#244 1995 · EDF · Electricity
EDF dyed the calendar three colours so France would cook dinner off-peak
the problem
Winter evenings overwhelmed the grid
background
France's grid, heavy on nuclear baseload, had a narrow but brutal problem: on the coldest winter evenings, electric heating across millions of homes spiked demand hard enough to require firing up expensive, rarely-used peaker plants. EDF had already tried a version of demand-shifting with its EJP tariff from 1982 — a simple two-price system, cheap almost always, expensive on roughly 22 called days a year — but EJP's plain price number gave households no easy way to plan around it.
EDF replaced the single number with three colours: every day is announced the evening before as blue, white or red, and red-day peak electricity costs roughly triple the base rate. A number requires a household to check a tariff table to know whether tonight is expensive; a colour on the calendar tells them at a glance, no arithmetic required. (The exact launch year is not precisely documented in the sources available — retail-energy sites place it anywhere from the mid to late 1990s.)
the move
Tempo tariff: days are dyed blue, white or red the evening before, with red-day power an order of magnitude dearer than blue.
the payoff
Households shifted load off the ~22 red days a year, shaving national winter peaks without new plants.
what came after
Tempo is still running three decades later, with roughly 300 blue, 43 white and 22 red days announced each year, still moving demand off the coldest evenings without new generating capacity. It stands as a reference case for legibility as a pricing tool — encoding the price signal into something instantly readable rather than a number that requires arithmetic before a household will act on it — though some subscribers have since traded it back for EDF's flat regulated tariff, unwilling to track a daily colour alert for savings that only pay off if red days stay rare.
filed under
references
- [1]Understanding EDF 'red days' and their impact on your French energy billThe Connexion, 2025connexionfrance.com
- [2]Schedule of Tempo-type supply offeringsRTE (French national grid operator), 2025services-rte.com