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Power Density: A Key to Understanding Energy Sources and Uses
The first systematic, quantitative appraisal of power density, offering detailed reviews of power densities of renewable energy flows, fossil fuels, and all common energy uses.“There's no author whose books I look forward to more than Vaclav Smil.”—Bill Gates
In this book, Vaclav Smil argues that power density is a key determinant of the nature and dynamics of energy systems. Any understanding of complex energy systems must rely on quantitative measures of many fundamental variables. Power density—the rate of energy flux per unit of area—is an important but largely overlooked measure. Smil provides the first systematic, quantitative appraisal of power density, offering detailed reviews of the power densities of renewable energy flows, fossil fuels, thermal electricity generation, and all common energy uses.
Smil shows that careful quantification, critical appraisals, and revealing comparisons of power densities make possible a deeper understanding of the ways we harness, convert, and use energies. Conscientious assessment of power densities, he argues, proves particularly revealing when contrasting the fossil fuel–based energy system with renewable energy conversions.
Smil explains that modern civilization has evolved as a direct expression of the high power densities of fossil fuel extraction. He argues that our inevitable (and desirable) move to new energy arrangements involving conversions of lower-density renewable energy sources will require our society—currently dominated by megacities and concentrated industrial production—to undergo a profound spatial restructuring of its energy system.
In this book, Vaclav Smil argues that power density is a key determinant of the nature and dynamics of energy systems. Any understanding of complex energy systems must rely on quantitative measures of many fundamental variables. Power density—the rate of energy flux per unit of area—is an important but largely overlooked measure. Smil provides the first systematic, quantitative appraisal of power density, offering detailed reviews of the power densities of renewable energy flows, fossil fuels, thermal electricity generation, and all common energy uses.
Smil shows that careful quantification, critical appraisals, and revealing comparisons of power densities make possible a deeper understanding of the ways we harness, convert, and use energies. Conscientious assessment of power densities, he argues, proves particularly revealing when contrasting the fossil fuel–based energy system with renewable energy conversions.
Smil explains that modern civilization has evolved as a direct expression of the high power densities of fossil fuel extraction. He argues that our inevitable (and desirable) move to new energy arrangements involving conversions of lower-density renewable energy sources will require our society—currently dominated by megacities and concentrated industrial production—to undergo a profound spatial restructuring of its energy system.
319 pages, Kindle Edition
First published May 22, 2015
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About the author
Vaclav Smil
81 books4,341 followersVaclav Smil is a Czech-Canadian scientist and policy analyst whose work spans energy, environment, food, population, economics, history, and public policy. Educated at Charles University in Prague and later at Pennsylvania State University, where he earned his Ph.D. in geography, Smil emigrated from Czechoslovakia to the United States in 1969 following the Soviet invasion, before beginning his long academic career at the University of Manitoba in 1972. Over the decades he established himself as a leading voice on global energy systems, environmental change, and economic development, with particular attention to China. Smil has consistently argued that transitions to renewable energy will be gradual rather than rapid, emphasizing the persistence of coal, oil, and natural gas and highlighting the difficulties of decarbonizing critical industries such as steel, cement, ammonia, and plastics. He has also been skeptical of indefinite economic growth, suggesting that human consumption could be sustained at much lower levels of material and energy use. Widely admired for his clear, data-driven analyses, Smil counts Bill Gates among his readers, while colleagues have praised his rigor and independence. Known for his reclusiveness and preference for letting his books speak for him, he has nonetheless lectured extensively worldwide and consulted for major institutions. A Fellow of the Royal Society of Canada and a member of the Order of Canada, Smil remains a highly influential public intellectual.
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Displaying 1 - 18 of 18 reviews
April 3, 2018
Power density is a ratio which measures the intensity of power by a unit of area. One could measure power density as a ratio with something other than area, but it is the focus of this book and serves an illustrative purpose. The author performs calculations of power densities for various forms of energy production industries like coal, wind, hydro, and nuclear. He also performs similar calculations for power use in cities. This constitutes the bulk of the book's text but these calculations are not the important part.
