100 Energy Slaves per American

I was watching this guy, James Howard Kunstler, on TV talk about his book The Long Emergency who believes that we are going to run out of energy soon and it will dramatically change life in America. He said that buildings over 7 stories were going to go away because we wouldn't have the energy to run elevators and we were all going to live in small agricultural communities because the energy to transport things would no longer be available. Overall I thought he was crazy. But one questioner made a statement that I found interesting. He said that each American had 100 "energy slaves" working for us. So I decided to run the numbers and see if it is true.

The average American consumes 2,200 calories a day. The US uses 100 quadrillion BTU of energy a year (as of 2004). Divided by 300 million Americans that works out to 913,000 BTU a day. And Google tells us that converts to 230,226 calories or just over 100 times the 2,200 we eat a day. So it is true that we have 100 energy slaves each.

Our energy slaves allow us to consume much more than we would otherwise. In manufacturing, energy slaves in the form of machines build our cars, sew our clothes, and create our TVs. Our slaves provide so much that the typical American family owns more than most Egyptian pharaohs. At home we use energy slaves to wash our clothes and clean our dishes.

Of course, there are also other forms of energy we use that don't really have a slave equivalent: heating, air conditioning, refrigeration, lighting, transportation, and computing. While the slave analogy might be a little off, it is true that we feed our air conditioners, water heaters, computers, cars, factory machinery and appliances 100 times as much energy as we feed ourselves and our standard of living would be no where near as great without them.

I then became curious, how much land is needed to feed us compared to our machines?

Each year, each average American uses 341 mil BTU or 100,000 kWh. How much land would that require? As solar is the long term solution, let's calculate in terms of solar cells. 11% efficient solar cells in Austin can capture 200 kWh/yr/m^2. The average American therefore needs 500m^2 of solar cells to produce the energy he uses.

To feed humans, lets look at how much land it would require to supply all of our calories with wheat. Many foods such as meat, fruits, vegetables and nuts yield fewer calorie per acre than wheat. Others like sugar (and I believe corn) yield many more calories per acre than wheat. Using wheat might underestimate the amount of land needed, but it gives a feel for what is needed.

The FAO puts the wheat yield in the US at 3 tonnes/ha. There are approximately 1100 calories (or kCal) per pound of bread, which we will assume is the same as wheat. This works out to 2428 kCal per kg. 3 tonnes/ha therefore equals 7,284,000 kCal/ha or 728 kCal/m^2. The average American eats 2,200 kCal a day or 800,000 kCal a year. This requires 1,100 m^2 of land planted in wheat to produce that many calories.

So while our energy slaves use 100 times as much energy, they only require 1/2 as much land in order to produce that energy. This is because solar cells are approximately 200 times more efficient than creating energy through wheat. These numbers are rough, so they could be off by quite a bit, but it is definitely true that our energy slaves are much more efficient in terms of land needed to feed them than humans are.