> The general idea is that you grossly overbuild your renewable energy production (solar and wind mostly) and during the middle of the day when the grid is fully saturated and all of the storage systems are filled up you dump the excess energy into carbon sequestration

Or you build solar and wind plants specifically for carbon sequestration. Then you don't have to worry about coordinating with the needs of the grid. You don't even need the plants to be on the grid. That frees you up to put them places where there is plenty of wind or solar but no infrastructure transporting electricity which would otherwise by useless for solar and wind currently.

California currently gets much of its electricity from a 500 mile long intertie to the Pacific Northwest. There are plenty of plausible places to put a big solar farm which are less than that distance from civilization, e.g. Arizona or Nevada. At which point you want any of its output during peak consumption hours to go to decarbonizing the grid, regardless of what you do with the off-peak.

And then you need to pump these giant amounts of CO2 sludge (or whatever form it will have) back where you drilled oil out of, hoping it will stay down. That will cost a lot of energy too.

No, this is incorrect. You can absolutely burn hydrocarbons, use the energy to do carbon capture, and end up with less CO2 in the air than when you started.

Compressed CO2 is still a lower energy state than the hydrocarbons, so you can get net energy out.

You couldn't end up with the same hydrocarbon that you started with, of course - that would violate the laws of thermodynamics.

There is no place to store all that - and don't say depleted gas and oil wells since those are ruined as long term storage by whats been done to them to get the oil or gas out.

So you need to build the structures to keep 20km³ of liquefied CO2 each year (liquefying also takes energy).