Rundstyrning
Sweden had a working, widely installed demand-flexibility mechanism in the mid-1990s — ripple control switching water boilers and street lamps, able to curtail up to 7–8% of peak load in smaller DSO networks — a decade before "flexibility market" was a term anyone used.
CoordiNet reports it was phased out around 2000 with the absence of delivery responsibility in the no longer vertically integrated utilities, a reminder that market restructuring can dismantle working flexibility infrastructure as a side effect, not just create the need for new infrastructure.
Rundstyrning (ripple control) was a Swedish DSO mechanism for remote load switching: a kHz-frequency signal superimposed on the standard 50 Hz supply, used to switch between low and high tariffs or to turn street lamps, domestic water boilers, and other controllable loads on or off from a central point (Source - CoordiNet D4.7.2 Swedish Demonstration (2022)). It is the historical predecessor to today’s digital Demand Response and Flexibility Market mechanisms — a working, deployed flexibility system a full generation before either term entered common use.
How it worked
Many Swedish DSOs had ripple control systems installed in substations, which sent a kHz signal on top of the base 50 Hz frequency to change between low and high tariffs or to turn streetlamps and domestic water boilers on or off in times of high grid congestion. Typical curtailment was about two hours per day, or 15 minutes out of 60 in a congested hour. No separate communication network was required: the signal rode on the power line itself. This contrasts with IP-based protocols like OpenADR, which came decades later (a wiki comparison, not a claim from the source).
Scale and results
Installed by many Swedish DSOs by the mid-1990s. Figures reported by CoordiNet (Source - CoordiNet D4.7.2 Swedish Demonstration (2022)):
- Up to 7–8% of peak load curtailable in smaller DSO networks, where 10–20% of customers could each provide 1–3 kW (a possibility, not a measured system-wide outcome). A few hundred MW might have been available nationally at one point, per interviews cited there.
- Värnamo Elnät (10,000 customers) still had 6 MW of ripple-control flexibility installed in 2008, after the general phase-out; a 19% (45 EUR/month) tariff discount for disconnectable 16A customers was still on its price list in 2021.
- Fixed monthly tariff discounts were the customer-facing incentive — participants paid less in exchange for accepting utility-controlled interruption, an early rules-based/explicit flexibility arrangement conceptually similar to today’s Villkorade Avtal (though villkorade avtal are a connection-agreement mechanism for DSOs managing capacity, where rundstyrning was aimed at system-wide peak reduction).
Why it was phased out
CoordiNet states that domestic ripple-control flexibility was quickly phased out around the year 2000 “with the absence of delivery responsibility in the no longer vertically integrated utilities”, and that this had little impact because consumption was then declining. The source does not say the technology failed. The wiki’s reading (inference) is that once the integrated utility’s bundled delivery responsibility was unbundled, the commercial rationale for centrally switching customer loads weakened, and the mechanism lapsed rather than being re-engineered for the new market structure. Some installations persisted (see Värnamo above).
This makes rundstyrning a concrete illustration of a pattern worth naming explicitly: market restructuring can dismantle working flexibility infrastructure as a side effect of an unrelated reform, not only create the need for new flexibility mechanisms. The wiki’s broader flexibility narrative (DSOs as neutral market facilitators, market-based procurement as the EU/Swedish default) developed in a landscape that, twenty-five years earlier, had already solved a version of the same problem with a simpler, centrally-controlled tool — before the market structure that made that tool workable was itself dismantled.
Modern relevance
The CoordiNet demonstration project’s own framing describes today’s demand-flexibility mechanisms as rundstyrning “reinvented in a more digital and market-oriented way” — explicit continuity, not a coincidental resemblance. The key differences in the modern approach:
- Market-based, not utility-mandated: today’s Demand Response and Flexibility Market mechanisms generally price flexibility through competitive procurement, rather than a flat tariff discount for accepting interruption.
- Digital, addressable, two-way: modern control protocols (e.g. OpenADR) support per-resource addressing, acknowledgement, and richer signal types, rather than one broadcast signal switching every receiver in range identically.
- DSO-neutral-facilitator model: today’s regulatory framework requires DSOs to procure flexibility on a level playing field rather than directly command-and-control loads they don’t own, a structural difference from rundstyrning’s utility-operated model.