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The Future of Energy: Why Power Density Matters

The Energy Transition

This is the first column in The Energy Transition series by Robert Wilson. This series, exclusive to, will take a critical look at the prospects of a transition away from fossil fuels, and promises to abide by the advice of Richard Feynman that reality must take precedence over public relations.

Hong Kong Wind Farm Wakes

The twenty first century will almost certainly witness a transition to an overwhelming urban human population, and hopefully a transition to a low carbon energy system. The former however will have a significant impact on the latter, because a fundamentally urban species cannot be powered locally.

The  continued, and essentially unabated, accumulation of carbon dioxide in the atmosphere may at times make considerations of the requirements of a de-carbonised energy system appear somewhat self indulgent, but I must ask the reader to indulge me, and at a little length.

What would a low carbon energy system look like? (And let’s avoid such fanciful ideas as “zero carbon,” because that would be truly self indulgent.) In essence we would get as much electricity as possible from some combination of renewable and nuclear energy, and electrify as many aspects of our energy systems as is feasible. Predicting the relative composition of such a system is a largely fruitless exercise. However, we can say something about the extent to which it a low carbon energy system will be distributed and “local”. This confidence comes from the difference between the high physical concentrate of energy use in cities, and the relatively low physical concentration of renewable energy resources.

Power density

There are fundamental physical limits to how much energy we can extract from renewable resources for a given area of land. If we want to rigorously quantify this we calculate an energy source’s power density in watts per square metre (W/m2 ).

To get an understanding of this concept consider the recently opened London Array wind farm to the south of England.This is the world’s largest offshore wind farm and according to its owners will generate “enough energy to power nearly half a million homes.” Its total capacity is 630 MW covering a total of 100 km2, and is expected to have a capacity factor of 39%. In other words the power density of the London Array will be 2.5 W/m2. This number is also very similar to the average calculated by David MacKay for existing UK wind farms. The United Kingdom is windier than a lot of the world, and some research suggests that large extraction wind farms will reduce average power density closer to 1 W/m2, so 2-3 W/m2 can be viewed as an upper limit on the power density of large scale wind power. This power density reflects average output, however peak power density of wind farms will be perhaps three times higher, and minimum power density will be close to zero. And it should be noted that it excludes the requirements for manufacturing steel required for turbine towers and the extraction of fossil fuels for conversion to plastics for wind turbine blades. However inclusion of these factors is not likely to result in a significant reduction to power density estimates.

Globally solar radiation available for conversion to electricity averages 170 W/m2, and in sunnier locations it can reach above 200 W/m2. This solar energy however is currently not converted at anywhere close to 100% efficiency. Commercial solar photovoltaic panels typically average between 10 and 15% efficiency. Power density of solar installations must also account for space between panels, either for servicing in solar farms or for spacing between houses in rooftop solar installation. As a result the highest power density achieved is around 20 W/m2 in desert solar PV farms, whereas solar farms in Germany generally achieve 5 W/m2. Future improvements in panel production will hopefully see significant improvements in panel efficiency. However there will remain a firm physical upper limit of 200 W/m2, which will be significantly lower when only considering large scale deployment of residential rooftop solar, due to obvious physical restrictions on panel placement.

At their best biofuels might be able to produce close to 2 W/m2. However power densities of 0.5 W/m2 and below are more typical, with prominent examples of this being corn ethanol for transport and the burning wood for electricity. We will see later that this is a very important consideration for the scalability and sustainability of biofuels.

In contrast typical generation of fossil fuel and nuclear electricity has a power density of at least an order of magnitude greater than that of renewable energy. Power densities are comfortably above 100 W/m2 after accounting for mining etc. And conventional power plants often have power densites in excess of 1000 W/m2. A simple example of this higher power density is this small propane powered generator, providing in excess of 1000 W/m2. This is far in excess of the power density of any conceivable new method of generating renewable energy.  


