So, a friend pointed out some holes in my first post, and while they are valid for normal homes, for underground homes (while they come with their own risks) fill in the holes.
Heat from the ground is also cooling from the ground. If you build it properly, the undergound house maintains a cool temperature all year round. Add some basic heating and a convection cooling system, and it should work pretty much on its own. Obviously there's more research to be done, but it's an interesting concept.
Electicity, yes, on the grid is good, both to get and send back if one can figure out a good system. I haven't done too much research on it, apart from the obvious solar panels.
There's more information here.