[raverbashing]

More or less what happens is

There's a pool of generators that put energy onto the grid. Each one has a price per MW generated (or MW/$)

Generation is metered and consumption is metered.

So the consumer will say "bill me for the cheapest one" or "bill me for renewal one" (or better, contract a certain amount of power from 'FlowerPower Gen'), and the producer will have "I'll have to produce X MW to provide for contracted demand"

But in the grid it's mixed, of course.