f97.beERIK SCHMIDT’S WORKSHOP
← All terms

Glossary · Energy industry & energy transition

Bidirectional charging

Bidirectional charging vehicle-to-grid vehicle-to-home vehicle-to-building Electromobility storage charging infrastructure flexibility electricity grid

With bidirectional charging, the battery of an electric vehicle can not only take in electricity but also release it in a targeted way. This requires suitable charging infrastructure. The parked vehicle thus temporarily becomes a controllable electrical storage unit. Technically, it is about the energy flow between battery, charger, building installation and power grid. In practice, it comes down to one question: is the vehicle only charged, or does its battery also serve self-consumption, emergency power, load shifting or grid services?

Two quantities must be distinguished. Energy in kilowatt hours indicates how much electricity is stored in the battery or can be drawn from it. Power in kilowatts indicates how fast charging or discharging takes place. A vehicle with a battery capacity of 60 kilowatt hours sounds like a lot. A household with an annual consumption of about 3,500 kilowatt hours needs, in arithmetic terms, just under 10 kilowatt hours per day. However, as a rule only part of the battery is usable. The vehicle manufacturer limits the permissible state of charge, and users want to keep a minimum range. If, for example, 20 to 30 kilowatt hours are released, that covers one to three days of household consumption. For grid relief, balancing energy or peak shaving, by contrast, what counts is the power that can be called up at the given moment. Bidirectional charging thus combines storage capacity with controllable connection power.

Technical setup: direct current or alternating current

The battery stores direct current, while the home and the grid work with alternating current. An inverter must therefore convert it somewhere in the system. With DC charging, this power electronics sits in the charging station, i.e. in a DC wallbox or charging column. The vehicle supplies direct current, and the station converts it into grid-compatible alternating current. With AC charging, by contrast, the vehicle itself needs a bidirectional on-board charger. The wallbox is then mainly a switching, protection and communication unit. The two variants shift costs and responsibility differently between the vehicle manufacturer and the wallbox manufacturer.

In addition there are communication, protection technology, metering concept and grid connection rules. An important basis is the ISO 15118 series of standards. Only the ISO 15118-20 version expressly provides for bidirectional power exchange between vehicle and charge point. In addition, feeding back has so far also been implemented via other protocols such as CHAdeMO. A vehicle must not simply feed into the home grid or the public grid like a small generator. Voltage, frequency, islanding detection, grid and system protection and metering must suit the application. In Germany, the technical connection rules of the grid operator apply to feeding into the low-voltage grid. As a rule, the installation must be registered.

Vehicle-to-grid, vehicle-to-home, vehicle-to-building and vehicle-to-load

Vehicle-to-grid refers to feeding electricity from the vehicle battery back into the public grid. Individual vehicles are usually pooled for this purpose and controlled by an aggregator. Together, many vehicles deliver a relevant amount of power. They can provide flexibility, support grid operation or trade on electricity markets. For vehicle owners, this only pays off if remuneration, battery use, availability and minimum range are reliably regulated.

Vehicle-to-home means supplying a household from the vehicle battery. Typical applications are higher self-consumption of photovoltaic electricity and charging at low prices in order to use the electricity in the home later. In addition there is a limited backup power supply. What matters is whether the vehicle works in parallel with the grid or whether, in a power outage, it builds up an island grid safely disconnected from the grid. Not every bidirectional wallbox is an emergency power solution. This additionally requires grid disconnection and a suitable changeover device.

Vehicle-to-building transfers the principle to larger buildings, commercial sites and depots. There, several vehicles can avoid power peaks at the grid connection, coordinate charging with on-site photovoltaics or limit grid connection costs. Fleets are particularly suitable because standing times, driving profiles and charge points are more predictable than with private individual vehicles. Company cars, delivery vehicles, municipal vehicles or buses can provide considerable storage capacity as long as their driving tasks do not suffer.

Vehicle-to-load must be distinguished from this. Here the vehicle supplies devices directly via a socket, for example tools, camping equipment or a mobile pump. This is practical, but it is not feeding back into a building installation or the grid. Controlled charging is also something different. In that case only the charging time or charging power is adjusted. With bidirectional charging, stored energy actively flows back.

Why vehicle batteries are interesting for the power system

Cars stand still for most of the day. During this time, their battery is an existing, already paid-for storage unit. This gives rise to the idea of using part of it in a way that serves the system. However, a benefit only arises if several conditions come together. The vehicles must be connected and the control must work reliably. Users must keep their desired range, and market or grid incentives must justify the use.

With more wind and solar power, shifting electricity over time becomes more important. Photovoltaics often delivers a lot of energy at midday, while demand is often high in the evening. Wind power is sometimes plentiful, sometimes scarce. One reference measure for this is the residual load, i.e. the electricity demand that still has to be covered after deducting weather-dependent generation. If vehicles charge at low residual load and discharge at high residual load, the need for other generation falls. This requires price signals, metering and control that reflect scarcity over time. Flat-rate electricity tariffs set hardly any incentives for this.

In the distribution grid, bidirectional charging can reduce local loads. One example is a vehicle that supplies electricity to the home in the evening, or a fleet that cuts peaks at the grid connection point. Uncoordinated feed-back can, however, create new problems. If many vehicles in one street react to the same price signal at the same time, voltages and power flows change significantly. Its value therefore only arises through control that takes location and timing into account.

