Roaming allows drivers to charge electric vehicles at public charge stations via the network of their mobility service provider (EMSP).

To facilitate roaming, EMSPs enter into agreements with charge point operators (CPOs) and implement a communication system based on open protocols.

Protocols are a set of rules that standardise communication between networks and software platforms. Roaming protocols support a range of functionalities, most importantly authorisation. CPOs and EMSPs can also use protocols to exchange charge point and tariff information as well as offer advanced features like app-based start and stop of charging sessions.

In the European EV market, four main roaming protocols are currently in use: OCPI, OICP, OCHP, and eMIP.

OCPI

The Open Charge Point Interface protocol (OCPI) was developed by eViolin, an association of Dutch charge point operators and mobility service providers, in collaboration with ElaadNL, a group of major Dutch grid operators. OCPI is currently managed and maintained by the EVRoaming Foundation.

The OCPI protocol supports a wide range of use cases, such as:

• Providing charge point information
• Authorising charge sessions
• Sharing tariff information
• Enable app-based charging

OCPI supports both peer-to-peer (P2P) and roaming hub connections. In P2P roaming, CPOs and EMSPs have direct bilateral connections via which they exchange data. Meanwhile, in hub-based roaming, a charge point operator or mobility service provider can access many roaming partners via a single, standardised connection.

OCPI is the only protocol with a smart charging module, allowing drivers to choose whether they want to charge as cheaply or as fast as possible or optimise for the use of green energy.

While the module is not widely used yet, at GreenFlux we expect this to change as smart charging becomes increasingly important to stabilise the grid, and further smart charging use cases are built out.

Currently, OCPI is the most widely used roaming protocol in Europe thanks to its broad feature range and highly open approach to development.

OCPP

The Open Charge Point Protocol (OCPP) is a free open communications protocol that allows any OCPP-compliant software to work with OCPP-compliant hardware. As such, OCPP gives EV charging networks more interoperability. Therefore, network operators can choose hardware and software based on price point, market demand, or other criteria, rather than on compatibility alone.

Functionally, OCPP is a “syntax” that allows a network charging station to communicate with charging software. The Open Charge Alliance (OCA) writes and publishes OCPP as part of its interoperability advocacy. OCPP charging is available for free; download the latest version from the OCA’s website.

Here are some of the key features:

• Device management: Charge point operators can configure and monitor charging stations.
• Load balancing: Allows limited power on an electric circuit to be balanced depending on how many vehicles are plugged in. OCPP allows the load-balancing conversation to happen between charging station management systems and EV chargers.
• Transaction processing: Facilities charging authorizations and billing.
• Security and access control: Network managers can control charger access and set user parameters.
• Display and messaging support: Sends messages to the EV driver with critical information.

OICP

The Open Intercharge Protocol (OICP) was developed by Hubject, a group of German automotive and energy companies, in 2012. Along with OICP, Hubject also offers an ad-hoc payment solution and a contractual framework for EV roaming.

The OICP protocol supports a range of use cases, such as:

• Roaming via the Hubject hub
• Ad-hoc payments
• Authorisations
• Real-time exchange of charge point information
• Billing and reservations

Along with OCPI, OICP is one of the two roaming protocols that facilitates the exchange of signed meter data. Signed meter data confirms the amount of electricity provided to an EV during charging, and thereby helps charge point operators conform to German calibration law requirements (Eichrecht). This is invaluable to companies operating in the German market.

OICP connects hundreds of companies across Europe and is widely used in the DACH market.

Table 1: Comparison of roaming protocols

FEATURES	OCPI	OICP	OCHP	EMIP
Hub roaming
P2P roaming
Providing charge point information
Charge point search module
Authorising charge sessions
Reservations
Remote start and stop
Providing session information
Ad-hoc payments
Billing
Smart charging support
Calibration law (Eichrecht) support
Platform monitoring
Communication	Real-time	Real-time	Asynchronous	Real-time

*Please note: The ocpp protocol is not included in the table for comparison for the time being

OCHP

The Open Clearing House Protocol (OCHP) was developed by SmartLab Innovationsgesellschaft GmbH and ElaadNL, and is managed by the roaming hub e-clearing.net.

OCHP facilitates hub-based roaming with features like:

• Authorisation
• Billing
• Providing charge point and sessions information
• Remote start-and stop

The extension OCHP-Direct allows CPOs and EMSPs to make use of the same functionality via a peer-to-peer connection.

OCHP relies mainly on asynchronous, as opposed to real-time, communication. For example, it creates so-called ‘white lists’ of users, instead of authenticating them in real-time based information from the EMSP. This means that even if the roaming hub were to ever go down, charge sessions would still work, as a single point of failure is avoided.

eMIP

The eMobility Interoperation Protocol (eMIP) is designed and managed by GIREVE, an integrated platform founded by EDF, Renault, CNR, and Caisse des Dépôts. It is most widely used in France.

EMIP supports both roaming via the GIREVE platform and peer-to-peer connections, with functionalities including:

Providing charge point and session information

• Authorisation
• Billing
• Platform monitoring

eMIP lets CPOs and EMSPs add any sort of data messages or identification methods, thus allowing new features to be implemented quickly, without the need for repeat protocol version updates.

Also, eMIP is the only protocol that supports a charge point search module, which allows EMSPs to retrieve a list of charge points located in a given geographic area and fulfilling a set of charging criteria (e.g. connector type).

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