1) Gas peakers - where every kilowatt hour delivered by solar or wind is just a kilowatt hour of gas that would otherwise have been burned. We are generally still here - still burning gas while it's sunny and windy.
2) Pumped storage and batteries gets us to 98% carbon free grids with ~5 hours of storage with 90% roundtrip efficiency - https://reneweconomy.com.au/a-near-100-per-cent-renewables-g...
(98%/5 hours is for australia and will vary for different countries but probably not wildly).
3) Syngas fills in that last 2-5% with ~50% roundtrip efficiency. Every kilowatt hour used in those 5% times - those dark, windless nights will be quite expensive although, counterintuitively still cheaper than an every kilowatt hour generated by a nuclear power plant - https://theecologist.org/2016/feb/17/wind-power-windgas-chea...
3 and to some extent 2 will require natural gas to be prohibited or taxed heavily.
One study determined the cheapest energy grids for many countries. IOW, if you had to rebuild the energy grid from scratch today, what would be the cheapest way to meet your needs?
And the answer was 90 - 95% renewables, depending on country. Solar + wind + batteries for 90 - 95% of the power, with natgas peakers for the rest. And that 90-95% number increases every year.
Another survey noted that while Australia and many other equatorial countries are optimal for solar, Finland is pessimal. Most countries have already passed the point where solar is best in pure financial terms. Finland hasn't, but it's very close. Which is insane, given that Finland is a poor place for solar, but a great place for wind, nuclear & geothermal.
I doubt there are any places in the world where some carbon free combination of solar, wind, hydro, pumped storage, batteries and syngas isnt economic.