EDF in France has some really complex tariffs geared toward electric heating and encouraging users to economize during periods of high demand.
Their "Option Tempo" divides the year up into red, white, and blue days. I can't recall the exact numbers off hand, but they're limited to something like a maximum of 30 red days per year, and a greater quantity of white days. Red days are the most expensive, white moderately so, and blue the "standard" rate. Within each of those divisions there are then day and night rates, giving SIX distinct cost-per-unit rates.
Within the limits set out, EDF decides each evening whether the following day will be red, white, or blue, based upon the weather forecast from the meteorological office in Toulouse. Consumers can have installed a signal box which displays the appropriate indication for the following day so that they know how much they will be paying.
