V2X means "vehicle-to-everything" and is a collective term for the technology in which the energy stored within an electric vehicle (EV) battery can be exported and used in a house, by other buildings or to help balance the electricity grid. V2X requires ‘bi-directional chargers’ that can charge and discharge the battery in an EV.
Different terms are used to describe use cases for V2X technology depending where the energy from the electric vehicle is used. Examples of this include:
Smart charging is where the rate and/or time at which a vehicle is charged can be controlled while the vehicle is plugged in and involves the one way flow of energy from the charger the car (uni-directional or V1G). The rate or time of the charging can be modified based on user settings to charge when electricity is cheapest, cleanest or in response to signals from the electricity market, network or system. Unlike V2X, smart charging is only able to provide a demand turn-down service by changing the rate of charging (including starting or stoping). In contrast V2X involves charging or discharging of the vehicle battery, allowing for more modes of response to signals, acting in a similar way to stationary storage. V2X is a more powerful tool than smart charging but more complicated.
V2X requires four things:
A V2G enabled vehicle is one that can safely and securely export the energy in the EV battery to the charger. At present only a small number of production vehicles are able to do so. These include i.a. the Nissan LEAF, Nissan e-NV200 and Mitsubishi Outlander – by means of the ChaDeMo protocol (see following section for more information).
A bi-directional charger is one that can charge an EV (whereby the power flows from the charger to the car), and discharge an EV (whereby power flows from an EV to the charger).
To export the energy in the EV battery the car and charger must communicate in order to send and receive signals. This is done using standardised communication protocols. At present there are at least 4 communication standards and protocols used widely in the EV market for DC charging. These are ChaDeMo (Japanese), CCS (EU and US), GB/T (Chinese) and Tesla (worldwide) Of these, only the ChaDeMo protocol currently supports V2X. The CCS protocol is planned to support V2H from 2020 and V2G from 2025, with testing ongoing on a draft form of the protocol.
Finally, a control system is required to manage the discharging process, ensuring that the exported energy is used safely and effectively. Various control or energy management systems are available in the market. These control systems also have a standard communication protocol, called the Open Charge Point Protocol or OCPP. The current version (OCPP 2.0) does not support V2X but this will change over the next couple of years.
An EV battery is charged and discharged using direct current (DC). However houses, businesses and the electricity grid generally use alternating current (AC). Therefore, in order to charge an EV, you need to convert the AC power supplied to the charger into DC power to charge the battery. Conversely, when discharging the battery, you need to convert from DC power in the battery to AC power for use in the electricity system. This is conversion is done via an inverter which can either be located in the charge point (option 1) or the car (option 2).
Option 1 is the DC ‘charger’ solution.
This uses a converter in the charger to convert the AC power supplied to the charger, to DC power, which is then used to charge the vehicle. When discharging, the car exports in DC, which is then converted to AC by the charger. DC solutions are well developed with a number of DC bi-directional chargers and bi-directional vehicles commercially available.
Option 2 is the AC ‘on-board’ solution. Here the charger supplies AC power to a converter in the car. This onboard converter then converts the power to DC, at which point it is used to charge the battery. When discharging from the battery, the DC power from the battery is converted to AC on board, before then being exported to the charger as AC.
For more information about the differences between AC and DC see this link
V2X enables EV owners to use the batteries in the vehicles to manage their electricity use in a smarter, more flexible way to reduce the cost of energy or earn additional revenue. EV owners can save money through V2X by using electricity stored in the EV when prices are high and recharging the EV when prices are low. If there is on-site solar then V2X can also help increase the amount of solar consumed locally by that home or business by using that stored electricity at a later time (for example in the evening). EV owners can earn additional revenues by charging or discharging the vehicles in response to signals to support the electricity network. These potential benefits need to be offset against the cost of V2X chargers.
For more details on the potential services V2X can provide see services page.
The impact of V2X on EV batteries is a key concern for vehicle owners. It is also a complicated issue, with battery lifetime driven by a whole host of factors. Many studies have been conducted on this issue, with one by the University of Warwick showing that V2X could actually extend the life of batteries (through having the battery at a lower average State of Charge). Overall the evidence suggests that the impact depends on how the battery is used As an example Nissan maintain the same warranty conditions for cars that provide V2X services. It is however good practice to consider this potential impact when assessing the potential benefits of the service to vehicle owners.