Hydro power is a great thing, it was the first renewable energy that was available in meaningful quantities. However, great sites for hydro power are definitely limited. We will not suddenly find a great spot for a new huge dam. Imagine the only source of vegan B12 to be some obscure plant that can only be grown on a tiny island. In this scenario, the possible extend of vegan consumption is fixed.
In the regions where it works (PNW, Quebec, etc) we could easily build more. The hurdles are regulatory. The regulation isn’t baseless - a dam will affect the local ecosystem adversely. But that’s a tradeoff we choose rather than a fundamental limitation.
The other trade off is correlated with the energy stored : potential for catastrophic disaster in case of failure. as a society, living below is not risk free in the long run.
