Originally Posted by Ligeia
You can't get more energy out of it than you put in. That's the laws of thermodynamics.
I just looked up some information on fusion energy more generally, and it looks like the highest efficiency you can get is around 80% (that is, for every 1 MW you put in, you get 0.8 MW out; by comparison, a coal plant would produce about 0.35 MW). This is very, very good, as nuclear fusion produces the most energy per mass unit of any technique we know. The only known way to get higher efficiency would be to convert mass directly to energy, which we are not yet capable of doing.
Just as I had suspected, this technology will be limited by resources. Though the high efficiency means that we can produce a sizable amount of power with significantly less resources than we currently do with other technologies, it still relies on a non-renewable resource (fresh water) which is bound to encounter some supply issues.
Actually it uses seawater not fresh water.
However I think the ridiculous amount of money spent and continuing to be spent could have been better spent on alternative energy technologies like solar, wind and tidal.