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.)
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.
But you are talking about volumetric efficiency - the portions of the sun where fusion is actually taking place are far more efficient than that surely?
I always believed they were trying to duplicate the suns core, not the whole ball of gas.
That's easy enough to calculate. You end up with 46 cubic miles. That's equivalent to 100 foot building 50 miles on each edge.
Much smaller - still pretty large, but doable. Your energy output in comparison to capturing solar energy is now 3 times as much rather than 1/20 as much.
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.