I-SEM Daily Briefing — 26 May 2026

Price Profile #

Std dev €26.04/MWh · Median €140.65/MWh · Periods above €150: 20 of 48 (42%)

Tuesday after a bank holiday, with the wind drought continuing. Mean €151.18 (basically level with yesterday’s €152.78). The structural feature: a morning-dominated day, where the morning peak outran the evening for the first time since May 18. Periods 1–2 (23:00–23:30) at €196 and €172 are the familiar SEM day boundary issue — these prices are Monday’s evening peak spilling into Tuesday’s file. From 00:00 onward the “real” Tuesday begins: overnight floor €128–160, climbing into the morning. Morning ramp climbed €127 at 06:00 → €212.05 at 07:30 — the day’s peak. The morning peak block (07:00–08:30) averaged €198, with both periods at 07:30 and 08:00 clearing above €200. By 10:00 the morning peak had collapsed to €141. Midday belly held €119–128 from 11:00 to 15:30, with the floor at €119.00 at 13:30. The evening then built a contained second peak — €127 at 16:00 → €184 at 18:30 — and held €179–184 across 19:00 to 20:30. Notably, the evening peak failed to clear €200, despite mean wind being 6.6%. The evening shoulder wasn’t deep enough to break into peakers. 20 of 48 periods cleared above €150 (the highest count of the run); 2 above €200 (both in the morning block).

Price vs Wind #

Mean wind: 6.6% · Range: 2.0%–23.0%

Two-decline wind shape, with a sharper morning shortfall than evening one — the inverse of May 18. Wind started elevated at 21–23% in the boundary periods (Monday’s tail), then immediately dropped to 6–7% overnight and stayed essentially absent through the working day (2–6%). It then recovered through the late evening (8% at 20:00 → 19% by 22:30). The morning peak landed in the absolute wind trough (2–3% from 07:00 to 09:30); the evening peak landed in slightly better but still poor wind (5–9% from 18:00 to 20:00). The differential matters. May 18 had a similar profile but in reverse: morning at 1% wind produced €255; evening at 50% wind capped at €162. May 26 has morning at 3% wind producing €212; evening at 6–9% wind producing €184. The relative depth of the wind shortfall in each window dictates which peak wins — and the optimiser will follow the depth, not the calendar. Removing the boundary periods, the corrected mean wind for the “real” Tuesday is around 5% — placing this day inside the May 25 wind-drought regime. The drought is two days deep and still building.

Week in Context #

Wind: 31% Saturday → 16% Sunday → 4% Monday → ~5% Tuesday (corrected). Four-day wind decline, no recovery yet. Compare to the May 4–7 wind drought (13% → 8.5% → 3.8% → 11%) — the current drought is now structurally deeper than that one.

Price Duration Curve #

Periods above €150: 20 (42% of day) · Above €200: 2 (4% of day)

Today’s PDC has a sharp morning-peak spike at the top (2 periods €201–212), then a smooth, gradual descent through 18 periods in the €150–200 band (the evening cluster + boundary spillover), and a moderate tail of 28 periods between €119 and €150. The most periods above €150 of the entire 22-day run — but only 2 above €200, because the evening peak couldn’t quite reach peaker territory. This is the “high-and-moderate” archetype — sustained elevated prices across the day with limited scarcity at the top. Compare to May 5’s PDC (high-and-flat, 6 periods above €200, no real trough). Today has a real trough (€119) and more time spent above €150, but less true scarcity. A high-priced day for everyone — but not a top-tier BESS day, because what storage wants is a wider gap between trough and peak, not a higher floor.

Peak / Off-Peak Spread #

Peak avg (07:00–22:00): €154.49/MWh · Off-peak avg: €145.65/MWh · Spread: €8.84/MWh

Spread €8.84 — a small number that this time genuinely understates the day. Peak avg €154.49, off-peak avg €145.65. The peak window contains the morning peak block (€198 average), the midday trough (€122 average), and the evening peak (€181 average) — three distinct events that the averaging dilutes. The off-peak window contains the boundary spillover at the start (€196 → €172) and the overnight floor (€128–160), and comes out higher than usual. The captured spread the BESS actually earned was €77 — between a €121 midday charge and a €198 morning discharge. The peak/off-peak metric reported €9. The captured spread is closer to nine times the headline spread.

BESS Dispatch Signal #

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

Updated 2026-08-27: the BESS simulation previously allowed the discharge window to occur before the charge window ended, which is physically impossible for a battery — in this case, by picking the 07:00–08:30 morning peak, which falls before the midday charge. Recalculated enforcing charge-before-discharge; gross profit corrected from €94 to €66.

€66 gross. The day’s highest-priced block was actually the morning (07:00–08:30, averaging €198.45), beating the evening peak’s best block (18:30–20:00, €184.91) by €13/MWh — but the charge sits in the midday belly (13:00–14:30, €121 avg), after the morning peak has already happened. A same-day cycle can only reach the evening, so today discharges into the lower of the two peaks: €182 average at 18:30.

Commentary #

A working Tuesday inside the wind drought. Mean €151.18 (level with yesterday), and the structural feature is a morning peak that outpriced the evening: wind 2–3% through the morning ramp produced €212 at 07:30, while wind 5–9% through the evening capped the second peak at €184. For a battery, though, the morning peak isn’t reachable — it happens before the midday charge — so the market’s own highest price and the battery’s actual payday are two different windows today. The current wind drought (May 23–26: 31% → 16% → 4% → ~5%) is now structurally deeper than the May 4–7 one and shows no sign of breaking. The boundary periods at 23:00–23:30 (€196, €172 with 21–23% wind) are Monday’s evening peak spilling into Tuesday’s file — the familiar SEM day boundary artifact that keeps appearing on high-volatility transitions. Strip those two periods and Tuesday’s real-day mean wind is closer to 5%. For storage, €66 gross — a modest mid-range day made smaller by causality. The market’s real peak was the morning (€212 at 07:30), but it fell before the midday charge, so the battery could only reach the lower evening peak (€182 at 18:30). The gap between “the day’s best price” and “the best price a same-day cycle can actually capture” is the operational lesson: a real asset with an overnight-charge option would have priced this very differently.

For the week-level picture and what it means if you're buying, see Weekly Analysis — 10–16 August 2026.