Store surplus energy from your PV system in your car and use it again in the evening? Charge your electric car at work and use the energy at home? Or buy cheap electricity with a dynamic electricity tariff and later feed it back into the grid at a higher price?
Sounds like a dream? In this article, we reveal what it's all about!
What is bidirectional charging?
With bidirectional charging, electricity doesn’t just flow in one direction; it can also flow in the opposite direction. The battery of your electric vehicle (EV) not only stores electricity but can also release it when needed. This means you use your car’s battery not just for driving but also as storage for surplus electricity, especially on very sunny days or when you don't have enough use for it in your home.
There are different approaches to bidirectional charging, all of which fall under the term Vehicle-to-X (V2X), and they are divided as follows:
Vehicle-to-Load (V2L): The electricity is directly supplied to external devices with a voltage of 230V. For example, you can use it to operate a hairdryer or make fresh coffee.
Vehicle-to-Vehicle (V2V): Electricity flows from one vehicle to another to resolve range issues when no charging station is nearby.
Vehicle-to-Home (V2H): The electricity flows from the vehicle to your home network, making you more independent and lowering your electricity costs. On average, you use about 7 kWh between 6 PM and 6 AM, which is sufficient for most car batteries.
Vehicle-to-Grid (V2G): Here, surplus electricity is fed back into the public grid. This helps improve grid stability and promotes the integration of renewable energy.
However, the last two types only work if both your vehicle and the charging infrastructure (i.e., the EV charger) support bidirectional charging.
Since April 2022, the ISO standard 15118-20 regulates the communication standards for all the aforementioned technologies. It aims to ensure compatibility between bidirectional EV chargers, electric cars, and energy management systems for bidirectional charging.
How does bidirectional charging work?
For bidirectional charging to occur, several prerequisites must be met. But first, here are some basic concepts to help you understand better:
Direct Current (DC) and Alternating Current (AC):Our public electricity grid works with alternating current (AC), while electric cars use direct current (DC) in their batteries. For the car to be charged, the AC from the grid must first be converted into DC for the car’s battery. When electricity is fed back into the grid, it must be converted again.
Electricity Conversion in the Vehicle:During AC charging, the conversion of the grid’s electricity happens through the onboard charger in your vehicle. The electricity is charged into the car through a Type 2 plug, typically at a rate of up to 11 or 22 kWh per hour. Depending on the vehicle, it may take 6-8 hours to fully charge the car. This is ideal for longer stops, such as during the workday or overnight at home.
Electricity Conversion Outside the Vehicle:When the electricity isn't converted in the car, it happens in the bidirectional EV charger. Here, a rectifier is installed that converts AC from the grid into DC for the car’s battery. With CCS charging, the charging speed is less limited, and fast charging (up to 280 kW) is possible. Some vehicles can be charged from 20% to 80% in less than 20 minutes. This is ideal for longer trips where a quick charge is needed.
Can I now use my EV as a battery storage?
Local battery storage solutions are very expensive, especially if your PV system generates a lot of electricity and the storage capacity needs to be large. So, it seems like a good idea to use your car’s battery as additional storage. Not only does it provide larger storage capacity, but it’s also mobile.
With PV surplus charging, it’s already possible with DaheimLader chargers to store surplus PV power directly into your electric car. You can transport and use large amounts of electricity flexibly, for example, for lighting or sound systems at a campsite.
The question now is whether the electricity from your car’s battery can also be used to power your house. You could store surplus electricity in your car during the day and later use it to power your home, or feed it back into the grid (Vehicle-to-Grid). Alternatively, you could charge at work and supply your home with electricity at night (Vehicle-to-Home).
However, Vehicle-to-Home or Vehicle-to-Grid is much more complex than it first appears and, at the moment, is not yet feasible in most cases. This is because an entire ecosystem must be created that is 100% compatible.
Preparing for bidirectional charging: Current status
More and more manufacturers of electric cars and charging infrastructure are advertising bidirectional charging. However, the actual implementation is still not possible in most cases. This is not due to technical feasibility but rather due to the lack of legal frameworks, communication standards, and incomplete specifications from grid operators. Additionally, the VDE standard still does not regulate the connection of bidirectional charging systems. For bidirectional charging to work at home in the form of Vehicle-to-Home, car manufacturers, EV charger manufacturers, charging station operators, grid operators, and energy providers need to collaborate to ensure full compatibility of all involved systems.
