As a consumer interested in reducing your carbon emissions, (a) which should you

Question

As a consumer interested in reducing your carbon emissions, (a) which should you do: (1) install more efficient lighting for your home, or (2) buy a car that gets more miles per gallon? To answer this, consider that a 100 W light bulb that is run 3 h a day every day will use around 100 kWh a year. A high-efficiency light uses about 25 percent of a conventional light bulb. Replacing it with a 25 W compact fluorescent bulb would save 75 kWh a year. This would equal 150 lb of carbon dioxide or the same amount of carbon dioxide emissions associated with burning 7.5 gallons of gasoline. (b) Given that the average U.S. household uses 10,000 kWh a year of which 8.8 percent is lighting, how many gallons of gas and pounds of CO2 could be saved by switching all of the bulbs in a home? (c) For comparison, if you drove 12,000 miles a year and upgraded from a car that gets the national average of 20 miles per gallon (mpg) to one that got 30 mpg, how much would you reduce your gas consumption and CO2 emissions on an annual basis? (d) What if you upgraded to a car that gets 30–37 mpg? (Combustion of 100 gallons of gasoline releases 2,000 lb of carbon dioxide.)

Explanation / Answer

In order to reduce carbon emissions I'll be buying a car that gets more miles per gallon as even after using a high-efficiency light which uses about 25 percent of a conventional light bulb saves CO2 equivalent of 7.5 gallons of gasoline. But if we talk about the car the worst mileage can be 15-17 miles per gallon and best is 32-35 mile per gallon and if one person is driving 20 miles per day then he or she can save around half gallon of gas per day and around 182 gallons per year.

(b) 8.8% of 10,000 = 880kWh

we can save 75% of this 880 kWh i.e. 660 kWh if we use efficiency lights.

Now 1 kWh = 2 lb of carbon dioxide

therefore, 660 kWh = 1,320 lb of carbon dioxide can be saved by using energy efficient lights

Now 1 kWh = 0.1 gallons of gasoline

therefore, 660 kWh = 66 gallons of gasoline can be saved by using energy efficient lights.

(c) 12,000 miles a year means

12,000/20 gallons by a normal car = 600 gallons of gasoline

12,000/30 gallons by a upgraded car = 400 gallons of gasoline

1 gallons of gasoline = 20 lb of carbon dioxide

200 gallons of gasoline = 20 x 200 lb of carbon dioxide = 4,000 lb of carbon dioxide can be reduced on annual basis.

(d) If we upgrade to 30–37 mpg car and let's keep the average mileage as 35 mpg then we can save:

12,000/35 = 342.85 gallons of gas is needed

Normally we need 600 gallons, so we save 600-342.85 = 257.14 gallons or

257.14 x 20 lb of carbon dioxide = 5142.85 lb of carbon dioxide can be reduced on annual basis.

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