I'm pretty excited about the methane generator idea. The most exciting part is that my wife is fully on board with it (to be honest, she actually suggested that we look into a methane generator originally, since the greenhouse will be located on a farm with 400 head of cattle...).

I'll probably focus on building the greenhouse first, but I do need to figure out what type of heat I'll be utilizing. Forced air would be easy, but I'm guessing it would not be good for the plants, especially in the winter. In-floor is the other option, but I need to figure out what type of water heater to use, and if using methane is acceptable.

The other big one with the methane generator is the storage of the methane. I wonder if it is possible to pressurize it in tanks similar to propane, so that I can store large amounts of it over the summer to be prepared for winter. Lots of stuff to look into.