Worth stressing is that even though all these calculations are expressed in the same unit, it would be a mistake to make blind comparisons of the resulting values. Coal production has power densities that are orders of magnitude larger than wind, because most of the above-ground land use of coal is small relative to the power that it generates. On the other hand an apples-to-apples comparison of two wind farms does make sense, where it tells us the greater efficiency of one over the other, possibly because it's in a windier location. The power density of two different photo-voltaic panels would also be insightful, and could tell us whether one arrangement of cells is more efficient than another. There's also the question of whether the land itself has economic value other than its use in generating power, and if not the then the power intensity of land is less valuable as a metric.
The book's main thesis is not very clearly stated in the introduction and the reader could be forgiven for asking what the point of this exercise is even as far as two thirds of the way into it. But there is a point to all the number crunching. You just have to push on into the final few chapters to find it (or just skip right to it.)
Once the calculations of the preceding chapters are done there is a clearer picture of both the power consumption of cities and the power density of various industries that produce energy. From here the author explores what the land use claims would be for a 100% renewable civilization, and the outlook is not good. For starters, there is today no technology to replace jet fuel with batteries and so no way to do without liquid fuel to power flight. Biofuels made from corn or grass could be a substitute in theory but it would not be practical because the power densities are so low; in order to make enough biofuel for the world's commercial flights a land mass the size of Brazil would have to be devoted to growing corn exclusively. Other means of substitution are also quite bleak. To completely replace coal and natural gas in the generation of electricity to power homes and businesses, a great part of the continental US would have to be covered in windmills.
None of this is to say that we cannot substitute a large amount of fossil fuel for renewables in electricity generation, even if we fall far short of 100% globally. The absurd land claim of wind farms mentioned above is only due to the differential power density of farms; some places are windier than others so that there is a diminishing return on investment for each additional farm. That's not to say that the first few are not worth building. Many sites would have sufficiently high power densities and it still make sense to harness them for the grid. One could make a similar argument for solar and sunshine. The book does not talk much about the possibility of commercialized nuclear fusion, I suppose because its not technically a renewable source, but as far as decarbonization goes, it is by far the most promising prospect.
As of this writing (2018 or just 5 years after the publishing of the book) the country of Scotland is generating 2/3 of its electricity from renewable sources, England and Sweden roughly 1/2 with the latter making ambitious plans to push further. China, which today consumes half of the worlds coal alone, is also moving towards substitution with by the far the greatest investment in solar panel production in the world (7 panels every second). There are even many towns and cities that have managed to go 100% owing mostly to their natural endowments (like access to hydro or geothermal.) By current estimates, in 2017 about 20% of the worlds energy was produced by renewables. During this time the US saw an increase of 3% despite the elimination of subsidies. It also saw a net closure of coal fired plants despite the elimination of environmental regulations on that industry.
When considering these numbers one has to keep in mind that 30 years ago there was no such thing as a renewable energy industry. It is now taking an increasing share of investment. So even if it's not practical to move to a 100% renewable energy economy, it seems more than plausible that the world will pass 50% by the end of the century. And that is only projecting current trends without trying to anticipate any sudden innovations that make renewables more attractive.
Worth stressing is that even though all these calculations are expressed in the same unit, it would be a mistake to make blind comparisons of the resulting values. Coal production has power densities that are orders of magnitude larger than wind, because most of the above-ground land use of coal is small relative to the power that it generates. On the other hand an apples-to-apples comparison of two wind farms does make sense, where it tells us the greater efficiency of one over the other, possibly because it's in a windier location. The power density of two different photo-voltaic panels would also be insightful, and could tell us whether one arrangement of cells is more efficient than another. There's also the question of whether the land itself has economic value other than its use in generating power, and if not the then the power intensity of land is less valuable as a metric.
The book's main thesis is not very clearly stated in the introduction and the reader could be forgiven for asking what the point of this exercise is even as far as two thirds of the way into it. But there is a point to all the number crunching. You just have to push on into the final few chapters to find it (or just skip right to it.)
