Is this based on cost per Watt without the expenses related to keeping the grid perfectly synchronized or not?

A significant and stable base load is important and it has shown that wind/solar makes it substantially more expensive to keep the grid stabilized, which is of course a no brainer if you don't want a blackout.

> Is this based on cost per Watt without the expenses related to keeping the grid perfectly synchronized or not?

It's the LCOE, you can read what it encompasses in the link I provided.

> A significant and stable base load is important and it has shown that wind/solar makes it substantially more expensive to keep the grid stabilized, which is of course a no brainer if you don't want a blackout.

I assume you mean the utility frequency [1] when you say "base load", because you said "synchronized" and "stabilized". The frequency indeed has to be stable with a rather small margin of tolerance. Today that's mostly a job for gas turbines, though. One can hope that we find ways to store all the surplus regenerative power soon, so that we can retire those, too. Nuclear power plants, in any case, are too slow for that purpose.

Just in case you really meant load, load has no requirement to be stable. The power demands at any time can be met by dispatchable power plants, but utilities like to plan long-term, so they use some averaged load over time to determine a "base load" and buy accordingly on the electricity market. That's prudent business practice, but there is no technical reason to run low-variability power plants because of that.

[1] https://en.wikipedia.org/wiki/Utility_frequency