> Storage + Intermittent is not enough to power a modern grid.
As a previous comment pointed out, one solution is to just over-construct renewables. You can look through a graph of output of wind+solar for a large area and find the minimum output compared to its rated capacity. The output from wind+solar is never zero, and the minimums are usually short. Last time I looked at the numbers for UK, if I remember correctly, it looked like they had to have 2-3 times the rated capacity to produce enough for the vast majority of days with minimum production.
It's more accurate to say that nobody has demonstrated that storage + intermittent can power a large scale modern grid (there are plenty of examples for micro grids and islands). Whether it actually can or not is unknown.
And part of the reason is that nobody has really needed to demonstrate it yet. There have so far been other workarounds that have been acceptable. UK and Germany doesn't have their own hydro-power, but has built grid connections to tap into Norway's for instance.
> Also yes you do need to always meet demand to ensure the frequency is stable, otherwise you'll have massive problems.
The other side of this, that is increasingly being taken more seriously, is to have more adaptive loads. There are for instance large parking garages built for EV car ride sharing or rental services that are V2G capable. The cars have quite a lot of flexibility in when they do their charging, and they can even feed energy back into the grid. There have been studies of anything from varying the temperature of freezers and hot water tanks across the country, to varying production rate or temperatures is metal production.
To me, if we're serious about solving climate change, this is essentially a problem that solves itself: we absolutely need to make a MASSIVE amount of green hydrogen.. for trucks, ships, planes, e-fuels, fertilizers, steel, etc. That's a HUGE amount of load that can easily be load-balanced to follow the production from renewables. You can even feed some of the stored hydrogen back into the grid in rare cases with extremely low production, probably using existing gas peaker plants.
I'm not against nuclear btw, but feels like the most enthusiastic nuclear proponents often have a very myopic view of the problem. That is, they assume in 20-30 years, everything will look exactly the same as before, except all electricity is nuclear+some renewable. Assuming we don't solve the energy storage and load balancing problem is equivalent to assuming we don't solve the climate crisis, because CO2 emissions are about so much more than just electricity production.