The study was done by Greenpeace, so I'm skeptical of its truthfullness. Solar has an average capacity factor of around 20% while wind is around 30%, compared to nuclear being over 90% and coal around 75%.
No amount of technology can make the sun shine longer or the wind blow harder, it's up to nature if she wants green electricity to be made.
Sure, they say it's cheaper megawatt to megawatt, however, what they don't tell you is they have to produce 5 times more solar to equal that one megawatt of nuclear. Rated output means nothing when you can only produce 20% of it over the course of an average day.