​On 4 August 2026, shortly after 09:00, Polish transmission operator PSE declared obligation periods on the capacity market for 17:00 to 19:00 that evening. It was the fourth call since the market went live in 2021, and the second call of the year.

Counterintuitively, the main price action in energy and balancing markets happened after the two hours of capacity obligation period had passed. Asset optimisers needed to balance de-rated capacity obligations with revenue optimisation opportunities, falling short carries performance penalties.

Summer heat, wind lulls, coal plant outages due to river temperatures reaching the 35°C discharge limit, all contributed to the event. The heat sat over the whole region, so the scarcity did not just affect Poland but its neighbours at the same time. Solar generation peaked at 12.8 GW at midday and pushed net load down to a trough of 6.8 GW. Evening wind came in at 949 MW, around half the summer average. By 20:00 net load had climbed to 12.2 GW. The ramp was steep but not unprecedented.

Key takeaways

• GB and Poland are the only two European Capacity Markets that declare system stress events by design. GB has never declared one in all its history, while Poland is on its 4th.
• Both of Poland's 2026 capacity market calls unusually landed in summer. The first two events, in September 2022 and November 2024, were autumn and winter evenings.
• 2026 was the first delivery year for foreign units with Polish Capacity Market contracts. Sweden, the only zone with such contracts sent practically no energy during the stress event. Foreign units’ only obligation is to be available to their transmission area.
• Honouring the capacity obligation would have costed a 1MW/4MWh battery 138 PLN of day-ahead margin, against 5,870 PLN of penalty for failing to deliver*.
• 4.9 GW of coal and lignite sat on planned summer maintenance when the evening ramp began. Neither the ramp nor the wind was extreme on its own: 16 of the 65 summer days in 2026 ran a steeper climb than 4 August's 12.2 GW, without a capacity call.
• Day-ahead prices averaged 926 PLN/MWh across the called hours and 1,567 PLN/MWh in the two hours after the window closed, while the imbalance price inside the window fell to 19 PLN/MWh as the system ran long.
• Batteries covered under 0.2% of Polish demand in the called hours, because Poland has barely any operational batteries yet. That changes from 2027.

*assumes perfect DA market energy arbitrage, a 61.3% BESS de-rating factor (KWD), and applies performance penalty value of 6,576.81 PLN/MWh set for the 2025 delivery period.

A capacity market call obliges contracted units to deliver in named hours

A capacity market call is the procedure PSE runs when it expects the power system to fall short of capacity. It obliges contracted units, which include power stations, storage and consumers paid to reduce demand, to raise generation or cut consumption across the hours PSE names.

PSE declares the window with lead time. On 4 August the announcement gave obligation holders eight hours' notice. That lead time fixes the window in place while the system's actual tightest hour keeps moving.

The trigger is PSE's forecast operational reserve, the capacity available above forecast demand. On 4 August it fell as low as 656 MW.

No other European capacity market has ever called an event

All 11 of Poland's called hours have fallen in the evening ramp, and none at the annual demand peak.

Great Britain has run a capacity market since 2017, and has never declared a system stress event. However, it has issued 13 Capacity Market Notices. A notice in Great Britain is a four-hour-ahead warning that the margin has fallen below 500 MW, and it carries no obligation to deliver.

Italy has had a capacity market since 2022 but it cannot call an event at all, because its obligation is a reliability option instead of a delivery instruction. Contracted units receive a fixed annual premium and repay Terna the difference whenever the market price exceeds a strike price set by regulator ARERA, so scarcity is settled financially and continuously, with no system stress hours called by the operator. Belgium and Ireland’s capacity markets follow the same approach.

Germany’s capacity market design is still in the works. Currently, scarcity is rationed by price in the wholesale market, with a 2 GW capacity reserve held outside it that is barred from bidding. First auctions for a German capacity market are due in 2026 with delivery from 2031, and Modo Energy covers what is known about the design.

Solar, planned maintenance and a 12.2 GW evening ramp produced the call