The electric vehicle (EV) market's demand for ultra-fast charging has never been higher, as automotive batteries aim to replicate the convenience of filling up a tank at a gas station in minutes.
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 that for refueling of conventional gasoline vehicles. Today’s fast charging typically takes about 20 minutes for charging up 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 that drivers can easily refuel and greatly extend the driving range of their vehicles.
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, as well as even faster, ultra-fast recharging tech.
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 impacts include harmonic contamination in the transmission lines and high current adding to peak-hour consumption concerns. Also, the high power and current ratings of the recharging facilities require supervised operation at specially designed stations.
Types of Rechargers
There are basically 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 small.
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 the installation of 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 as well as 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. Used most often in public charging stations, especially along heavy traffic corridors.
Depending upon the type of EV battery, how depleted it is and its capacity, the charging rate amongst these three categories can be anywhere from less than 30 minutes to 20 hours.
Another type of charging, currently being researched by the Department of Energy (DoE) and provided to certain 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.