On demand doesn't mean instantly. Even gas peaker plants aren't instant, they can take 15 minutes to warm up and connect to the grid.
If the sun is down no amount of calling up a solar farm will increase output, if the wind isn't blowing or if it's blowing too strongly no amount of pleading will increase the output of an off-shore wind farm. This is because they aren't dispatchable. This is not the case with Nuclear.
Nuclear can do load following, they do it in France. How else do you think they balance a grid which has 70% Nuclear? They use reactors with grey rods which can reduce the reactivity in the reactor without distorting the shape of the reaction.
If the sun is down no amount of calling up a solar farm will increase output, if the wind isn't blowing or if it's blowing too strongly no amount of pleading will increase the output of an off-shore wind farm. This is because they aren't dispatchable. This is not the case with Nuclear.
Nuclear can do load following, they do it in France. How else do you think they balance a grid which has 70% Nuclear? They use reactors with grey rods which can reduce the reactivity in the reactor without distorting the shape of the reaction.