Would this cost money? Yes. But it would likely cost less than a grid based on nuclear power plants. The key insight is that hydrogen can feed combined cycle power plants, which cost a factor of 10 less than a nuclear power plant of the same power output. So, one could (if necessary) back up the entire grid with CC plants at a fraction of the cost of powering the same grid with nukes. If desired, one could use simple cycle power plants, which (while less efficient) are even cheaper by another factor of about 2, or 20x cheaper than the nukes.
