There are two common myths with respect to wireless charging systems for electric vehicles. The first is that wireless EV charging systems are less efficient, and the second is that they are more expensive than wired EV chargers at the same power level. While wired electric vehicle (EV) charging systems have made remarkable strides in promoting green energy and sustainability, particularly with passenger vehicles, it is important to objectively understand the tradeoffs and differences between the two charging methods.

Wireless makes on-route charging possible

On-route wireless EV charging occurs during routine stops that a vehicle makes along its regular route. For example, an electric public transportation bus making its stops on wireless EV charging pads installed at bus stops. Power transfer begins immediately as soon as the vehicle stops over the pad, one of the many benefits of on-route wireless EV charging, a superior choice for keeping vehicles charged throughout the day. Increased efficiency from using wireless EV charging is achieved because of several reasons, described below.

*(Image: On-route wireless EV charging pad for an electric bus installed by InductEV™)*

Energy transmission efficiency is largely the same with wired and wireless EV charging

The process of charging electric vehicles involves three common steps, regardless of whether the charger is a wireless charger or wired AC charger, or wired DC fast charger. Step one is the conversion of 480V AC (alternating current) power from the grid to a form used by the charging system. Step two is the transmission of that power to the vehicle. Step three is the transfer of that energy in the form of DC (direct current) power into the vehicle’s battery.

Regardless of the charging methods, all three steps share two common elements. The first are the components that do the conversion. The efficiency for conversion is largely identical in all three steps mentioned above. The second is an isolation layer between the battery and the grid. In the case of wired AC chargers and wired DC fast chargers, this isolation layer is accomplished by two coils, which produce a magnetic field separated by a gap inside a common component, which is a transformer.

In the case of wireless chargers, the isolation layer is the air gap between the magnetic field in the charger in the ground and the magnetic field in the vehicle unit. Thus, in all three cases, there is one air gap and virtually identical voltage conversion electronics. This is why the end-to-end transmission efficiency from the grid to battery ranges between 88-92% for wireless charging, wired DC fast charging and wired AC charging. There is no material efficiency difference or loss between the three techniques.

Inefficiency caused by the air gap in wireless EV charging is a common myth

Contrary to common assumptions, the air gap in wireless EV charging systems does not cause inefficiency. These systems' resonant inductive coupling technology allows efficient energy transfer across the air gap. This technology uses two coils, one in the charging pad and one in the vehicle's underside, tuned to resonate at the same frequency. This resonance creates an efficient magnetic link between the coils, enabling power to flow through the air gap.

As such, the system can transmit power across an air gap without significant losses, proving that on-route wireless EV charging can have the same average efficiency of 90% common in wired chargers. Companies such as InductEV™ have commissioned independent research to measure and validate these efficiency numbers. In some cases, on-route wireless EV charging equipment is more efficient than wired chargers.

On-route wireless EV charging equipment offered by InductEV uses highly coupled inductors operating in a near-field system that does not radiate into free space. This innovative technology makes InductEV’s chargers as efficient, or more efficient, than any wired EV chargers on the market.

Improved economics from wireless charging, better for EV battery health, life and cost

When a vehicle is charged wirelessly on-route, it's more likely to charge in the 50-70% state of charge (SOC) range that is optimal for the EV's battery. This is accomplished by sophisticated AI-powered software that makes charging decisions in real time based on the route and energy prices. Therefore, this scenario is not only more efficient, but better for the life of the battery. When charging at a depot, it is common that vehicles are charged to 100% overnight after being discharged to nearly 0% during their daily routes. Charging in the 50-70% state of charge range is common during on-route wireless EV charging, for example, when an electric bus stops along its route and charges wirelessly when stopped. The ultimate result is that batteries charged with wired chargers wear out and must be replaced and recycled. This is not the case with batteries charged wirelessly on-route.

Improved economics from wireless EV charging include lower-cost vehicles

Another benefit to on-route wireless charging is that it allows smaller batteries in the vehicle, making the process economically superior to wired charging at a depot and enabling dramatic reduction in vehicle costs due to much lower battery capacity. Lower battery capacity is possible as the on-route charge locations are known, and frequent, so don't require the battery to be sized with sufficient capacity to return to a charging location at night. The lighter battery also adds value by allowing one more ton of freight to be carried.

Improved economics for on-route wireless EV chargers with respect to maintenance

Because on-route wireless EV chargers have no moving parts, compared to their wired (plug-in), robotic, or pantograph charger equivalents, this results in virtually no maintenance after installation. There are no cables to fray, no connectors to break, and no risk of damage to the charger by being struck by a vehicle, as everything is in the ground. Lack of physical connectors in wireless EV charging means less wear and tear, increasing the lifetime of the on-route wireless charging system and reducing costs.

Improved economics for on-route wireless EV chargers from lower electricity costs

Most wired charging systems, either for passenger vehicles or electrified commercial vehicles, use a centralized depot-oriented charging paradigm. Passenger cars generally charge overnight in one location. Commercial and transit vehicles generally charge in a depot overnight as well. Overnight charging presents a challenge to reaching net zero carbon emissions because electricity produced at night comes from fossil fuels, as solar and wind renewable energy is not online at night. Thus, electricity prices are near zero during the daytime and skyrocket in the evening when renewables go offline. As a result, depot-oriented charging using wired chargers consumes electricity at the highest rate. On-route charging enabled by wireless technology shifts consumption of electricity to the daytime when renewables are plentiful and thus less expensive.

John Rizzo, Chief Strategy Officer at InductEV said:
"The world is facing a crisis on two fronts – racing to net zero carbon emissions by electrifying our transportation sector and a complete lack of electricity to charge these vehicles at night because of the traditional depot or at-home charging paradigms being employed. The transformation of vehicle charging to on-route using wireless technology addresses both issues, creating an opportunity for EVs to be charged with cheap, available renewable energy."

*(Image: InductEV's wireless EV charging vehicle assembly units (VA) on the underside of an electric transit bus)*

Wired charging takes more time and, therefore, is less efficient

On-route wireless electric vehicle (EV) charging provides a more efficient alternative to traditional plug-in methods due to its automation and convenience. This technology eliminates the need for drivers to physically plug in their vehicles, thereby reducing user interaction and diminishing the likelihood of mishandling or forgetting to charge. It also saves time when vehicles need to be repositioned to get near cables, which can be challenging when they must navigate tight-turning radii and avoid colliding with the bollard foundations on which wired chargers reside. Bollards and foundations are also required in pantograph and robotic systems.

On-route wireless EV charging, an efficient alternative

For all the reasons stated above, on-route wireless EV charging is a superior choice for charging electric vehicle fleets. On-route wireless charging is better for battery health, saving battery life and replacement costs. Removing the need for drivers to plug in their vehicles to charge makes the charging process more efficient from a labor cost perspective and saves time. Having fewer moving parts than wired EV charging, wireless EV charging offers a more efficient design, which translates to long-term savings. In general, total cost of ownership (TCO) and annual operating expense (OpEx) measurements by companies such as InductEV and its customers demonstrate 30% TCO and 40% OpEx savings over wired chargers when implementing wireless EV charging instead.

Written by Bill Pierce, Publisher EVinfo.net

Debunking Wireless EV Charging Myths: Energy Efficiency and Cost