Why power density matters

A simple thought experiment can demonstrate why power density needs to be a fundamental consideration when evaluating renewable energy. Here it is: Imagine a world where all energy comes from bio-energy. What would be the requirements?

Currently the planet consumes energy at a rate of over 16 TW (16 trillion watts). If we include non-commercial biomass energy used in Africa and Asia, an uncertain figure, this number would increase. However for simplicity I will ignore non-commercial sources and will round our figure down to 15 TW. If we got all energy from corn ethanol we would need to convert a total of 75 million km2 to corn ethanol plantations. This is roughly half of the land surface of the entire planet, land which is somehat scarce. So this simple thought experiment shows there very real limits on how much energy we can, and should, get from biofuels. If we want large scale biofuels to become truly sustainable, a questionable prospect, we will need to see significant improvements to their power density, perhaps improvements of at least an order of magnitude.

Physical concentration of energy consumption

How much energy do we consume per unit of land? For ease of comparison this figure again can be calculated in W/m2. On a global level this is 0.1 W/m2, if we only consider land surface area. Global averages however are not very instructive, power density averaged at the scale of countries and cities is much more important. David MacKay has visualised this much better than I can in his “Map of the World.” Here is the average rate at which countries consume energy, in W/m2, compared with the power density of different renewables: Ideally a country wants to have lots of available land for renewable energy, i.e. they want to be in the bottom left of this graph. Being in the top right however may lead to some problems.

Consider first the United Kingdom and Germany. Both use energy at a rate of just over 1 W/m2. So a back of the envelope calculation will tell you that getting all of their energy needs from onshore wind will require covering half of the UK or Germany in wind turbines. If you have ever been confused by why these countries are building wind farms in the North Sea, instead of on land where it is much cheaper, now you know why. Wind energy’s low power density means you need to put it in a lot of back yards. And there are not as many of them in the North Sea.

Things are even worse in Japan and South Korea. If you covered all of South Korea in wind turbines they would generate less energy than is consumed there. Japan has a similar problem. And this ignores another difficulty: trees. Both Japan (68%) and South Korea (63%) have very high forest cover. If we ignore forested land (which should be out of bounds for large scale renewable energy generation, unless large scale biomass plantations are deemed acceptable) energy is used with a power density of almost 6 W/m2 in Japan and 7.5 W/m2 in South Korea. This calculation makes it clear that these countries can only be predominantly powered by renewable energy through the large scale utilisation of the more power dense solar energy. And social and political constraints may mean this can only happen if the efficiency of typical solar panels increases significantly from their current 10-15%.

Local Energy Is Not A Solution

Some environmentalists and renewable energy advocates have an ideological preference for small and community scale renewable energy. However what if your community looks like this: missingTokyo skyline

Some people may like the idea of running Tokyo on local renewable energy. They will have some difficulty actually doing it, and that’s putting it mildly.

Since 2008 the majority of humanity live in cities. And by 2050 it is probable that we will see seventy or eight percent of humanity living in cities. The key energy challenge this century will be providing energy for these cities, and quite clearly local distributed energy is not a solution. To see why this is the case requires untangling some issues.

Here are some considerations. An average North American has an annual energy consumption of just over 7 tonnes of oil equivalent (toe)., which is the equivalent of a rate of 9,000 watts. However, this is almost double what it is in countries such as Germany, France and Japan. A comparison of these countries in terms of key well being measures makes one thing clear: there is no evidence that North Americans have greater well being as a result of their excessive energy use. Americans don’t live longer, aren’t healthier, or better educated than countries that consume half as much energy per capita. That this high per capita energy consumption comes with a very significant environmental cost – global carbon dioxide emissions would drop by almost 10% if North Americans consumed like Europeans – but little gain in terms of human well being, suggests that is is not desirable for other countries to emulate North American consumption patterns.

