Renewables are now EU's main source of electricity
ember-climate.org
ember-climate.org
Austria and Sweden appear to have had nearly 80% of their energy in 2020 generated from renewable sources. It doesn’t appear that they had any issues with their power not working.
I take your point, but hydroelectric power depends on geography and doesn't work remotely close to everywhere. (Same thing with Iceland's geothermal. Nice they can do it, but not general.) Austria and Sweden are both close to best case scenarios for hydro, and do not generalize. This is before even beginning to think about the environmental pushback, etc. on hydro plants. (And bio-energy has many of the same 'dump carbon into the atmosphere' issues that are so problematic.)
Whatever the number is, it will naturally decrease over time as batteries improve, more renewable sources are installed, and other ways of smoothing out demand are invented.
We're not really anywhere near the limits yet. There may be some floor which is always supplied by fossil fuels, but that floor isn't relevant to the goal of drastically reducing carbon dioxide output. The next steps to take, adding more renewable sources and removing more fossil fuel capability, is straightforward, and we'll see the limits well before we get there.
The number matters to the extent that there are other goals in addition to lowering carbon output.
I get that it's existentially important to lower CO2, but if you can't reliably deliver power that society has come to expect, you're going to have a hard time keeping society's eye on the ball. CO2 reductions are easier to sell to a society that has reliable light, heat, etc.
To put this in concrete terms, you mention fossil fuels as a potential for base load service - another important part of the portfolio is nuclear. Unfortunately, a number of these plants are shutting down, at least in the US, as rule-based incentives shift toward renewables. The incentives are meant to do what you advocate - reduce CO2 emissions. But it is really a win to replace nuclear generation capacity with a combination of renewables that can't replace base load and, I guess, additional fossil fuel generation at the base level to make up for the lost nuclear?
I don't claim to know the answers here, but there's more to it than just a focus on CO2, which is why I asked the question I asked at the head of my initial comment.
But even without that, it's a smooth curve. The existing fossil fuel plants can cover base load, and will last long enough that they can be shut down when they're no longer needed. By the time we need to consider replacing them, technology will have shifted, and we can't really know whether we'll want to replace them with new fossil fuel plants, Nth generation nuclear, batteries, superconducting grids, or fusion. The timeline for shutting down all of the exiting fossil capacity is the same as the practical-fusion time scale.
The point is that there's no reason for the public to worry about base load. The planners have to, of course. But it's a problem with a solution, rather than a leap into the unknown.
Nuclear is a nice add-on, if it succeeds, and allows us to shut down fossil fuels faster, but it's not necessary and not the long pole in the tent of reducing carbon. Renewables are built much faster and will reduce much more carbon before the first new nuclear plant is completed.
I hope you're right, but I'm not as sanguine as all that.
Coal plants are usually most efficient when running in a continuous, almost max generation condition.