Fleet Electrification Step 9: Coordinate with Local Utility Service

The first step in determining the role of the utility and facility in modifying electric service equipment to handle EVSE impacts is to determine equipment ownership. Figure 1 below outlines a typical electric distribution system, including facility equipment and EVSE. Discussions between the facility infrastructure manager and local utility representative will better inform where the ownership divide exists. However, in almost all circumstances, the facility will own and operate equipment to the right of the meter (see Figure 1). As building loads and overall facility size increases, this line of ownership tends to shift more to the left, leaving the facility responsible for a wider scope of equipment.

The ownership divide line is important because everything the facility owns and maintains must be updated and completely paid for by the facility. These upgrades will most often include increased service drop—the wire between either the feeder conductors or distribution transformers and the meter or load center—or distribution transformer capacity. However, these upgrades should only be necessary if an additional service panel or larger main circuit breaker are installed. For the rest of the situations where upgrades may be required on electric utility owned equipment, the responsibility of installing and paying for these upgrades will be different depending on local utility practices.

Every piece of electrical service equipment (EVSE, service conductors, circuit breakers, service panels, meters, transformers, feeder lines, etc.) is rated for an appropriate power level. If exceeded, that equipment will fail and may become unsafe. Therefore, it is critical to assess each element in the chain, at least up through the service transformer, which is typically protected by a main distribution panel.

The main distribution panel shown in Figure 2 has an open breaker position (red oval) where an appropriately sized circuit breaker could be installed, a 400-A 208-Y enclosure rating, and a three-phase 400-A main breaker, indicating 144 kW of three-phase power capacity. For context, this panel is served by a 150-kVA transformer.

Electrical loads are sometimes measured (such as with a demand meter) and sometimes must be estimated. Energy management information systems often store power load data over time, which is useful when assessing the inconsistent nature of these loads and sizing equipment correctly. Figure 3 shows the maximum monthly peak demand for the main distribution panel (shown in the Power Capacity section above), indicating that no more than 67 kW is ever required at this location. Therefore, 77 kW of capacity is available from the service panel out of the total 144 kW of capacity. Even more capacity may be available if the facility limits ZEV charging when facility demand is low (managed charging) rather than during peak demand.

This information allows an EVSE site assessment team to determine how many EVSE ports at a particular power level could draw power from this panel. In the example shown in the Power Capacity section above, nine Level 2 EVSE at 208 V (6.7 kW each) could be installed (after accounting for NEC requirements to oversize protective equipment for continuous loads). This may be sufficient for a relatively small transportation motor pool, but a managed charging solution or a new main distribution panel and transformer may be necessary for larger numbers of EVSE or higher power equipment.

It is important to also assess the effect of EVSE load on the overall electricity demand and consumption at a federal location or facility. The major issue with adding EVSE load is the impact on peak demand, and the capacity of the current electric service to support that demand.

As an example, a federal facility with an on-peak maximum demand of 54,379 kW decides to install EVSE to support electrification of its fleet. The fleet at the facility locations includes 682 light-duty vehicles and 648 medium- or heavy-duty vehicles. If the fleet transitioned all of those vehicles to electric and, during the existing peak, 50 percent of those vehicles were charging on Level 2 chargers simultaneously, they would increase the maximum power demand by 4,459 kW or 8 percent. This could require new feeder lines and upgrades to substations (managed by either the facility or the utility) as well as result in substantially increased demand charges on the utility bill.

Issues at a facility-level tend to become more significant for larger vehicles and BEVs because they require higher power EVSE. For example, buses sometimes use 65-kW DCFC for depot charging, requiring approximately 10 times more power than Level 2 EVSE. Therefore, controlling bus loads is more significant for demand charges and system upgrades than cars and SUVs on a vehicle-by-vehicle basis. Distributing EVSE across the facility reduces the demand on low voltage transformers.