Further evidence for the desirability to limit, and probably reduce, per capita energy consumption in modernised countries is given by its evolution in recent decades. Instead of increasing in the long term, per capita energy consumption now appears to have peaked in almost all modernised countries. Here are some examples:

Per capita consumption has declined steadily in the United Kingdom for the last decade and is now at its lowest point for over four decades:

United Kingdom

The United States saw peak per capita consumption in the 1970s, with consumption now seeing an apparent decline. And the fact that per capita consumption did not rise in the age of the Hummer suggests significant room for movement.


Germany is also now seeing declines in per capita consumption.


In Japan per capita consumption appears to have peaked in the late nineties and is now in decline:


So, many modernised countries are now seeing reductions in per capita energy consumption, and this is not being accompanied by a reduction in quality of living. Any sensible long term energy and climate policy should include a strong desire to continue this trend. The belief that the world can transition to both American levels of energy consumption and to a low carbon energy system by the middle of this century ignores the vital lessons of previous energy transitions, and given the current position of renewable and nuclear energy it appears delusional. The world therefore must be much more like Japan than America.

And cities must play a key role in reducing energy consumption. The most important and effective way to do this is simple: make them dense. For a full elucidation of why, I recommend books by Edward Glaeser and David Owen. But the key reasons are easy to understand: a dense city lets you walk or take public transport instead of drive and it lets you live in a more energy efficient apartment building instead of a large inefficient house. Packing people more tightly together in cities may not be to the taste of everyone, but it appears to be one of the most achievable and practical ways to reduce how much energy people consume.

Let us now move forward to 2050, and the world is as I hope it will be. Global population will have peaked below 9 billion as a result of the spread of the demographic transition to modernising countries, and the success in reducing infant mortality and widespread availability of contraception. Perhaps 7 billion of us will live in cities, and they will consume much more like modern day Japanese than Americans.

How will we provide energy for these cities? The answer appears to be large, centralised power plants, whether they are wind, solar or nuclear. Here I assume, wishfully, that we have managed to get rid of fossil fuels, an unlikely prospect. The answer however is almost certainly not local distributed energy, and for simple reasons.

Consider Manhattan, not what many would typically look at as the green ideal. Yet here you will find significantly lower per capita energy consumption than in almost every American city. You will also find energy consumption far greater than can conceivably be provided by local renewables. A recent study managed to map energy consumption in the city that never sleeps right down to the individual city block. This is what it looks like:

A typical block in Manhattan consumes energy at a rate of over 1,000 kWh per square metre each year, a power density of over 100 W/m2. This is almost two orders of magnitude greater than the power density of wind power, and obviously you could not plaster Manhattan in wind turbines. Solar power is not much better. Imagine that we could cover 20% of Manhattan in solar panels. This would give us no better than 5 W/m2. Clearly Manhattan is not getting its energy locally. And as you can see from the above map the other boroughs of New York are not going to fare much better.

How about the rest of North America? If we reduced per capita energy consumption to Japanese levels, a sensible but unpopular idea, could many American cities run largely on local renewables? The graph below shows population density versus energy use density in this lower consumption America: usDensity

Low density Phoenix perhaps has a shot at getting most of its energy from solar power. Covering 25% of Phoenix in solar panels would produce as much energy as is consumed in Phoenix. The practicality of this is of course rather questionable, and getting more than 50% of Phoenix’s energy from local solar will require something that currently does not exist: a cheap way to store energy on a large scale. A system involving more than 50% of energy coming from solar will thus inevitably require the accounting of land requirements for large scale storage, an uncertain prospect, and significant losses of solar panel output due to efficiency losses during storage and curtailment of excess.

The prospects of American cities running largely on local renewables thus seems unlikely, and 83% of Americans live in cities.

