As the pace of school bus fleet electrification increases and charging infrastructure continues to pose challenges, many fleets find themselves puzzling over the question: how do I install charging infrastructure faster and more cost-efficiently?

There are many answers to this question, most involving functions of the Charge Management Systems (CMS), but one strategy that is increasingly popular is leveraging a site’s existing electrical infrastructure.

Why Use Existing Infrastructure?

Unlocking capacity on existing electrical infrastructure can be the key to turning an unviable site viable. Some fleets may be under time pressure as they look to rapidly deploy infrastructure to take advantage of a grant with an expiration date, such as the EPA Clean School Bus rebate. Others might simply want to implement an EV pilot at minimal cost to learn about the technology.

For fleets looking to deploy a handful of vehicles, the time and cost of requesting a new service from the utility and constructing that service is likely overwhelming and overkill. For fleets with quick deployment timelines, waiting for a dedicated service for EV charging may be a non-starter.

Many sites have an existing 200–800 amp panel that can be used to support charging infrastructure, with the right load management technology.

How Can I Make the Most of My Existing Panel?

Two features of an advanced CMS enable fleets to maximize the number of chargers that can be installed on an existing panel. The first is Automated Load Management (ALM), which allows the nameplate capacity of chargers to exceed panel capacity. The second is site-integrated load management, whereby the CMS monitors building loads and adjusts charging up and down as the building load changes (e.g., the HVAC turns off), based on real-time available capacity.

If the number of chargers that can be installed is not limited by the nameplate capacity of the panel and uncontrolled loads on site can be monitored, then chargers can be installed and controlled under a required electrical limit, even as building loads change. The result is that chargers can be installed and be code compliant on sites where otherwise no chargers could be added.

An Example

Consider the following scenario:

• A school bus fleet wins a state grant to fund four electric buses.

• The bus barn has an existing 100% rated, 400-amp main panel.

• The electrical load calculations indicate that the panel has no additional capacity.

• However, the actual load overnight is significantly under 400 amps, approximately 100 amps.

• To ensure each bus can make its route, a 19.2 kW 80-amp AC charger is recommended. The fleet requires each bus to have a plug so that staff does not need to rotate buses overnight.

• Modeling shows that, to satisfy charging needs for four bus routes, the total draw will never exceed 250 amps.

At face value, without the combined capabilities of the CMS, the scenario above would require a service upgrade or new service to support any additional charging. However, by leveraging a combination of ALM and site-integrated load management, this fleet can provide a plausible, safe, and effective plan to their utility and local permitting authority to install all four chargers immediately, maintain compliance with the National Electric Code, proceed with the desired pilot, and not have to give any grant money back.

- Sam Hill-Cristol is a manager of strategy and business development at The Mobility House in North America. He oversees the company's school bus segment.