V2G and V2X: bidirectional charging
How a car can send energy back to a home, a building or the grid, explained from the standards: who controls what at each link of the chain, and which document governs it. “V2X” here means bidirectional charging, not vehicle-to-vehicle radio such as C-V2X or DSRC.
Power flow: V1G to V2G
Five ways a car’s battery can trade energy with the world, from one-way smart charging to pushing power into the grid, and why it matters whether the inverter is in the charger (DC) or in the car (AC).
- V1G
- V2L
- V2H
- V2B
- V2G
A bidirectional session, step by step
An ISO 15118-20 bidirectional power transfer session in the order one open-source implementation runs it, with the messages that carry the discharge limits and the charge or discharge flag.
- ISO 15118-20
- BPT
The energy window
What a car asks for in an ISO 15118-20 session: energy requests and a departure time, and how the Scheduled and Dynamic control modes divide the work between car and charger.
- Scheduled
- Dynamic
- ISO 15118-20
The control chain
From the grid operator through an aggregator and the charging network’s back office to the charger and the car: who sends what to whom, and the interconnection rules at the end.
- OCPP 2.1
- IEEE 2030.5
- OpenADR
- IEEE 1547
The V2X standards map
Which standard governs which link between the grid and the car, for AC and for DC, and where each one stands: published, draft or still under consideration.
- ISO 15118-20
- OCPP 2.1
- IEC 61851
- IEEE 1547
- UL 1741
- CHAdeMO