Very cool, but still basically fiat thinking. The energy is coming from increased caloric cost for people to walk, so its really transferring the cost of electricity to the cost of food. And I'd be very surprised if it does so efficiently - you would have to measure the cost of manufacturing, installing, maintaining, and disposing, in terms of energy - so, a balance sheet denominated in joules - and see if that's less than the energy returned. So, this is probably just a cleverly camouflaged tax.