On Monday 8 June something unusual happened in the Swedish power system. Two faults, entirely independent of each other, occurred within the space of an hour. The frequency fell to a low of 49.80 Hz, every upward regulation bid in price areas SE3 and SE4 was activated, and when the bids ran out Svenska kraftnät started four gas turbines. The event was reported by Swedish media including Göteborgs-Posten, and Svenska kraftnät has published a detailed account with a full chronology.
It is worth walking through what actually happened. Not because anything went wrong in the response, on the contrary, Svenska kraftnät's control room handled the situation quickly and methodically. But because that afternoon gives an unusually clear picture of what flexibility is worth in a power system under pressure.
What happened, hour by hour
At 14:20 Svenska kraftnät received reports of people climbing high transmission towers outside Bollnäs. For personal safety reasons the line was disconnected at 14:33, which reduced transmission capacity between price areas SE2 and SE3. To manage the resulting risk of overloads, exports on the Fenno-Skan cable to Finland were increased.
At 15:16 the second blow landed. The Swe-Pol Link cable between SE4 and Poland tripped, and with it 500 MW of imports disappeared. Two independent faults had now occurred within roughly an hour, and the system frequency fell to a low of 49.80 Hz.
Svenska kraftnät then activated every available upward regulation bid in SE3 and SE4. "To maintain operational security, ancillary services were activated to such an extent that all bids in SE3 and SE4 ran out. We therefore also had to start four gas turbines," said Pontus de Maré, head of operations at Svenska kraftnät, in the agency's account (our translation). The turbines started were Halmstad G11 and G12 and Barsebäck G13 and G14.
At 15:43 Svenska kraftnät declared a yellow state, meaning heightened operational alert, and sent out a notice about the risk of a power shortage. At the same time 200 MW was purchased from Lithuania and 200 MW from Norway. Shortly before 16:00 the turbines could begin shutting down, and by 17:15 Swe-Pol Link was back in service. The whole sequence, from first alarm to normal operations, took about three hours.
The gas turbines are the system's last line
The gas turbines in the disturbance reserve are not an ordinary generation resource. They are the system's insurance policy, built to step in when everything else has already been activated. Starting them is rare, and that is exactly why this event is interesting. On 8 June, the flexibility procured on the market in southern and central Sweden was not enough, even though the faults themselves were manageable and the weather was nothing extreme.
The numbers show how fast it moved. In a single quarter hour, between 15:30 and 15:45, 701 MW of manual frequency restoration reserves (mFRR) were activated in SE3 and 255 MW in SE4. That is close to a full nuclear reactor's worth of power that had to be found, activated and delivered within minutes.
Prices spiked, and will likely be adjusted down
The large activations drove very high mFRR and imbalance prices in SE3 and SE4. Svenska kraftnät is now reviewing the prices under its standard procedure and considers it likely they will be adjusted down, on the principle that major grid incidents should not hit balance responsible parties financially.
That is a reasonable position for an event caused by external faults. But the price signal itself says something important: in that moment, the willingness to pay for flexible power was effectively unlimited. Whoever could deliver upward regulation in that quarter hour held one of the most valuable resources in the system.
What the event says about flexibility
Three things are worth taking away.
The first is that the system worked. The ancillary service markets did their job, the control room acted fast, neighbouring countries stepped up, and the disturbance reserve was there as the last resort. Nordic cooperation proved its value in real time.
The second is that the margins were thinner than most people assume. It took just two independent faults on an ordinary Monday afternoon in June, not a cold winter peak, to empty the entire bid stack in two price areas. As electrification grows the load and more weather dependent generation connects, situations like this are unlikely to become rarer.
The third is that the depth of the bid stack is a shared resource. Every battery, heat pump and controllable load that participates in the ancillary service markets makes the stack deeper, which reduces the risk that the system operator has to go all the way to the gas turbines. That is precisely the development Svenska kraftnät itself points to when it highlights the need for more flexibility in the system.
The bottom line
On 8 June, the value of flexibility stopped being theory. The bids ran out, the turbines started, and power had to be bought from neighbouring countries. For anyone who owns or is considering a battery, the lesson is the same one we have written about before: future revenue lies in selling credible capacity, not just kilowatt hours. And for the power system as a whole, every newly connected resource means one less quarter hour of risk that the reserves run dry next time.
Want to know how your battery can participate in the ancillary service markets? Start with our guide to frequency control reserves and FCR, or get in touch.