Once the calculations of the preceding chapters are done there is a clearer picture of both the power consumption of cities and the power density of various industries that produce energy. From here the author explores what the land use claims would be for a 100% renewable civilization, and the outlook is not good. For starters, there is today no technology to replace jet fuel with batteries and so no way to do without liquid fuel to power flight. Biofuels made from corn or grass could be a substitute in theory but it would not be practical because the power densities are so low; in order to make enough biofuel for the world's commercial flights a land mass the size of Brazil would have to be devoted to growing corn exclusively. Other means of substitution are also quite bleak. To completely replace coal and natural gas in the generation of electricity to power homes and businesses, a great part of the continental US would have to be covered in windmills.
None of this is to say that we cannot substitute a large amount of fossil fuel for renewables in electricity generation, even if we fall far short of 100% globally. The absurd land claim of wind farms mentioned above is only due to the differential power density of farms; some places are windier than others so that there is a diminishing return on investment for each additional farm. That's not to say that the first few are not worth building. Many sites would have sufficiently high power densities and it still make sense to harness them for the grid. One could make a similar argument for solar and sunshine. The book does not talk much about the possibility of commercialized nuclear fusion, I suppose because its not technically a renewable source, but as far as decarbonization goes, it is by far the most promising prospect.
As of this writing (2018 or just 5 years after the publishing of the book) the country of Scotland is generating 2/3 of its electricity from renewable sources, England and Sweden roughly 1/2 with the latter making ambitious plans to push further. China, which today consumes half of the worlds coal alone, is also moving towards substitution with by the far the greatest investment in solar panel production in the world (7 panels every second). There are even many towns and cities that have managed to go 100% owing mostly to their natural endowments (like access to hydro or geothermal.) By current estimates, in 2017 about 20% of the worlds energy was produced by renewables. During this time the US saw an increase of 3% despite the elimination of subsidies. It also saw a net closure of coal fired plants despite the elimination of environmental regulations on that industry.
When considering these numbers one has to keep in mind that 30 years ago there was no such thing as a renewable energy industry. It is now taking an increasing share of investment. So even if it's not practical to move to a 100% renewable energy economy, it seems more than plausible that the world will pass 50% by the end of the century. And that is only projecting current trends without trying to anticipate any sudden innovations that make renewables more attractive.
Read
November 18, 2019Although dense, numerically rigorous and at times not the most riveting read, the final two chapters of the book make the slog extremely worthwhile. Smil splashes a bucket of harsh cold water onto the naive and ardent ambitions of optimistic proponents for renewables.
The perspective of power density (W/m^2) or various energy sources, transmission and processing exemplifies the profound challenges and complexities that alternative forms of energy are faced with for decarbonization of society. Keeping in mind the severe threat of climate change, rapid decarbonization in light of Smil's wide ranging and extremely rigorous analysis leads one to a nuanced but deeply concerning outlook regarding the future of power systems in the 21st century.
The perspective of power density (W/m^2) or various energy sources, transmission and processing exemplifies the profound challenges and complexities that alternative forms of energy are faced with for decarbonization of society. Keeping in mind the severe threat of climate change, rapid decarbonization in light of Smil's wide ranging and extremely rigorous analysis leads one to a nuanced but deeply concerning outlook regarding the future of power systems in the 21st century.
March 19, 2017
Interesting topic and good insight. Perhaps only reading chapter 7 will be enough.
June 28, 2020
¿Cuántos metros cuadrados de terreno se necesitan por cada kWh de energía si la sacamos del carbón? ¿Y si es solar fotovoltaica? ¿Nuclear? Y luego, ¿cuántos metros cuadrados para gastarla, en el campo, transporte, ciudad? Así durante centenares de páginas, de forma muy prolija y pesadísima. La conclusión, que lo llevamos chungo para sustituir el mix actual por renovables.
May 27, 2020
Interesting book, although it could have been written in a more engaging way. It is way too technical for a layperson, but perhaps Smil’s aim wasn’t to reach that audience.
