MID meters and EV charging billing

What MID means

MID (Measuring Instruments Directive) is EU Directive 2014/32/EU on measuring instruments. It sets requirements for, among other things, active electrical energy meters used for billing. A MID-compliant meter has undergone a conformity assessment involving a notified body, so its accuracy is confirmed, not just declared by the manufacturer.

In practice, this means that a reading from such a meter can be the basis for charging someone for energy — something that cannot be defended in the same way with indicative metering.

How to recognise a MID meter

In the photo above, on the left: a meter built into a charger, with the “M21” marking next to the CE mark. On the right: a panel in a charging station cabinet with two digital energy meters (P1 and P2) — a separate one for each socket.

• The CE marking plus the supplementary metrology marking: the letter “M” and the last two digits of the year it was affixed, in a rectangle — e.g. “M21” means 2021.
• The four-digit number of the notified body that assessed conformity (placed next to the “M” marking).
• The accuracy class according to EN 50470-3: A, B or C — the further along the alphabet, the smaller the permissible error. Class B is the most common in chargers.
• Seals and safeguards that prevent tampering with the meter without leaving a trace.

When MID matters, and when it matters less

• Housing communities and housing co-ops: energy from the common area is passed on to residents — metering should be able to withstand challenge.
• Office buildings and car parks: the cost of charging is passed on to tenants or customers.
• Companies and fleets: billing for charging company cars at an employee’s home or private cars at the company.
• Hotels: adding charging to the guest’s bill.
• Less important: free charging, or your own car charged from your own grid-operator meter, without passing costs on to others.

Meter in the charger or in the switchboard

A MID meter can be built into the charger or installed separately in the switchboard — in which case the charger reads it via a communication interface. Both solutions are correct; what matters is that each billed charging point has its own metering. For a charger with two sockets, this usually means two meters or one meter that handles both points separately.

The built-in current measurement in the charger’s electronics alone, without a MID meter, is used to control charging and gives an indicative result. It is enough for statistics, but less suitable for passing costs on to others.

From meter to bill

The charger reads the meter at the start and end of the session and sends this data via the OCPP protocol to the billing system. The system assigns the session to a user, calculates the cost according to the site’s tariff and compiles everything in reports — monthly, per unit, tenant or employee.

In the event of a dispute, consistency is what matters most: the reading on the meter display, the session history in the system and the amount charged should all match. That is why, during inspections, we also check that the meter is working, sealed and reporting correctly to the system.

Meters used for billing are subject to legal metrological control regulations (Poland’s Law on Measures), which may require re-verification after a certain period. We confirm the requirements for each specific site and billing model individually.

How we approach this in practice

At the equipment selection stage, we establish how the site will bill for charging and choose chargers with a MID meter, or external meters, wherever energy is passed on to other users. In the Domena Power system, each session records the energy used, the time and the rate charged, and the reports are a ready basis for billing — with no commission on energy sales.