MOBILEcharge: potential cost savings of a charge management system

Ein E-Bus wird mit einem Pantographen geladen.

Many operational processes must be redefined or adapted to deploy battery electric buses in daily service. However, charging vehicles is a completely new operational procedure. It presents public transport companies with new challenges, but also offers opportunities, which can be seized using the intelligent charge management system MOBILEcharge.

In order to meet operational requirements, it is essential to connect the charge management system to the other operational systems – particularly the depot management system. INIT ensures this by integrating MOBILEcharge into its overall solution eMOBILE for the efficient operation of electric buses.

INIT’s charge management system

MOBILEcharge ensures that buses are ready for operation, charged as needed and pre­conditioned – as cost-effectively as possible. In the event of an unplanned interruption of a charging process, the system restarts the process or – if this is not possible – alerts the central management system. At the same time, MOBILEcharge ensures the loading process is as cost-effective as possible – how is shown in this article.

The main objective is to reduce the maximum charging capacity as this is the primary factor when it comes to the price of electricity to be paid. To this end, unnecessary peak loads must be avoided by means of controlled load shifting, or ‘peak shaving’ for short. What does this mean specifically?

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Peak capacity and load shifting

Without external intervention, the charging process starts immediately after connecting a vehicle to a charging station. The charging process will be completed as quickly as possible and therefore it is started at maximum charging capacity. With load shifting, the load is shifted over time and adjusted in capacity. In practice, this means that even though vehicles will be connected to the charging cable when they arrive at the depot, the charge management system may start the charging process later with reduced capacity.

The main factor influencing electricity costs is the peak load. In order to reduce the peak load, MOBILEcharge calculates a charging schedule for all pending charging processes, which uses the effects of load shifting.

Less known in practice, but worth to look into are variable electricity tariffs. Here, variable prices are fixed in advance throughout the day, for example on a 24-hour basis, which results in further saving potential. These calculations also require the support of an intelligent charge management system. The following economic analysis shows the potential savings to be expected.

Fig. 1: Taking into account the fluctuations in the electricity price results in further saving potential.

Fig. 2: Controlled and uncontrolled charging processes. Peaks loads can be avoided by shifting the load.

Optimisation potential through load shifting

The case study presented is based on a fleet of 40 electric buses with a battery size of 300 kWh each, which are only charged at the depot. The depot has 40 charging points with a charging capacity of 70 kW each.

In the case of uncontrolled charging (Fig. 2, shown in blue), all buses start their charging process directly after entering the depot. There is a peak of about 1150 kW during the evening and at night due to overlapping of charging processes that have just started and processes that are not yet completed. A peak can also be observed in the morning as the vehicles are preconditioned before leaving the depot.

Savings of about 15 percent

Active management of the charging processes (Fig. 2, red line) causes a shift of the loads, reducing peak loads to below 800 kW, while still having the preconditioned vehicles ready for leaving the depot on time. A reduction in peak load of more than 30 percent is achieved as a result. This provides savings of about 15 percent in terms of the overall cost.

Costs can be reduced even further if variable electricity tariffs are added to the measures for reducing load peaks. High-cost phases, such as between 6 and 8 p.m. in the evening are avoided and the loads are shifted to later, more cost-effective times. This means further savings of 3–5 percent can be made. All in all, the cost reduction potential through load shifting with the aid of an intelligent charge management and variable electricity prices can be as high as 20 percent. Fortunately, these effects can also be realised with a smaller fleet of 10 vehicles.

MOBILEcharge offers many functions which can make electric bus operations more efficient and more robust. Moreover, energy costs can be lowered considerably by actively controlling loads.


Heiko Bauer