One night of prices and one grid signal
The commuter's car is full and leaves at 7 AM. Behind the night stands one table: the prices the controller received for every quarter hour, the one grid signal that arrived, and what the wallbox did in response.
The table is composed, but every column exists: the day-ahead price per quarter hour, the retail price a dynamic contract builds on it, and the control signal under the German rules.
The questionWhy did the car charge between 2 and 3 AM, what did the grid signal change, and what did the night cost?
Guess firstThe wholesale price fell from 16.2 to 7.0 ct per kWh. By how much did the retail price fall?RevealHide
By the same 9.2 ct plus VAT on it, about 11 ct: from 38.7 to 27.7 ct. Grid fees, levies and the supplier's margin stay the same at every hour; only the wholesale part moves.
What you are looking at
A dynamic electricity contract passes the day-ahead price through to the customer, quarter hour by quarter hour since the market moved to 15-minute units in October 2025. EU law gives every customer with a smart meter the right to such a contract. On top of the wholesale price sit the parts that do not move: , levies and taxes, the supplier's margin, and VAT on everything. The grid signal in the middle of the table is the German rule for controllable devices: a temporary reduction to a guaranteed minimum.
Select the lines to follow the controller's reasoning.
Selected quarter hours. Retail is composed as day-ahead plus 16.3 ct of grid fees, levies, tax and margin, plus 19% VAT.
- Line 1The job for the night
The controller knows three things from the driver: plugged in, leaves at 7 AM, needs about 10 kWh (stop 04). Everything below is its answer.
QUARTER HOUR DAY-AHEAD RETAIL EVENT kWct/kWh ct/kWh18:30-18:45 16.0 38.4 0.019:00-19:15 15.6 38.0 0.020:00-20:15 14.2 36.3 grid signal continues 0.021:00-21:15 12.5 34.3 0.022:00-22:15 10.4 31.8 0.023:00-23:15 9.1 30.2 0.000:00-00:15 8.3 29.3 0.001:00-01:15 7.6 28.4 0.002:15-02:30 7.0 27.7 11.002:30-02:45 6.9 27.6 11.004:00-04:15 7.4 28.2 0.006:00-06:15 9.8 31.1 0.0
wb-27-night.txt: the whole file, to copy
Wednesday 14 October 2026, Europe/Berlin. Wallbox WB-27, 11 kW. Car plugged in 7:10 PM, departure 7:00 AM, 10 kWh needed.
QUARTER HOUR DAY-AHEAD RETAIL EVENT kW
ct/kWh ct/kWh
18:00-18:15 16.2 38.7 0.0
18:30-18:45 16.0 38.4 0.0
19:00-19:15 15.6 38.0 0.0
19:15-19:30 15.4 37.7 plugged in, 7:10 PM 0.0
19:30-19:45 15.1 37.4 GRID SIGNAL: limit 4.2 kW 0.0
20:00-20:15 14.2 36.3 grid signal continues 0.0
20:15-20:30 13.8 35.8 GRID SIGNAL ENDS 8:10 PM 0.0
21:00-21:15 12.5 34.3 0.0
22:00-22:15 10.4 31.8 0.0
23:00-23:15 9.1 30.2 0.0
00:00-00:15 8.3 29.3 0.0
01:00-01:15 7.6 28.4 0.0
02:00-02:15 7.0 27.7 charging starts 11.0
02:15-02:30 7.0 27.7 11.0
02:30-02:45 6.9 27.6 11.0
02:45-03:00 7.1 27.8 charging ends 2:55 AM 11.0
04:00-04:15 7.4 28.2 0.0
06:00-06:15 9.8 31.1 0.0
07:00-07:15 12.9 34.7 departure 0.0A composed night. Day-ahead prices per quarter hour as the market publishes them; the reduction to 4.2 kW follows the German rules for controllable devices.
7:15 PM, at 37.7 ct
the controller's choice, 27.7 ct
one night, one car
of every retail price, whatever the market
Computed from the table. Over 200 charging nights a year the saving is a few hundred euros; the fixed part of the price is what no schedule can avoid.
