Vehicle-to-grid, often called V2G, lets an electric vehicle act like a movable battery for a home or electric grid. Instead of only taking energy from the charger, the car can also send stored energy back when it is useful. This matters because solar and wind power change with weather and time of day, while the grid needs electricity supply and demand to stay balanced every second.
A parked EV can help store extra renewable energy and release it during peak demand.
Key Facts
- Battery energy stored: E = P t
- Charging or discharging power: P = V I
- Round-trip efficiency: efficiency = useful energy out / energy put in
- Energy cost or value: money = energy in kWh × price per kWh
- V2G requires a bidirectional charger that can move power into and out of the EV battery.
- Many EVs are parked most of the day, so their batteries can provide grid support without being driven.
Vocabulary
- Vehicle-to-grid
- Vehicle-to-grid is a system that allows an electric vehicle battery to send electricity back to a building or the power grid.
- Bidirectional charger
- A bidirectional charger is a charging device that can both charge an EV battery and discharge energy from it.
- Grid demand
- Grid demand is the total electrical power that homes, businesses, and devices require at a given moment.
- Peak load
- Peak load is the highest level of electricity demand during a period such as a day or season.
- State of charge
- State of charge is the percentage of usable energy remaining in a battery compared with its full capacity.
Common Mistakes to Avoid
- Assuming V2G drains the car completely, which is wrong because systems can set a minimum state of charge so the driver still has enough range.
- Treating power and energy as the same quantity, which is wrong because power is a rate in kW while energy is an amount in kWh.
- Ignoring efficiency losses, which is wrong because charging and discharging lose some energy as heat in the battery, charger, and electronics.
- Assuming every EV can do V2G, which is wrong because the vehicle, charger, software, and utility connection must all support bidirectional operation.
Practice Questions
- 1 An EV sends 6 kW to a home for 3 hours during a peak demand period. How many kWh of energy does it supply?
- 2 A car battery has 60 kWh of usable capacity and must keep at least 40 percent charge for driving. If it starts full, how many kWh can be used for V2G?
- 3 Explain why V2G is especially useful in a neighborhood with many solar panels, even if solar power is not available at night.