Which bidirectional EV charger can I use (in the future)?
If you want to power your house with electricity from your car, the question arises as to which charger can make this possible. The choice of EV charger for bidirectional charging depends on several factors.
First, you need to check if your car can convert the DC electricity stored in its battery back into AC electricity for your home. If it cannot, you’ll need a DC EV charger to convert it into AC. If your vehicle can perform bidirectional charging via AC, you should check if it includes Vehicle-to-Load, Vehicle-to-Home, or Vehicle-to-Grid.
Currently, there’s no clear tendency as to whether bidirectional charging will be implemented in the future with AC or DC chargers. Many German car manufacturers have decided to initially offer bidirectional charging only with DC chargers. In this case, the electricity would be converted to and from DC within the charger, saving additional costs for the EV. However, DC chargers are significantly more expensive than AC chargers. Whether bidirectional charging will be more cost-effective with AC or DC chargers remains uncertain.
Additionally, your home will need the appropriate equipment, such as operating and metering systems, and an energy management system to transmit current consumption data and potentially the amount of electricity generated by your PV system. The EV charger must be controllable and integrated into the energy management system. Your electric car must also transmit its current battery status and indicate how much electricity can be drawn from the battery or how much needs to be charged to ensure enough battery power for the next trip.
Which EVs can currently perform bidirectional charging?
Currently, only a few electric vehicles can perform bidirectional charging. The available models are:
Nissan Leaf
Nissan e-NV200
Mitsubishi i-MiEV
Mitsubishi Outlander
Hyundai Kona, Ioniq 5, Ioniq 6 (restricted to V2L)
Kia EV6 (restricted to V2L)
Volkswagen offers bidirectional charging (V2H) for ID models with a 77 kWh battery, but only in combination with a special DC system.
Other manufacturers have announced that they will enable bidirectional charging soon:
BMW iX3 Neue Klasse (from 2025)
BYD Dolphin (from 2024)
CUPRA Born 77kWh (from 2024)
Skoda Enyaq 77kWh (from 2024)
Polestar 3
Volvo EX90 (from 2024)
Legal Framework for Bidirectional Charging
In Germany, several laws need to be amended or expanded:
The Charging Station Ordinance needs to define the technical requirements for bidirectional charging.
The Electromobility Act needs to define various backfeeding possibilities.
The Renewable Energy Act (EEG) must account for electric vehicles as mobile storage.
The Energy Industry Act (EnWG) and the EEG need to harmonize their definitions of the end user.
Furthermore, connection standards must be defined:
TABs of grid operators
VDE standard
Other open questions include:
Warranty Conditions: If you use your car as additional storage, the battery will be charged and discharged more often. To avoid violating the car manufacturers' warranty conditions for batteries, restrictions on bidirectional operation may be imposed.
Tax Issues: The tax treatment of bidirectional charging needs to be clarified, similar to PV systems. If you use electricity from your employer to power your home, the tax handling must also be addressed.
Political Guidelines: The Federal Government’s Master Plan for Charging Infrastructure does not yet include specific guidelines for bidirectional charging.
Future Outlook and Conclusion
Bidirectional charging with a bidirectional EV charger holds immense potential for the future of energy supply and e-mobility. It enables more efficient use of renewable energy, contributes to grid stability, and can reduce costs.
Although the technology is still in its early stages, the announcements from various car manufacturers suggest that bidirectional charging could soon become the standard. With the development of the technology and the adaptation of legal frameworks, bidirectional charging is expected to play an increasingly important role in our energy system. For owners of electric vehicles and PV systems, it’s worth keeping an eye on developments in this field.
In our assessment, a market-ready solution for bidirectional charging (V2H & V2G) is not yet available. Furthermore, it is likely that an investment in a DC charger will be necessary. Due to the high investment costs of DC chargers, which can exceed €5,000, the concept of bidirectional charging is currently not economically feasible for preparation or implementation.
We are therefore working hard on a "cost-effective" DC charger that enables economically viable bidirectional charging.
In addition to the development of new chargers and the associated technical certifications (e.g., CE testing), the concept of bidirectional charging still requires defining connection regulations in the VDE standard, as well as technical connection requirements for electricians in the domestic environment (TABs) across over 500 grid operators.
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