel I think both are a great way to get free heat. The main problem for me is that my garage is located directly north of my two story house and sits in the shade most of the day. I might be able to put a small hot air panel on the SE corner, but its not going to be a huge heat source.
So, I've been thinking of alternative ways to heat the garage. One way that I'm really liking is the idea of a rocket stove type heater. Just run it off twigs and sticks that are normal deadfall during the summer/fall. If I don't have enough on my ~1 acre, my next door neighbor would be happy to clear off his lot.
The heater would be designed with either tons of thermal mass, or enveloped mostly in a water jacket so I could pump the hot water out to say a car radiator or something to blow and heat the garage. The later is more likely since I'm not out there for a long duration of time and would need quick heat rather than long constant heat.
At this point I'm open to other options for heating, but I'm not really thinking there are a ton. Let me know if there are!