That would work if personal/residential consumption used the majority of power production but industrial and transportation uses far outpace the demand of consumers: http://www.nap.edu/books/12621/xhtml/images/p2001b2d5g186001...
The costs associated with throttling/halting these sectors far outweighs the cost of overbuilt infrastructure. Electricity is already sold by the megawatt in "day ahead" commodity form so businesses have already priced this information into the market.