Vehicle-to-Grid: How Electric Vehicles Become Storage Storage Systems in the Smart Grid
Electric vehicles are increasingly evolving from mere electricity consumers into active power grid components. Vehicle-to-Grid (V2G) refers to the use of electric vehicle batteries to feed stored energy back into the grid when needed, and thus balance out peak loads. This turns them into decentralized storage systems that contribute to grid stability and the integration of renewable energy. It requires bidirectional power electronics that controls the flow of energy in an efficient and grid-compliant manner.
How does bidirectional charging work?
In conventional charging of an electric vehicle, electrical energy flows in one direction: from the power grid into the vehicle battery. Bidirectional charging also enables energy to flow in the opposite direction. As a result, the electric vehicle can feed the electricity stored in the battery back into the power grid. Depending on the destination of the current flow, a distinction is made between the following scenarios:
- Vehicle-to-Home (V2H): Powers the home’s own network
- Vehicle-to-Building (V2B): Powers building or corporate networks
- Vehicle-to-Grid (V2G): Powers the public power grid
Since the vehicle’s high-voltage battery uses direct current (DC), but the power grid uses alternating current (AC), the current needs to be rectified or inverted accordingly using power electronics in the form of AC/DC or DC/DC converters. Depending on the charging concept, the conversion takes place either directly in the vehicle (AC-V2G) or in the wallbox (DC-V2G).
On-board or off-board: Where does the current conversion take place?
The basic options for the power electronics required for bidirectional charging are what are referred to as on-board or off-board configurations. In the on-board concept, or AC-V2G, AC-DC conversion takes place directly in the vehicle. It requires a bidirectional on-board charger (OBC) that enables both battery charging and energy feedback into the AC grid. In the off-board concept, or DC-V2G, the conversion takes place directly in the wallbox.
Various inverter and converter topologies are used within the on-board and off-board configurations to enable bidirectional energy flow between the power grid and the vehicle battery. The architecture used for bidirectional charging affects not only the power electronics but also the overall cost and complexity of both the vehicle and the charging infrastructure.
How do electric vehicles stabilize the smart grid?
With V2G, electric vehicles can not only draw power from the grid, but also feed stored energy back into the grid when needed. That allows grid operators to integrate vehicle batteries into the smart grid as flexible storage systems. For example, if there is an oversupply of renewable energy, vehicles can draw electricity that exceeds the simultaneous demand. If electricity demand rises again at a later time, the vehicles can feed the stored energy back into the grid.
Looking ahead, clusters of vehicle batteries could also provide power grid system services. The research project “Bidirectional Charging Management” examined, among other things,
- operating reserve,
- redispatch, and
- local grid services
as V2G use cases. As a result, vehicles could not only buffer energy, but also provide their charging and discharging capacity to stabilize the power system.
What interfaces and standards does V2G require?
For manufacturer-independent use, interoperable communication must be possible between the vehicle, charging infrastructure, backend, and energy system. The following standards currently apply for this:
- ISO 15118 serves as a key basis for communication between electric vehicle and charging equipment.
- The Open Charge Point Protocol (OCPP), on the other hand, connects the charging station to the backend or charging point management system.
- The Open Smart Charging Protocol (OSCP) addresses the exchange of available grid capacity between the energy system and the charging infrastructure.
However, communication between the vehicle and the charging station alone is not sufficient for grid-serving control. According to the VDE, suitable feedback from the power grid is currently still lacking. For example, existing systems are guided by the electricity price but don’t take into account whether a surplus of renewable energy is currently available. In the future, that kind of information could help adapt charging and energy feedback processes specifically to the situation in the power grid.
What are the technical and regulatory limitations of V2G?
One technical challenge with V2G is currently still the additional strain on the vehicle battery. The repeated charging and discharging increases the number of charging cycles, which can accelerate the battery’s aging process. However, the extent of this effect depends on the respective usage profile, battery technology, and other influencing factors. For example, smart charging strategies can help limit additional aging. Recent studies indicate that intelligently controlled V2G can limit additional battery aging.
Added to that are energy transmission losses. In the field trial of the “Bidirectional Charging Management” research project, the electric vehicles used achieved, for example, an average round-trip efficiency of around 80 percent. Thanks to optimized control and scheduling, efficiency improved over the course of the trial. For V2G, it is therefore important to weigh the additional use of the battery and the energy losses against the benefit of the flexibility provided.
Power electronics connects mobility and the power grid
As sector coupling increases, the power grid is becoming the central hub for renewable energy. This boosts the importance of power electronics and digital systems. Alongside converting energy, converters are increasingly performing grid-serving functions and contributing to the stability of decentralized smart grids. Technologies based on silicon carbide (SiC) and gallium nitride (GaN) can offer advantages at the system level.
The relevance of power electronics for the electronica community
For electronica 2026, the focus will be on technologies along the entire conversion chain: power semiconductors and power modules, SiC and GaN, gate drivers, passive components, as well as embedded systems and energy management.
Forums at the trade fair, such as the Power Electronics Forum and the Automotive Forum will address current trends in the fields of V2G and power electronics and provide insights into key issues related to these technologies.