I have many thoughts on this law, but I probably am in the minority in those thoughts. A few cycles ago I wrote this law, tested it, revised it, retested it, etc for several hours before I finally scrapped it. The purpose of the law is to try to make it economical for an individual to run a power generator, but with IGs being extremely expensive it made more sense to just buy IGs than to try to create a balanced energy economy. It's probably possible to find the sweet spot of payouts/etc, but it seemed far easier and more efficient to just run everything through a Fed power plant.
But if you want to keep the law I suggest you use the "power generated" amount instead of "power available" or whatever it is. I actually had some extra steps in my law to ensure we never paid more than we charged, but you probably don't need those. I would calculate the price based on fuel prices, so that it covers fuel costs but isn't more than triple fuel costs.
I would also exclude gov owned power plants, otherwise you are putting money into individuals bank accounts because of power generated on gov property which is unconstitutional.
There are several other suggestions I have but honestly I personally prefer Fed to just buy IGs and run power centrally. If someone wants to run power generators privately they still can, just don't know if you should be shoveling money at them