So... the electric company can't become a monopoly because you can spend the money and effort to create your own electric company? How can that not be said for anything anywhere that becomes an obvious monopoly?
I can't hook up my own ISP or manufacture my own prescription drugs quite as easily as I can put up solar panels or buy a generator.
Whatever fuel you have access to that's cheapest. For most people, that will be natural gas or propane.
If we ignore the non-fossil fuel solution mentioned, yes. The point is it's a weak natural monopoly due to multiple alternatives.