One of the most important uses for energy in the Northern Hemisphere is space heating. This includes both residential and commercial applications where an area is heated above the ambient temperature. Energy has been so cheap in the US for so long that people think the number one choice for staying warm is to keep their home or office set at 72 deg. F.
This is not the assumption in the rest of the world. I spent several years working in the temperate climates of South America, in particular, Chile. For people in this part of the world, space heating is not the first choice. Instead, they just add another sweater. That being said, space heating is important in the US so it is something that solar energy proponents are really pushing.
One of the most cost effective ways to heat a home is with radiant floor heat. Combining solar and radiant floor heat makes a very affordable heating medium. It is very easy to incorporate in floor heating systems into a new home because whether the home has wooden floor joists or is on a concrete slab, the polyethylene tubing required for the hot water is easily added during construction. For an existing home it may be a little more difficult.
If an existing home has a crawl space then the tubing can still be strung between the existing joists. But, if it sets on a slab, about the only two options are to either cut into the slab or to lay out the tubing and then install a 2″ layer of floor cement over the top. Both of these are expensive and probably won’t offer a payback period that is acceptable. Most people who go this route do it because of their belief in alternative energy as opposed to the financial benefits to be gained.
Considering the load that space heating puts on the US energy grid, combining solar and radiant floor heat can add to a lot of savings.