Audi and the Hager Group, a supplier of solutions and services for electrical installations in residential, commercial and industrial buildings Increasing network stability, lowering electricity costs, and contributing to climate protection, are researching bi-directional charging to integrate electric vehicles into the domestic power grid to reduce electricity costs and increase grid stability.

In the first half of 2020, the proportion of green electricity as a percentage of the total electricity mix in Germany exceeded 50% for the first time. As this proportion grows, however, the basic dilemma associated with these renewable energy sources remains: first, electricity cannot always be supplied when it is required and second, on sunny days and in high-wind conditions, there is often a lack of capacity for storing the energy generated.

Hager Group and Audi are thus \ bidirectional charging at home, otherwise known as Vehicle to Home (V2H).

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.

Audi and the Hager Group have developed a research and solution approach that creates financial incentives and offers greater security of supply.

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.

—Martin Dehm, technical project manager for bidirectional charging at Audi

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 electricity. When the sun is no longer shining, the vehicle can supply the stored electricity back to the house.

V2H has great potential to reduce the homeowner’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.

An Audi e-tron with near-series charging technology was used in a 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. Due 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.

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.

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. 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.

—Martin Dehm