Environmental Science

Question

a) i. The U.S. uses roughly 4.0 million Gigawatt-hours per year in electricity. Currently 50% of our electricity comes from coal. If every 1.0 kilowatt-hour of coal burned releases 2 lbs. of carbon dioxide, how much carbon dioxide is released from burning coal for electricity each year in the US?

ii. What will be the reduction of carbon dioxide entering the atmosphere each year if coal usage could be reduced by 15% by utilizing solar energy?

 iii. List and discuss TWO advantages to using wind energy to generate electricity.

Answer 1

Hey James!

i. How much carbon dioxide is released from burning coal for electricity each year in the US? To answer this, we can use the valules given in the question. We use about 4 million gigawatt-hours of electricity per year, and 50% of it comes from coal, so about 2 million gigawatt-hours of electricity come from coal. Each kilowatt-hour of coal releases 2 pounds of carbon dioxide. Since we are dealing with both gigawatt-hours and kilowatt-hours, we should convert these values so that their units match. To convert gigawatt-hours to kilowatt-hours, we can multiply by 1 million (since 1 gigawatt-hour = 1 million kilowatt-hours). So the amount of electricity coming from coal is 2 million (gigawatt-hours) * 1 million (kilowatt-hours per gigawatt hour) = 2 trillion kilowatt-hours. Each of these kilowatt-hours releases 2 pounds of carbon dioxide, so the total amount of carbon dioxide released is 2 * 2 trillion = 4 trillion pounds.

You can also multiply the values and eliminate all of the units that cancel out:

4 million GWh * 50% * 1 million kWh/GWh * 2 pounds/kWh = 4 trillion pounds

ii. If 15% less coal is used, the amount of carbon dioxide released would also decrease by 15%, since the two are directly proportional (the relationship is always 2 pounds of carbon dioxide released for every 1.0 kilowatt-hour of coal burned). So the amount of carbon dioxide reduction would be 15% of 4 trillion, which is 0.6 trillion pounds (or 600 billion pounds).

iii. Less coal can be used, which would reduce carbon dioxide emission into the atmosphere. Also it's cheap.

~Kaleab