An electric vehicle spends most of its life parked with a large battery doing nothing. Vehicle-to-grid (V2G) taps that idle capacity: with a bidirectional charger, an EV can not only charge but also discharge energy back to the grid or a home, providing storage and grid services from a fleet that already exists.
Working principle
Charging normally converts grid AC to battery DC. V2G adds the reverse path: a bidirectional AC–DC converter can invert the battery's DC back into grid-synchronised AC. An aggregator or DERMS platform coordinates many vehicles, deciding when each charges or discharges based on grid signals, electricity prices and the owner's departure needs. The car effectively becomes a dispatchable battery.
| Mode | Power flow | Service |
|---|---|---|
| V1G (smart charge) | Grid → EV (timed) | Load shifting |
| V2H | EV ↔ home | Backup, self-consumption |
| V2G | EV ↔ grid | Frequency reg., peak shaving |
Key challengeThe chief concern is battery degradation from extra cycling; modern schemes use shallow cycles and high-value services (frequency regulation) so revenue outweighs wear.
Applications
- Frequency regulation and peak shaving for the grid
- Home/building backup power (V2H) during outages
- Renewable balancing — soaking up midday solar, discharging at peak
References & further reading
- Kempton & Tomić, “Vehicle-to-grid power fundamentals,” J. Power Sources, 2005.
- Sovacool et al., “The neglected social dimensions to a vehicle-to-grid transition,” Nature Energy, 2018.
- ISO 15118 / IEC 61851 EV communication & bidirectional charging standards.