Wednesday, November 2nd, 2011
Tom Murphy is an associate professor of physics at the University of California, San Diego. His blog, Do the Math, takes an astrophysicist’s-eye view of societal issues relating to energy production, climate change, and economic growth.
Many Do the Math posts have touched on the inevitable cessation of growth and on the challenge we will face in developing a replacement energy infrastructure once our fossil fuel inheritance is spent. The focus has been on long-term physical constraints, and not on the messy details of our response in the short-term. But our reaction to a diminishing flow of fossil fuel energy in the short-term will determine whetherwe transition to a sustainable but technological existence or allow ourselves to collapse. One stumbling block in particular has me worried. I call it The Energy Trap.
In brief, the idea is that once we enter a decline phase in fossil fuel availability—first in petroleum—our growth-based economic system will struggle to cope with a contraction of its very lifeblood. Fuel prices will skyrocket, some individuals and exporting nations will react by hoarding, and energy scarcity will quickly become the new norm. The invisible hand of the market will slap us silly demanding a new energy infrastructure based on non-fossil solutions. But here’s the rub. The construction of that shiny new infrastructure requires not just money, but…energy. And that’s the very commodity in short supply. Will we really be willing to sacrifice additional energy in the short term—effectively steepening the decline—for a long-term energy plan? It’s a trap!
When I first encountered the concept of peak oil, I was most distressed about the economic implications. In part, this was prompted by David Goodstein’s book Out of Gas, which highlighted the potential for global panic in reaction to peak oil—making the gas lines associated with the temporary oil shocks of 1973 and 1979 look like warm-up acts. Because I knew Professor Goodstein personally, and held him in high regard as a solid physicist, I took his message seriously. Extrapolating his vision of a global reaction to peak oil, I imagined that the prospect of a decades-long decline in available energy—while we strained to institute a replacement infrastructure—would destroy confidence in short-term economic growth, thus destroying investment and crashing markets. The market relies on investor confidence—which, in some sense, makes it a con job, since “con” is short for confidence. If that confidence is shattered on a global scale, what happens next?
I still consider economic panic to be a distinctly possible eventuality, but psychology can be hard to predict. Market optimists would see the tremendous investment potential of a new energy infrastructure as an antidote against such an outbreak. Given this uncertainty, let’s shy away from economic prognostication and look at a purely physical dimension to the problem—namely, the Energy Trap.
Energy Return on Energy Invested
Our goal will be to quantitatively assess the Energy Trap, and see if there is any substance to the idea. We will rely on a concept that has acquired a central role in evaluating our energy future. This is energy return on energy invested, or EROEI.
In order to utilize energy, we must exert some energy to secure the source and prepare it for use. In order to burn wood in our fireplace, we (or someone) must chop down a tree, cut it into logs, and split the large logs. To drive our gasoline-powered car, we must expend energy finding the oil, drilling and possibly pumping the oil, then refining and distributing the gasoline. To collect solar energy, we must invest energy to fabricate the solar panels and associated electronics. The result is expressed as a ratio of energy-out:energy-in. Anything less than the break-even ratio of 1:1 means that the source provides no net energy (a drain, in fact), and is not worth pursuing for energy purposes—unless the form/convenience of that specific energy is otherwise unavailable.
In its early days, oil frequently yielded an EROEI in excess of 100:1, meaning that 1% or less of the energy contained in a barrel of oil had to be expended to deliver that barrel of oil. Not a bad bargain. Oil production today more typically has an EROEI around 20:1, while tar sands and oil shale tend to be about 5:1 and 3:1, respectively. By contrast, it is debatable whether corn ethanol exceeds break-even: it may optimistically be as high as 1.4:1. Switching from conventional oil to corn ethanol would be like switching from a diet of bacon, eggs, and butter to a desperate survival diet of shoe leather and tree bark. Other approaches to biofuels, like sugar cane ethanol, can have EROEI as high as 8:1.
To round out the introduction, coal typically has an EROEI around 50–85:1, and natural gas tends to come in around 20–40:1, though falling below the lower end of this range as the easy fields are depleted. Meanwhile, solar photovoltaics are estimated to require 3–4 years’ worth of energy output to fabricate, including the frames and associated electronics systems. Assuming a 30–40 year lifetime, this translates into an EROEI around 10:1. Wind is estimated to have EROEI around 20:1, and new nuclear installations are expected to come in at approximately 15:1. These are all positive net-energy approaches, which is the good news.
The Inevitable Fossil Fuel Decline
Let’s explore what happens as we try to compensate for an energy decline with an alternative resource having modest EROEI. On the upslope of our fossil fuel bonanza, we saw a characteristic annual growth rate of around 3% per year. The asymmetric Seneca Effect notwithstanding, a logistic evolution of the resource would result in a symmetric rate of contraction on the downslope: 3% per year. I borrow a graphic from the post on the meaning of “sustainable” to illustrate the rationale for expecting an era of decline for a one-time finite resource.
On the long view, the fossil fuel age is a blip, with a down side mirroring the (more fun) up side.
We could use any number for the decline rate in our analysis, but I’ll actually soften the effect to a 2% annual decline to illustrate that we run into problems even at a modest rate of decline. By itself, a 2% decline year after year—while sounding mild—would send our growth-based economy into (more…)