Three columns, three sources
- Day-ahead. Set by the coupled European market the day before, for every quarter hour of the next day. The controller downloads it once and plans the night.
- Retail. The supplier's formula: wholesale plus the fixed components plus VAT. Different suppliers, different fixed parts; the shape of the curve is the same.
- Event. The driver's inputs and the grid operator's signal. The signal reaches the wallbox through the control box the grid operator installed, or through the energy management system of the house; it overrides any price.
Why the signal changed nothing here, and would have elsewhere
At 7:30 PM this wallbox was idle, so the limit of 4.2 kW cost it nothing. A neighbour charging at 11 kW lost about 4.5 kWh of progress in those forty minutes and made it up later in the night. In the German rules the grid operator's reduction has priority over the market when the two conflict, and it always leaves the minimum (stop 06). A controller that knows both, the prices and the possibility of a signal, keeps a margin before departure for exactly this case; Load management, stop 06 shows the same night from the car park's side.
Check your understanding
3 questions. Answer all of them to complete this stop. Each answer explains itself.
The day-ahead price at 2 AM was 7.0 ct per kWh. Why did the wallbox's owner pay 27.7 ct?
Only the wholesale part of a retail price moves with the market; about 16 ct of fixed components and VAT come on top.
What did the grid signal at 7:30 PM do to this wallbox?
The reduction caps the power of controlled devices for a time; a device at 0 kW stays at 0 kW. Charging at 2 AM was the price's doing, not the signal's.
What was the night's charging worth compared with charging on arrival?
The difference of about 10 ct per kWh times 10 kWh. Small per night, a few hundred euros over a year of nights.
- Grid fee What a grid operator charges for the use of its grid; it is part of the electricity price and, for larger connections, often also depends on the highest power drawn. Business models, stop 01 Glossary
- OKTE (nominated electricity market operator): 15-minute MTU in SDAC was implemented, 1 October 2025. https://okte.sk/en/information/news/2025-10-01-15-minute-mtu-in-sdac-was-implemented. Checked 09 Oct 2026.
- EUR-Lex: Directive (EU) 2019/944 on common rules for the internal market for electricity, Articles 11 and 33. https://eur-lex.europa.eu/eli/dir/2019/944/oj. Checked 09 Oct 2026. © European Union, reused under Commission Decision 2011/833/EU.
- Bundesnetzagentur: BK6-22-300, Annex 1, sections 2.4 and 4.5. https://www.bundesnetzagentur.de/DE/Beschlusskammern/1_GZ/BK6-GZ/2022/BK6-22-300/Beschluss/BK6-22-300_Beschluss_Anlage1.pdf?__blob=publicationFile&v=1. Checked 09 Oct 2026.
- OKTE (nominated electricity market operator): 15-minute MTU in SDAC was implemented, 1 October 2025. https://okte.sk/en/information/news/2025-10-01-15-minute-mtu-in-sdac-was-implemented. Checked 09 Oct 2026.
- Bundesnetzagentur: BK6-22-300, Annex 1, sections 2.4 and 4.5. https://www.bundesnetzagentur.de/DE/Beschlusskammern/1_GZ/BK6-GZ/2022/BK6-22-300/Beschluss/BK6-22-300_Beschluss_Anlage1.pdf?__blob=publicationFile&v=1. Checked 09 Oct 2026.
- OKTE (nominated electricity market operator): 15-minute MTU in SDAC was implemented, 1 October 2025. https://okte.sk/en/information/news/2025-10-01-15-minute-mtu-in-sdac-was-implemented. Checked 09 Oct 2026.
- Bundesnetzagentur: BK6-22-300, Annex 1, sections 2.4 and 4.5. https://www.bundesnetzagentur.de/DE/Beschlusskammern/1_GZ/BK6-GZ/2022/BK6-22-300/Beschluss/BK6-22-300_Beschluss_Anlage1.pdf?__blob=publicationFile&v=1. Checked 09 Oct 2026.