A Proterra electric bus has set a new EV record for distance traveled in one day by logging more than 700 miles in a 24 hour period. Its batteries didn’t need to store all the energy, though, as the bus has several charging stations along the route. Strategically placed charging stations allow the bus to grab a few kWh of energy at each passenger stop, and provide near-complete charging at five to ten minute “layover” stops. Periodic charging lowers the battery weight and cost, giving increased range and a shorter payback period.
In addition to going the distance, these buses rack up an impressive 27 MPGe (miles per gallon equivalent), more than five times the fuel economy of comparable sized diesel or compressed natural gas (CNG) buses. How good is that? My four-cylinder, five-passenger SUV gets about 27 MPG on the highway!
Six US cities are currently using Proterra buses, and two more have recently signed contracts to purchase them.
Image credit: Proterra
The Hardware
Sporting a high-efficiency 150 kW (200 hp) electric drive motor, the bus is capable of reaching highway speeds, although for the record-breaking test, it averaged 29 mph. To reduce weight, its body is made of a composite material: balsa wood surrounded by carbon fiber and infused with resin. This gives a one inch structure that has the strength of a 2.5 inch I-beam. High-power wiring allows for a ten-minute fast-charge.
Image credit: Proterra
Charging
As the bus approaches a charging station, wireless controls automatically assure a solid connection to the overhead docking station. The rapid charging system can give the batteries up to 95% charge in less than 6 minutes, with a 92% charging efficiency. These chargers make an electrical connection; they aren’t inductive charging stations like some other electric buses. That makes the docking a little more complex but increases the energy transfer efficiency.
Cost Savings
Using conservative numbers and not assuming an increase in fuel or electricity prices, Proterra estimates that these buses will save over $300,000 in fuel costs over the twelve year expected life of the bus. While electric rates have increased by about 40% over the last decade, diesel prices have increased nearly 400%, so it’s safe to say that Proterra’s estimate is on the low side. Also, the simpler drivetrain requires less maintenance and the regenerative braking system takes care of 90% of the braking. Those factors provide up to $150,000 in savings over the vehicle's life.
Of course there's a trade-off: the Proterra bus costs about $400,000 more than an equivalent diesel powered bus. Municipalities that invest in a fleet of electric buses are doing so for two reasons: first, to improve air quality; second, they're hedging their bets on fuel price increases compared to electric rate increases. As more of these electric buses are built, their prices will decrease, and as fossil fuel costs continue to rise, the EV payback period and return on investment will improve.
Carbon Footprint
One common criticism of EVs is that “the power plant is their tailpipe.” Fair enough, but when you consider that an internal combustion engine (ICE) is about 30% efficient and an electric motor is about 80% efficient, EVs are still cleaner than ICEs. And yes, there are electrical losses in transmission lines, but it also takes fuel to deliver gasoline to a filling station. The tanker is 30% efficient and the grid is 92% efficient - do the math. Given the current breakdown of electricity generation today, the electric bus has a smaller carbon footprint than a comparable diesel or CNG bus.
Today, Fleet Vehicles. Tomorrow …
The only factor that prevents EVs from completely replacing ICEs is the limited range. That’s not a problem for buses since they can stop and recharge as they pick up and drop off passengers. When cars can charge quickly and charging stations are abundant, cars powered by fossil fuels will go the way of dinosaurs.
Quick charging technology is making its way to the electric car market. I predict that in five years we’ll see a significant infrastructure of charging stations along the interstates and the emergence of industry standards for car charging systems. Think that’s too optimistic? Check out Tesla’s plan for quick charging stations in 2015:
Image credit: Tesla Motors
The automobile was once considered a toy, impractical for reliable long-distance travel. Then an infrastructure of filling stations emerged, and the rest is history. It's just a matter of time before that history repeats itself in the EV market.