The sun is an extremely diffuse energy source. If we wanted to power the US using a power source with the same volumetric efficiency as the sun you'd need a device that's about 3000 cubic miles in size.

Assuming a 100 foot tall building, that would be a building 400 miles on each side. For comparison the amount of solar energy delivered to that same area is 20 times higher! (Assuming you could capture all of it.)

http://www.wolframalpha.com/input/?i=%283.3991%C3%9710^12+wa...

So to make fusion practical for human use it's not enough to duplicate the sun - they actually need to make it work far better than what happens in the sun. That's one of the reasons they use D-T reactions instead of H-H - it's much faster.