Daily guide · PT · 2026-09-14
Charging an EV in Portugal this week: what the prices actually said
All numbers computed from the week's published auction results at publication and frozen — this article is an honest snapshot, not a page that rewrites itself. Reproduce via the API.
The clearest signal this week in Portugal is the size of the gap between midday and evening prices. The cheap daytime window averaged 20,37 EUR/MWh across the seven days, while the evening peak averaged 215,81 EUR/MWh. That is a gap of 91 percent, and it held every single day, not just on isolated occasions.
The midday window is where the value sits, and it deepened as the week went on. Prices fell to 2,02 EUR/MWh on 9 September, reached 0 on 12 September, and briefly turned negative at -0,14 EUR/MWh on 13 September. The window itself opened between 10 and 14 hours depending on the day, so the exact timing shifted, but the pattern of a cheap midday trough and an expensive evening was consistent.
The concrete takeaway: charging during the daytime window rather than the evening peak would have saved 29,32 EUR over the week on 150 kWh of charging, which scales to 1.524 EUR across a year. If you can shift your charging to the middle of the day, the numbers this week made a strong case for doing so.
Every day at 13:00 CET, an auction sets electricity prices for every hour of tomorrow — separately, for each European bidding zone. Those prices routinely differ by a factor of two to three within a single day, because solar floods the middle of the day and demand peaks in the evening. If you charge an EV, that spread is money: the car doesn't care when it charges, only that it's full by morning. This is what the spread looked like in PT this week.
91%
cheaper to charge in the best 3h window than at the evening peak, on average this week
20.37 vs 215.81
€/MWh: best window vs 18–21h evening habit (week average)
≈€1524
a year on the wholesale component, for 150 kWh/week of charging at this week's gap
Day by day: when the cheap window actually fell
| Day | Cheapest 3h window | Window avg €/MWh | Evening 18–21h | Gap |
|---|---|---|---|---|
| 2026-09-07 | 12:00–15:00 | 70.85 | 237.89 | −70% |
| 2026-09-08 | 12:00–15:00 | 45.97 | 198.65 | −77% |
| 2026-09-09 | 14:00–17:00 | 2.02 | 185.59 | −99% |
| 2026-09-10 | 12:00–15:00 | 12.1 | 249.72 | −95% |
| 2026-09-11 | 12:00–15:00 | 11.78 | 224.36 | −95% |
| 2026-09-12 | 11:00–14:00 | 0 | 195.25 | −100% |
| 2026-09-13 | 10:00–13:00 | -0.14 | 219.23 | −100% |
Local time. Notice the window MOVES — sometimes after midnight, sometimes midday when solar peaks. A fixed night tariff catches some of this; following the auction catches all of it.
Automate it in ten minutes
You don't need to read auction results at 13:00 every day — ask the API for the cheapest window and let your wallbox follow it. One call:
curl -X POST -H "Authorization: Bearer YOUR_KEY" \
-H "Content-Type: application/json" \
-d '{"zone":"PT","duration_minutes":180,
"objective":"balanced",
"tariff":{"grid_fee_eur_kwh":0.10,
"supplier_markup_eur_kwh":0.02,
"vat_percent":25}}' \
https://voltcast.com/api/v1/optimize/cheapest-window
Home Assistant users: the Voltcast integration
exposes the recommended-window timestamp plus charge_now and
negative_price_incoming; evcc users get a ready-made tariff config.
Enter the variable grid fee, supplier markup and VAT from your bill for cost context.
Optional carbon/balanced modes are experimental trailing historical production-profile
heuristics—not weather-conditioned forecasts or emissions claims. The
Home plan (€9/mo) covers one
zone of your choice with 7-day forecasts, these action signals and the battery simulator;
public pages and widgets let you inspect the data before subscribing.
And if you want to charge on a forecast of tomorrow before the auction even publishes, that's the
P50 curve — scored publicly every day so you know exactly
how much to trust it.
Method & citation. Prices are hourly means of published day-ahead auction results (native 15-minute periods averaged; ENTSO-E/SMARD, attributed). Wholesale-price component only — grid fees and taxes come on top and vary by supplier. Cite as "Voltcast Research, voltcast.com/guides/ev-charging-pt-2026-09-14".
Next issue 2 Oct
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