According to the US Office of Energy Efficiency and Renewable Energy (EERE), more than 80% of EV charging takes place at the driver's residence via basic wall outlets (100V/120V) or dryer outlets (220/240V). This makes sense as residential charging is convenient and inexpensive.
Problems arise when the EV is driven far enough away from the residence to warrant a recharge to get back home or continue the journey. This scenario is why fast-charging stations are growing in demand. Fast charging aims to recharge EV batteries within a short period of time, similar to refueling conventional gasoline vehicles. Today's fast charging typically takes about 20 minutes to charge up to 80% capacity.
The growth of fast-charging stations will help address the common driver concern of the limited range of their EV. The increase of fast-charging stations will mean drivers can easily refuel and significantly extend their vehicles' driving range.
But fast charging comes at a price. Until recently, many EV battery systems were not compatible with the fastest charging system. Fortunately, the major EV car manufacturers are investing in high-speed chargers with capacities of 150kW or higher and even faster, ultra-fast recharging technology.
Companies are working to address the issues between fast charging systems and battery capacity and safety. For example, Peter Kelly-Detwiler, Principal at NorthBridge Energy Partners, LLC, has been tracking the developments from SK Innovations.
"Why carry a huge canteen (or battery) on your hike if you know you can fill quickly at a stream every two or three hours on your journey," asked Kelly-Detwiler? "Of course, the charging infrastructure will need to be there, with liquid-cooled cables, etc., but I do think a portion of the industry will end up at 350-400 kW capability to support the Hummers or SK Innovations supported EVs."
The need for liquid-cooled energy cables hints at another challenge for fast-charging EV stations, namely, their adverse impact on the electrical power system. Common effects include harmonic contamination in the transmission lines and high current, adding to peak-hour consumption concerns. The high power and current ratings of the recharging facilities require supervised operation at specially designed stations.
Types of Rechargers. There are two types of recharging "fuels," namely, alternating current (AC) and direct current (DC). A standard cord set is provided with each new vehicle that typically enables 3.6kW of charging via a conventional wall socket. Using this approach, the impact on the electricity grid is limited as the charging rate is so low.
There are three major categories of chargers, based on the maximum amount of power the charger provides to the battery from the grid, according to the EERE):
- Level 1: Provides charging through a 120 V AC plug and does not require additional charging equipment. This level can deliver 2 to 5 miles of range per hour of charging. Most often used in homes, but sometimes used at workplaces.
- Level 2: Provides charging through a 240 V DC (for residential) or 208 V (for commercial) plug and requires the installation of additional charging equipment. It can deliver 10 to 20 miles of range per hour of charging. Used in homes, workplaces, and public charging.
- DC Fast Charge: Provides charging through 480 V AC input and requires highly specialized, high-powered equipment and special equipment in the vehicle itself. (Plug-in hybrid electric vehicles typically do not have fast charging capabilities.) It can deliver 60 to 80 miles of range in 20 minutes of charging. This service is used most often in public charging stations, especially along heavy traffic corridors.
Another type of charging, currently being researched by the Department of Energy (DoE) and provided to specific vehicle models Qualcomm and others, is cord-free wireless battery charging. For example, Qualcomm's Halo tech is currently fitted to the Formula E Safety Car and Medical car. The main advantage of wireless charging is convenience and not necessarily a faster charging rate.
A common concern with EV owners is the effect of faster-charging systems on the vehicle's battery life. The issue is that the chemical processes involved in rapidly charging a battery can lead to greater thermal loads that may degrade the battery faster than regular charges. The result could be reduced battery life and a decrease in driving range.
According to Jim Francfort, project manager in INL's Advanced Transportation Group and quoted from an INL article, "The value of building infrastructure is a difficult thing to measure. To put DC fast-charging stations along interstate corridors could encourage people to take longer trips even if they don't stop to charge."
The fact that fast charging is available gives EV drivers the confidence they might otherwise lack. This new breed of drivers will know that fast charging is available, like gas stations for traditional vehicles, if they need it.