Exploring EVSE Architecture Options and Their Impact on ROI

Rick Sander, CEO, Tuesday July 20, 2021

Our last blog explored measuring TCO and ROI for electric vehicle (EV) support equipment (EVSE), and how choices that look good when only looking at the EVSE piece can increase overall solution costs. A good example of this is the architecture of an EVSE installation, particularly for medium- and heavy-duty (M/HD) EVs. In general, M/HD EVs require dedicated vehicle yards for charging because of vehicle size and the extended time it takes to charge these vehicles (pulling a 40-foot long transit bus into an automobile parking lot for an 8-hour charging session really doesn’t work!). In these dedicated vehicle yards, remote dispensers (with a 1:1 ratio between dispensers and vehicles) are almost always used to maximize the density of vehicles in the parking spaces. There are a number of architectures in use today with remote dispensers, and picking the right one (or the wrong one) can have a huge impact on ROI and TCO. The architectures most common are:

  • A dedicated power control system (PCS) for each dispenser: In this approach, each dispenser is connected to directly to a PCS, and the PCSs are generally all located at the grid power infeed point. While this approach is generally the most expensive option (most PCSs), it also allows the most power “egress capability” for vehicle to grid (V2G) operations (each vehicle can potentially put power back onto the grid for the entire peak load window, only limited by the power capacity of the PCS and the amount of energy remaining in the vehicle.
  • A shared PCS connected in parallel to several dispensers: This approach (and the serial approach below) share one PCS across several dispensers (typically 4 or less). The parallel approach today utilizes a dedicated DC power feed to each dispenser, as well as high-power DC switching equipment located inside or next to each PCS, and the power is switched to each vehicle. The positive of these approaches are that larger PCSs can be utilized, reducing the PCS portion of the total costs, though the switching equipment tends to eat up some of those savings.
  • A shared PCS connected serially to several dispensers: This approach also shares one PCS and a common DC power feed across several dispensers, putting the switching components in each dispenser. While the equipment portion of this approach is likely similar to that of the shared parallel PCS approach, it does significantly reduce installation costs by cutting down the number of dispensers required.

The TCO of each of these approaches is highly dependent on the vehicle use case parameters such as whether V2G used/desired, the battery capacity of the vehicles, and average energy use of each vehicle. For instance, it could be completely appropriate to have some dedicated PCSs for long-haul buses (with large battery capacity), while short-haul buses (with less battery capacity) might utilize a shared architecture. One thing is for certain though – picking the wrong approach can significantly increase TCO and reduce ROI.

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 excels 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.

Find out how we can help you by contacting us at news@rhombusenergy.com, or by reading our Vehicle to Grid Solution Brief.