#11 1998 · EDF · Electricity
EDF dyed the calendar three colours so France would cook dinner off-peak
问题
Winter evenings overwhelmed the grid
背景
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. Per a French National Assembly written question and the government's official response (2010), EJP was phased out for residential customers in 1998, specifically because Tempo's colour-coded structure proved more effective than EJP's plain price number at inciting off-peak behaviour — the government's own account frames the replacement explicitly as an efficiency upgrade, not a rebrand.
换别人会怎么做
The standard demand-response tool is a plain price signal — charge more per kilowatt-hour during peak periods, publish the rate, and trust customers to check it and adjust. EDF had already tried a version of exactly that with its 1982 EJP tariff, a simple two-price system, and it worked to some degree, but a plain number requires a household to actively look up a tariff table before knowing whether tonight is expensive — friction that limits how many people actually act on the signal in the moment that matters.
他们看到了什么
EDF saw that the EJP tariff's limitation wasn't the size of the price differential, it was the format the signal came in — a number buried in a table doesn't get checked reflexively the way a glance at a calendar does. Replacing the number with a colour announced the evening before converted a signal that required deliberate lookup into one that could be absorbed instantly, at a glance, the same way anyone already checks a calendar or a weather forecast — moving the friction from 'do I remember to check the price' to nothing at all.
那一手
Tempo tariff: days are dyed blue, white or red the evening before, with red-day power an order of magnitude dearer than blue.
为什么管用
By encoding the price signal as one of three colours rather than a number, Tempo made the state of tonight's electricity price something a household could register without any deliberate calculation — a red day is unmistakably different from a blue day at a glance, in a way that '€0.40/kWh' versus '€0.13/kWh' requires active comparison to register. Because the colour is announced the evening before rather than revealed only at the moment of use, households have time to actually plan around it (running the dishwasher tonight instead of tomorrow), converting a reactive price shock into a signal people can act on proactively. The mechanism's durability — still running roughly three decades later, per the case's own sourcing — is itself evidence the format solved a real behavioral bottleneck EJP's plain pricing hadn't: shifting enough winter-evening load off the roughly 22 red days a year to shave national peaks without building new peaker capacity, at a fraction of the cost of physical grid infrastructure.
值了多少
Households shifted load off the ~22 red days a year, shaving national winter peaks without new plants.
什么时候会失灵
This mechanism depends on the signal being simple enough to encode in a small number of discrete categories — a three-colour system works because there are meaningfully only three price tiers worth distinguishing, but a pricing structure with many fine gradations would lose exactly the at-a-glance legibility that makes the colour format work, forcing a return to something closer to a lookup table. It also depends on households having genuine flexibility to shift consumption to off-peak hours — a household reliant on continuous electric heating with no way to defer usage gains little from knowing a day is red, since knowing the price is high doesn't help if there's no way to act on it, which the case's own sourcing notes as a real reason some subscribers have since switched back to EDF's flat regulated tariff. And the tool only pays off if the expensive days stay genuinely rare — a household betting on Tempo's savings is implicitly betting that red days won't become frequent enough to erase the benefit of the many cheaper blue days, a bet that depends on EDF continuing to hold red days to roughly 22 a year rather than expanding them as grid strain increases.
后来呢
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.
资料来源
- [1]Understanding EDF 'red days' and their impact on your French energy billThe Connexion, 2025connexionfrance.com
- [2]Réponse ministérielle à la question écrite n° 70042 (tarif EJP / Tempo)Assemblée Nationale (French National Assembly), official government response, 2010questions.assemblee-nationale.fr