Jeff Speck, the author of Walkable City: How Downtown Can Save America, One Step at a Time, is one of my heroes. Back in October, his TED Talk entitled Jeff Speck: The walkable city debuted, which is also available on YouTube. At 14:09, he makes the statement that “Changing all your light bulbs to energy savers saves as much energy in one year as moving to a walkable city does in a week.”
While I trust Jeff Speck and his statement makes perfect sense to me, as I have mentioned it to my colleagues and classmates, they’ve basically told me “Show me the numbers!” So, earlier this week, I set out to actually quantify his statement.
The first thing that I had to do was establish a relationship between gasoline and electricity. After some searching on Google, I found a nifty table created by the Alternative Fuels Data Center explaining the relationship among various fuels. Basically, the relationship is established by converting each fuel into British thermal units (BTUs) or, in other words, finding out how much heat each unit of energy produces. Burning one gallon of gasoline produces 116,090 BTUs. Applying one kilowatt-hour of electricity to a heating element produces 3,414 BTUs. This results in one gallon of gasoline equaling 34 kilowatt-hours of electricity.
The next step is to examine household lighting consumption. I found an interesting report from the Office of Energy Efficiency and Renewable Energy that outlines average household lighting consumption. When it comes to incandescent bulbs, the average household bulb is 48 watts. There are an average of 67 bulbs per household. On average each bulb burns for almost 2 hours a day. This totals around 5 kilowatt-hours per day or 1,878 kilowatt-hours per year. Assuming that compact florescent bulbs use 75% less energy than incandescent bulbs, this drops the average household bulb wattage to 12 watts. The average of 67 bulbs per household burning for almost 2 hours a day remains the same. This results in about 1 kilowatt-hour per day or 469 kilowatt-hours per year. Subtracting the two annual consumption amounts results in a savings of 1,408 kilowatt-hours per year.
The final step is to examine household gasoline consumption. I found a useful table from the Energy Information Administration, which states that the average household gasoline consumption is 1,143 gallons per year or roughly 22 gallons per week. This translates into 741 kilowatt-hours per week. Let’s assume that the “walkable city” imagined by Jeff Speck allows its households to significantly reduce the amount of driving necessary by allowing its citizens to complete most of their travel by walking, biking, and riding transit. Let’s say it’s a 95% reduction. The result would be reducing the household gasoline consumption to 57 gallons per year or just over 1 gallon per week. This translates into 37 kilowatt-hours per week. Subtracting the two annual consumption amounts results in a savings of 704 kilowatt-hours per week.
So in conclusion, the 704 kilowatt-hours saved per week by moving to a walkable city is only half the 1,408 kilowatt-hours saved per year by switching to energy-efficient light bulbs. But wait! There’s more! Upon taking a second look at that useful table from the Energy Information Administration, I discovered that the average annual household gasoline consumption is actually per vehicle. A quick search reveals that there are almost two vehicles per household according to this study also by the Office of Energy Efficiency and Renewable Energy. In the end, Jeff Speck’s statement that “Changing all your light bulbs to energy savers saves as much energy in one year as moving to a walkable city does in a week” is accurate!
