Audi, in partnership with the Hager Group, is researching bidirectional charging technology, which would allow use of EVs as an electricity source.
The idea is pretty well presented in the video above - an electric car is connected to the home installation which includes solar installation (and an optional energy storage) not only to charge, but to charge or discharge depending on the situation.
If there is an excess of solar electricity, the vehicle will recharge. Then, when solar electricity is not available (or only a little bit of it is) and the electricity cost is high, the vehicle acts as a power source - until electricity is available at a lower cost (off-peak night time). In any given moment, the vehicle can power the entire household during a power outage.
"Bidirectional charging focuses mainly on use cases where home owners use their own photovoltaic system to benefit from cost-optimized charging with their domestically generated electricity. The electric car stores the excess electricity from the PV system that is not used by appliances in the house. If the customer has variable rates, the electric car can supply the entire house in phases where electricity prices are high. At night or during non-productive times of the rate, the car then uses inexpensive electricity to charge up to the desired target SOC (state of charge)."
A separate use case is a stand-alone power supply for a home that does not have a grid connection.
Audi's solution utilizes the DC power, through CCS Combo connector. In the near-series prototype, the vehicle can provide up to 12 kW of power through the DC wallbox (inverter).
Optional home energy storage will be 9 kWh (extendable to higher values), but the system should work only with solar installation and a vehicle too. A positive cost-saving thing is that since the wallbox itself is already a bidirectional charger/inverter, there is no need for a separate PV inverter. Everything (EV, PV, and ESS) is connected to the DC wallbox, which then connects to the home's electric installation.
"What sounds simple in theory requires a high level of technical intelligence and coordinated interaction between different technical components in terms of infrastructure and in the vehicle in practice. An Audi e-tron with near-series charging technology was used in the research project."
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Since the vehicle user can pre-set a target state-of-charge and possibly minimum state-of-charge when discharging to supply power to a home, it should never be stranded. Especially since the 95 kWh e-tron battery is big enough for at least days.
Martin Dehm, technical project manager for bidirectional charging at Audi said:
“Maintaining mobility is at the center of our attention. Customers therefore don’t need to restrict themselves in order to make bidirectional charging suitable for everyday use. The intelligent charging management manages the optimum use of the battery, thereby maximizing the cost-effectiveness of the overall system. The system is very easy for customers to use – all they have to do is plug in the car, and the rest happens automatically.”
Electric cars as part of the energy transition: Audi is researching bidirectional charging technology
- Intelligent use of electric cars offers great potential for the energy transition
- Temporary storage of domestic PV electricity possible thanks to bidirectional charging
- Cost-optimization and domestic electricity supply provide financial incentives
Increasing network stability, lowering electricity costs, and contributing to climate protection – that is the vision that Audi and the Hager Group are pursuing. The incorporation of the electric car into the domestic grid is at the core of an innovative research project on bidirectional charging. This offers major advantages in combination with a photovoltaic system in particular. Excess PV electricity can be stored temporarily and output as needed.
Audi has committed to the objectives of the Paris Climate Agreement and is working on making its vehicle fleet CO2-neutral by 2050. In order to achieve this aim, the brand with the four rings is pursuing a broad electric offensive that involves launching around 20 fully electric models by 2025. And not only that: The electric car is to evolve into part of an increasingly broad mobility offer and become an element of the sustainable energy transition.
In the first half of 2020, renewable energies contributed more than 50 percent to the German electricity mix for the first time. However, the increasing percentage is also accompanied by a basic dilemma of wind and solar power: The generation of electricity is not always constant. On sunny days and phases with strong winds, there is often a lack of capacity to store the generated energy that the grid cannot use.
As the number of registered electric cars increases, the number of mobile energy storage units also rises. This offers great potential, provided that the storage capacity can be used intelligently. This is why Audi and the Hager Group joined hands and developed a research and solution approach that creates financial incentives and offers greater security of supply: bidirectional charging. “Electric mobility is bringing the automotive industry and the energy sector closer together. The battery of an Audi e-tron could supply a single-family home with energy for around one week independently. Looking ahead, we want to make this potential accessible and make the electric car part of the energy transition as an energy storage device on four wheels,” says Martin Dehm, technical project manager for bidirectional charging at Audi.
The electric car as a flexible energy storage unit
The idea is as simple as it is genius: The high-voltage battery of the electric car not only is charged via the wall box at home but can also supply energy back to the house as a decentralized storage medium. If the customer has a photovoltaic system, the electric car serves as a temporary storage medium for the domestically generated eco-electricity. When the sun is no longer shining, the vehicle can supply the stored electricity back to the house. Bidirectional charging at home – also known as Vehicle to Home (V2H) – has great potential to reduce the home owner’s electricity costs and increase network stability. As a further expansion stage in combination with a home storage unit, it is possible to achieve near complete energy independence and increased security of supply in the event of a blackout. “Using the battery of electric vehicles to contribute to climate protection while lowering electricity costs at the same time is a vision that we have found fascinating since the very beginning. And we have found an ideal partner in Audi,” explains Ulrich Reiner, project manager at Hager Group.
Near-series technology in use
What sounds simple in theory requires a high level of technical intelligence and coordinated interaction between different technical components in terms of infrastructure and in the vehicle in practice. An Audi e-tron with near-series charging technology was used in the research project. In the test grid, the fully electric Audi model operated with a DC wall box, which enables a charging capacity of up to 12 kW, and a flexibly extendable home storage unit with a capacity of 9 kWh. While it could provide additional flexibility in possible series production, it is not a necessary requirement for bidirectional charging. Thanks to the DC voltage level in the overall grid, the connection between the PV system and the vehicle does not require an inverter and is thus a particularly efficient solution.
Charging with PV electricity saves money
Bidirectional charging focuses mainly on use cases where home owners use their own photovoltaic system to benefit from cost-optimized charging with their domestically generated electricity. The electric car stores the excess electricity from the PV system that is not used by appliances in the house. If the customer has variable rates, the electric car can supply the entire house in phases where electricity prices are high. At night or during non-productive times of the rate, the car then uses inexpensive electricity to charge up to the desired target SOC (state of charge). Bidirectional charging also provides a security of supply that extends beyond pure cost optimization: In the event of a blackout, the system can supply the house with energy via the high-performance HV battery or it can even operate a building without a grid connection independently in what is known as stand-alone operation.
Everyday usability in the focus of the developers
The developers made everyday usability a top priority. “Maintaining mobility is at the center of our attention. Customers therefore don’t need to restrict themselves in order to make bidirectional charging suitable for everyday use,” Dehm describes the focus of the development. “The intelligent charging management manages the optimum use of the battery, thereby maximizing the cost-effectiveness of the overall system. The system is very easy for customers to use – all they have to do is plug in the car, and the rest happens automatically.”
The joint research project with the Hager Group has proven two essential things: Customers who have their own PV system can design their mobility to be optimized in terms of cost and CO2 consumption while taking some of the burden off the grid at the same time. As a positive side effect, customers who own an electric car from Audi can make an important contribution to the success of the energy transition. The intelligent use of the HV battery in the vehicle also opens up possibilities to use an existing resource that was previously used for mobility purposes alone in a sustainable way.