OK, can you just buy a solar heating panel? You and your best friend can install it...depending on location you can easily get hot water for 6-10 months a year. That's quite a savings. You don't have to solve everything today ;)
And some making sure the roof/attic floor doesn't collapse, which usually is not a problem.
This can be _build_from_scratch_ in a couple of weekends with a best friend.
But for the construction codes. And unions.
It's so low-tech, so I wonder why I haven't heard of 19th century installations. Me, I actuially built two in places where construction codes are not an issue. And have seen functioning installs dating from 1950s.
I don't think it even makes any sense to mass-produce heat boxes the way the solar-electric panels have to be. It all can be either made on site or included into the house design from start.
That's maybe why you can't buy solar heating off the shelf.
You usually want a water tank to buffer the thing, so you can get hot water at night. Temperature will be all over the place without that. Giant hot water tanks in attics need extra structural support, which was a problem in Florida at one time.
There are some fancier setups that will work in cold weather. Some systems use antifreeze in the panels, and a heat exchanger.
[1] http://www.alternative-energy-tutorials.com/solar-hot-water/...