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This lecture will discuss how electric vehicles can be used as an energy storage and the potential for vehicle to grid. The following topics will be covered:

• The concept of vehicle to grid
• The benefits of using EV as storage
• The implementation of vehicle to grid
• The key challenges of vehicle to grid

The concept of vehicle to grid

Vehicle to grid (V2G) refers to the concept of using the electric vehicle battery to feed power back to the grid. V2G uses electric vehicles not only as a car, but also as a battery on wheels, which is capable of energy storage. Besides feeding energy to the grid, an electric vehicle can also feed its energy to a building (V2B), home (V2H), or another load (V2L). In general, the term vehicle to X(V2X) can be used to include all applications.

The benefits of using EV as storage

The storage in electric vehicles and V2X has several benefits:

• V2G enables the storage of electricity in the car, especially from renewable sources which leads to the dual benefit of managing the variations of renewables and reducing emissions of electric mobility.
• V2X can be used for peak shaving by feeding energy stored in the battery back to the grid at moments of peak electricity demand.
• V2X can be used as a backup energy storage when, say there are grid blackouts or power failures.
• Ancillary services like frequency control and voltage control can be offered to the grid using an electric car with V2X configuration providing a revenue stream to the EV user.

These benefits are possible due to the large amount of the battery in an EV. A typical EV battery contains a storage of 30 to 100 kWh. An electric bus or truck can even store 100 to 500 kWh. Such large batteries can power a house for several days, or even a week.

Besides the energy perspective, an EV battery via vehicle to grid can be a significant source of power. Assume each vehicle being able to deliver 10kW of power, a mere 100 cars can provide 1 megawatt of power when required. Such a virtual power plant can play a key role in future grids with large scale of variable generation from solar and wind energy.

The implementation of vehicle to grid

The common way to charge an EV is AC charging, where an onboard converter converts the AC power into DC power. This typically has a power rating of 22 kW. However, V2G is at this moment not possible for AC chargers, since most EV’s only contain a unidirectional charger. Therefore, the energy can only flow from grid to EV and not the other way around. Therefore, bidirectional chargers are needed. Additionally, V2X requires a high level of communication, which is not possible with the PWM (Pulse Width Modulation) communication that is used in type 1 and type 2 AC chargers.

Due to these reasons, bidirectional off-board DC chargers are used for V2G operations, which use a higher level of communication between EV and the charger. Two types of communication are Power Line Communication (PLC) or Control Area Network (CAN) communication. It is important to keep in mind that V2G powers are usually limited to 20 kW, despite the DC chargers having a higher rating. Also, not all DC chargers are bidirectional and V2G capable.

The key challenges for vehicle to grid

There are still a few challenges for vehicle to grid and for V2X:

• V2X needs bidirectional chargers, which are bigger and more expensive than unidirectional chargers.
• The lifetime of an EV could be reduced, since the bidirectional charging demands more charging and discharging cycles.
• The ICT infrastructure, required standardization, regulatory framework, and financial incentives needed for V2X are still under development.

Conclusion

This lecture covered the topic of vehicle to grid and vehicle to X. First the concepts were introduced, and the benefits were listed. After this, the implementation of V2G was discussed. This was followed by mentioning the key challenges for vehicle to grid.