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Real or Imagined Limits?

To the Editors:

“Revisiting the Limit to Growth after Peak Oil” by Charles A. S. Hall and John W. Day, Jr. (May–June 2009) presented an excellent historical review and insightful analysis on the issues of population and resources. Given the energy challenges that the world is facing, a transformation of our fossil fuel-based economy to a clean and sustainable energy-based economy is crucial. Without this transformation, grave consequences may well result. Nature will establish a new equilibrium within its boundary and capacity, for better or for worse. But future generations will benefit if we act collectively and wisely today to understand and make every effort to solve these problems. In this regard, we need not only more intellectual leaders like these authors but also a well-educated public that understands the urgency of these issues and that is willing to sacrifice short-term interests for the planet’s long-term environmental, ecological and societal health. To produce this on a global scale is a much more challenging task than the actual problems waiting to be solved.

Charles Rong
U.S. Army Research Laboratory
Adelphi, MD

To the Editors:

I agreed with nearly every argument Charles Hall and John Day made in “Revisiting the Limits to Growth After Peak Oil.” Two points, however, deserve more up-to-date treatment. The first involves the energy-return-on-investment (EROI) of photovoltaic (PV) technologies. I have been active in the field of life-cycle assessment of PV for nearly a decade. Since last year I have been a Spanish technical representative for the International Energy Agency’s Photovoltaic Power Systems Programme ( The article states that the “EROI of most ‘green’ energy sources, such as photovoltaics, is presently low.” In Figure 10, an EROI well below 10 can be inferred to be assigned to PV. To the best of my knowledge, this is no longer true. Most recent studies agree that the energy payback time of state-of-the-art PV systems ranges from approximately one to three years. Combined with an industry-standard lifetime of 30 years for the PV systems, the resulting EROIs roughly range between 10 and 30.

Also, the article states, “the annual increase in the use of most fossil fuels is generally much greater than the total production (let alone increase) in electricity from wind turbines and photovoltaics.” While this may have been true of the 1990s, and even early 2000s, the world PV market is changing rapidly thanks to second-generation technologies such as thin films. The latest prospective analyses performed by the IEA and by independent researchers suggest a likely large-scale deployment of PV, far beyond what has been accomplished so far.

Marco Raugei
Pompeu Fabra University
Barcelona, Spain

To the Editors:

In their doomsday analysis of the future of the world as oil supplies dwindle, Hall and Day overlook the key element that has been instrumental in preventing a Malthusian disaster, namely innovation. The world that could not handle a population of hundreds of millions in the 16th century is now home to more than 7 billion people, admittedly with some strains on the ecology of a planet inhabited by haves and have nots.

Too many soothsayers have pronounced the end of the world and have been proved wrong. Science has conquered many problems presented by an ever-increasing population with giant strides in agriculture, appropriate handling of natural resources and new energy supplies. Among all professions, the scientific community should be the most sanguine about the future and its ability to continue to handle the needs of an expanding population.

Nelson Marans
Silver Spring, MD

Dr. Hall responds:

We appreciate Charles Rong’s comments and the many others we have received from scientists and policy experts applauding our article. We hope Marco Raugei is correct. We have not, however, seen any reviewed literature with numbers of the sort he suggests. Our own interaction with engineers installing large-scale photovoltaics in harsh environments and elsewhere suggests that EROI might not be so high when the many hidden energy expenditures are considered. Just a portion include research and development efforts, equipment failures, transporting installation and maintenance workers to remote locations, the construction of long transmission lines and, especially, the construction of backup storage and transmission systems for periods when the sun is not shining or shining strongly. New higher-efficiency systems often use exotic and energy-expensive doping materials. Rare metals are, well, rare. Finding them is energy intensive. We must examine not just the EROI of the devices but of whole systems of supplying reliable energy into the future.

As for Raugei’s second point, the most recent data I have received from my colleague Jean Laherrère show that, until at least 2008, there were far greater absolute annual increases in fossil fuel use internationally than in “new solar.” In the United States, wind and photovoltaics account for far less than one percent of all energy used, although that percentage certainly is increasing.

Nelson Maran’s comments are certainly the most common response one gets from people who reject the limits- to-growth concept. Their skepticism must be taken seriously as there may be something to it. It is true we have avoided “Malthusian disasters” so far (unless you are one of the world’s 2 billion hungry or malnourished). But agriculture is linked closely to increasing fossil-fuel use. The “green revolution” of 30 years ago was in large part based on breeding alterations in key crop plants that allowed higher fertilizer use and, hence, more production. That produced much more demand for inorganic fertilizer, the majority of which, in this country, is nitrogen-based and produced with natural gas, a fossil fuel. Fossil energy use rises in step with increases in population and affluence.

Obviously humans have increased their control of energy through technology over time—with spear points to concentrate force; fire to break down cell walls and access more foods; agriculture to concentrate solar energy into useful food products; human slaves; animal power; Dutch windmills; New England water power and so on, including the very wide gains from fossil fuels. The real question is whether oil, gas and coal are the last step. Will they be followed by another transition? I cannot answer what that transition could be. We once thought nuclear power was the answer, but it appears that there is not nearly enough uranium, and the politics are daunting. Breeders have been attempted in France, Scotland and Tennessee but abandoned as too expensive (implying low EROI). Commercial fusion recedes each decade. Solar, as Marco Raugei notes, may expand significantly in some parts of the world. Technology may make some low-grade natural gas or thorium reactors more viable. But in all cases we have to ask whether there will be sufficient monetary and energy resources to make the transitions. It is time to make the study and discussion of the limits to growth, or perhaps the nonlimits to growth, at least as scientific, central and important as our discussions regarding climate change. Its effects are probably as great, but they will be felt sooner. Why we have not done this yet is a great mystery to us.



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