A global appraisal

The world’s two hundred largest urban areas are home to over 1.2 billion people, and a quarter of these areas are more densely populated than New York (10,000 people per square kilometre). This is shown below: PopDensity

Before asking if these cities can run on local renewables I must first mention the too real disparities in global energy consumption. Below is a comparison of the population of countries with their per capita energy consumption, with population plotted on a logarithmic scale due to China and India being much larger than other countries. And I include lines showing typical European and North American per capita energy consumption. GlobalEnergyComp

While there are about 350 million North Americans who can, and should, reduce their energy consumption to European levels, there are even more at the bottom who must increase their energy consumption significantly to improve their quality of life. Quantitative comparisons are sobering. Over 35 countries have per capita consumption at less than 10% of North American levels, with populations totalling over 2 billion. Despite the apparent desires of some environmental NGOs (for an example see page 11 of this WWF report) it is therefore undesirable to propose reductions in global energy consumption. The modernised world may consume excessive energy, but energy consumption is much too low in modernising countries to let us decrease global energy consumption without negative humanitarian impacts.

We therefore should have a desire to both reduce excessive consumption in modernised countries and increase energy consumption in modernising countries. I am not going to suggest a prescriptive end point. Instead I will assume that consumption levels in modern day Japan can provide a very good quality of life, and exceeding these levels is unnecessary.

If the populations of the world’s 200 largest cities consumed energy like modern day Japanese energy use density would look like this:


In total 10 cities would have power density greater than 100 W/m2, 56 would have power density greater than 50 W/m2, while 181 would have power density of over 10 W/m2. That is 90% of the planet’s 200 largest cities almost certainly cannot be powered predominantly by local renewable energy. The population densities of these cities are not significantly different than the rest of the world’s cities, so we can conclude that the the vast majority of cities cannot be powered by local renewables. And this suggests very serious limits to the role of local distributed energy in a world where more than 70% of us will probably live in cities.

The prospects are even worse in individual countries. Of the world’s 200 largest urban areas, 17 are in India. Below I have isolated these cities.

India power density

120 million people live in these cities. Covering any of them entirely in 10% efficient solar panels will generate less than half of their energy needs. And look at that dot in the top right, that is Bombay. For Bombay to get all of its energy needs from solar in my hypothetical future it would need to harness almost 100% of the solar radiation that strikes it, a remote prospect. This extremely high population density is routinely ignored by western environmentalists calling for distributed energy to be the solution to India’s energy problems. It quite clearly is not.

In this century the bulk of humanity will live in large densely populated cities. If the citizens of of these cities are to attain a high quality of life they will require large centralised energy generation. This is not a matter of ideological preference, but of engineering reality.

Robert Wilson's picture

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Bob Meinetz's picture
Bob Meinetz on August 9, 2013

Perhaps. It’s been a while since I’ve done this calculation. Let’s bring it up to date:

Avg output for solar panels ~160W m2

* capacity factor .19 (Arizona) = 30W m2;

U.S. annual energy consumption 3886 TWH/yr;

U.S. avg power consumption = 3886/8760 = 444GW.

How many solar panels does it take to generate 444GW?

444,000,000,000/30 = 14,800,000,000 m2 of solar panels.

Solar panel cost ~ $4/watt * 160 = $640/m2;

640 * 14,800,000,000 = $9,500,000,000,000.00 to provide the U.S. demand equivalent of raw power (please correct me if I’ve made a mistake or unrealistic assumption). A far cry from what I originally posted, admittedly, but roughly three times the entire U.S. budget – not including any infrastructure, transmission, storage, or backup, maintenance – and all must be replaced every twenty years.

Stephen, we can’t afford solar in the U.S. and the developing world certainly can’t afford it. How can anyone consider solar power remotely up to the task of being a significant player in global energy? It won’t be, and here’s the problem: there’s nothing to suggest an imminent breakthrough in tech which would be a gamechanger. So instead we play a shell game, as Germany is, and sneak coal in to fill in all the spaces where solar can’t. By indulging unrealistic hopes we’re only making a bad problem worse.

Max's picture
Max on August 9, 2013

When we take large-scale storage into account, the “useful power density” (amount of land needed to feed a given amount of power predictably into the grid) of the whole renewable energy system is lower than the values calculated for individual generators without storage in your article. That is something to keep in mind I think.

Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013

Nathan, You don’t see hydrogen as either a direct energy source or as a chemical feedstock for an energy source? You don’t see that if the result of the electrolysis is a net carbon sink, that it is indeed carbon negative?  That surprises me.

“…if a large market for hydrogen or ammonia develops,…”

You do know that a large and growing market for hydrogen worth 10s of billions already exists, right? Have you seen mid to long term hydrogen market forecasts recently? 

Willem Jan Oosterkamp's picture
Willem Jan Oosterkamp on August 9, 2013

Energy density mattersand cities can not be selfsufficient in food and energy. The discussion on the spacing of windmills is only relevant for small countries as the Netherlands with a high population densities. In the province of flevoland that was sea before the war it is quite clear that farming can co-exist with windfarms. It would be interesting to get the data on the ruduction of agricultural yields in that area due to the windfarms.

With regard to biomass food production and energy production can co-exist. The German and American praxis to use corn for energy is a waste of resources. Making biogas from manure and straw can reduce world oil consuption by about 10 %.

Willem Jan Oosterkamp Oosterbeek Netherlands


Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013

 A far cry from what I originally posted, admittedly”

$500 trillion to $9.5 trillion. Yes, that is a far cry.

“So instead we play a shell game, as Germany is”

Is it your assertion that Germany is in the process of purposely destroying her own economy for no reason whatsoever?

Did you see this report from last month?

Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013
DOE Secretary Moniz has said that the U.S. should be, “pushing on solar across the board,” and that, “it’s going to be a lot bigger than a lot of people think, sooner than they think.” His philosophy is forward looking and pretty much in sync with the man he replaced, Steven Chu. I don’t see either of these men as incompetent.

There was a 40% Drop In EV Battery Prices From 2010 To 2012. It is an ongoing price trend that, given the nature of the technology and like the similar solar cell price trend (regardless of trade wars), can only continue. 
Warren Darrell's picture
Warren Darrell on August 9, 2013

Presuming the facts, logic, and math are correct, the article is excellent. 

The article does not adequately cover the potential and energy density of geothermal.

We need large central station electricity, plus much improved efficiency in energy production, transmission, and consumption, materials, industry, commerce, agriculture, land use, and transportation.  In addition, natural carbon sequestration in soils and vegetation, while it does not produce useful energy, can be a signifiant part of alleviated energy related global climate disruption. 

Nuclear energy is already safer and more envirnmentally friendly than coal.  It’s not perfect, e.g. Fukashima, but we can and should make nuke safer.  

The major issue is external costs.  If we stop allowing fossil fuel productdion and consumption to damage the earth and pollute the air for free, our businesses, industries, and scientific institutions will develop improved efficiency and environmentally friendly energy. 




Thomas Gerke's picture
Thomas Gerke on August 9, 2013

Are you aware that the goal is not a 100% non-fossil Electricity system, but a 100% fossil-free Energy system?

How much storage capacity does a 100% nuclear energy system require? Do you have a study looking into that? There are several extensive studies on the requirements of a 100% renewable energy system, but I couldn’t find a single study on a nuclear system.
1. Propably because too many required technologies are still in the “proof of concept”-stage.
2. Even in a maxed out nuclear centered system renewable energy sources are better suited for many jobs – for example ambiant enviromental energy “heat-pumped” for low-temperature heating energy needs OR bio-coke for making iron/steel. (BTW: 2.5% of the German primary energy use) 

When one honestly thinks things through, the storage (power-to-gas/hydrocarbon conversion) capacity needs are actually in the same range as for a renewable energy centered system. 

But as I said, it’s hard to argue about these things with fans of nuclear…To my knowledge there is simply no good nuclear study based on current/near-future proven technology out there, that shows that a sustainable nuclear centered energy system is feasable. Lot’s of optimizm and idealistic wishful thinking, but little fact. 

As for renewable energy, there is loads of it, but most anti-renewable people decide they don’t like those facts… they choose to live in a simpler time when nuclear was “the obvious solution” and renewables “never work”. 

