Vehicle-to-Grid

In an energy supply system with a large, if not dominating, share of renewably generated energy, stabilizing the electrical grid becomes crucial. The challenge is compounded not only by fluctuations in energy consumption but also by variations in energy production caused by intermittent renewable sources. In addition to stationary energy storage solutions and the conversion of surplus energy into chemical energy carriers, such as hydrogen through electrolysis, another promising solution is readily available in many garages – electric vehicles (EVs). Efforts to utilize EVs as batteries on wheels have been ongoing, with research focusing on vehicle-to-grid (V2G) technology and other charging technologies. With V2G-technology, EVs are no longer reduced to uncontrollable consumers but can potentially contribute actively to a more resilient, stable, and dynamic energy ecosystem. An example of such an energy ecosystem is schematically shown in Fig. 1.

In the pursuit of a more sustainable energy future, V2G technology offers a transformative approach with both advantages and challenges. On our campus at Forschungszentrum Jülich GmbH, we are actively engaged in pioneering research and development initiatives focused on advancing V2G technology for a greener tomorrow.

Vehicle-to-Grid
Figure 1: Energy ecosystem with “demonstrators”, such as PV, stationary energy storage, consumers (building) and V2G infrastructure.
Copyright:
— Forschungszentrum Jülich GmbH, Icons created by DinosoftLabs, monkik, and Flat Icons von https://www.flaticon.com/de/ (M) by Luc Raijmakers

Different Charging Modes of Electric Vehicles - Potential and Challenges

EVs can undergo charging through various methods. The simplest approach initiates the charging process of the vehicle's battery immediately when the EV is connected to the charger. Fig. 2a shows this approach in a schematic way. The time of charging and the charging power cannot be controlled, which can make the power grid unstable, as charging simply starts when plugging in the charger.

The so-called V1G technology (smart charging) manages both the timing and the intensity of the charging power supplied from the grid to the EV in a 'smart' way. This scenario is schematically shown in Fig. 2b. In a V1G scenario, EVs are still primarily consumers of electricity from the grid. However, unlike the simple charging process shown in Fig. 1a, V1G can avoid grid destabilization and even actively contribute to grid stabilization. This can be achieved by regulation of the grid frequency and congestion management, where the grid is effectively relieved of excessive burdens during periods of high power demand. In addition, V1G is required for charging integration of EVs with renewable sources like photovoltaics (PV). When renewable energy sources are readily available, EVs can be charged accordingly at the appropriate power levels. Hence, V1G offers a strategic and responsive solution to stabilize power grids.

With V2G technology (bidirectional charging), EVs can also return energy to the grid when needed. Fig. 2c schematically shows this concept. The bidirectional energy flow, which is time- and intensity-controlled, enables EVs to act not just as energy consumers but also as potential contributors to grid stability and flexibility.

EVs can regulate the grid frequency (Fig. 3a) and discharge stored energy back to the grid during peak demand periods (peak shaving Fig. 3b) or when the grid requires additional support, potentially reducing strain on the grid infrastructure and lowering electricity costs. If well-controlled, V2G holds the potential to significantly enhance grid stability and resilience.
The V2G feature effectively turns EVs into mobile energy storage units, such as graphically shown in Fig. 3c. The example in Fig. 3c shows that the EV can be utilized as a decentralized local battery storage system for backup power in a household. It chargers the battery with excess PV energy and discharges when there is energy demand.

V1G and V2G technology is just an example in the broader context of V2X technology (Vehicle-to-Everything). V2X enables communication and interaction between vehicles and other entities in their environment. The 'X' in V2X represents the multitude of entities or systems that vehicles can communicate with, including other vehicles (V2V), infrastructure (V2I), pedestrians (V2P), the cloud (V2C), a building (V2B), a load (V2L) and of course V2G. The implementation of V2X technologies has the potential to improve road safety, reduce traffic congestion, and pave the way for more efficient and intelligent transportation systems. It also plays a crucial role in the development and deployment of autonomous vehicles, as these technologies enable vehicles to communicate with each other and with the infrastructure in real time.

Vehicle-to-Grid
Figure 4: AC charging (normal charging) versus DC charging (fast charging).
Copyright:
— Forschungszentrum Jülich GmbH / L. Raijmakers, S.B.C. Lehmann

Obviously, the different modes of charging also include fast charging, which is designed to significantly reduce the charging time of EVs by delivering a higher charging power compared to standard methods. Fig. 4 shows a comparison between normal alternating current (AC) charging and direct current (DC) fast charging. Fast charging enables EVs to reach an 80% charge in a fraction of the normal charging time, alleviating concerns about range limitations and enhancing the overall convenience for users. Fast-charging standards such as CHAdeMO and CCS dictate the physical connectors and communication protocols, contributing to the development of a robust charging infrastructure and hence playing a pivotal role in the widespread adoption of electric vehicles.

