Modo Energy's ME BESS PL benchmark shows a modelled, unconstrained four-hour battery in Poland earning 1.89 million PLN/MW-year in August 2026, up 13% from 1.67 million in July. Shorter evenings and a tighter supply stack pushed day-ahead spreads to record levels.

Day-ahead energy and frequency containment reserve (FCR) together added 312,000 PLN. Automatic frequency restoration reserve (aFRR) capacity revenue fell by 94,000 PLN. That cut aFRR's share of the stack from 67% to 54% in a single month. The entire month-on-month gain came in the twelve days from 3 to 14 August.

Key takeaways

• A four-hour benchmark battery earned 1.89 million PLN/MW-year in August, a 13% increase on July. The two-hour battery earned 1.71 million PLN/MW-year.
• aFRR's share of revenue fell from 67% to 54%. Growth came from day-ahead energy, up 43%, and FCR, up 98%.
• The twelve days from 3 to 14 August account for the entire month-on-month gain. Across the other seventeen days, battery revenue returned to average.
• The daily peak accounts for the entire increase in spread, rising by 510 PLN/MWh. Lower wind, higher demand, and shorter days tightened the evening, while strong midday solar held the floor down.

To learn more about the Polish benchmark, reach out to alex.kelham@modoenergy.com

aFRR still leads the stack, but by much less

As was the case in July, aFRR remains the largest revenue source, though its share has fallen. aFRR capacity made up 54% of the four-hour battery's August revenue, down from 67% in July. Both day-ahead energy and FCR took a larger share.

​FCR-up capacity prices rose 24.5% month-on-month, up in every four-hour block except the solar-heavy midday window - the same evening-tightness pattern driving higher spreads this month.

Meanwhile, a two-hour battery leant on aFRR more heavily, since it has less energy to arbitrage. aFRR capacity makes up 60% of its 1.71 million PLN/MW-year, against 16% from day-ahead.

A significant portion of the increase came from higher day-ahead and FCR revenues, adding 174,000 and 138,000 PLN month-on-month. aFRR revenues contracted by 94,000 PLN as downward regulation saw less action.

Downward aFRR revenues fell 45% on an 8% price fall. This is related to the higher spreads this month. Downward reserve pays best at midday, when batteries position themselves to charge and later discharge into the evening. With day-ahead spreads high, holding midday capacity in reserve created an opportunity cost in forgone arbitrage. The optimiser favoured the trade over reserve.

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A twelve-day window delivered the month-on-month upside

The uplift from July to August came from 3 to 14 August. The rest of the month remained around the summer average.

Those twelve days ran at 2.20 million PLN/MW-year, 32% above the 1.66 million achieved over the other seventeen days.

Within the window, day-ahead revenue was 61% higher than in the rest of August, and upward aFRR 62% higher, pointing to evening tightness as the cause.