Hydro isn't carbon free. It takes a lot of cement to build a hydro dam. Even earth damns need to have their central and powerhouse structures made of cement.
Hydro emits less carbon per unit of electricity than solar [1]. And drastically less than the renewables + natural gas mix that's used in practice to accommodate renewables' intermittency.
In a 100% renewable economy, where is the carbon emission coming from in PV? PV doesn't make carbon atoms out of nothing. Also, that chart is ROOFTOP solar. Rooftop solar is not what would be used to power a renewable-powered society; it's more of a con to game current utility rate structures.
Hydro will always have a problem with methane emissions.