Unfortunately, the material is already outdated which greatly reduced my motivation to finish this book. For example, Smil calculates with 2-3MW wind turbines; however, onshore wind now offers 5-6 MW turbines while the largest commercial available offshore turbine is 15MW! That is 5 times the size of what Smil used in his calculations. That makes all wind energy calculations in the book outdated, and therefore the comparison to other energy sources are not ‘true’ in our contemporary world.
Unfortunately, the material is already outdated which greatly reduced my motivation to finish this book. For example, Smil calculates with 2-3MW wind turbines; however, onshore wind now offers 5-6 MW turbines while the largest commercial available offshore turbine is 15MW! That is 5 times the size of what Smil used in his calculations. That makes all wind energy calculations in the book outdated, and therefore the comparison to other energy sources are not ‘true’ in our contemporary world.
September 8, 2023
First off, the C3P0 narration made this book absolutely unlistenable. Seriously I’ve never heard someone rattle off endless strings of numbers without any inflection or intonation. The 1980s robot voice has more emotion.
The writing is similarly stifled and no real comparisons or grounding are given for the numbers given. In fact, my biggest gripe of the book lies in the delivery of the material presented. The entire book suffers from reading like a list of statistics ripped from Wikipedia pages of random fuel sources. Ok, so 50,000 hectares of wood burned per hour in 16th century England, that’s kind of neat but what does that mean exactly? Is it the equivalent to a car battery running for an hour or a Chicago street lamp burning all night? It’s hard to judge the differences in these materials and technologies with just pure numbers being thrown left and right without reprieve.
There are brief moments where the author takes a step back but even then the story is mired with overloaded long winded quotations. The section on 15th English deforestation concerns was fascinating but a half page list of random wooden creations quickly killed any desire to flip to the next page.
The information itself is interesting and the concept is intriguing but this author desperately needs to learn how to make the material engaging or hand his research off to someone that can craft a story out of the raw data.
The writing is similarly stifled and no real comparisons or grounding are given for the numbers given. In fact, my biggest gripe of the book lies in the delivery of the material presented. The entire book suffers from reading like a list of statistics ripped from Wikipedia pages of random fuel sources. Ok, so 50,000 hectares of wood burned per hour in 16th century England, that’s kind of neat but what does that mean exactly? Is it the equivalent to a car battery running for an hour or a Chicago street lamp burning all night? It’s hard to judge the differences in these materials and technologies with just pure numbers being thrown left and right without reprieve.
There are brief moments where the author takes a step back but even then the story is mired with overloaded long winded quotations. The section on 15th English deforestation concerns was fascinating but a half page list of random wooden creations quickly killed any desire to flip to the next page.
The information itself is interesting and the concept is intriguing but this author desperately needs to learn how to make the material engaging or hand his research off to someone that can craft a story out of the raw data.
September 11, 2024
***.5
A deep quantitative dive into an often overlooked aspect of power generation and usage, namely the amount of space that various types take up. By comparing the land usage of biofuels, coal, oil, gas, nuclear, wind, and solar, it's a lot easier to understand why we rely so heavily on fossil fuels, and how difficult it is to wean off of their use.
This book is very specific and highly detailed, with endless facts and figures to justify the relatively sparse conclusions. His more general books cover this topic in sufficient detail for most readers, but for those looking to learn more, especially policy makers, investors, and pundits, it's a great resource to understand one of the often overlooked trade-offs when comparing competing projects hankering for funding. For instance, it's readily apparent after looking at the numbers that growing corn to turn into ethanol to be added to gasoline is just plain stupid, whereas nuclear power is so efficient that it's equally stupid to reject it out of hand.
As with his other books, Smil is skeptical of meeting targets to decarbonize the economy, this time focusing on the amount of space that would be taken up by wind and solar farms to reach the scale necessary to replace coal and gas fired power plants. I personally think that he's a bit too pessimistic, but his objections are certainly valid and must be addressed if we have any chance of meeting the targets set by the Paris Agreement and other ambitious milestones.
