A nuclear power plant may take a decade to build, whilst one can put solar panels on the roof of a house and connect it into the grid in a day, a wind turbine in a few weeks or months. But the rooftop solar installation produces a few kilowatts (when the sun is shining) and the turbine a few megawatts (when the wind is blowing), whilst the nuclear station produces several gigawatts, 24*7 and almost 52 weeks a year. How can we compare them?
One way is to look at how fast countries have been able to build clean electricity generating capacity per person in that country. This grahic compares the rate over the best decade for various countries and technologies. We can see that the world record is held by Norway's hydro-electricity construction between 1980 and 1990, followed by Sweden's nuclear build-out from 1976-86. The twelve fastest build-outs have been hydro and nuclear; despite the long times it takes to build these technologies, the sheer scale of the amounts of energy they produce when they are running outweighs their relatively long build times.