A Brief Overview of Bidirectional Charging
Bidirectional charging is a key technology for the near future. It combines sustainable mobility with the energy transition by enabling electric vehicles to make their battery capacity available not only to buildings and our homes, but also to the power grid. This requires both a vehicle capable of bidirectional charging and the corresponding bidirectional charging infrastructure.
In our A-Z guide to bidirectional charging, you’ll find brief descriptions of all the key terms related to this new technology.
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Aggregator
What is the role of an aggregator for bidirectional charging? - An aggregator is a service provider that bundles data on the availability of energy flexibilities and offers this to meet the needs of participants in the energy market. This could involve the batteries of many electric vehicles being bundled to form a large, flexible electricity storage system, or meeting the demand for V2G services from distribution and transmission system operators, or responding to price signals from the energy market. The aggregator dynamically links cars and bidirectional charging infrastructure to the power market with the aim of balancing supply and demand in the grid and marketing the stored energy or available free battery capacity.
Balancing energy
How do you define balancing energy? - Primary balancing power refers to the essential balancing energy required to maintain a stable grid frequency of 50 hertz (available within 30 seconds and maintained for 15 minutes). This power can relate to both the supply of energy (discharging the electric vehicle) and the uptake of energy (controlled charging of the electric vehicle).
Bidirectional charging
What is bidirectional charging? - Bidirectional charging refers to the smart charging and discharging of electric vehicles.
EVs capable of bidirectional charging can be controlled not only to draw electricity from the grid when there is a surplus of renewable energy available, but also to feed energy back into the grid during periods of low generation (known as Vehicle-to-Grid or V2G functionality). In this way, the many additional, decentralised storage units in electric vehicles make it easier to connect ever more renewable energy sources to the electricity grid. Users benefit from payments for their V2G services.
In homes and businesses, bidirectional charging can support efficient energy management, save costs and increase the consumption of self-generated solar power.
Controllable consumers
What are controllable consumers according to the German energy law? - In accordance with Section 14a of the German Energy Industry Act, wallboxes and charging stations are controllable consumers that are subject to a registration requirement on the distribution network.
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Day-ahead arbitrage
What does day-ahead arbitrage mean in the context of bidirectional charging? - Time-based arbitrage (for the following day) is referred to as day-ahead arbitrage and specifically exploits price differences in electricity trading at different times.
Distribution system operator (DSO)
What is an DSO? - A distribution system operator (DSO) is a company that operates electricity networks (or gas networks) to distribute energy to end users such as households, businesses or small-scale industrial facilities. In operating what are generally low-voltage and medium-voltage grids, the DSO is responsible for grid connections and the feed-in of renewable energy. The DSO’s role also includes ensuring system security – in certain cases, the DSO relies on grid-supporting services that can be provided using V2G technology.
EEBus
What ist EEBus? - EEBus is a communication protocol that, regardless of the manufacturer, enables communication between energy systems – such as charging infrastructure – on the one hand, and (home) energy management systems on the other. This facilitates an efficient flow of energy and allows energy usage to be conveniently managed in line with user requirements.
Energy management system (EMS)
What is an EMS? - An energy management system (EMS) dynamically controls the loads within a building as well as the energy flows between the vehicle, the building and the electricity grid.
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Home energy management system (HEMS)
What does HEMS mean? - A home energy management system dynamically controls the loads in a person’s own home or flat, as well as the energy flows between the vehicle, the building and the electricity grid.
Increasing self-consumption
How do you increase the self-consumption of your self-generated solar energy? - The efficiency of domestic solar installations can be improved by increasing the amount of solar power consumed on-site. Using V2H technology, surplus solar power is stored in the vehicle’s battery during the day and is then available for consumption in the evening. Depending on how many hours the bidirectional charging vehicle is connected to the charging station, the level of self-sufficiency can be further increased, and it may also be possible to shift electricity self-generation and consumption across several days.
Intelligent metering system (IMSys)
What does IMSys mean? - iMSys stands for the intelligent metering system, which consists of a digital electricity meter and a smart meter gateway acting as a communication module. Thanks to the iMSys’s ability to transmit meter readings and requests securely and in encrypted form, users are able to offer V2G services via their bidirectional-charging-capable vehicle and the bidirectional charging infrastructure.
Intraday Arbitrage
What does intraday arbitrage mean in the context of bidirectional charging? - Arbitrage within a single day is referred to as intraday arbitrage and specifically exploits price differences in electricity trading at different times of the day.
ISO 15118-20
What does ISO 15118-20 stand for? - An international communication standard which, amongst other things, defines V2G communication for the bidirectional charging and discharging of electric vehicles and charging infrastructure. Its implementation in charging infrastructure will be mandatory from 2027 (AFIR).
ISO/IEC 63110
What does ISO/IEC 63110 stand for? - This standard covers the terminology, use cases and architecture for the management of bidirectional charging infrastructure for electric vehicles. It includes the requirements for establishing an e-mobility ecosystem, covering communication processes between various e-mobility stakeholders as well as data exchange with the electricity grid.