(Not talking explicitly about you Nathan) 

A study conducted by the Fraunhofer Institute found that in a rather unrealistic/extreme 100% renewable energy system (German energy autarcy) 88 GW of power-to-gas capacity would be required to meet all heat, power & transport needs. 

If one would generate the requried gross-electricity with nuclear power, one would need approx. 100 GW of baseload power. With electricity demand going as low as 35 GW, one would still need 65 GW of storage/negative load. 

Since power-to-gas capacity isn’t predicted to be really that expansive ($1-1.2/W) at a lifetime of 20+ years it’s not really a realistic argument against the feasabiltiy of a renewable energy system.

Roger Faulkner's picture
Roger Faulkner on August 9, 2013

LENR at least does not violate thermodynamics and might be real. I’m betting against the free energy schemes because they do violate both the first and second laws of thermodynamics, producing work with no waste heat from the ether. If they work, they will turn loose a future where space travel will be mundane, and so many other things too, that I hope I am wrong. LENR, which does look real to me, is still a heat engine, though one with very low fuel cost. In a short time, if LENR is fully exploited, waste heat will become a big issue. There will still be a place for a supergrid in an optimum LENR future with the main function of allowing the waste heat to be generated where it is needed, rather than where the electricity is needed. I think, at least electricity’s role as the universal carrier of energy will survive for millenia.

Roger Faulkner's picture
Roger Faulkner on August 9, 2013

A modern pumped storage facility has a round-trip efficiency ~83%.

Robert Bernal's picture
Robert Bernal on August 9, 2013

We all seem to accept the social limits of nuclear… (but the public does NOT know about LFTR, etc).

Yet the “social” accepts fossil fuels.

The social costs of covering 100,000 sq mi of desert with concentrated solar power with molten salt heat storage is also “unacceptable”… another solution, killed!

And again, the social costs of wind has already become “unacceptable”. (Granted, we don’t have cheap storage for wind… yet).

Another “unacceptable” thing to do is mining. Without that, ALL solutions are killed!

Innovaton, and then actual physical construction are required to build low carbon but “everyone” is against “everything”!

The ONLY way we are going to build the low carbon energy infrastructure, I mean, the ONLY way we are going to survive, is if we can overcome that hardest of challenges… scientific illiteracy and that really stupid thing… social acceptance!

Robert Bernal's picture
Robert Bernal on August 9, 2013

Enviro’s will block anything that will generate electricity because they don’t care about the powerful solutions to excess CO2. If they did care, they would advocate molten salt reactors and or 100,000 square miles of concentrated solar thermal power, at any cost.

Perhaps they don’t realize that, currently, there is no other way to prevent biofry.

Max's picture
Max on August 9, 2013

Pumped storage is great, but in most countries, the potential resource is too small to even out the fluctuations on a grid with a high share of variable renewables. In Germany, there are several days each year with close to zero wind and solar output. You need to store a lot of energy to cover that, which rules out pumped storage and batteries, leaving synthetic chemical fuels as the only viable option.

Robert Bernal's picture
Robert Bernal on August 9, 2013

“It might be real”.

Let’s go for what is already proven to be real and abundant enough to power MORE than one whole planetary civilizations. CSP and or MSR

Robert Wilson's picture
Robert Wilson on August 9, 2013


Combined Heat and Power is either not low carbon enough, i.e. fossil fuelled, or is very dubious, i.e. biofuels. So I have not discussed it. And I don’t see how geothermal heat pumps will help you get around the high density use of energy in cities.

On your point about climate change. I thought what I was saying was quite clear, was it not? My chief argument is that the rate at which you could extract renewables within citieis is far lower than the rate of energy consumption within them. So we will need centralised energy production, whether these are massive GW scale wind farms or nuclear power plants, or more likely fossil fuelled power plants. I just don’t see how an urban species can be run on local energy.

Mike Barnard's picture
Mike Barnard on August 9, 2013

No, actually, Willem, the latest findings do not support that unless you talk about anti-wind reports of low reliability.

