Black circles indicate a definite ‘yes,’ whereas hollow ones denote a partial ‘yes.’ For instance, it isn’t entirely clear whether nuclear fission can ever be economically viable in the absence of government subsidies. Empty squares denote a probable ‘no’ while question marks indicate situations too uncertain to render any judgment upon.
A few of these technologies are so speculative that it is hard to make a decision. That said, this is probably a relatively good summary of the state of the debate at the moment.
Many of these technologies are discussed at greater length in other posts.
Why does fusion potentially require major infrastructure changes?
Fusion might only be practical in really massive power plants. As such, it might require changes in energy transportation infrastructure.
“The infrastructure of suburbia can be described as the greatest misallocation of resources in the history of the world.”
—JH Kunstler