I've always assumed hydrogen would end up having a place as a spillover. Renewable + battery systems will need to be overbuilt for the worst parts of the year,

I've always assumed hydrogen would end up having a place as a spillover. Renewable + battery systems will need to be overbuilt for the worst parts of the year, so in the average case there's going to be an excess. You have to do something with this power, and hydrogen allows you to store a lot of energy very cheaply at poor efficiency, perhaps for heating as gas is used today. In the summer, the excess could be used to remove carbon from the atmosphere.