One cable, two directions: Bidirectional charging of electric vehicles as game changer!

Thanks to the ability to not only charge but also discharge the vehicle battery, bidirectional vehicles can provide enormous decentralized storage potential for the energy system. There are already around one million electric vehicles on German roads today with batteries with a capacity greater than the sum of Germany’s pumped-storage power plants. As often only a small amount of battery capacity is required for the actual mileage, a large proportion can be used for energy use cases and open new revenue opportunities for vehicle owners while the vehicle is stationary. These use cases were developed and driven forward in the projects “Bidirectional charging management – BDL” and “unIT-e² – Living Lab for Integrated E-Mobility”, among others. The following text summarizes the most important findings on bidirectional charging.

Attractive use cases still struggle in part due to regulatory issues

A large number of bidirectional use cases were identified, defined and evaluated as part of the projects. In general, the revenue potential of the applications is highly dependent on vehicle and EVSE parameters, the load of the property, market prices and user behavior. For example, savings of €150 – €690 per vehicle and year are possible by exploiting time arbitrage on the intraday market.  As the costs of bidirectional charging will fall sharply in the future, particularly due to a reduction in the price of for EVSE, we assume that vehicle-to-home (V2H), vehicle-to-building (V2B) and vehicle-to-grid (V2G) will be economical in the future. The economic viability of V2H and thus the optimization of self-consumption with one’s own PV system is the most robust, as it is the least dependent on applicable regulations and price fluctuations on the energy markets and is the easiest to implement. However, V2G in particular is currently in a worse regulatory position than stationary storage systems. To become competitive, the double burden of taxes, levies and surcharges when storing energy in the public grid must be eliminated.

The impact of bidi charging on the integration of renewables and the grid load

Our simulation results show that in the future cost-optimal energy system, around 30% of electric vehicles will be bidirectional. These bidirectional electric vehicles play a decisive role in the integration of renewable energies into the electricity grid. They can serve as daily storage and thus contribute to the improved integration of PV electricity. Despite the additional costs for the hardware, they therefore offer a decisive advantage over vehicles that are controlled but can only charge unidirectionally. This development also has a significant impact on the demand for conventional power plants (-32 GW) and stationary battery storage (-60 GWh), the expansion of which can be reduced in Europe by 2050 as a result. As a result, this will lead to annual savings of around €7 billion per year for the European energy system.

Abbildung 1: Systemic effects of Bidirectional Charging in the European energy system until 2040

The analyses of the repercussions on the distribution grids can be divided into five main findings, which are shown in Figure 2.

  1. The electrification of the transport and heating sector by 2040 leads to a need for expansion in 43 % of the low-voltage grids without the use of flexibility in demand-led operation.
  2. This need for expansion will be significantly increased (to 69% of the grids) by controlled (unidirectional) charging (V1G) with dynamic electricity tariffs, which, assuming that all electric vehicles participate, will result in high simultaneity. Dynamic electricity tariffs must be offered by every electricity supplier from 2025.
  3. Bidirectional Charging (V2G) increases the expansion requirements in this scenario to 71% due to the higher flexibility.
  4. Mixing the V2H and V2G use cases (real; participation rate of 30 % of buildings) leads to lower expansion requirements than demand-led charging.
  5. The need for expansion can be reduced through targeted intervention by the distribution grid operators (Real, §14a; see discussion on EnWG §14a) or dynamic grid tariffs.
grid load, distribution grid, use cases, bidirectional charging
Figure 2: Grid expansion requirements in low voltage by 2040 with optimization of electric vehicles and battery storage (simulation of 1,000 real grids from Bavaria)

Field test in the BDL project and implementation via the smart metering system

In a field test with more than 50 vehicles at private and commercial locations, a number of general and use case-specific findings were gained over the course of a year. Bidirectional use cases are particularly attractive because vehicles are parked for a large amount of the time.  Customers should therefore be encouraged to connect their vehicles during these periods and set a low target SoC to increase the potential for optimization for the use cases. On average, the test subjects were able to save 7.5% of their electricity costs in the PV self-consumption optimization use case, as they had to draw less energy from the grid. Furthermore, the investigations showed that the overall efficiency in the intraday use case was around 80%, which is roughly comparable to a pumped storage power plant.

The technical implementation of the use cases was carried out via the smart metering system. Communication via the smart meter gateway offers the possibility of seamless integration into the EEBUS standard, with verification management already integrated. Tests in the laboratory setup showed a reliability of 98% in the transmission of power specifications.

Outlook for unIT-e² and BDL Next

The BDL project has already demonstrated the technical implementation of some use cases in a protected project environment. The unIT-e² project extends the horizon to include further, unidirectional use cases as well as a holistic view of the energy management system including electrical heat supply. A project structure with four parallel implementation clusters is being used to cover different framework conditions in the field test areas and to demonstrate interoperability between the various chains of action.

The direct successor project BDL Next is intended to precisely close those gaps that remained open in BDL and thus bring bidirectional charging management closer to mass production. These gaps concern both the technology and the regulatory and process-related fundamentals. In addition to linking with existing market processes, this also includes the grid-friendly operation of vehicles in practice, so as not to jeopardize the rapid ramp-up of electromobility due to bottlenecks in the electricity grid. Together with simple system integration, this should make it possible to convince vehicle users of the added value of the technology.

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