Typical EV Charging Use Cases for School Bus Charging
Joseph, Gottlieb, CTO, Tuesday October 5, 2021
Somewhere in the mid-space between light-duty (LD) electric vehicles (EVs) and heavy-duty (HD) EVs are electric school buses. While school buses come in a wide variety of sizes (from 14,500 lbs up to 36,200 lbs), the larger “non-cutaway” buses (those not based on truck chassis) tend to weigh in at 33,000 lbs or over, with a battery capacity of around 150 kWh and a range of roughly 120 miles. The typical daily distance driven by these buses is roughly 50 miles in each of two shifts (morning and afternoon), for a total of 100 miles per day. This consumes slightly over 80% of the bus’s battery capacity each day (roughly 125kWh). These buses typically have two charging windows: late morning/early afternoon (5 hours between 9am-2pm), and evening/night (12 hours between 5pm and 5am), for a total of 17 hours, requiring 7.35 kW of power per hour to fully charge.
Now let’s look at the charging options for these vehicles. If a Level 2 AC charger is used (7.2kW of output for a dual-port AC Level 2 charger), it can almost fully charge one of these buses. However, this requires the charger to be running continuously during the charging windows (5 hours in the heat of the afternoon, and 12 hours at night). If you remember the description of the duty cycle of Level 2 AC chargers in our previous blog, this is incompatible with the scenario described above, and could cause excessive charger failures. Worse yet, if the buses get in late to the chargers, they will potentially be sent out with significantly less than a full charge.
A better approach would be to utilize a DC fast charger power control system (PCS) that shares its output across multiple dispensers such as the Rhombus RES-D3-CS20 remote dispenser with Sequential Power Switching (SPS). A 60kW PCS could charge a single bus in a little over 2 hours; given the charging windows described above, it could easily support charging five buses sequentially with time to spare. Since chargers such as the Rhombus DC fast chargers are made to run continuously at full rated power, charger reliability will not be an issue. There is also the added benefit that even if a bus arrives late, it can still easily be fully charged within the charging window.
If you are looking for made in the USA high-power DC fast charging systems for those EVs, look to Rhombus Energy Solutions. Our market-leading bi-directional EV charging systems (which are designed from the start for the needs of fleet operators) are designed and built in the USA. Rhombus also excel in the design of high-power smart inverters for next-generation renewable energy and energy storage deployments. Our expertise in energy management system (EMS) software is also embedded in our VectorStat EMS controller and software which is embedded in our EV charging systems and smart inverters. We have built over a thousand V2G-capable high-power, high-reliability chargers and bi-directional smart inverters for a variety of different sizes and classes of EVs.