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Most-Efficient Electric Vehicles – Bridgestone World Solar Challenge

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Nuna7, Most-Slippery Electric Vehicle in the World
Nuna7, Most-Slippery Electric Vehicle in the World

This weekend, the world’s most-efficient electric vehicles will compete in a 3,000km race across the Australian Outback in the Bridgestone World Solar Challenge.

It might be easy to say that you can run practically any electric vehicle 3,000km from north to south, between Darwin and Adelaide. After all, even Tesla Motors CEO Elon Musk is planning on taking his family across the United States, approximately 4,500km, powered only by Tesla Superchargers, but could he do it on solar power? True, some of the Superchargers are supposed to be solar powered, but not all of them.

That being said, the rules of the Bridgestone World Solar Challenge are, indeed, challenging. The basic rules are:

  • Maximum 3m2 high-efficiency, >22.5%, gallium-arsenide, or 6m2 of low-efficiency, <22.5%, silicon solar cells.
  • Maximum on-board energy storage of 5kWh
  • Absolutely no other external energy source, other than the sun’s rays which, admittedly, are especially strong in the Outback.
  • One class of this year’s Challenge requires more conventional car features, such as having four wheels and exterior lighting.
  • Finally, first one to make it to Adelaide, wins!

So, how do the teams of these solar-powered electric vehicles make the course? Efficiency is the name of the game. Gather as much solar power as possible, use as little of it as possible, and go as fast as possible within those restrictions. Given that the 2011 winner, the Tokai Challenger, ran the race an average of 91.5kmh, these are tough standards to meet. Clearly, no conventionally-styled electric vehicle could ever make the trip.

Aerodynamics play a huge role in efficiency. The Tesla Model S electric vehicle measures in at a slippery 0.24cd [my old Jeep Wrangler a staggering 0.58cd], while the highest-speed winner of the Challenge, the Nuna 3, measures in at just 0.07cd. Rolling resistance is another major consideration, which challengers address by reducing weight, via lightweight composite materials and eliminating all but the most essential components, as well as ultra-low rolling-resistance tires, with offer about 10% of the rolling resistance of passenger-vehicle low-rolling resistance tires. In a conventional vehicle, rolling resistance is responsible for up to 20% of fuel consumption.

Finally, in electric vehicle energy consumption, special attention is paid to eliminating excess electrical loads so, other than the required communications equipment, minimal lights, and no home theater systems. The drivetrain is also unique, featuring in-wheel direct-drive electric motors that eliminate losses that can occur, up to 20%, in a traditional transmission.

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