At the recent Fleet Technology Expo in Long Beach, California, Tesla Motors’ co-founder and founder of Wrightspeed, Ian Wright, delivered a keynote to the gathering of fleet managers, suppliers, and consultants that turned the conventional wisdom of vehicle electrification on its ear. While mandates like the California Zero Emission Vehicle (ZEV) program and various federal and state tax incentives seek to displace millions of fossil fuel-burning vehicles with electric equivalents, Wright says we’re asking entirely the wrong question. Rather than asking how to maximize the efficiency of the mass of vehicles, Wright said we should be asking: “How do we save the most fuel per vehicle per year?”
On the surface, those might seem like the same question. However, when you actually start doing the math, the resulting answer is quite different. Vehicle emissions, including CO2, are directly related to how much fuel is consumed. Unfortunately, most people tend to think of efficiency in miles per gallon (mpg). When we plot fuel consumed versus mpg, the consumption curve asymptotically approaches zero as mileage goes up. In fact, the curve of incremental fuel savings flattens out dramatically at about 35–40 mpg. Beyond that, increasing mileage comes at a very high cost with little to actually show for it in terms of reductions in total energy use and emissions.
The big gains come when you start from very low mpg, where each incremental improvement yields much larger reductions in fuel consumption. That’s where Wright has focused his efforts in recent years. Wright joined Tesla co-founders Martin Eberhard and Marc Tarpenning and financial backer Elon Musk early on in 2003 to help the tech entrepreneurs with the technical aspects of actually building a car. While Wright left Tesla long before the Roadster finally went to customers in 2008, he continued working on electrification.
Different Solutions for Different Applications
Wrightspeed has developed a micro-turbine, range-extended powertrain system for medium and heavy duty trucks, the vehicles with the biggest potential for fuel savings because they use the most fuel. These big trucks typically only achieve 3–4 mpg running on diesel and even less on natural gas. While the Nissan LEAF or Chevrolet Volt can save individual owners hundreds of dollars a year in fuel compared to similar gasoline-fueled models, the actual amount of fuel saved is relatively small.
A refuse truck is an ideal application for hybridization since it operates at relatively low speeds and makes hundreds of stops and starts per day. In order to get the 130–150-mile range needed for its daily rounds, a fully electric version would need to carry so many batteries it would consume more than half its payload; however, a plug-in hybrid with 30 miles of electric range is entirely viable. Wrightspeed developed its geared traction drive, a 250 hp unit that integrates a traction motor, two-speed gearbox, and inverter, to provide propulsion and regenerative braking. In combination with a small 80 kW turbine range extender sized to run at its optimal efficiency, Wright claims the system delivers a 50% reduction in fuel consumption, saving $35,000 in fuel and $20,000 in maintenance per vehicle annually with a 3–4-year payback time.
Navigant Research’s Automotive Fuel Efficiency Technologies report projects that a wide variety of solutions will be required to meet future efficiency and emissions targets. In order to get the maximum overall benefit, we need to ask Wright’s question and pick the best solution for each application—not one solution for every application.
Tags: Advanced Transportation Technologies, Alternative Fuel Vehicles, Conferences & Events, Electric Vehicles, Transportation Efficiencies
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