Well no, the grid is pretty stable today because fossil fuels are very predictable and base-loady. The point is that renewables aren't, so if you push too hard on renewables then you will have more outages due to losing control of the supply/demand balance.
Maybe because I live in a municipality known for hydro power, so I don't consider that an issue. But it's a renewable that's just as easy to control as gas. Even better, can pump up water and store energy when solar or wind have excess power.
Yes hydro and geothermal are exceptions, but also irrelevant on a global scale. Hydro sources are already tapped and won't take us any further. When people say renewables in this context they mean the sources that can be scaled up. Pumped hydro is nice when you can get it but again there isn't enough.
Re-reading I didn't quite understand your original point. What do you mean big power plants have the exact same grid problem? The issue comes from the dispatchable nature. You can tell a combustion plant to set output to a particular level and it will do so. That's what you need to keep a grid stable. Wind/solar can't do that.
When people talk about gas and the grid, I often feel them talking about some external factor shutting down the grid (weather etc), and thus how having gas for heating is better than electric because you're not as dependant on the grid. And in that context it doesn't matter if it's a gas plant or a solar farm making the energy anyways.
Well, there's that too yes but I think that's not the main thing people mean in this context. The issue is that in most parts of the world a 100% renewable grid can't satisfy demand on a still night, and storage tech isn't there to ride you through - but even if it was, long stretches of cloudy still days are easily possible. Also the grid is very hard to restart once it has a big enough outage. Even once power is available at all the stations again, a black start is no joke and most countries have never been through one ever.
Why would anybody need a 100% renewable grid? Renewable grids will be 150% grids, that provide 50% more load than you normally need and 100% for 98% of the time. The remaining 2% of time where renewables can't deliver (windless/sunless winter days) will be covered by gas peaking power plants.
The goal is to avoid CO2 emissions at reasonable economic prices.
You can't build 2x the generation capacity (which is what you're suggesting) at economic prices anyone would today consider reasonable. Remember you have to be able to cover 100% of demand from non-renewable sources. It's not just the gas plants, it's the pipeline network, the gas wells, the LNG import terminals, the ships, the whole shebang. It's extremely expensive to have it available but not actually use it.
