Our choice of car propulsion system is getting more difficult. We want the cheapest, most efficient, cleanest and highest performing car that we can.
But different fuels and motor-technologies make this difficult. How do we make informed choices? How many Watt-hours-per-mile does your electro-car get? Is that better than 35 mpg? What’s it’s km/MJ efficiency?
Cars Are Getting Complicated
Most of us fill our vehicles with gasoline and diesel fuels. Some even get around with compressed natural gas (CNG) in their fleet-vehicle or metro-bus. We compare efficiency in terms of miles-per-gallon or liters-per-100-km. Life is simple.
But it’s the future now. We’re worried about oil and CO2-emissions. We’re talking about hybrid motors, hydrogen fuel-cells and electric-powered (battery) automobiles. Comparisons just got a lot more complicated: How many Watt-hours-per-mile does your electro-car get? And is that better than my Toyota Prius?
What Are We Comparing?
Yes, there are more variables to compare, and more questions to ask. You, like me might wonder about issues like these:
- If I burn coal for electricity, and send the juice down the line to my battery-charger, is that cleaner and more efficient than delivering gasoline to the local station, filling up my car and burning it in my engine?
- If we’ve got a battery-powered car, we’ve got no liquid to measure in liters or gallons. So we can compare cost-per-mile or cost-per-km, but we’re not sure if lower cost means a cleaner world. We don’t foul the air for pedestrians when we drive by them, but the coal-fired electric plant has to burn a bit more to load our batteries. Cleaner air in my town might mean more acid rain for Canada.
- If we’ve got a hybrid car (battery and petrol), we can still talk about our liquid consumption per distance. But does the inclusion of both a battery and a motor in every vehicle add a drain on natural resources?
- With hydrogen fuel cells and CNG, we’ve got to wonder about the costs of safely transporting the fuels, and the energy involved in producing and compressing them. Are they dirtier overall than gas or diesel?
We need apples-to-apples comparisons. Some way to know that this car is cleaner than that one. Or that car A is more efficient than car B.
Well-to-wheel Efficiency to the Rescue?
Luckily smart people (and marketing departments) are working on this problem. They’ve come up with “life cycle assessments” that talk about how efficient a fuel-usage cycle is from extraction to consumption.
If you start Google-ing around, you’ll bump into phrases such as: well-to-station, station-to-wheel, well-to-tank, tank-to-wheel. These are all sub-stages of the entire well-to-wheel efficiency process. The “well” is the proverbial oil-well or fuel source, and the “wheel” is where your car puts it to use.
Recently, I found such information on the Tesla Motors web-site. Tesla markets completely-electric, high-performance autos (which are fast and look cool, by the way!), and have recently captured my attention.
Understanding the need for apples-to-apples comparisons, Tesla have come up with an interesting chart and matrix that compares efficiencies of cars that use different fuels and technologies.
The comparison includes an electric car (from Tesla), a hybrid gas/electric car, along with cars powered by gasoline, diesel, hydrogen fuel-cell, and natural gas.
The chart summarize well-to-station efficiency for various fuel types, compares vehicle efficiency in distance/energy, then the full well-to-wheel efficiency for each auto.
You can take a closer look at the details of Tesla’s Well-to-Wheel chart and matrix by clicking this image.
I’m not going to get into an analysis of this chart. And keep in mind that this is marketing material to some extent. But it is good to know that comparison models are being produced that will help us to make better decisions in the near future!