Daily guide · FI · 2026-07-29
What a home battery earned in Finland this week, hour by hour
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.
Finnish day-ahead prices stayed low this week, and the arbitrage a home battery could capture reflected that. Across the seven days the average spread between the cheap and peak windows was 11,07 EUR/MWh, with a 10 kWh battery at 90 % round-trip efficiency earning 0,65 EUR for the full week. The best single days were 23 and 27 July, each worth 0,14 EUR per cycle, when peak averages of 22,43 and 21,78 EUR/MWh sat well above cheap windows near 6 EUR/MWh.
The weaker days show why. On 26 July the cheap window averaged 0 EUR/MWh, but the peak only reached 5,55 EUR/MWh, leaving 0,05 EUR per cycle. When the whole price curve is compressed low, a cheap charge alone does not pay; you need a peak with somewhere to sell into. The timing also shifted, with cheap windows landing overnight some days and mid-afternoon on others such as 24 and 28 July.
The concrete takeaway: at these spreads, arbitrage alone projects to about 34 EUR a year. Automate the charge-discharge schedule and treat that figure as a floor, not a reason to buy a battery outright.
A home battery makes money on one thing: the gap between the day's cheapest and priciest hours. Charge low, discharge across the evening peak instead of buying it, repeat daily. The size of that gap is set every afternoon at the day-ahead auction — so it's measurable, not hypothetical. Here is what one full daily cycle of a 10 kWh battery (at 90% round-trip efficiency — losses included, unlike most brochures) would have captured in FI this week.
€0.65
captured this week — one cycle per day, wholesale component, after losses
11.07
€/MWh average cheapest-2h → priciest-2h spread this week
≈€34
a year at this week's spreads — the honest run-rate, not the best-day fantasy
Day by day: the two windows that mattered
| Day | Charge (2h) | at €/MWh | Discharge (2h) | at €/MWh | Cycle value |
|---|---|---|---|---|---|
| 2026-07-22 | 22:00–24:00 | 16.81 | 19:00–21:00 | 22.53 | €0.03 |
| 2026-07-23 | 03:00–05:00 | 6.02 | 11:00–13:00 | 22.43 | €0.14 |
| 2026-07-24 | 15:00–17:00 | 7.33 | 21:00–23:00 | 19.44 | €0.1 |
| 2026-07-25 | 02:00–04:00 | 2 | 18:00–20:00 | 10.28 | €0.07 |
| 2026-07-26 | 05:00–07:00 | 0 | 20:00–22:00 | 5.55 | €0.05 |
| 2026-07-27 | 00:00–02:00 | 5.56 | 09:00–11:00 | 21.78 | €0.14 |
| 2026-07-28 | 14:00–16:00 | 1.98 | 00:00–02:00 | 15.17 | €0.12 |
Local time, hourly auction means. Days where charging was negative-priced mean you were paid to fill the battery.
Do it automatically
The windows move every day — automation is the whole game. One API call returns a cost-optimal schedule your inverter or energy manager can follow, and there's a full battery simulator to backtest your exact capacity, power and cycle limits against realized prices before you trust it:
curl -X POST -H "Authorization: Bearer YOUR_KEY" \
-H "Content-Type: application/json" \
-d '{"zone": "FI", "capacity_kwh": 10, "max_power_kw": 5,
"round_trip_efficiency": 0.9, "max_cycles_per_day": 1}' \
https://voltcast.com/api/v1/optimize/batteryHome Assistant users get the schedule as a sensor via the integration. And because the value depends entirely on tomorrow's spread, the P10–P90 forecast — scored publicly every day — tells you whether tomorrow is worth a deep cycle at all.
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/battery-arbitrage-fi-2026-07-29".
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