Daily guide · GR · 2026-09-09
What a home battery earned in Greece 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.
The week's defining feature was the collapse in midday power prices. From 4 September onward, the cheap window averaged effectively zero, with 0.01 EUR/MWh on the 4th, 5th, 7th and 8th, and a clean 0 on the 6th. Against evening peaks that held between 222.95 and 255.42 EUR/MWh, that produced spreads wide enough to lift daily cycle value to 2.10 EUR and above on four consecutive days, up from 1.64 and 1.26 EUR early in the week.
The pattern is consistent: charge around 11:00 to 12:00, when solar depresses daytime prices, and discharge into the 19:00 to 21:00 evening peak. That timing barely moved across the week, which makes the strategy easy to automate. A 10 kWh battery at 90 percent round-trip efficiency captured an average spread of 219.19 EUR/MWh, earning 13.59 EUR over the seven days.
The takeaway for a home operator: the value now sits almost entirely in the evening peak, since the buy side is close to free. Extrapolated across the year, that same 10 kWh cycle points to 709 EUR. Prioritise disciplined evening discharge over chasing the cheapest charge hour.
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 GR this week.
€13.59
captured this week — one cycle per day, wholesale component, after losses
219.19
€/MWh average cheapest-2h → priciest-2h spread this week
≈€709
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 |
|---|---|---|---|---|---|
| 2026-09-02 | 11:00–13:00 | 89.67 | 20:00–22:00 | 281.72 | €1.64 |
| 2026-09-03 | 12:00–14:00 | 109.88 | 20:00–22:00 | 262.4 | €1.26 |
| 2026-09-04 | 11:00–13:00 | 20.01 | 21:00–23:00 | 255.42 | €2.1 |
| 2026-09-05 | 11:00–13:00 | 0.01 | 19:00–21:00 | 233.48 | €2.1 |
| 2026-09-06 | 12:00–14:00 | 0 | 19:00–21:00 | 222.95 | €2.01 |
| 2026-09-07 | 11:00–13:00 | 0.01 | 19:00–21:00 | 249.95 | €2.25 |
| 2026-09-08 | 14:00–16:00 | 0.01 | 21:00–23:00 | 247.98 | €2.23 |
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": "GR", "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-gr-2026-09-09".
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