I wonder how much of that is biomass, and how they’re planning to grow enough vegetation to renew iy

You can check it out in real time here: UTE Generation Biomass is not something so actively sought, it’s more of a consequence of other industries here. You are correct that we have other renewable sources that work when wind is not on its peak. There are two hidro plants that can work when demand is large and wind is not on its peak, and they’ve managed to keep this regime even on dry or draught conditions.