There is storage. Batteries can keep up and more importantly there are a lot of options that are better (in terms of costs and ressources) than the lithium-ion ones we here so much about. Because a stationary installation doesn't have the same requirements as a mobile device or car (although even there they already move to other materials). Cheap materials and longevity for example are more important than energy densitiy because no one cares if the building is 30% heavier (for a phone however that's important).

Also batteries are not the storage we usually talk about. They are more short-term and more used in balancing out short-term fluctuations (for example even pumped storage also uses batteries as a buffer because it makes no sense to start pumping big amounts of water when they are only needed to provide smaller loads right now). And for this reason the needed capacities are much smaller and heavily de-centralized, too.

What we primarily need when we talk about full renewables is long-term storage. The kind of storage you collect the overproduction of months in, to use it all in the 5-7 in a row once a year when neither solar nor wind produce proper amounts. And it's no concidence I mentioned hydrogen production as one part of France' future plans. Because that is storage. We will need green hydrogen to electrify a lot of industries and some transport. Maybe even green efuels (=putting even more electricity in to bind carbon to the hydrogen for a higher energy densities) for some kinds of air travel for example.

That's potential long term storage right there. Yes it isn't very efficient, but it doesn't need to be. You already need a constant supply for industries and having some buffer to smooth out production (that will be linked to renewable excess production) is already economically benefical. Making that buffer capacity bigger (so it can also double as storage for the small amounts of time renewables don't suffice) only costs the money you need to build it. And most of it doesn't need to be build but can be converted from existing natural gas storage.

So the takeaway is: Build renewables. Neither a nuclear plus renewable model nor a renewable plus storage model works without them. Then start building nuclear. Or storage. Or even a mix will do.

But the most important thing: do it now and massively so. Storage models need about 115-125% production (depending on how well you diversify renewables), nuclear models also need 65%+. Of the long term demand in 2+ decades... So there is exactly no country at any risk to build too many renewables right now. The 35% base load numbers basically show us that you can reach 65% renewables in your mix without problems, so all the talk about grid stability is bullshit. Again...You won't manage to build too much.

Also the most important part. Every single solar panel or wind turbine build today has a direct impact on co2-reduction. Which means you have more time to reach 100%.

That's the other problem with nuclear build times. Let's say every country manages to decide today to build the sufficient amount of nuclear base load and also manages to do the planning, construction and everything in 15 years (which would be impressive, when most need longer after all planning and location finding is done just for construction). Then they will still fail to meet the climate goals the agreed to as they can't afford today's co2-production for another 15 years. So again, they need to start a massive renewable upbuild just as a buffer to even reach the day when their reactors come online.

Oh, and of course renewable energy is cheap as fuck. So providing enough of it will automatically trigger changes in the way you use electricity. If there are enough times when electricity is basically free (most countries with higher amounts of renewables already have these a few hours a day) private companies will build storage without public investments, just because they can make money with it. Or industries using a lot will change their working pattern to need it when it's cheap. Or they will build their own batteries.

TL;DR: Build renewables! Now! Many! You can't do wrong here as it's not only the fastest way to reduce co2-output now but also a requirement no matter what your complementary plan (storage or nuclear) is.

Remember: 65% (nuclear) to 125% (renewables with sub-optimal diversification) are needed. In a future with at least 2,5 times today's electricity demand. So that's 162,5% of today's production at the very least, just in renewables before any base load. There is no excuse not to start today.