Probably better to discuss it in the other thread and keep this to EV's but I'll just say that so far as the grid is concerned, the problem isn't with how to shift solar energy from midday to 6pm or how to keep the lights on overnight. That's relatively easy to solve via batteries and small pumped hydro schemes based on old quarries etc.
The problem is how to cope with multiple consecutive days of far below average wind and solar yield and doubly so when, as often occurs in practice, those periods coincide with above average consumption. Batteries and small hydro is nowhere near up to the task - what works, with present technology, are fossil fuels or large scale hydro and by that I mean storing far more water than can be achieved with a disused quarry.
There's a great example of the problem in Victoria over the past few days.
Sunday 26 March VRE (wind + solar) yield was just 50.9% of the daily average for the past 12 months.
Monday 27th it was 20.2% of the average.
Tuesday 28th it was 41.9% of average.
Much the same in SA:
26th = 69.6% of average
27th = 61.5% of average
28th = 61.1% of average
Tasmania:
26th = 32.1% of average
27th = 58.5% of average
28th = 85.9% of average
NSW
26th = 83.7% of average
27th = 52.2% of average
28th = 46.9% of average
So the whole of south-eastern Australia has the same issue at the same time.
Solutions:
1. Build far more wind and solar than we need overall, so there's still enough on relatively calm days. Downsides = huge financial cost. Also environmental impact = when you need that many of them, you don't get to be too fussy about where they're installed.
2. Backup generation using, in practice, fossil fuels. Downsides = CO2 emissions and reliance on imported fuels. Also potentially expensive.
3. Large storage hydro. Downsides = upfront high cost. Environmental impact of land use change - opposition to large hydro projects is after all the very issue upon which the Greens were founded.
4. The problem can be reduced but not eliminated by major transmission projects over long distances. Queensland and WA have both experienced far better conditions over those three days for example. Downsides = over that distance the cost is huge and those lines are going to upset someone no matter where they're put. Farms or natural bushland including National Parks - there's not much land that isn't one or the other and both will attract howls of protest.
So overall it's a "choose your poison" situation but there's no option that won't upset someone somehow.
General industry consensus at present = gas is the path of least resistance.