All the electricity produced gets mixed in. To incentivize renewable energy production, "Renewable Energy Credits" are used for the bookkeeping of what kinds o

All the electricity produced gets mixed in. 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.