1、.Gas versus Electric Cars: Carbon FootprintInstructor NotesThis activity develops some understanding and experience computing fuel economy and carbon emissions of gas versus electric autos, with a short section also included on the carbon emissions associated with riding a bike. Below are examples o

2、f how to make these calculations, and on Page 3 is a sample student activity.1. Gas-powered vehicleIn the U.S. we use miles per gallon as a measure of the fuel economy of a car. From this, we can calculate the associated carbon emissions using the following method.Data: Average fuel economy of Chevy

3、 Cobalt: 26 miles per gallon (mpg)Average number of miles driven per year: 12,000 milesCarbon emissions per gallon of gas used: 19.6 lbs of CO2 Method: Number of gallons of gas per year: 12,000 miles / (26 miles per gallon)=462 gallonsCarbon emissions per year: 462 gallons*19.6 = 9055 lbs of CO2 per

4、 yearDriving a gas-powered car produces 9,055 lbs of CO2 emissions per yearTo make the connection between driving and carbon emissions clearer, we can characterize an auto by the amount of CO2 emissions per mile, where the smaller the number the more efficient and less polluting the car is. So, for

5、the above Chevy Colt, we can divide the 9055 lbs of CO2 by the 12,000 miles driven to get: 0.75 lbs of CO2/mileThe nice part of this way of measure fuel economy is that we can then directly compare gas powered cars with electric autos and even bicycles. 2. Electric Vehicles: To power an electric veh

6、icle one uses their local electricity provider to charge batteries to run the car. The carbon emissions associated with the electricity generation depends on how the electricity was produced. If you generate electricity using a coal-fired power plant, that emits a lot of carbon emissions compared to

7、 electricity generated from other sources such as natural gas, hydroelectric sources wind and solar. Below is a list of the carbon emissions for electricity generation in different states, given in units of CO2 emissions per kWh of electricity (kWh is a unit of energy typically used for home energy

8、use).California0.61 (CO2 lbs per kWh of electricity)Colorado 1.93 (CO2 lbs per kWh of electricity)North Dakota 2.24 (CO2 lbs per kWh of electricity)US Average 1.34 (CO2 lbs per kWh of electricity)So, then to calculate the carbon footprint of driving electric auto, we need to know how much electricit

9、y is used per mile. Based on available electric autos (like the Tesla Roadster), we can assume that an electric car travels about 3 miles on a kWh of electricity. Method: So if we wanted to calculate the carbon footprint of driving an electric car 12,000 miles in California, we would 1) calculate th

10、e amount of electricity needed and 2) the carbon footprint1) 12,000 miles/(3 miles per kWh)= 4,000 kWh of electricity per year2) 4,000 kWh * 0.61 lbs of CO2 per kWh = 2440 lbs of CO2 per year.So in this case,Driving an electric-powered car in California produces 2440 lbs of CO2 emissions per year3.

11、Food-powered bicycle: (This is a bit more complicated, but included here for interest)We can extend this calculation now to riding a bike. In this case, the fuel for a bike rider is not gas, or electricity, but food. To calculate the CO2 emissions of riding a bike 12,000 miles per year, one must kno

12、w the CO2 emissions per calorie of food. However, the carbon emissions of foods vary widely, so lets consider two cases a beef and a veggie burrito. · The carbon emitted to produce an 800 calorie beef burrito is 4.47 lbs of CO2, or (4.47/800) 0.0056 lbs of CO2 per calorie.· The carbon emit

13、ted to produce an 800 calorie veggie burrito is 0.6 lbs of CO2 or (0.6/800) 0.00075 lbs of CO2 per calorie.Also, an average bike rider (150 lbs) who rides at 12 miles per hour can travel about 21 miles on an 800 calorie burrito, or (21 miles/800 calories) 0.0265 miles/calorie. Thus, to ride 12,000 m

14、iles in a year, one would need:12,000 miles/ (0.0265 miles/calorie) = 450,830 calories! So, we can calculate the annual carbon emissions of bike rider fueled by either beef or veggie burritos:Beef powered biker: 450,830 calories * 0.0056 = 2524 lbs of CO2Veggie fueled by biker: 450,830 calories * 0.

15、0056 = 338 lbs of CO2So riding a bike fueled by beef produced 2524 lbs of CO2 per year, while riding a bike fueled by veggies produced 338 lbs of CO2. Student Activity: The carbon footprint of gas versus electric carsThis activity asks you to compare annual CO2 emissions for three gaspowered carswit

16、h an electric car driven in three different states. Note that each state uses adifferent energy mixture (e.g. coal, natural gas, hydroelectric, nuclear, wind andsolar) to generate their electricity, so CO2 emissions per unit of electricity vary stateto state. After making your calculations summarize

17、 yourfindings and answer the following questions. A) How do electric cars compare to conventional vehicles in terms of CO2 emissions. B) China is considering largescale adoption of electric vehicles to reduce urban air pollution. How will this affect global warming (China's electrical fuel mixtu

18、re is about 2.3 lbs CO2/kWh)?Data:Gas powered autos: The average vehicle in the US is driven 12,000 miles per year.Based on the fuel economy for a particular auto, one can calculate the number ofgallons of gas used each year. From that, if we assume that each gallon of gasburned produces 19.6 lbs of CO2 in the atmosphere, we can then calculate the annualCO2 emissions per year. Listed below is the fuel economy for the followi