I-SEM Daily Briefing — 29 May 2026

Price Profile #

Std dev €30.88/MWh · Median €117.67/MWh · Periods above €150: 9 of 48 (19%)

The day’s headline statistics hide a top-5 BESS day. Mean €128.35 looks unremarkable — essentially identical to yesterday’s €128.37. But std dev jumped to €30.88 (vs €20.46 yesterday), range to €112 (vs €76), and the day produced 3 periods above €200 — all in the late evening from 21:00 to 22:00.

The profile is wind-rich morning bleeding into wind-poor evening. Overnight (after the boundary periods) ran €110–121 from 01:00 to 05:30 — a soft floor at 53–64% wind. The morning ramp was the gentlest of the working week: €127 at 06:00 → €135 at 08:00. No real morning peak. Mid-morning prices fell smoothly into the midday trough — €91.00 at 14:30, the day’s minimum and the second-deepest trough of the run after May 23’s €78.

Then the evening built relentlessly. €92 at 15:30 → €107 at 16:00 → €146 at 18:00 → €180 at 20:00 → €203 at 22:00. The four consecutive half-hours from 20:30 to 22:00 averaged €200 — straight scarcity territory. Then €189 at 22:30 fading.

9 of 48 periods cleared above €150; 3 above €200.

Price vs Wind #

Mean wind: 39.4% · Range: 13.8%–63.9%

The widest wind range of the entire run — 50 percentage points across 24 hours. Wind started at 53–54% (after the boundary glitch — periods 1–2 show 20–22%, the boundary error), climbed to 62–64% from 04:00 to 05:00, drifted down through the morning to 35% by 13:00, then drained sharply through the evening: 35% at 17:00 → 29% at 18:30 → 22% at 19:30 → 18% at 20:00 → 14% by 21:00.

The structural pattern: wind-rich morning → wind-shortage evening. Exactly the inverse of the May 26–28 morning-shortage regime. Wind produced 62% during overnight when nothing was happening, then drained into the evening demand peak when it mattered. The merit order had nothing to fill the gap, and the late evening cleared €200+.

Today’s mean wind is 39.4% — higher than May 27’s 32.3%. May 27’s peak was €227 (morning); today’s peak is €203 (evening). Different shape, different time of day, different peak height — but both produced 3 scarcity prints, and the structural cause was identical: wind drained into the day’s demand peak. Mean wind is a useless summary statistic for predicting scarcity. The cleanest predictor is the minimum half-hour wind during the day’s highest-demand window.

Week in Context #

Wind shapes across the week: May 27 V-into-morning, May 28 V-out-of-evening (wind held high through evening), May 29 V-into-evening. Three working days, three distinct wind shapes, three different peak times, three different BESS dispatch outcomes. The wind-shape variance week.

Price Duration Curve #

Periods above €150: 9 (19% of day) · Above €200: 3 (6% of day)

The PDC has a clear three-tier shape: a sharp top spike (3 periods €201–203 — the late evening), a gradual upper shelf (6 periods €146–189 — the evening build), and a long cheap tail (15 periods below €115). The middle is gradual — no flat section.

This is the “scarcity tail” archetype — distinct from May 27’s morning spike. The morning spike PDC has three sharp tops at the very left and a smooth drop. The scarcity tail PDC has a top spike followed by an extended upper shelf — the evening build is visible on the curve as a gradual climb rather than a sharp step.

For BESS, both shapes deliver — but in different ways. May 27 cycled into a sharp narrow morning peak. May 29 cycled into a sustained late-evening climb. Captured spread on both days exceeded €95.

Price Spread #

Captured spread: €107/MWh · Charge: €93/MWh (14:00) · Discharge: €200/MWh (20:30)

BESS Dispatch Signal #

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

€155 gross — the new fourth-best day of the 26-day run. Tied with the May 17 scarcity event. ROI 83.4% — third-highest of the run after May 23 (84.4%) and May 18.

Charge €93 at the deep midday trough (14:00–15:30 at €93 avg) — the second-cheapest charge of the run after May 23’s €79. Discharge €200 at the late-evening scarcity block (20:30–22:00 at €200 avg). Captured spread €107.

The 26-day BESS series moves to €2,691 cumulative, mean €103/day. The new top 5 days are May 18 €168, May 24 €163, May 17 €161, May 29 €155, May 15 €156 — €803 from 5/26 = 19% of days = 30% of cumulative. Three of the top 5 BESS days are now Friday-or-weekend days (May 15 Fri, May 24 Sun, May 29 Fri). The original working-week-scarcity assumption keeps weakening.

Commentary #

The day that hid a top-5 BESS event inside an unremarkable daily mean. Mean €128.35 is essentially identical to yesterday’s €128.37 — and yet the day delivered 3 scarcity prints in the late evening (€201–203 from 21:00 to 22:00), a captured BESS spread of €107, and gross BESS revenue of €155. Std dev jumped from €20 yesterday to €31 today on the same mean.

The structural cause is the wind shape — and specifically the widest wind range of the 26-day run (14% to 64%, 50 percentage points). Wind held 53–64% across the entire overnight and early morning. Then drained steadily through the day to bottom at 13.8% at 21:30 — exactly inside the late-evening demand window. From 19:30 to 22:00 wind ran at 14–22% while demand was at its evening peak, and the merit order climbed into scarcity. Mean wind 39% on the day; effective wind during the late-evening peak window 16%. Mean wind is uninformative.

For storage, the captured spread €107 unlocks gross €155 — the fourth-best day of the run. Charge €93 in the deep midday trough (the second-cheapest charge of the run after May 23), discharge €200 in the scarcity block. ROI 83.4%. 26-day cumulative €2,691, mean €103/day. Three of the top 5 BESS days now sit on Friday or weekend (May 15 Fri, May 24 Sun, May 29 Fri) — the working-week-scarcity assumption continues to weaken. The single best predictor for BESS revenue in the data so far is not the day of the week; it is the wind decline rate into the day’s demand peak window.