More than a century ago, Nikola Tesla studied high-power electromagnetic energy transfer without wires. Which raises the question: Why would Elon Musk, today’s tender of the Tesla flame, be investing more than $100 million ina network of Supercharger stations that still require you to plug in.
The answer is that Nikola’s wireless concept isn’t quite ready for electric-car use. The scientific principle he exploited, inductive coupling, uses the magnetic field surrounding a primary coil to produce an electrical current in an adjoining secondary coil with no physical contact between the two. This works fine in transformers, AC motors, and pads capable of recharging small appliances ranging from toothbrushes to laptops.
Factoring in a second principle, magnetic resonance, allows inductive coupling to be scaled up to higher power levels. The key is configuring the magnetic fields linking the two coils to operate on a common natural frequency. A charging system so arranged has kept 30 electric buses running in Genoa and Turin, Italy, for more than a decade. Coils buried in the road restore 10 to 15 percent of the bus battery’s charge during each stop for passengers. The system’s German manufacturer, Conductix-Wampfler, claims a 95-percent energy-transfer efficiency, no weather-related issues, and longer battery life attributable to the frequent charging cycles. And the bus floors are insulated to keep the magnetic fields from interfering with pacemakers and other electronic devices. Utah State University has a similar system under development with seed funding provided by the Federal Transit Administration.
LIKE SPEED 2, BUT WITH A BUS
If the speed of KAIST’s electric buses drops below 50 mph, they won’t explode, but they don’t need to come to a stop just to top off their charge. Here’s how the institute’s on-the-go bus charging works.
These wireless charging systems mark progress toward the ultimate goal: recharging EVs as they roll down the road. Last August, the Korea Advanced Institute of Science and Technology (KAIST) launched the first true electric highway. Two electric buses operate on a 15-mile public-transit route in Gumi, South Korea, with recharging power supplied by strips buried under 5 to 15 percent of the roadway. Energizing the strips in sync with bus movements minimizes power consumption. KAIST hopes to expand its system to a dozen buses this year.
During our Tesla Model S versus Ford Model T race [February 2014], ancient technology almost won because the 21st-century electric car was parked for nearly 10 hours of battery charging. In our recent test of six electric cars [“Field of Dreams,” March 2014], we spent five hours charging for every hour of driving. This start-stop palsy is why electric cars are slow to catch on—they represent roughly half a percent of all vehicles sold in the U.S. But imagine an electric highway equipped to recharge cars cruising at 70 mph. Smaller, lighter, and cheaper batteries would suffice. Automatic toll billing could cover both the cost of the electricity consumed and the underlying infrastructure.
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