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.

€94 gross. Morning discharge again — the third time in the 23-day series after May 5 and May 18. The dispatch logic: today’s four consecutive highest-priced half-hours are 07:00, 07:30, 08:00, 08:30 (averaging €198.45). The evening peak’s best four-period block (18:30–20:00) averaged €184.91. €13/MWh of difference, and the optimiser picked the morning. Charge sits in the midday belly (13:00–14:30 at €121 avg). The morning-discharge pattern is now structurally clear: when overnight wind is below ~10% and demand climbs sharply into the morning, the morning peak outprices the evening peak. May 5 (8.5% mean wind, morning discharge), May 18 (25% mean wind but 1% morning wind, morning discharge), May 26 (6.6% mean wind, morning discharge). Three for three on the rule. A real operator’s dispatch strategy needs to predict where the wind shortfall sits before predicting where the price peak sits. The 23-day BESS series moves to €2,326 cumulative, mean €101/day. The four-day weekend-plus-bank-holiday run (May 23–26) added €518 — close to a quarter of the running total earned across 17% of days. A reminder of where the revenue lives.

Commentary #

A working Tuesday inside the wind drought. Mean €151.18 (level with yesterday), but the structural feature is the morning peak winning over the evening for the third time in the series. Wind 2–3% through the morning ramp produced €212 at 07:30; wind 5–9% through the evening capped the second peak at €184. The optimal discharge window today was morning — and that’s now an established pattern: low overnight wind plus a demand surge into the morning consistently outprices the evening peak. 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, €94 gross — solid mid-range BESS in difficult conditions, with morning discharge restoring the May 18 pattern. The four-day weekend-plus-bank-holiday run (May 23–26) added €518 to cumulative across 17% of the running calendar — over a quarter of the series total. The BESS revenue concentration story holds: top days, weekend days, and scarcity days carry most of the portfolio, while the wind-rich working week (May 11–14, May 19–21) does the maintenance work in the €40–100 range. 23 days, €2,326 cumulative, mean €101/day. The case for forecasting and two-cycle dispatch on volatile days writes itself.