The Ideal Urban Bus
Recent breakthroughs in battery and drive technology allow electricity to be the perfect power source for urban transit. The electric bus can work the way buses have always worked, only better.
At the heart of Proterra LLC’s EcoRide™ electric bus, showcased earlier this year at Applied Materials, is a bank of non-toxic lithium titanate cells, mounted under the floor. These batteries may last the 500,000 mile lifetime of the vehicle, and can be charged in an amazing 6 to 10 minutes. The fast charging also enables 90% efficient regenerative braking, approximately 10 times better than current hybrid cars, which are forced to dump most of the vehicle’s kinetic energy when slowing down.
All this adds up to a zero-emission vehicle that delivers the equivalent of 15-30 miles per gallon (mpg), an enormous improvement over diesel buses that struggle to reach 4 mpg.
The 30 mile (50km) range of the battery pack may seem short, but perfectly fits the way urban buses are used: They run the same route repeatedly and the short recharging cycle is easily accomplished during the driver’s rest breaks. Placing the charging stations at electric rail stations, which already have the necessary high-power grid connections, minimizes the need for any incremental infrastructure. The batteries can also be charged overnight at the bus depot using conventional 220V sources, or even on the move through existing overhead wires that are found in San Francisco and many cities around the world.
Of course, an electric vehicle isn’t inherently greener than a fossil fuel vehicle because it just shifts emissions from the bus to the electricity generator, although using 80 percent less energy in the first place helps! However, if the electricity to recharge the bus comes from clean, renewable sources such as solar power, a virtually carbon-neutral system is possible.