In my city they had everyone switch to renewable energy, they sent Mail out stating that your energy source will automatically change unless you opt out.
LOL how are they going to change the energy source that powers an individual house if they "opt out" ??
Did they run separate power lines to every house that is on a switch between the power sources? It's not like a network packet that you can route to a destination, it's going to go down the lines the same way unless the circuit is broken.
Suppose Provider A is 100% renewable and Provider B is 100% fossil. Both providers generate power and feed the same grid (which is managed separately from the various energy providers). The same grid powers all homes. Householders get to choose whether to buy from Provider A or Provider B. If you support renewables then you buy from Provider A; their share goes up and B's share goes down. And vice versa for B. In addition the government juggles A,B as well as C,D,E,etc to provide the overall service to the country.