I-SEM Daily Briefing — 12 May 2026

Price Profile #

Std dev €20.34/MWh · Median €112.28/MWh · Periods above €150: 1 of 48 (2%)

The headline stat is misleading. The peak of €161.70 prints at 23:00 — period 1 of the delivery day — which is the tail of Monday’s evening, already fading from €195 by the time this file opens. The I-SEM delivery day runs from 23:00 the prior evening to 22:30 of the named date: eight borrowed half-hours of yesterday’s evening, then forty half-hours of the named date. Worth understanding once and noting here; from here it won’t come up every post.

The actual May 12 shape is conventional and wind-heavy. Morning ramp: 05:00 (€112) → 07:30 (€138), +€26 in 2.5 hours — the softest working-day ramp of the run. Wind held 35–44% through that window; the marginal plant didn’t have to climb far. Then the floor fell away. €100 arrived at 09:30, €85 by noon, €79.40 at 15:00. 13 consecutive half-hours below €100 from 10:00 to 16:30, sustained 54–56% wind pushing mid-merit gas down the dispatch stack. The cheapest working-day window of the run.

The evening peak proper — the actual May 12 evening — ran €130–137 from 19:00 to 20:30. Contained, no scarcity, wind still at 55–57%. Three features, three reads: the 23:00 spike is yesterday’s residue, the morning ramp is wind-muted, and the evening peak is unremarkable. Take the headline stat with the boundary footnote.

Price vs Wind #

Mean wind: 47.4% · Range: 22.9%–65.6%

Wind drove the day, with one anomaly worth flagging. The official range is 22.9%–65.6%, but the 22.9% reading at 00:00 is almost certainly a data artefact: period 2 (23:30) shows 65.6%, period 3 (00:00) shows 22.9%, period 4 (00:30) shows 24.0%. A 43-point system-level collapse in a single half-hour doesn’t happen physically. Treat any cannibalisation arithmetic for that hour with caution; the rest of the day’s wind series is internally consistent.

Through the actual working day, wind was strong and well-timed: 35–44% during the morning ramp (prices €112–138), 54–56% through the midday trough (prices €79–95), 55–57% through the evening build (prices €112–137). Wind generated heavily during both the cheap midday and around the 23:00 boundary spike — those two periods roughly cancel each other for capture-price purposes. Wind’s capture rate today sits close to the daily mean, marginally below. A neutral cannibalisation day.

Week in Context #

The arc sharpens. Monday-to-Tuesday: demand essentially unchanged (3,810 → 3,767 MW), wind doubled (23% → 47%), mean fell €25. As close to a controlled experiment as the I-SEM gives you in live data. Tuesday’s line should sit materially below Monday’s across every working hour, with the one exception at the 23:00 open where Tuesday inherits Monday’s elevated close.

Price Duration Curve #

Periods above €150: 1 (2% of day) · Above €200: 0 (0% of day)

1 period above €150 (the 23:00 boundary carryover), 0 above €200. Drop that first period and the entire day clears below €150 — the lowest working-day PDC of the run, structurally identical to last Saturday’s shape.

The parallel is worth stating: weekday demand at 3,767 MW with 47% wind produces the same PDC archetype as weekend demand at 3,503 MW with 57% wind. Wind closes the weekday demand premium entirely. The market doesn’t know it’s a Tuesday.

Peak / Off-Peak Spread #

Peak avg (07:00–22:00): €107.69/MWh · Off-peak avg: €120.47/MWh · Spread: €-12.78/MWh

Off-peak (22:00–07:00) averaged €120.47; peak (07:00–22:00) averaged €107.69. Nights more expensive than days. The inversion is partly a boundary effect, not purely a structural signal.

The off-peak window opens with the carryover half-hours from Monday’s evening: 23:00 (€162), 23:30 (€136), then €121–136 through 01:30 — Monday dragging the off-peak average up. The peak window sits on top of a 13-period midday slab below €100 (10:00–16:30), dragging the peak average down.

Strip the carryover hours: the genuine May 12 off-peak (02:00–07:00) runs around €110, the peak window around €108. Essentially flat. The -€12.78 is real for any algorithm bidding the standard windows. But the underlying shape of May 12 isn’t an inverted day — it’s a flat day with a boundary artefact at the open. Flat is a structurally different read from genuinely inverted.

BESS Dispatch Signal #

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

The model charged at 14:30 (€81, midday wind surplus) and discharged into the 23:00–02:00 window averaging €140. Mechanically correct — those are the highest consecutive hours in the SEM day. Operationally misleading. That 23:00 discharge block physically belongs to Monday’s evening; a rolling 24-hour optimisation would have cycled those half-hours into Monday’s discharge window (€195 average) and earned closer to Monday’s €107 gross.

Today’s genuine BESS signal is the charge floor: €81 at 14:30 is the first sub-€85 charge window of the working week. The wind-rich midday is shifting the optimal charge slot firmly to the afternoon — and giving the battery a cheaper fill price than the overnight window managed on Monday.

Commentary #

Tuesday cleared at €112.48 — €25 below Monday on essentially unchanged demand (3,767 MW vs 3,810). Wind was the entire difference: 47.4% today, 23.2% yesterday. Same load, different wind, different market. As close to a controlled experiment as the I-SEM gives you in live data.

The €161.70 peak at 23:00 needs a footnote. The I-SEM delivery day runs from 23:00 the prior evening to 22:30 of the named date — so today’s first period is the tail of Monday’s evening peak (which closed at €195 at 21:00 in yesterday’s file). The actual May 12 profile is softer: a morning ramp to €138, a deep wind-suppressed midday belly with 13 periods below €100 between 10:00 and 16:30, and an evening peak that capped at €137. Zero scarcity hours on the day itself. The reported negative spread (-€12.78) is the same effect — strip the carryover hours and the underlying shape is flat, not inverted.

The floor at 15:00 (€79.40) is the real signal: the lowest working-day price of the run. Seven consecutive half-hours below €85, wind at 54–56%, full working-day demand on the system, and the market still couldn’t clear above €85. That’s the mark of 12 May. Not the borrowed evening peak at the top — the wind-suppressed trough at the bottom. For storage, €77 gross; but the discharge window physically belonged to Monday evening. Sub-€85 midday charging is the new working-day norm in a wind-rich week.