I've been thinking about what it would actually take to have a carbon-free economy at a large scale. I've built several house-scale off grid solar/wind/generator systems before, all using lead-acid batteries. They all needed generator backups for when the wind & sun doesn't work.

Without a fossil fuel generator backup of some sort (or some other on-demand backup that's always available), there will be times when the batteries get dangerously low and the system will have to go offline.

Depending on the location this could be a few times per year or several times per week.

Scaling this up to the entire grid means you're going to need HUGE batteries.

Utility-scale battery storage tech will have to continue scaling (immensely) to have a truly carbon-free economy. Is the battery or storage tech ready for this? There will also be an environmental impact to constructing & maintaining batteries of this immense scale.

Perhaps other carbon-free storage technologies (flywheel, hydrogen, etc.) will also be applied.