Believe it or not you can turn a reactor off if necessary, or up and down. Crazy I know.
Biomass isn’t practical as it releases far too much emissions to be worth it, you almost might as well use gas. Actually thinking about how much land use it would take, it might actually be worse than gas overall. Biomass is only really sensible when talking about material we would waste anyway like food waste and other waste that can be burned, but that would barely make a dent in our energy needs.
Not everything is about economics, otherwise we probably wouldn’t be talking about renewables at all.
As for “free energy”, no energy is free. Solar panels and wind turbines still have a finite life span. Nuclear fuel is cheap enough to the point where it too might as well be free if we are willing to call wind turbines free. This is especially true for Thorium technology or actinide burners. Actinide burners literally reuse nuclear waste.
Can you link a source that isn’t pay walled?