Mobility meets energy: Connecting an electric bus fleet to the power grid

December 06, 2021

Estimated reading time: 3 minutes

Charging is by far one of the most critical components of any electric bus fleet, and making the connection between a fleet’s charging and the local electricity grid is equally as important.

School buses at the charging station

Power connectivity - and how it works

The grid connection is the point where a depot connects to the electricity grid. All electricity for the site’s operation is drawn from the grid power connection – unless part of the electricity is generated on site through renewables like solar.  Since the power grid needs to supply enough energy to charge the high-power demand of the electric bus fleet, the power connection and transformers at that location must be appropriately dimensioned to meet the necessary charging capacity. If the network operator has to upgrade the power connection, they can demand a surcharge. Adding more transformers would be another increased expense.  Without a charging and energy management system, even a mid-sized electric bus fleet can rack up a six-digit price tag for charging infrastructure alone.

Determining charging capacity

For electric buses, a connection with enough capacity is essential to ensuring reliable charging and operations.  The capacity needed at a given depot or charging location will depend mainly on the number of simultaneous charging events (simultaneity factor) and the charging power. Proper charging and energy management can reduce the simultaneity factor and/or the charging power per bus and thereby avoid cost-intensive expansion of the grid connection.

Itemized general electrical costs

Once the charging infrastructure is built, fleet owners and operators still need to take into account standard electricity costs.  Electrical costs for commercial and industrial customers are comprised of three components: Energy charges The energy charge is based on the energy volume (kWh) used over a specified period. The rate per kWh can differ according to the time of day. In such cases, charging electric buses during the periods when energy is cheaper can lead to significant savings. Demand charges Demand charges are fees for using the power grid. The amount of the demand charges is determined by the peak load ($/kW/month), which is normally calculated according to the highest consumption during any given 15-minute interval within a month.  Depending on the service territory and electric rate structure, demand charges can make up the largest component of an electricity bill when EV chargers are involved. Customer charges Customer charges are usually fixed monthly fees that the local utility collects to cover operating costs and infrastructure upgrades.

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Saving infrastructure expenses with proactive charging & energy management

The expansion of the power connection can easily take several years. Instead, fleet owners and operators can leverage a charging and energy management system, like The Mobility House’s ChargePilot®, to reduce the necessary maximum connected load by 30 to 80 percent. This can quickly amount to millions of dollars saved in investment costs.  Beyond reducing infrastructure expenses, ChargePilot® prevents fleets from charging at high-cost times and instead shifts to lower-cost times throughout the day or night.  A U.S.-based transit authority, for example, worked with The Mobility House during its process of electrifying 97 buses in its fleet. Creating a robust charging strategy, The Mobility House’s ChargePilot® system distributed the electric load over time and allowed the buses to charge during off-peak hours in the day as well throughout the night. The maximum electric load at the charging site lowered from 4.7 MW to 1.4 MW daily, enabling the transit to utilize its existing grid connection and avoid lengthy and expensive grid connection updates. In addition, ChargePilot® generates great savings on operational costs: with the lower network load, the electrical costs were reduced by $54,326 per month, equal to savings of $651,912 per year and more than $3.2 million after five years.  To learn how The Mobility House’s smart charging and energy management solution can optimize your electric fleet operations, contact us at [email protected].