At FOSDEM 2025, Andreas Heinrich of PIONIX delivered a session in the Energy Devroom, titled “Bidirectional Charging: Protocols, Challenges & Strategies with EVerest.” His talk explored the fundamentals of bidirectional charging, its benefits, various charging strategies, and the role of open source initiatives like LF Energy EVerest in addressing challenges within this evolving space. A summary follows, and the full video is available at the end of this post.
What is Bidirectional Charging and Why Does It Matter?
Bidirectional charging enables electric vehicles (EVs) to not only charge their batteries but also discharge energy back into the grid or a local energy system. Heinrich emphasized the importance of this capability for several reasons:
- Grid stabilization: EVs can act as decentralized energy storage, helping to balance supply and demand in power grids.
- Cost optimization: EV owners can leverage dynamic pricing, charging when electricity is cheap and discharging when prices rise.
- Backup power: EVs can serve as emergency power sources or even as mobile power banks for activities like camping.
Charging and Discharging Strategies
Heinrich discussed multiple charging strategies, ranging from simple to complex:
- Fast Charging: This strategy prioritizes rapid energy replenishment. For example, an EV may start charging at 50 kW but then reduce to 20 kW after 30 minutes due to external limitations.
- PV-Optimized Charging: This method aligns charging with solar energy production. By dynamically adjusting the charging rate based on available photovoltaic (PV) power and other household energy consumption, it maximizes self-consumption and minimizes reliance on the grid.
- Grid-Interactive Charging: This approach allows EVs to support the electricity grid by charging or discharging based on grid conditions, subject to user-defined constraints such as minimum and maximum state-of-charge levels.
The Communication and Protocol Landscape
A key challenge in bidirectional charging is ensuring seamless communication across the entire energy ecosystem. Heinrich outlined the primary protocols involved:
- ISO 15118: Governs communication between EVs and charging stations, with ISO 15118-20 introducing essential features like bidirectional charging and smart charging controls.
- OCPP (Open Charge Point Protocol): Manages communication between charging stations and backend systems. OCPP 2.0.1 includes support for bidirectional charging.
- eBus: Facilitates communication between local energy devices and building management systems.
The Role of LF Energy EVerest
EVerest is an open source software stack designed to facilitate interoperability among EV charging infrastructure components. Heinrich highlighted how EVerest integrates various protocols (ISO 15118, OCPP, eBus) and supports bidirectional charging implementations. EVerest is already running on over 10,000 chargers in the field, providing a scalable and open foundation for future developments.
Challenges and the Road Ahead
Despite significant progress, challenges remain:
- Protocol Adoption: Many EVs and charging stations still do not fully support ISO 15118-20, creating compatibility issues.
- Lack of Open Implementations: While standards exist, open source implementations are crucial for widespread adoption and interoperability.
- Battery Health Considerations: Frequent charging and discharging cycles impact battery longevity. While protocols like ISO 15118-20 manage these processes intelligently, long-term effects remain an area of research.
