Well that's what my friend's startup focuses on currently piloted in South Africa. The startup built a device that reliably saves power. You don't need to pay any fee up front for the device, you "pay as you go" on amount of saving made on monthly basis. No catch. Average savings currently are around 10-15%, engineering team is pushing the numbers up as we speak. Business has gotten necessary funding and even the primary energy supplier has come on board to put an initiative together that would implement the solution to all street lights in the country in the near future. South Africa is currently going through energy crisis due to huge demand and lack of supply.
PS. My wife is one of the co-founders. :)
