Why can't every car charge at full power?
An office car park with 20 AC charge points of 11 kW. Between 8:00 and 8:30 AM, fourteen cars plug in: ten charge on three phases at up to 11 kW, four on a single phase at up to 3.7 kW.
The car park's supply allows 80 kW for charging, 116 A on each phase. The fourteen cars at full power would need about 125 kW.
The questionWhy is the connection smaller than the chargers, and what happens to the cars?
Guess firstTwenty cars park for nine hours and each needs about 12 kWh. What average power do they need together?RevealHide
About 27 kW: 240 kWh spread over nine hours. The twenty charge points could deliver 220 kW, eight times as much.
A composed example, computed minute by minute. Without management the peak would reach about 125 kW; with it, the total stays below 80 kW, held at first by phase L1 (stops 03 and 05), and every car is full by 1 PM.
Why the connection is smaller
- Cost. In Germany, for example, the one-off contribution to the grid is calculated from the power of the connection, and for sites with power metering the annual includes a price per kilowatt of the year's peak.
- Grid. A grid operator may refuse a connection it cannot provide; in case of a capacity shortage it has to say which grid works would be needed. What that means for a site is the subject of Charging infrastructure, stop 02.
- Need. Cars that park for hours need far less power than their charge points could deliver, as the guess above computes.
names this case as the typical use of local : charge points in a parking garage whose grid connection is rated lower than the sum of the charge points.
Energy matters more than power
A car that stands for nine hours does not need 11 kW; it needs enough kWh by the evening. turns a peak into a plateau: the same energy, spread over the time the cars stand anyway. The units behind this are explained in eMobility and EV basics, stop 04.
Check your understanding
3 questions. Answer all of them to complete this stop. Each answer explains itself.
Why is the building's connection smaller than the sum of all charge points?
Cost, grid capacity and actual need all point the same way: cars standing for hours need energy, not peak power.
What does load management change for a car parked for nine hours?
The energy reaches the car over a longer time. By the evening, the result is the same.
Twenty cars each need 12 kWh over nine hours. What average power do they need together?
20 × 12 kWh = 240 kWh; divided by 9 hours, about 27 kW.
- OCPP Open Charge Point Protocol: the open protocol between a charger and its operator's backend. EV charging fundamentals, stop 03 Glossary
- Load management Shares a site's grid connection between the cars charging at the same time. EV charging fundamentals, stop 04 Glossary
- Grid fee What a grid operator charges for the use of its grid, as part of the electricity price; in Germany, sites with power metering also pay per kilowatt of the year's peak. Business models, stop 01 Glossary
- Smart charging Charging whose power is adjusted in real time, based on information received electronically, for example from the grid operator or a price signal; EU law calls it smart recharging. Bidirectional charging, stop 01 Glossary
- Bundesnetzagentur: Positionspapier zur Erhebung von Baukostenzuschüssen, Beschlusskammer 8, 20 November 2024: the power price model. https://www.bundesnetzagentur.de/DE/Beschlusskammern/BK08/BK8_06_Netzentgelte/70_BKZ/BK8_BKZ.html. Checked 13 Oct 2026.
- Gesetze im Internet: Stromnetzentgeltverordnung (StromNEV), § 17(2): annual power price per kilowatt of the year's peak. https://www.gesetze-im-internet.de/stromnev/__17.html. Checked 13 Oct 2026.
- Gesetze im Internet: Energiewirtschaftsgesetz (EnWG), § 17(2): refusal of a connection and the information owed in case of a capacity shortage. https://www.gesetze-im-internet.de/enwg_2005/__17.html. Checked 13 Oct 2026.
- Open Charge Alliance: OCPP 1.6 edition 2 (2017), section 3.13.4 Smart Charging Use Cases (load balancing, local smart charging) and section 3.13.6 on smart charging when a charge point goes offline; free download. https://openchargealliance.org/download-ocpp/. Checked 13 Oct 2026.