Roaming is the arrangement that lets a driver with one app charge on someone else’s chargers. OCPI — the Open Charge Point Interface — is the protocol that makes it work. Unlike OCPP, which connects a charger to a platform, OCPI connects two platforms to each other.
Two roles, and you may be both
- CPO — Charge Point Operator. You own chargers. You want other networks’ drivers to use them, and you want to be paid for it.
- eMSP — e-Mobility Service Provider. You own the driver relationship. You want your drivers to charge everywhere, on one account and one invoice.
Most networks of any size end up doing both: publishing their own chargers to partners while consuming partners’ chargers for their own drivers.
The modules, in the order they matter
| Module | Direction | What it carries |
|---|---|---|
| Credentials | Both | The handshake — mutual tokens, endpoint discovery, rotation |
| Locations | CPO → eMSP | Sites, EVSEs, connectors, power, live status, opening hours |
| Tariffs | CPO → eMSP | What a session will cost, so the partner app can show a price |
| Tokens | eMSP → CPO | Which driver identifiers the CPO should accept |
| Sessions | CPO → eMSP | Live session progress so the driver sees it in their own app |
| CDRs | CPO → eMSP | The billable record after the session — the basis for settlement |
| Commands | eMSP → CPO | Remote start, remote stop, reserve, unlock |
The technical handshake is genuinely quick — a credentials exchange, endpoint discovery, and a first sync of locations. Most connections can be technically live within a day. The commercial agreement takes considerably longer.
The commercial questions that actually decide it
- 01What does the eMSP pay per kWh, and is it your retail price or a wholesale one? Roaming drivers who pay full retail while the eMSP keeps a margin is one model; a discounted wholesale rate is another.
- 02Who bears the payment risk if the eMSP does not pay? You delivered the energy either way.
- 03What is the settlement cadence, and against which record — your CDRs or their reconciliation of them?
- 04What happens to disputes? A driver complains to their eMSP about your charger, and the dispute resolution has to route back to you with enough evidence to settle it.
- 05Do you publish all sites or a subset? There is rarely a reason to expose a private depot to a roaming partner.
- 06Are idle fees passed through? Many roaming agreements quietly omit them, and then someone occupies a bay for four hours.
Is roaming worth it?
For a network with strong sites and weak brand recognition, yes — emphatically. Roaming puts your chargers in front of drivers who would never have found your app, at a marginal cost close to zero. Corridor and highway sites benefit most, because that is where drivers are least likely to be on their home network.
For a network whose sites are already at high utilisation, it is less obvious: you may simply be substituting a full-margin driver for a discounted one. The decision is site by site, which is why the ability to publish a subset matters.