Portugal's power prices in 2026: wider spreads, more free hours

From 1 January to 24 October 2026, the average gap between Portugal’s four most expensive and four cheapest day-ahead hours was 119 €/MWh. In the same period of 2025 it was 87 €/MWh, and in 2024 it was 60 €/MWh. That gap is what a battery earns from: charge in the cheap hours, discharge in the dear ones.

We analysed every Portuguese day-ahead price published by OMIE, the Iberian market operator, from 1 January 2024 to 24 October 2026. This report sets out what the data shows and what it means for standalone and business batteries. The rules that govern storage in Portugal also changed this year; we cover them in a separate report, Portugal’s 2026 storage rules.

Key findings

• Spreads are widening fast. The average daily 4-hour spread rose 37 % year on year, and the 2-hour spread 31 %, comparing 1 January to 24 October in each year.
• Midday power is often free. Portugal had 929 hours at or below 0 €/MWh in 2026 so far, 750 of them negative, compared with 544 negative hours in the same period of 2025.
• Evenings carry the value. In 2026 the average price was 26 €/MWh between 10:00 and 16:00 CET and 113 €/MWh between 18:00 and 22:00 CET. The gap between the two has more than doubled since 2024.
• The arbitrage ceiling has doubled. The most a battery could have earned from day-ahead spreads roughly doubled between 2024 and 2026.
• Two-hour systems hold their own. Per MWh of installed capacity, the theoretical arbitrage value of a 2-hour battery was 8 % higher than a 4-hour battery in 2026.

What the price data shows

We analysed every Portuguese day-ahead price published by OMIE, the Iberian market operator, from 1 January 2024 to 24 October 2026. Since October 2025 OMIE has published 15-minute prices; we averaged them to hourly values so that the years compare like for like.

The pattern repeats every year, at a higher level each time. Spreads are lowest in winter, when solar output is weak and prices are flat across the day. They widen from spring, when solar pushes midday prices to zero, and peak in late summer and autumn, when evening prices stay high. In September 2026 the average 4-hour spread reached 197 €/MWh, the highest month in the data set. We have not analysed what drove evening prices this high in the third quarter of 2026, so we don’t treat that level as the new normal.

Zero and negative prices are now a structural feature of the Portuguese spring. Every year since 2024 has had more than 100 such hours in at least one month from March to May, and 2026 added more than 100 hours in February and June as well.

1 Jan to 24 Oct	2024	2025	2026
Average day-ahead price	53.6 €/MWh	64.3 €/MWh	80.8 €/MWh
Hours at or below 0 €/MWh	784 h	775 h	929 h
of which negative	247 h	544 h	750 h
Average price 10:00 to 16:00 CET	32.1 €/MWh	29.8 €/MWh	25.7 €/MWh
Average price 18:00 to 22:00 CET	70.7 €/MWh	91.4 €/MWh	112.7 €/MWh
Average daily 2-hour spread	67.1 €/MWh	97.5 €/MWh	127.9 €/MWh
Average daily 4-hour spread	59.5 €/MWh	86.9 €/MWh	118.7 €/MWh
Arbitrage ceiling, 2-hour battery	17,800 €/MWh	26,200 €/MWh	35,000 €/MWh
Arbitrage ceiling, 4-hour battery	15,700 €/MWh	23,200 €/MWh	32,300 €/MWh

The arbitrage ceiling is the most a battery could have earned from one full day-ahead cycle a day with perfect foresight, per MWh of installed capacity. It is an upper bound, not a forecast. Real assets capture less because prices are not known in advance, and because they pay grid charges, lose energy to degradation and need availability for other services. Its value is in the trend: the ceiling roughly doubled between 2024 and 2026.

What it means

For standalone projects and investors. Spreads at this level support the case for storage in Portugal, but they are volatile: the 4-hour spread ranged from 53 €/MWh in January 2026 to 197 €/MWh in September. A business case should be tested against a year like 2024 as well as a year like 2026. Day-ahead arbitrage is also only one source of revenue; combining it with intraday trading and reserve markets, through an experienced trading partner, reduces dependence on any one of them.

For businesses with solar. Midday power worth zero and evening power worth more than 100 €/MWh is the price shape that makes a business battery pay. A company on a supply contract indexed to OMIE can store its own midday solar instead of exporting it at a low price, and use it in the evening peak. Because the value comes from a few hours a day, a 2-hour battery earns more per installed MWh than a longer-duration one: 8 % more in our 2026 analysis.

Method and assumptions

• Data: OMIE marginal day-ahead prices for the Portuguese zone, 1 January 2024 to 24 October 2026. One day (26 March 2025) was missing from the download and is excluded.
• 15-minute prices (from October 2025) are averaged to hourly values. Times are OMIE market time (CET).
• Daily spread: the average of the k most expensive hours minus the average of the k cheapest hours of each day, for k = 2 and k = 4.
• Arbitrage ceiling: one cycle a day, perfect foresight, 88 % round-trip efficiency, no grid fees, no degradation cost, and no constraint on whether charging comes before discharging in the day. Expressed per MWh of installed capacity.
• Comparisons between years use the same calendar window, 1 January to 24 October.

Sources

1. OMIE, Portuguese day-ahead marginal prices (marginalpdbcpt), 1 Jan 2024 to 24 Oct 2026