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Modbus
What is Modbus? - Modbus is an open protocol that enables communication between energy generation facilities for the collection of power and consumption data, energy management systems and charging devices. Modbus enables data transmission in various operating modes, such as Modbus/RTU or Modbus/TCP.
OCPP 2.1
What is OCPP 2.1? - OCPP 2.1 is the latest version of the international communication standard for connecting charging infrastructure to charge point management systems. From version OCPP 2.1 onwards, bidirectional use cases are supported, ensuring seamless communication between charging infrastructure and backend systems.
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Peakshaving
What does peakshaving mean in the context of bidirectional charging? - At work EV fleets help balance energy demand. This enables the company to counterbalance hours of high power consumption (peakshaving). Employees can feed excess energy from their vehicle batteries into the local grid, thereby preventing extream peak loads and helping to reduce costs.
Reactive power supply
What does reactive power supply mean in the context of bidirectional charging? - The bidirectional charging infrastructure controls the supply of reactive power from the vehicle battery to stabilise the AC grid.
Redispatch
What is redispatch? - Redispatch is a key tool used by distribution system operators (DSOs) and transmission system operators (TSOs) to ensure the stability of the electricity grid in the event of congestion or overload.
Requirements for Generators 2.0 (RfG 2.0)
What is the RfG 2.0? - The EU Regulation "Requirements for Generators" specifies the technical requirements that a generation plant must meet in order to be connected to the grid. RfG 2.0 thus sets the EU minimum standard for the connection of bidirectional charging infrastructure to distribution networks. National requirements in EU Member States may go even further than this. RfG is currently being revised under the name RfG 2.0 – completion is still expected in 2026.
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Tariff-optimised/price-optimised charging & discharging
What is tariff-optimised charging? - A bidirectional-charging-capable car and bidirectional charging infrastructure are connected to an energy management system for intelligently controlled charging and discharging. Here, variable electricity prices and the driver’s mobility requirements serve as control signals for efficient charging of the vehicle battery.
Temporal arbitrage
What does temporal arbitrage mean in the context of bidirectional charging? - Temporal arbitrage refers to the deliberate exploitation of temporary price differences in the electricity market.
Transmission system operator (TSO)
What is a TSO? - A transmission system operator (TSO) is a company responsible for the operation, maintenance and expansion of the supraregional electricity grids at the extra-high voltage level. The TSO ensures the safe and stable operation of the grid. In certain cases, the TSO relies on grid-supporting services that can be provided using V2G technology.
Use Case
What are use cases for bidirectional charging? - Use cases for bidirectional charging refer to the potential applications of V2X technologies. Increasing self-consumption of solar power, peakshaving, reactive power and balancing energy, and much more, are just some of the scenarios that utilise bidirectional charging under varying conditions and with different levels of efficiency. For many motorists, multiple use cases simultaneously offer the opportunity to save costs or turn their electric vehicle into a source of income whilst it is charging. Users can offer flexibility from their vehicle battery without restricting their mobility habits - driving forward the energy transition at the same time.
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Vehicle-to-Building (V2B)
What does V2B mean? - In Vehicle-to-Building, a number of electric vehicles supply a building, e.g. a company building. V2B use cases include peak shaving, efficient load and fleet management, and – for buildings with solar power generation – increasing self-consumption and tariff-optimised charging and discharging.
Vehicle-to-Grid (V2G)
What does V2G mean? - In Vehicle-to-Grid, electricity is fed from the car into the public grid, or the vehicle battery offers spare capacity to draw surplus electricity from the grid. V2G use cases include, amongst others, time arbitrage by exploiting time-varying price differences in electricity trading, redispatch to stabilise the electricity grid in the event of congestion or surplus, as well as the provision of reactive power and positive and negative primary balancing power.
Vehicle-to-Home (V2H)
What does V2H mean? - In Vehicle-to-Home, energy is fed directly from the car into the home electricity network when electricity demand is high or electricity prices are high. V2H use cases include increasing self-consumption of self-generated solar power, as well as tariff-optimised charging and discharging.
Vehicle-to-Load (V2L)
What does V2L mean? - Thanks to bidirectional charging, the electric vehicle becomes a mobile electricity storage unit whilst on the move. Vehicle-to-Load supplies a wide variety of consumers and leads to greater convenience, for example whilst on holiday or when camping.
Vehicle-to-Vehicle (V2V)
What does V2V mean? - Vehicle-to-Vehicle refers to charging another electric vehicle from one’s own vehicle battery, e.g. at the side of the road.
Vehicle-to-X (V2X)
What does V2X mean? - Vehicle-to-X is the umbrella term for all technologies in which a bidirectionally chargeable car with bidirectional charging technology intelligently feeds electricity into and draws it from the grid.