Understanding ISO 15118-2 and ISO 15118-20: The Future of Vehicle-to-Grid (V2G)
1. Overview
ISO 15118 is the international standard that defines digital communication between electric vehicles (EVs) and charging infrastructure (EVSE – Electric Vehicle Supply Equipment). It enables secure, automated, and interoperable charging — including bidirectional power flow for Vehicle-to-Grid (V2G).
Two key parts of the standard are:
- ISO 15118-2 – The current widely deployed communication layer for AC and DC charging.
- ISO 15118-20 – The next-generation framework that expands functionality, scalability, and bidirectional energy exchange.
Together, they form the foundation for intelligent energy ecosystems where EVs act as distributed energy resources.
2. ISO 15118-2: What it defines today
ISO 15118-2 specifies:
- Digital communication protocol between EV and EVSE.
- Plug & Charge authentication using digital certificates.
- Session setup, charging negotiation, and metering data exchange.
- AC and DC charging workflows.
- Basic support for bidirectional energy transfer.
Key technical features:
- Communication layer: TCP/IP over Power Line Communication (PLC) (HomePlug Green PHY).
- Security model: Public Key Infrastructure (PKI) with digital certificates.
- Message format: XML-based messages exchanged in defined states.
- Core use case: automated payment and secure charging without user interaction.
Limitations of ISO 15118-2:
- Limited optimization for large-scale grid services.
- Less flexible control over dynamic power flows.
- Not fully aligned with modern energy market mechanisms.
- Limited support for advanced energy management strategies.
3. ISO 15118-20: What changes
ISO 15118-20 is a major evolution, not a minor update. It introduces a more modular and scalable architecture for smart charging and V2G.
"ISO 15118-20 is a major evolution... introducing a more modular and scalable architecture for smart charging and V2G."
Major improvements:
- Native support for bidirectional charging (V2G, V2H, V2B).
- Improved session management and state handling.
- More granular energy and power negotiation.
- Better integration with grid operators and energy markets.
- Support for multiple communication transport layers beyond PLC.
New communication options include:
- PLC (as in ISO 15118-2).
- Ethernet.
- Wi-Fi.
- Cellular (LTE/5G in future extensions).
This makes ISO 15118-20 more adaptable to real-world charging ecosystems.
4. How V2G works under ISO 15118-20
A typical V2G interaction follows these steps:
- EV connects to bidirectional charger.
- Mutual authentication via digital certificates.
- EVSE requests battery status and capacity.
- Grid or energy provider sends power flow request.
- EV negotiates allowed discharge rate and duration.
- Energy flows from EV to grid or building.
- Metering data is recorded and reported.
- Settlement occurs via backend systems.
This enables:
- Peak shaving for utilities.
- Frequency regulation.
- Backup power for homes (V2H).
- Energy arbitrage (charging cheap, selling expensive).
5. Interoperability: ISO 15118-2 vs ISO 15118-20
| Feature | ISO 15118-2 | ISO 15118-20 |
|---|---|---|
| Primary use | Charging | Charging + V2G |
| Transport | PLC only | PLC, Ethernet, Wi-Fi, Cellular |
| Bidirectional | Limited | Native and optimized |
| Grid services | Basic | Advanced |
| Scalability | Moderate | High |
| Security | PKI-based | Enhanced PKI model |
ISO 15118-20 is designed to be backward-compatible in many deployments, but not all legacy chargers will support it without firmware or hardware upgrades.
6. Industry implications
ISO 15118-20 enables:
- Smarter charging networks.
- Large-scale grid integration of EV batteries.
- Reduced need for stationary storage.
- More resilient electrical grids.
- Lower energy costs for consumers.
- New revenue streams for EV owners.
Automakers, utilities, and charger manufacturers are already aligning roadmaps to adopt ISO 15118-20.
7. Challenges remaining
Despite its advantages, several obstacles remain:
- Deployment cost of bidirectional chargers.
- Regulatory approval for V2G in some regions.
- Battery degradation concerns.
- Market standardization for energy trading.
- Cybersecurity risks at scale.
These issues are technical, economic, and regulatory — not purely protocol-related.
8. Conclusion
ISO 15118-2 laid the foundation for secure, automated EV charging. ISO 15118-20 transforms that foundation into a full V2G ecosystem.
Together, they represent the transition from passive electric vehicles to active grid participants.