A key consideration in Electrical Vehicle (EV) charging—whether you are an EV owner or a business professional tasked with installing charging stations for customers or employees—is the power supply you will need to feed the charging station or Electric Vehicle Service Equipment (EVSE). Implementing an EV charging system can change your power supply needs significantly. To put this into perspective, Christoper Michelbacker, EV Charging & Infrastructure Manager for Audi, describes it in terms of an average house. “An average home has a household electrical load of about 5kW, so adding a 9.6kW charger effectively doubles the load of that house.” So how do you anticipate your power supply needs for residential and commercial EV charging installations?
To understand whether your house or building can support this additional load, the first thing you need to do is have an electrician perform a load evaluation to determine if your current service is sufficient. Key factors include:
In the case of a residential installation, most charging stations deployed today fall within the Level 2 category, which require 240VAC power. A typical Level 2 charging station that delivers 7.2kW will draw 30A service. The electrical code specifies a circuit capacity that is 20 percent over the expected load, therefore this setup would require a dedicated 240V, 40A service. A 9.6kW Level 2 charger would draw 40A and require a 50A service. The maximum power output of Level 2 charging is 19.2kW, which would draw 80A and require a 100A service. If an additional service is needed to support the EVSE, that might include an additional meter and panel. Other considerations for residential installation include deciding:
Businesses installing a more robust charging solution also need to perform a building load assessment to determine what their current electrical service can support, but there are additional considerations. For example, if the charging solution involves multiple Level 2 charging stations, the calculation is similar to the one for a home installation, multiplied by the number of charging stations and their output capacity (amps and kilowatt). This installation might require multiple dedicated 240V services, and the total load can add significantly to the base load of the building. Installations with the DC fast-charging capability require 480V—and depending on the power output, can draw a lot of current. Most commercial buildings have 480VAC service that branches out to 240V sub-panels. A DC fast-charging station requires a dedicated 480V circuit.
For commercial buildings, there is another critical consideration. You need to make sure you are accurately calculating your base building load for purposes of negotiating commercial electric rates, which are based on demand. Michelbacher explains the challenge. “Typically, a commercial electric rate is negotiated based on power demand, which is the peak load that you expect from your operation. You are billed at that rate for your actual consumption, which is kilowatt hours. If you exceed the demand threshold, a new, much higher demand rate kicks in. Now let’s say the base load of your building is 40kW. Ideally you want to negotiate a rate as close to your actual consumption as possible. You wouldn't want to negotiate a 100kW power demand threshold when your normal usage is 20kW, because you would be paying for the availability of all that unused power. Now let’s say you’ve got your negotiated rate based on the 40kW building load, and you install a 50kW fast charger. Your building is humming along at 40kW, and all of a sudden someone plugs in a car, and now your energy consumption is 90kW for that small period of time. As soon as you cross that 40kW threshold, you start incurring a demand charge. Though demand charges vary by region and the utility company, they can have a high dollars-per-kilowatt-hour fee, which is added to your negotiated commercial rate. Once the demand rate kicks in, it can be in place for the rest of the billing cycle, even when you are operating below the demand threshold. So, it’s very important when installing EVSE in a commercial building to have that discussion with your power utility.
Another consideration for commercial buildings includes the cost of running power to the charging locations. If you are running a high capacity 480VAC service any distance, this becomes very expensive. Depending on the level of service you require, you might need the power company to install an additional high-voltage transformer.
Implementing a new EV charging system can significantly alter the power supply needs of both residences and businesses. Consequently, the power supply required for the charging station or EVSE is a crucial consideration.
David Talbott is an IT and Technology Analyst with Mighty Guides who focuses on emerging technologies including deep learning, cloud and edge computing, and ubiquitous connectivity, and how these technologies converge to create powerful self-learning systems.