That's not how it works at all. OP must be mistaken.

All the generators get together and auction their power to the grid. In my region it's PJM auctions. There's x amount of capacity needed on the grid. The grid operators say we need that much and then everyone says "well generate y dollars per MW of capacity". Renewables can only sell a small percentage of their capacity because they rarely produce at capacity (wind not blowing, sun not shining, etc.). So well in advance, they've sold their power.

Now things changed when it comes to realtime. Sometimes you have a polar vortex and natural gas can't run, wind isn't blowing and there's a lot of cloud cover. So the nuclear plant that sold their power at 29 per MW could now be selling it at 80+ per MW.

So that's a really narrow explanation of it all but it's a hugely complicated process. But it boils down to, you really are paying what the grid operators are charging and that's based off the auctions and realtime generation. You don't pay a premium for renewables.