A lot of grid is wasted during off peak times. Energy is stored or sold in inefficient manners. Instead, they should use any excess energy in mining bitcoins to sell. Rather than raising electric rates, they can increase their customer base. Their price discovery will be the electricity/btc pair. They can choose which will be most profitable. Storage can then be bought by customers for their needs based on rates. This just seems more efficient than being forced to sell to only one market.
Well in a lot of countries like Sweden Smart grids are coming up. So during off peak hours, most of the energy is now stored and not wasted .
So it would actually be hard to use that to mine bitcoins .However in some developing countries, the waste still happens , and those might be perfect places to do this.
Not sure how welcoming some of the companies would be to the idea, and would be willing to spend money into the mining gear for this.