But I've said it many times.
Expressing a 50-80% renewable and the rest NG.
Doesn't matter how many times you SAY it -- it's still a wildly wrong guess.
There's not a lot of solid analysis in ANY of the sources you've used. The writing is all about WANTS and not grid design.
Simplified analysis -- wind and solar are SUPPLEMENTS -- NOT ALTERNATIVES to anything we have now. The both operate at meaningful levels only 30 to 40% of the time.
In an analysis from the California ISO about 10 years ago -- the daytime PEAK -- for which supplements are USEFUL (especially solar) is only about 20% higher than the demand at 10PM. So -- as you approach 20% -- the SUPPLEMENTS are being misused (especially solar) since it naps a couple hours before sundown until a couple hours AFTER sunrise.
If you were to PUSH to 50% -- the ONLY goal you achieve is needing MORE NGas or other 24/7/365 facilities to PRESERVE the grid demand. That means the SUPPLEMENTS GET MORE EXPENSIVE because you're building out TWO power plants instead of just one.
And even as DAYTIME PEAKING supplements -- you STILL design the grid to survive the loss of ONE or BOTH wind/solar. Which means that THEY (wind/solar) were NEVER alternatives and as such were severely mis-named on purpose.