ISO 15118-20 Explained: Key Upgrades From ISO 15118-2

ISO 15118-20 is the second generation of the vehicle-to-grid (V2G) communication standard between electric vehicles (EVs) and charging equipment (EVSE). Where ISO 15118-2 established Plug & Charge and smart charging, ISO 15118-20 (published in 2022) extends the protocol family to cover true bidirectional energy transfer, wireless power transfer, stronger security, and richer data exchange. Here are the upgrades that matter most for charge-point operators (CPOs), OEMs, and software vendors.

1. Bidirectional Power Transfer (BPT)

• Dynamic and scheduled modes. ISO 15118-20 defines both a dynamic control mode, where the charger requests rapid set-point changes, and a scheduled control mode, where an entire power schedule is exchanged in one payload.
• AC and DC support. Unlike ISO 15118-2, which limited bidirectional flow to AC, ISO 15118-20 explicitly supports DC BPT.
• Grid-services ready. Fine-grained power schedules let the EV participate in frequency regulation and demand-response programs.

2. Enhanced Security (TLS 1.3)

• Mandatory mutual authentication. Sessions negotiate TLS 1.3 with certificate-based mutual authentication.
• Larger keys. ISO 15118-20 moves to stronger elliptic-curve profiles (secp521r1 and Ed448) versus secp256r1 in ISO 15118-2, which increases certificate sizes and secure-storage requirements.
• Second-generation PKI. The V2G public-key infrastructure is restructured to handle multi-contract and roaming scenarios.

3. Multi-Contract Handling

A single EV can present multiple e-mobility contracts and let the charging station select one based on tariff, roaming agreement, or user preference — a meaningful improvement for fleets that work with several mobility service providers.

4. Wireless Power Transfer & Automated Connection

ISO 15118-20 adds message sets for wireless (inductive) power transfer and for automated connection devices such as pantographs — the groundwork for hands-free depot charging of buses and other fleet vehicles.

5. Multiplexed Communication

A multiplexing layer allows multiple logical channels over a single V2G connection, so services can be added or renegotiated without tearing down the session.

Practical Implications

Plan for firmware upgrades on both the EV side (EVCC) and the charger side (SECC) to support TLS 1.3, larger certificates, and dynamic BPT. Back-office systems (OCPP 2.1) also need to process bidirectional schedules.

Looking Ahead

ISO 15118-20 is not directly backward compatible with ISO 15118-2. During the transition, coexistence strategies — dual protocol stacks and DIN 70121 fallback — will be common. Early adopters can unlock premium V2G and grid-service use cases sooner.