I-SEM Daily Briefing — 24 May 2026

Price Profile #

Std dev €35.63/MWh · Median €131.86/MWh · Periods above €150: 10 of 48 (21%)

Sunday, even lower demand than Saturday — and a scarcity event. Mean €143.77 lifts €21 from Saturday. The shape resembles May 23 in its first half (no morning peak, midday trough), then breaks dramatically: where Saturday’s evening capped at €174, today’s evening kept climbing — to €228.48 at 21:30, with 7 of 48 periods clearing above €200. The half-hourly: overnight ran €122–144 (a normal weekend floor), the morning ramp existed but modestly (€127 → €152 between 06:00 and 09:00), and the midday belly held €110–127 from 11:00 to 15:30 with the floor at €110.00 at 13:30. Then the evening built relentlessly: €127 at 16:00 → €152 at 18:00 → €212 at 19:30 → €228 at 21:30. The four consecutive half-hours from 20:30 to 22:00 averaged €226 — straight peaker territory. Two distinct days in one: a wind-rich weekend morning, and a wind-shortage evening scarcity. Mean demand only 3,358 MW — lowest of the run by 150 MW — and still 7 periods above €200.

Price vs Wind #

Mean wind: 16.4% · Range: 6.0%–30.4%

The wind shape did the entire structural work, and re-confirms a lesson the May 17–18 scarcity event taught. Wind ran 24–30% through the overnight and morning, drifted down to 13–21% through the working day, and then drained sharply through the evening — 17% at 17:00, 13% at 18:00, 9% at 18:30, 6% by 20:00. Wind effectively disappeared during the evening peak demand window. Even with demand at a weekend-low 3,358 MW, the merit order ran out of mid-merit gas and climbed into peakers. €228 at 21:30 is plant-scarcity pricing — same regime as the May 18 morning event. The takeaway: scarcity isn’t a demand event, it’s a wind-timing event. May 24 had the lowest demand of the run and still produced 7 scarcity prints, purely because wind drained into the evening peak. Most market commentary focuses on demand peaks; the I-SEM’s price formation in 2026 is driven much more by where the wind is than how much demand there is. A Sunday with 3,358 MW demand and 6% evening wind produces a higher peak than a working Wednesday with 4,028 MW demand and 50% evening wind.

Week in Context #

Sunday should be cheap. It wasn’t. The wind drought builds: 47% Friday → 36% Saturday → 31% Saturday (mean wind doesn’t tell you everything — the evening wind on Saturday was 27%) → 16% Sunday. Tomorrow brings 3.7% and a bank holiday.

Price Duration Curve #

Periods above €150: 10 (21% of day) · Above €200: 7 (15% of day)

10 above €150, 7 above €200. The curve has a clean two-tier shape: a sharp top plateau (the 7 scarcity periods clustered €200–228) and a long cheap tail (16 periods below €130, with the bottom 4 averaging €111). The middle is moderate — 25 periods between €130 and €150, smoothly transitioning. This is the double-shoulder PDC — both a real top step and a real bottom step, with a moderate slope in between. The visual signature of a day with a deep midday trough and a real evening scarcity. Compare to May 18’s PDC (steep top, no real trough — pure scarcity revenue) or to May 23’s PDC (steep bottom, no real top — pure trough revenue). Today’s PDC has both ends working at once, which is the structural condition for a top-quintile BESS day.

Peak / Off-Peak Spread #

Peak avg (07:00–22:00): €145.28/MWh · Off-peak avg: €141.25/MWh · Spread: €4.03/MWh

Spread €4.03 — a tiny number that hides a €228 evening peak. Peak avg €145.28, off-peak avg €141.25. Same metric problem as yesterday’s negative spread, in a different direction. The peak window (07:00–22:00) contains both the deep midday trough (€110) and the evening scarcity (€228). The trough drags the peak average down to €145; the off-peak average sits at €141 (overnight floor that didn’t move much). The two averages converge despite a price range of €118 within the peak window itself. This is now the third day in a row where the peak/off-peak metric materially misrepresents the day. May 22 reported €5.03 on a €58 range. May 23 reported −€9.88 on a €96 range. May 24 reports €4.03 on a €118 range. Whatever the peak/off-peak metric is good for, it isn’t reading wind-shape days.

BESS Dispatch Signal #

Simulated 1MW/2MWh battery, one optimal DAM cycle. Gross before network charges and capacity costs.

€163 gross — the second-best day of the 21-day run, narrowly behind May 18’s €168 and ahead of May 17’s €161. Sunday delivers a top-tier BESS outturn. Charge €111 in the midday belly (12:30–14:00 at €111 avg), discharge €226 in the late-evening scarcity block (20:30–22:00 at €226 avg). Captured spread €115 — the second-widest of the run. ROI 73.6% on the €222 charge cost. The 21-day cumulative now stands at €2,104 — crossing the €2,000 milestone. Mean €100/day. The new top 4 BESS days (May 18 €168, May 24 €163, May 17 €161, May 15 €156) sum to €648 — 31% of cumulative revenue from 19% of days. The concentration metric is stable as the series grows.

21 days of simulated I-SEM DAM arbitrage on a 1MW/2MWh asset. €2,104 gross. Three of the top four days landed on a Sunday or Friday — not Mondays. Conventional wisdom puts the best BESS days on working-week scarcity; the data so far says otherwise.

Commentary #

Sunday, demand at the run’s lowest (3,358 MW), and 7 of 48 periods cleared above €200. Mean €143.77 lifted €21 from Saturday. The structural cause was the wind shape: wind held 24–30% through the morning, drifted down through the working day, and then drained sharply through the evening peak — 17% at 17:00, 13% at 18:00, 9% at 18:30, 6% by 20:00. With wind effectively absent at peak demand, the merit order climbed into peakers and the day cleared €226 across four consecutive half-hours from 20:30 to 22:00. The May 17–18 lesson re-confirmed: scarcity isn’t a demand event, it’s a wind-timing event. Today’s demand was the lowest of the 21-day run; today’s evening peak was the third-highest. A Sunday with 3,358 MW demand and 6% evening wind cleared higher than working days with 4,028 MW demand and 50% evening wind. The relevant variable for I-SEM price formation in 2026 is wind timing, not load. For storage, the €2,000 cumulative milestone arrives. €163 gross — second-best day of the run — on a €115 captured spread (€111 midday charge, €226 evening discharge). The 21-day BESS series moves to €2,104, mean €100/day. The top 4 days (May 15, 17, 18, 24) anchor 31% of revenue from 19% of days, and three of the top four landed on Friday or Sunday. The working-week-scarcity assumption that underpins most BESS revenue modelling deserves a closer look.