I'm curious how this works. What happens if you pay for clean and the wind isn't blowing at night? What happens if everyone paying for clean turns on their appliances and the demand outstrips the clean supply?
I highly doubt there are blackouts in these occasions so it seems like someone is getting screwed.
edit: Going from memory... The fine print on your electric bill in Texas says something like: "If we, the electricity provider, don't have enough renewable energy to meet your current need, we promise to offset the amount of non-renewable energy we provide to you now with a future purchase of the same amount of renewable energy from an electricity generator." In other words, you get the electricity today, they get the money today, but they have to buy more renewable energy in the future.
So yes, if people stopped buying from companies selling wind and solar only the companies selling gas and coal would be putting energy into the grid.
To incentivize renewable energy production, "Renewable Energy Credits" are used for the bookkeeping of what kinds of energy is being generated, and are created when energy is produced by a renewable provider (handwaving a bit here...)
Consumers and businesses can have their electric plan provider purchase these credits per their usage to make sure they are getting the correct portion that actually comes from a renewable source.
So the demand and pricing is adjustable determined by the pricing of the credits.
It's pretty likely that the literature describing the plan mentions what happens when they can't buy renewable power.