Picture a train car, filled with anthracite coal. Let’s be picturesque and go back to the 1970s, when smaller and weaker train cars held about 100 tons of coal. Back then, they typically formed trainsets of 100 cars, each holding 100 tons of coal, for 10,000 tons in total. One of the longest trains in history was on the Sishen-Saldanha Railroad in South Africa, operated in August of 1989. It used 7 diesels and 9 50-kV electrics to move 660 cars, a tank car, and a caboose. It traveled 535 miles in 22 hours and 40 minutes. It took a whopping 4.3 miles to stop the train. The train was over 6 miles long.
Now, picture a longer train. Imagine the longest train ever conceived of—one with 378,000 cars loaded with anthracite coal. Although coal cars vary in length, you can often estimate about 100 cars to a mile. So picture a train 3,780 miles long—the distance from Dublin to Kandahar, or from Albuquerque New Mexico to Anchorage Alaska. It is 1,500 miles longer than the tar sands oil pipeline from Alberta to Texas that is being so vigorously disputed as I write this in January of 2012.
If you burn all the coal in that train—each of the 100 tons in each of the 378,000 cars—you will have consumed 1 quadrillion BTUs. And we give the energy liberated from that incredible quantity of coal a cute little name. We call it a ‘quad.’
In 2010, the world consumed energy equivalent to the coal loaded onto 500 of those trains. The world as a whole consumed 500 quads. And despite progress in getting power from nuclear, hydro, wind and solar, in actual fact 143 of those imaginary trains filled with coal were not imaginary—they actually were filled with coal.