Back to batteries;
For each Gigawatt power supply it has to backup it has to cover the
grid from 4pm to 8am and hope it can be fully recharged between 8am
and 4pm. Unless that can be done and the next night is also cold & still
then the power must fail.
That is also supposing there is enough wind and solar available above
the normal daily load to recharge the battery.
Of course that day may be overcast and still also.
Don't tell me that never happens.
All that is why the grid has to be very high power capable to move
it from anywhere to anywhere.
The whole 100% x 100% renewables depend on regular sunny days and
regular windy days and nights.
Days of overcast in a row are forbidden and still nights are also forbidden.
Aiden says the gas turbine stations will come on and save the day.
Just one or two or a dozen or so ?
That is not what the greenies demand.

Bazz,

Got it in one. Batteries are fantastic for short term (4hrs) power shortages. When wind and solar dip for several days you need real generation.

"Gas Project - Is It Hot Air". Lets hope so. You have to make the air pretty hot if you want to make steam to drive a generator.