Charging on the Go: Japan Explores Wireless EV Technology

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Japan's largest auto show, the Japan Mobility Show, wrapped up on November 9. Reflecting the global slowdown in electric vehicle (EV) sales, this year's event seemed to feature fewer cutting-edge EV exhibits than the 2023 show. Still, one next-generation technology with significant potential for the future of EV adoption stood out: wireless charging while driving.

Wireless power transfer is a technology that transmits electricity through the air using electromagnetic induction or electromagnetic waves, eliminating the need for charging cables. It is already used in devices like smartphones. When applied to EVs, the concept of wireless charging while driving aims to deliver electricity from the road directly to vehicles as they move.

Onboard Receiver Tests

DENSO, a major auto parts manufacturer, has developed an onboard receiver for this technology, which it showcased at the Japan Mobility Show. In September 2024, the company conducted a test run on a low-speed track at its headquarters in Kariya, Aichi Prefecture. Over the course of 50 hours, the test vehicle successfully traveled 500 kilometers without interruption.

According to DENSO, the EV's battery capacity remained virtually unchanged before and after the test. Based on these results, Takuya Osugi, a section manager in the R&D division, expressed optimism: "With wireless charging while driving, a car could theoretically keep running indefinitely."

Road Infrastructure Challenges

For practical implementation, the durability, constructability, and maintainability of road infrastructure are also critical. Construction giant Taisei Corporation is developing roads with power transmitters embedded more than 100 millimeters deep, using components designed to minimize damage and reduce the risk of failure.

Durability tests are currently underway. According to Tetsuo Endo, team leader of Taisei's Advanced Technology Development Division, "Based on the level of deformation and damage observed in the pavement so far, these roads should last around 10 years, even under highway-level traffic with heavy vehicles."

Taisei has already constructed such a road at its R&D facility in Tamura City, Fukushima Prefecture. In a proof-of-concept experiment, the company simulated an EV by towing a cart equipped with a receiver device behind a vehicle. Even at 60 km/h, the system achieved an average power transmission efficiency of 66%.

Driving Range

The increasing number of companies pursuing wireless charging while driving highlights the technology's potential to address current EV limitations.

For EVs, driving range per charge is a key measure of competitiveness. Automakers have extended range by increasing battery capacity. However, batteries depend on rare metals such as lithium and cobalt, and larger capacities add both cost and weight.

If EVs could charge while driving, drivers wouldn't have to worry about running out of power. Batteries could be smaller, vehicles more affordable, and performance more efficient — an all-around win for both consumers and manufacturers.

Optimizing Layout

The main challenge is cost. Installing power transmission systems across all of Japan's roads would be prohibitively expensive.

To tackle this, Associate Professor Yudai Honma of the University of Tokyo used a mathematical optimization technique called operations research to determine the most efficient layout.

In the city of Kawagoe, Saitama Prefecture, where the total road length is about 150 kilometers, Honma's analysis found that installing transmitters on just 1.6% of roads (around 2.4 kilometers) would be sufficient.

He noted that by strategically placing transmitters on roads with heavy congestion or long red lights, "EVs could keep running" without stopping at charging stations.

For highways, the study estimated that on the Tohoku Expressway, which stretches about 680 kilometers, equipping just 50 kilometers (7%) in one direction would allow more than 95% of vehicles to reach their destinations.

Global Competition

Europe is taking the lead in wireless charging while driving, with France conducting trials on highways near Paris. Japan has lagged behind in demonstrations, but new initiatives are emerging. A project by DAIHEN Corporation and Kansai Electric Power tested the technology on EV buses transporting visitors at Expo 2025 Osaka, Kansai.

Yoshinori Tsuruta, general manager of DAIHEN's Charging Technology Development Department, said, "We will monitor the equipment's performance over the six-month demonstration period and explore ways to improve it." The company plans another field test on public roads in Osaka City in 2027 and is also considering highway applications.

In June 2024, the Wireless EV Alliance was established. The alliance includes observers from central ministries and local governments, and its membership has grown to around 120 companies and organizations. Efforts are also underway to standardize specifications through collaboration among industry, academia, and government.

Currently, Chinese companies such as CATL and BYD dominate the global EV battery market, while Japanese firms have only a limited presence. Continued reliance on China for such a critical EV component poses a serious economic security risk — another reason Japan must accelerate the development of wireless charging.

(Read the article in Japanese.)

Author: Shunichi Takahashi, The Sankei Shimbun

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