Series of articles: The Path to Climate-Neutral Heavy-Duty Transport: Down with the Cost – Bidirectional Charging in a Truck Depot

To achieve Germany’s climate protection goals, emissions from heavy commercial vehicles must be reduced to net zero by 2045. With increasingly powerful batteries, a growing charging infrastructure, and rising economies of scale, the conditions are favorable to initiate the transformation towards climate-neutrality in the heavy commercial vehicle sector. This transformation is no longer a niche topic. The logistics industry is deeply engaged with the transition and is awaiting the entry of climate-neutral vehicles into the mass market.

The transformation faces both technical and infrastructural problems as well as energy and economic challenges. On the technical and infrastructural side, the primary issues are the lack of charging infrastructure and the associated speed of energy infrastructure expansion. Economically, the high initial investments for infrastructure and vehicles are the biggest obstacles. However, there are ways to address these challenges. Optimized, bidirectional charging at depots can help reduce costs. Additionally, the symbiosis of PV systems and public charging during midday presents a promising solution to meet charging needs.

In this five-part series, we will delve into various aspects of the transformation to a climate-neutral commercial vehicle sector, focusing primarily on battery-electric commercial vehicles.

In the previous parts of our series of articles on heavy-duty electrification, we analyzed the symbiosis of public charging and PV systems. In this article, the focus is on “private” charging infrastructure and the possibilities of controlled/bidirectional charging. Controlled and bidirectional charging has recently become an extensively discussed topic. Research projects like BDL predict its high relevance in the near future. The Original Equipment Manufacturers (OEMs) have discovered its importance as well, and the first bidirectional electric vehicles are on the market. Nevertheless, past considerations have mostly revolved around battery-electric vehicle (EV) passenger cars and not focused on battery-electric trucks (BETs). However, taking into account that heavy-duty and bus traffic is responsible for 6% of all European greenhouse gas emissions, a major wave of electrification in this area is necessary [1].

Various challenges impede the market roll-out of BETs. These challenges include the high acquisition costs and the limited availability of grid connection capacity in depots. The use of controlled and bidirectional charging can address these challenges by reducing operating costs and the required grid connection capacity. When evaluating the requirements for controlled and bidirectional charging, BETs can offer several advantages over passenger cars. Due to the higher charging power and the possibility of bundling many vehicles in one depot, a high marketable capacity can quickly be achieved at one location. Bidirectional charging offers the potential to exploit these advantages and support the roll-out of BETs. To evaluate this potential, the FfE investigated possible savings from bidirectional charging of BETs using an example depot. The results were published in the open -access paper „Multi-Use Optimization of a Depot for Battery-Electric Heavy-Duty Truck“ .

Modeling a depot for battery electric trucks

The depot is modelled based on real-life data from of a freight forwarding company in Germany [2] . The company primarily operates in the short-haul segment. The data were provided within the framework of the project NEFTON in which partners from industry and science jointly develop a Megawatt Charging System (MCS) for BETs. Mobility data of the company’s trucks, historical load profiles of its buildings, and information about the PV system are included in the data. The selected depot can serve as a real-life example.

Implementation of a multi-use optimization to combine different use cases

Bidirectional charging strategies are usually formulated as separate use cases. In this study, several use cases are combined in a multi-use optimization. Therefore, the optimization model eFlame was extended. The combination of the use cases arbitrage trading, peak shaving, and self-consumption optimization is implemented. The optimization model primarily manages the charging and discharging power of the vehicles to maximize the revenue. The optimization problem is solved sequentially considering the charging strategies: uncontrolled charging (ref), unidirectional charging (uni), and bidirectional charging (bidi). The results are examined separately for each charging strategy. Figure 2 shows the important time series from the optimization results for one example day. The results for the reference with uncontrolled charging are shown on the left, and those for bidirectional charging are shown on the right. In the upper diagram, the power of the different components is plotted as a stacked area diagram. The resulting power at the grid connection point (GCP) is shown as a black line. The center diagram illustrates for each time step how many vehicles are attendant and how many of them are charging or discharging. The given prizes are shown in the lower diagram. Levies and grid fees are not included in the prices. With uncontrolled reference charging, the vehicles are charged immediately when they arrive at the depot. Even though some vehicles arrive and charge at midday, this leads to charging processes in the evening and at night where the power of the PV system is unavailable. The unused energy from the PV system is fed into the grid at a low feed-in tariff, and more expensive energy is purchased from the grid in the evening hours. The situation is different with the bidirectional charging strategy. To maximize revenue, the optimization shifts the charging processes to times when PV power is available, since this power is not priced in the optimization problem. This shifting is clearly visible in the diagram because the area of the BET charging matches the PV generation. Energy can also be fed into the grid to maximize the revenue. Such a feed-in takes place on the example day from around 6 PM, when many vehicles are available and high energy prices are reached. The annual power peak of the reference of 1.3 MW is lowered in the optimization to 0.4 MW due to peak shaving. The power price only affects the purchased power, which allows the feed-in with a higher power. Figure 2 also clearly shows that outside the times with PV generation, the vehicles supply each other and also the building with energy.

High annual savings can be achieved through optimized, bidirectional charging

Figure 3 shows the annual savings for the optimization with unidirectional (uni) and bidirectional (bidi) BETs for different examined years. The savings are calculated from the difference between the costs in the reference simulation and the respective charging strategy and are normalized per vehicle. Before 2021, the savings are modest at about 2000 EUR/BET even with bidirectional vehicles. As energy prices rise from 2021, savings also increase significantly. Thus, almost 3300 EUR/BET can be achieved in 2021 with the bidirectional and 1500 EUR/BET with the unidirectional charging strategy. In 2022, the savings skyrocket up to more than 10,000 EUR/BET. On the one hand, this can be explained by the fact that the reference costs in 2021 and 2022 rise due to the higher prices. On the other hand, the increasing price spreads and falling levies are responsible for the high savings, as this makes arbitrage trading significantly more attractive. The high revenues in 2022 are achieved through a high amount of energy fed into the grid.

Due to the large PV system and the long duration of attendance of the BETs, the depot under consideration offers advantageous conditions for optimization. Using bidirectional charging, a self-consumption rate of 95% can be achieved and the peak load can be significantly reduced. Arbitrage trading is only worthwhile when price spreads are high  as observed in the years 2021 and 2022. Levies on fed-back energy impede arbitrage trading. According to the results of a conducted sensitivity analysis, the exemption from levies can significantly increase savings. At least a partial exemption from levies would be a precondition for the successful operation of V2G.

The described study was conducted by FfE in the “NEFTON” project funded by the German Federal Ministry for Economic Affairs and Climate Protection (BMWK) and presented at the 36th Electric Vehicle Symposium in Sacramento (EVS36) (funding reference: 01MV21004E).

View full paper

Further Information

• Electrification and Integration of Heavy Commercial Vehicles (NEFTON)
• SPIRIT-E – Shared private charging infrastructure and reservation for bidirectionally integrated truck elektrification
• Bid-E-V – Bidirektionale elektrische Vans

Literature

[1] CO2 Emissions from Heavy-Duty Vehicles Preliminary CO2 Baseline (Q3–Q4 2019) Estimate. 2022. Available online: https://www.acea.auto/files/ACEA_preliminary_CO2_baseline_heavy-duty_vehicles.pdf (accessed on 17 February 2024).

[2] Balke, G.; Adenaw, L. Heavy commercial vehicles’ mobility: Dataset of trucks’ anonymized recorded driving and operation (DT-CARGO). Data in Brief. 2023, 48, 109246. https://doi.org/10.1186/s42162-023-00288-x