I don’t think you cam anywhere close to answering what was being asked by that poster, instead you ignored it.
Alright then, it will come from the same place that the electricity for the 500,000 new homes a year will come from. It is not like the grid was built 100 years ago and we haven't expanded it since.
As to the specific energy source, as long as it isn't foreign oil (and it isn't) then it is an improvement, regardless if it is coal, natural gas, nuclear, hydro, wind, solar, whatever.