Science to Live By: Energy (Part One)


© J. Dirk Nies, Ph.D.

Ordinary and commonplace, mysterious and puzzling, in us and all around us, energy simply is. We desire it and constantly search for it. We complain when we don’t have it and go through tremendous effort to extract and to capture it. And we continually generate more and more of it. But what is energy; why is it so important to our lives and to our economy; and does it have a dark side?

As we embark on our exploration of energy, we will begin with the pragmatic, how energy fuels our economy.  An excellent place to start is the informative overview of energy provided in The U.S. Department of Energy (DOE) Annual Energy Review 2009, released in August 2010.

“Energy is essential to life. Living creatures draw on energy flowing through the environment and convert it to forms they can use. The most fundamental energy flow for living creatures is the energy of sunlight, and the most important conversion is the act of biological primary production, in which plants and sea-dwelling phytoplankton convert sunlight into biomass by photosynthesis. The Earth’s web of life, including human beings, rests on this foundation. Over millennia, humans have found ways to extend and expand their energy harvest, first by harnessing draft animals and later by inventing machines to tap the power of wind and water. Industrialization, the watershed social and economic development of the modern world, was enabled by the widespread and intensive use of fossil fuels. This development freed human society from the limitations of natural energy flows by unlocking the Earth’s vast stores of coal, oil, and natural gas. Tapping these ancient, concentrated deposits of solar energy enormously multiplied the rate at which energy could be poured into the human economy.”  (DOE removed this introduction from later editions of their annual reports.)

To what degree have we “enormously multiplied the rate at which energy could be poured into the human economy?”  Does the “watershed social and economic development of the modern world” multiply the rate by five times, 10 times, 100 times?  Before answering this question, we need a rudimentary knowledge of the relationships among energy, work and power.

In a scientific context, energy and work are both quantities.  Scientists and engineers in the nineteenth century made the profound discovery that they were interchangeable. That is, energy can be transformed into work and work can be transformed into energy.  Depending on the context, terms such as calories, Btu (British Thermal Units), kilowatt-hours, foot-pounds, and joules are used to quantify energy and work.

Unlike work or energy, power is a rate, a measure of how fast energy is generated or work is done.  The relationship between energy and power is analogous to volume and flow (gallons versus gallons per minute).  Terms such as horsepower, joules per second, and kilowatts describe power.

The American economy, when our first Congress convened in 1789, was based upon “natural energy flows.”  Coal supplanted the dominance of fuel wood one hundred years later, and in the 1950s, petroleum and then natural gas emerged as our two largest sources of energy.  By 2010, non-renewable sources supplied a whopping 92 percent.  Specifically, according to DOE, these sources are nuclear electric power (9%), coal (21%), natural gas (25%) and petroleum (37%).  In total, U.S. economic activity consumed 98 quadrillion Btu in 2010, of which 90 quadrillion Btu (98 x 92%) was derived from fossil and nuclear fuels.  Renewable sources contributed 8 quadrillion Btu and they comprise the remaining 8 percent.

The contribution of human physical work to the flow of energy into our economy is not addressed explicitly in the annual DOE energy reports.  Granted, it’s small enough to ignore.  But we can roughly estimate its contribution by comparing our dietary caloric requirements with our economy’s appetite for energy.  Remember that work is “transformed energy” and we can do no more physical work than the amount of food energy we take in.  These estimates will require a few paragraphs of calculations; bear with me, the insights will justify the effort.

On average, the human body needs approximately 2,000 food calories each day (8,000 Btu in commercial energy parlance) to grow, to maintain health, and to do labor and other activities.  Scaling this value up to the country as a whole, Americans eat 0.92 quadrillion Btu in food energy each year (8,000 Btu per day x 365 days per year x 314 million Americans).  For our present purposes, 0.92 quadrillion Btu will be taken as the amount of physical labor Americans contribute to the economy each year.  And by adding this contribution to the renewable sources, we arrive at 8.92 quadrillion Btu, the total natural energy flow into our economy.

Now we are in a position to provide answers to the question posed earlier, to what degree have we enormously multiplied the rate at which energy could be poured into the human economy?

By unlocking the Earth’s vast energy resources, we have multiplied by 107 times the rate at which energy is poured into our economy beyond what we can do unaided by outside sources of energy (98 quadrillion Btu divided by 0.92 quadrillion Btu).  Human physical work now represents less than 1 percent of the energy flowing through our economy (0.92 quadrillion Btu divided by 98 quadrillion Btu x 100).  When we consider the energy contributions made by non-renewable compared with renewable sources, the multiplier is 10 (90 quadrillion Btu divided by 8.92 quadrillion Btu).

This leads me to ask, how much of our national energy budget do we devote to food-related use, our natural source of energy?  The US Department of Agriculture estimated in 2007 that the amount of energy involved in sowing, raising, processing, packaging, distributing, storing and preparing our food constituted 15.7 percent of the national energy budget.  Applying this percentage to 2010 data, we spend about 15.4 quadrillion Btu in food-related energy use (98 quadrillion Btu x 15.7%).  Consequently, we are expending 17 times more energy to put food on the table than we need in food calories each year (15.4 quadrillion Btu divided by 0.92 quadrillion Btu).

These are mind-boggling quantities and challenging relationships to grasp.  Here are five insights to remember.

• Energy’s economic value is realized when we transform it into useful work, labor, and services;

• The amount of energy we are pouring into our economy is equivalent to the working capacity of 33 billion laborers (268 trillion Btu per day divided by 8,000 Btu per worker per day);

• Human energy combined with the contributions made by renewable energy sources deliver less than 10 percent of the energy used to run the US economy;

• The food sector of our economy consumes vastly more energy than we receive back in food calories; and from these observations we can surmise that,

• Powering our economy with biofuels likely will prove very hard to achieve.

The book of Ecclesiastes, noted for its wisdom, declares there is “nothing new under the sun.”  Our highly augmented use of energy to power our food system and our economy at large is an exception.  When viewed from the sweep of human history, both our 100-to-1 leveraging of our human capacity to do work by tapping the earth’s energy resources, and our 10-to-1 reliance on “ancient, concentrated deposits” of non-renewable energy are unprecedented.  This is something new.

In coming months, we will continue our exploration of energy, delve into mysteries, such as the recent scientific hypothesis that “dark energy” permeates the universe, and quantify the wealth we create by transforming energy into work. We will also consider options for powering our economy.