Despite the potential and the numerous advantages of advanced charging technologies, they are also facing various challenges. Besides political and regulatory hurdles as well as practical issues of the seamless integration such as standardized, interoperable communication protocols and hardware interfaces, the battery technology is challenged, too. It is not yet fully understood how the charging of the vehicle's battery with flexible and distinctly fluctuating power intensities over varying periods of time impacts the battery health and its long-term performance. The frequent charging and discharging cycles associated with bidirectional charging raise further questions about the consequences for the battery's longevity. In particular for fast charging, concerns about battery temperature, safety, and aging arise. The battery research group of IET-1 addresses the challenges of battery health by advancing battery technology and developing management systems to minimize long-term degradation.

Current Research

The battery research group at IET-1 is actively involved in the LLEC::VxG-project , which focuses on bidirectional charging technology. The research objectives at IET-1 encompass the investigation of battery aging processes influenced by V2G operations, along with the development of battery aging models. The aim of this research is to investigate if V2G charging processes influence battery aging with respect to normal charging and to propose innovative (fast) charging algorithms. Additionally, the team aims to design and improve electrochemical and thermal battery models at the cell, module, and pack levels. These models are accurately parameterized and validated through a combination of laboratory experiments and test drives involving the EVs mentioned below. The ultimate objective is to leverage these models to optimize battery (dis)charging profiles. Specifically, the team seeks to formulate (dis)charging profiles that have minimal impact on battery aging, are conducive to fast charging, and are well-suited for efficient V2G services.

In the LLEC::VxG-project, we are building upon our experience in battery aging and modelling research gained from previous research in other (EU) projects, such as DEMOBASE, AUTODRIVE, and LImeSI. The insights and expertise acquired from these projects are instrumental in shaping our research approach within the LLEC::VxG project.

In parallel to the LLEC::VxG-project, the i2Batman project is developing an Artificial Intelligence (AI)-supported Battery Management System (BMS) that facilitates the integration of performance and longevity enhancements, prioritizing safety advancements. By accurately predicting performance deterioration or failure for each cell and integrating this insight with real-time operational data, it is aimed to establish an innovative safety checkpoint for the BMS. The enhanced BMS not only ensures safety but also paves the way for additional improvements that would have been deemed too risky to implement otherwise.

Infrastructure at IET-1

At present, two charging stations from the Italian company NEX2, both consisting of a charging post and a power cabinet, are installed: One bidirectional charging station, enabling charging and discharging of EVs with bidirectional charging capabilities. The second, unidirectional charging station is used to study variable loads on a stationary battery storage system, which serves as uninterruptible power supply (UPS) and peak shaving system. Both charging stations have three connectors: CCS2, CHAdeMO, and a Type 2 connector and therefore every EV or plug-in HEV sold in Europe can be charged.

Vehicle-to-Grid
Figure 5: Research EVs in front of a 150 kW unidirectional and 250 kW bidirectional charging station.
Copyright:
— Forschungszentrum Jülich GmbH / L. Raijmakers

An additional, a bidirectional charging station has been procured from the company EVTEC. The EVTEC charging station, designed as a wallbox-type station, boasts a power capacity of 10kW and is mounted on a metal pillar. Similar to the NEX2 charging station, it features both CCS2 and CHAdeMO connectors. Consequently, it can accommodate the direct-current (DC) charging needs of any EV. For bidirectional charging, this station is specifically suitable for Nissan EVs (CHAdeMO connector) and the Honda e (CCS2 connector).

In addition to the previously mentioned charging stations, high-power bidirectional charging stations will be procured and installed soon on our research campus for grid balancing purposes and for research on EV batteries.

Four EVs are currently being used as research vehicles: a Nissan Leaf, a Nissan e-NV200, a Honda e, and a Tesla Model 3. The first three EVs support bidirectional charging and are used for that purpose, whereas the Tesla Model 3 is used as a benchmark for testing fast charging. The EVs are shown in Fig. 5, with the NEX2 charging stations visible in the background. In addition to bidirectional charging and fast charging in combination with the above-described charging stations, all EVs are being monitored during driving. A telematics unit from the company AutoPi  is used for that purpose, which is plugged into the OBD-II connector of each EV. This unit reads various EV states, sending the data directly to the cloud for further analysis.

Further scientific reading material about our work can be found in

Contact

Dr. Luc RaijmakersActing Department HeadBuilding 09.7 / Room 201+49 2461/61-85221

Last Modified: 11.02.2025