A deep quantitative dive into an often overlooked aspect of power generation and usage, namely the amount of space that various types take up. By comparing the land usage of biofuels, coal, oil, gas, nuclear, wind, and solar, it's a lot easier to understand why we rely so heavily on fossil fuels, and how difficult it is to wean off of their use.
This book is very specific and highly detailed, with endless facts and figures to justify the relatively sparse conclusions. His more general books cover this topic in sufficient detail for most readers, but for those looking to learn more, especially policy makers, investors, and pundits, it's a great resource to understand one of the often overlooked trade-offs when comparing competing projects hankering for funding. For instance, it's readily apparent after looking at the numbers that growing corn to turn into ethanol to be added to gasoline is just plain stupid, whereas nuclear power is so efficient that it's equally stupid to reject it out of hand.
As with his other books, Smil is skeptical of meeting targets to decarbonize the economy, this time focusing on the amount of space that would be taken up by wind and solar farms to reach the scale necessary to replace coal and gas fired power plants. I personally think that he's a bit too pessimistic, but his objections are certainly valid and must be addressed if we have any chance of meeting the targets set by the Paris Agreement and other ambitious milestones.
December 25, 2023
As a preface, I'm on a mission to read Smil's entire oeuvre. One of the things challenging for a non-scientific reader is that Dr Smil is a very, very, thorough writer, so much of what he writes does not read like a narrative; the meaning must be deduced. Sometimes he uses impactful language when he has a strong point to make, but at other times when it's directional he leaves it to the reader to form their own impression.
What I love about his energy work is that it is driven by data and emotionless rationalism. In book after book, it's clear his interest is in following where the data (rather than hype) wherever it leads, and asking the relevant "what if?" questions that most media ignore.
Smil's work is never easy reading, but the reward is always worth the effort.
What I love about his energy work is that it is driven by data and emotionless rationalism. In book after book, it's clear his interest is in following where the data (rather than hype) wherever it leads, and asking the relevant "what if?" questions that most media ignore.
Smil's work is never easy reading, but the reward is always worth the effort.
January 30, 2020
The data presented is dense and probably useful for researchers but it is easy to get lost in the forest. I felt much data could have been presented in visual/graphical form to give context. It was difficult to push through to the final few chapters where insights are extracted. It was, however, fascinating to compare power generation and power density for all the widely different forms of electrical power generation.
June 30, 2025
DNF
I really respect Dr. Smil but some of the traits that are minor annoyances in his other books are turned up to 11 in this one. His refusal to clearly state his thesis up front is maddening and his claims of complete novelty are possible only because he has substituted the term "power density" for "land requirements." He spends chapter going through his calculations in detail but many of the assumptions are now wildly out of date due to rapid innovation in renewables efficiency.
I really respect Dr. Smil but some of the traits that are minor annoyances in his other books are turned up to 11 in this one. His refusal to clearly state his thesis up front is maddening and his claims of complete novelty are possible only because he has substituted the term "power density" for "land requirements." He spends chapter going through his calculations in detail but many of the assumptions are now wildly out of date due to rapid innovation in renewables efficiency.
August 17, 2021
Excellent read and great proof on why replacing all of our energy needs with renewables is unfortunately not possible. The book is just a bit repetitive, chapter 7 kinda sums up the previous chapters in a rather long way.
July 5, 2022
Even if I like numbers. Thos was too much. Still interesting perspective
July 14, 2022
An excellently analytical and well-written book describing the bottlenecks driving factors in transitions of energy systems.
November 11, 2022
works better as a reference manual than a book you read front to back.
Read
November 30, 2022Stopped at page 70. I wasn’t able to finish this one. Heavy on science and an overly strong dose of assertiveness.
December 4, 2022
It gets a little dull, with a lot of numbers that can be a little too much. But overall great book, really intresting.
September 22, 2023
Incredibly good book on comparing different energy sources, highlights the importance of nuclear energy
Read
May 25, 2019Very good book for everybody that want deeper understanding of this field
Displaying 1 - 18 of 18 reviews