Legal framework in Germany (as of November 2026)

For a long time, a double burden hampered economic viability. When charging, electricity was burdened with grid charges and levies like normal consumption. If the battery fed it back and later charged again, the charges were incurred a second time. Section 118 (6) EnWG exempts newly built electricity storage facilities that go into operation between 4 August 2011 and August 2029 from grid charges for 20 years for the withdrawal of the electricity to be stored. The prerequisite is that the electricity is drawn from the grid and fed back into the same grid with a time delay.

An EnWG amendment that the Bundestag adopted in November 2025 refers in Section 118 (6) to the Energy Financing Act (Energiefinanzierungsgesetz). As a result, mixed-use storage facilities and charge points used bidirectionally are also included. According to trade reports, the rule has applied since the beginning of 2026. The exemption concerns only grid charges in the narrower sense, not levies or concession fees. According to one analysis, it is open whether capacity charges and basic charges are also waived proportionately. Because of the deadline for commissioning, the rule is also time-limited. A successor rule within the general reorganisation of grid charges is still pending.

Settlement is regulated by the Bundesnetzagentur in its determination on the market integration of storage facilities and charge points (MiSpeL). It was adopted on 1 October 2026. In it, bidirectional charge points are treated, as far as possible, equally to electricity storage facilities. Temporarily stored solar power retains EEG support. Grid electricity that was drawn earlier and is fed back later is netted. As a result, levies and grid charges for grid withdrawal are reduced accordingly. The rules also apply to non-subsidised installations and to sites without their own electricity generation.

MiSpeL provides two routes. The delimitation option is open to everyone and determines the electricity quantities precisely. This usually requires two meters; in special cases one is enough. The flat-rate option is intended for households with a solar installation of up to 30 kilowatt peak and manages with one meter. However, it may only be applied once the European Commission has approved the statutory basis under state aid law. Grid operators and metering point operators have until the end of September 2027 for implementation. Before then, application is only possible with their consent. In autumn 2026, the model is therefore largely clarified legally, but not yet billable in practice everywhere.

Misconceptions and limits

First, electric cars are not a simple replacement for power plants. In arithmetic terms, many vehicle batteries add up to a large amount of energy. However, it is only available if the vehicles are connected, sufficiently charged and technically released, and the users agree. Vehicle batteries are short-term storage. They are not the main solution for multi-day periods of low wind and sunlight (Dunkelflauten) or seasonal shifting. They replace neither grid expansion nor long-term storage nor firm generation capacity.

Second, feeding back costs battery lifetime. Additional energy throughput contributes to cycle ageing. How much depends on cell chemistry, state of charge, temperature and power. Bidirectional charging is therefore not automatically harmful, but it is not free either. In addition there are conversion losses during charging and discharging. Serious business models factor in both. Manufacturer warranties and approved operating modes therefore belong to the economic assessment. Some manufacturers, for example, limit the amount of energy fed back or permit only certain applications.

Third, self-consumption is not the same as system benefit. With vehicle-to-home, a household can reduce grid withdrawal and its electricity bill. This only helps the power system if grid load, generation costs or emissions also fall as a result. If a battery discharges while electricity is plentiful and recharges later in a scarce hour, the problem is merely shifted. An assessment requires timing, location and comparison options.

Fourth, settlement is often underestimated. Electricity that is charged into the vehicle, later supplied to the home or fed back into the grid falls into different legal categories. Grid charges, levies, metering point operation, the supplier relationship and balancing group allocation may be affected. With vehicle-to-grid, it must be clear who supplies and markets the electricity in balancing terms. It must likewise be established which measured values apply and how deviations are treated. Individual tax questions, for example on electricity tax, should be examined case by case.

Responsibilities and economic viability

Bidirectional charging touches many responsibilities. Vehicle manufacturers decide whether the battery and battery management permit feeding back. Wallbox manufacturers supply power electronics, protection functions and communication. Grid operators look after connection rules, voltage quality and operational security. Suppliers, aggregators and direct marketers organise tariffs, forecasts and market access. Often an energy management system in the home controls the processes. Users determine when the vehicle is available and what range must remain. If one link is missing, the whole thing does not work. A bidirectional vehicle without a suitable wallbox cannot feed back. A bidirectional wallbox without a proper metering and protection concept may not be operated arbitrarily.

Private households can save or earn money in several ways: through higher self-consumption of solar power, time-variable electricity prices, lower power peaks or remuneration for market-serving flexibility. Against this stand costs for charging infrastructure, metering, control, conversion losses and battery wear. For fleets, the conditions are often more favourable. The vehicles stand more predictably, the charge points are operated centrally, and load peaks at the site can be expensive.

Bidirectional charging is closely related to the term storage, but differs from a stationary battery storage unit. The vehicle battery serves mobility first. Any use for energy-industry purposes must be subordinate to that. The available capacity therefore fluctuates, depends on the users and is harder to plan than with permanently installed systems. Bidirectional charging is thus not a single technology that would be taken care of by installing a wallbox. It arises from the interplay of battery, power electronics, grid connection, control, market rules and user decision. Whether this becomes a reliable contribution to the power system depends on rules and mode of operation.

Sources

Related glossary entries

Edited by eCMS on 11.11.2026 15:38

© 2026 Erik Schmidt. All rights reserved. Quotations with a link to the source are welcome.