Electric vehicle charging stations: four trade-offs that secure your
Four technical trade-offs shape your EV charging infrastructure sizing
Most EV charging operating cost overruns come from the initial under-sizing of the infrastructure, not from the choice of charging stations. Public debate on charging focuses on unit power output and station brands, whereas the dominant economic factor is the meter reserve at the Enedis delivery point. For an Energy Manager subject to the OPERAT tertiary decree, the central trade-off is not 7.4 kW versus 22 kW: it is the scalability of the upstream supply over 10 years. Four decisions determine economic viability: unit power output versus point density, meter reserve scalability, single-phase or three-phase balancing under NF C 15-100, and the interface with the main low-voltage distribution board. Kytom has integrated design and delivery since 2006, with a cost of between EUR 1,200 and EUR 2,800 per charging point and a lead time of 6 to 12 weeks depending on the electrical upgrades required, a range we calibrate to the building configuration, the number of points and the scale of the electrical work.
Sizing a charging infrastructure involves four technical trade-offs rarely addressed simultaneously at the preliminary design stage.
- Unit power output versus point density: 6 x 7.4 kW stations serve more users on long charges than a fleet of 3 x 22 kW stations for an equivalent budget, but they saturate the board during the morning peak.
- 5 to 10 year scalability: anticipating fleet growth requires reserving 30 to 40% additional power at the meter from the design stage, failing which post-installation upgrades become difficult to avoid.
- Single-phase or three-phase distribution: the mix of light vehicles (often 7.4 kW single-phase) and vans (11 or 22 kW three-phase) determines phase balancing under NF C 15-100.
- Electrical network interface: a direct connection to the existing main low-voltage distribution board or the creation of a dedicated EV charging submeter affect operating costs and the amounts that can be re-invoiced to occupants.
Scalable infrastructures cost more to install, but significantly reduce the total cost of ownership over 10 years once the fleet grows.
Our reading differs from the prevailing EV charging orthodoxy on this point: the industry over-values 22 kW stations as the “futureproof” standard. In practice, on our recent projects, 7.4 kW stations cover the vast majority of office uses (parking longer than 4 h), with far lower board saturation. True scalability is not determined by unit power output, it is determined by the upstream meter reserve.
When this scalability logic is not justified: for a fleet of fewer than 6 points with no prospect of fleet growth (a stable headquarters, no company vehicles planned within 5 years), over-reserving meter power generates an oversized Enedis subscription whose annual extra cost exceeds the savings on future upgrades. In this scenario, strict sizing based on current use remains preferable.
