Electric Load Profile and Charging Characteristics

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Lets take a look at possible load profiles for 2 different charging usages:  A charging lot at a business, and a EV charging hub off a highway. 

At a business parking lot, drivers are entering the lot and begin charging their vehicles between the hours of 7-10am. It can be expected that most cars are not coming in at a fully depleted battery from a days commute, but most likely coming in half charge. Likely, by 2:00pm most of all the cars are fully charged. The charging characteristic may resemble the load profile below in Figure 1: 

At a charging station hub off a highway, there can be expected another relative constant flow of cars charging at Level 3 chargers. Perhaps on a normal day, only half the chargers are being used. The load profile may resemble the chart below.

 With each application, it can be noted each have different peaks and lows in the load profile. What if these peaks and lows can be averaged in order to limit peak load on a system? This is where load management plays a key role. Often an additional line of service from a charger manufacturer, load management for EV chargers allow peak loads to be diminished and spread out over a period of time. This allows for smaller-rated electrical gear to be used - minimizing cost impact and the electrical loading impact on the grid. The NEC 625.42 actually provides an exception to gear sizing by means of peak load managing controls. Additionally, utility companies may prefer the ability to control large installations in order to regulate the grid better and avoid brown-outs.

Deploying load management on the previous commercial lot scenario, we would be able to see the following adjustments to the load profile:

With this adjustment, the peak charging in the morning can be distributed over the few remaining hours of the work day. 

At a charging station hub, this may be the one case where we do not want to limit peak charging. At these locations where drivers are eager to get back on the road as quick as possible, we want to ensure that all chargers are able to charge at the fastest rate possible during all levels of utilization. Charge management will likely not be utilized so that all chargers can be used at 100%, all the time.