Remember the Maslow pyramid? It is often used to illustrate human needs, with the largest, most fundamental needs at the bottom, and the self-fulfillment needs at the top. This idea also applies to light-duty EV charging infrastructure.

The EV charging pyramid represents what I expect the market shares of the basic charging use cases to be once the EV charging infrastructure is more widely deployed, in a decade or so. The market share is expressed as the overall percentage of the delivered energy for each case. Obviously, these market shares are only indicative and will vary between regions, depending on various factors such as the rate of home ownership and urbanization. Also, individual EV drivers will have different charging patterns, with some drivers using some use cases much more than others.

These four segments are the fundamental use cases for light-duty EV charging. Each has its own characteristics (see table below). Overall, home charging is the largest segment because it is the most convenient and the least expensive mean to charge an EV. On-the-go fast charging (like going to a gas station) is the least convenient and the most expensive. Charging at various destinations is in between these extremes. 

All EV drivers may use all of these options, and each one is good in its own way. However, some drivers will use some of them more than others. For example, a salesperson often driving to see clients in distant cities may use a lot of on-the-go charging, whereas a retired couple may only use home charging, except for occasional trips to see family in other cities. A city dweller parking on the street may primarily use destination charging at work or while shopping, but use home charging at their cottage. The pyramid only illustrates the overall market share; it does not represent individual patterns.

The key then is to match the speed of charging to the expected duration of stay. For on-the-go charging, a driver is stopping to charge the vehicle. Charging needs to be as fast as possible. For destination and home charging, charging occurs while the EV is parked and the driver doing something, like shopping, visiting or sleeping — it’s charging while parked. Charging time needs to match park duration. Some destinations have longer park duration than others, as one may spend a day at a national park (good for Level 2 charging) but less than an hour at a shopping mall (good for a moderate fast charger). The basic rule is that the charging speed needs to match the expected dwell time at a site. Too fast or too slow charging both result in suboptimal customer experience.

Stopping to Charge vs. Charging While Parked

The other characteristics stem from this observation. 

Convenience. On-the-go charging at a service station is the least convenient: drivers only go there for the chore of charging and, perhaps also for a restroom break and to get coffee. Other cases are more convenient, as charging occurs naturally while the drivers do what they need to do — no time wasted waiting. 

Criticality. On-the-go charging is the most critical situation, since drivers usually stop with a nearly depleted battery. If there is a line-up or if a charger is broken, they are stuck unless there are other fast chargers in the vicinity. In contrast, destination charging does not require waiting for a fully depleted battery. Drivers will instead charge their vehicles whenever they have the opportunity. And there are far more Level 2 chargers than fast chargers — there’s always another one nearby.

Costs. On-the-go charging is also the most expensive to use, as these fast chargers have the most expensive hardware and the highest power costs. Destination chargers are less expensive than on-the-go chargers, cost less in electricity and may be subsidized to attract shoppers. Home charging is the least expensive, sometime as little as a dollar for a full charge, especially when charging at off-peak electricity rates. Level 1 (120 volts) chargers may be used at home, avoiding the purchase of a more expensive Level 2 charger. 

Public site owners and charging operators need to understand the pyramid to optimize customer experience and the economics of charging sites. Too many sites have been built with a poor match between charging speed and stay duration: 

• Moderate (50 kW) fast chargers along highways (too slow) backed up by a Level 2 charger (way too slow).
• Moderate fast chargers at a hotel (too fast, as drivers need to come back to move the vehicle after charging). 
• Very fast chargers at a shopping mall (too fast, as the drivers needs to wait for charging to complete before shopping).
• Level 2 charger at a fast food restaurant (too slow, as a few minutes of charging doesn’t provide a meaningful charge).

Hopefully, as more charging site owners and operators become EV drivers themselves, we will see emerging a public charging infrastructure that is convenient and resilient, supporting the transition away from fossil-fuel vehicle.