All of the high reliability studies on wind energy, noise and health agree that setbacks are just fine at about 500 meters. If you don’t believe me, read and assess them as I did here:

Regarding cattle, more BS. No credible findings from anywhere indicate any problems with livestock for wind turbines. Literally incredible anecdotes assert there’s a problem, but reading them is a source of comic relief, not evidence gathering.

Once again, you’ve been reading anti-wind blogs more than sources of actual information.

Mike Barnard's picture
Mike Barnard on August 9, 2013

More completely inaccurate and inept arguments from those opposed to wind energy. First this commenter starts by ignoring the argument made and asserting the opposite without references or evidence of reality. He certainly hasn’t read the completely referenced material provided.


Then he claims the backup myth. Wind farms don’t require any more backup than coal or nuclear plants do until they are supplying a very large percentage energy, and when wind energy drops, it’s predictable and minor, unlike major transmission or generation failures.

Then, because he hasn’t embarassed himself enough, he claims the CO2 myth. Wind farms reduce greenhouse gases; real world results in Texas, the UK and Australia prove this is true. Industry standard, full lifecycle analyses for all forms of energy find that wind turbines pay back their carbon debt faster than any other form of generation. Every MWh produced by wind energy eliminates 99.8%+ of the CO2 that would have been generated by shale gas or coal, as they are first to be eliminated from the grid as generation sources. As the full lifecycle analyses show shale gas has 50 times the CO2e and coal has 100 times the CO2e per MWh, that’s a lot of global warming gases that are eliminated with every MWh of wind energy.

This commenter really quit while he’s so far behind, but he’s shown no ability to do so in the past and will likely continue to argue these dead points (with support from others on this odd collective of energy reality deniers).

Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013

What seems to be lost in this discussion is that regarless of the energy sources we choose; climate change is going to require that build our cities and just about everything in them differently. 

Robert "Bob" Mitchell's picture
Robert "Bob" Mitchell on August 9, 2013

Excellent article and discussion!  Not that I agree with everything that was said, but it’s nice that people are thinking about the practical aspects of switching to renewable energy in such a way as to power a growing world.

That said, even with all of the number crunching that was done, it strikes me as a bit simplistic.  As was pointed out in a couple of the comments, is anybody really saying that population dense urban areas have to or should have to get their power locally?

Basic economic theory states that the markets will guide resources towards their highest and best use and in this case, low/no population density areas seem to be better at producing renewable energy.  That’s not to say that urban areas can’t pitch in and produce power locally and reduce demand by increasing efficiency, but that’s not what they do well.  So, why not accept that big cities are going to have to import a good percentage of the power that they consume?

Personally, I think that the most likely way that we are going to end up powering our society in the future is through renewable energy….one way or the other because, in the long run, we won’t have a choice. 

What mix of renewables is going to produce this power?  My guess is that it will vary depending upon what resources are available locally and how fully we develop and improve our electrical grid (in order to efficiently import power).  Whatever the mix, it will also be accomplished by improving how we utilize energy.

Regarding the fact that renewable energy is less dense than fossil fuels or nuclear, it really doesn’t matter.  Because, as I mentioned, in the long run we aren’t going to have a choice but to find a way to engineer around the lower energy density.  And while this is the first energy transformation that we’ve gone through where we are moving from a more dense form of energy to a lessor dense one, there is no reason that we can’t accomplish this feat!


Bob “The Clean Energy Guy” Mitchell


Bob Meinetz's picture
Bob Meinetz on August 9, 2013

The point is that solar is not a significant source of energy generation, it won’t be for decades, and may never be. The numbers prove it. You can wish upon a star, or you can make informed decisions based on facts. Again, if I’ve made unrealistic assumptions or errors please point them out.

The link you provided is a perfect example of gilding the lily and cherry picking data to support an ideological mindset. The author, Julia Mengewein, is not coincidentally German and not coincidentally shows an anti-nuclear bias across the entire spectrum of her reporting. Read carefully:

“The reductions, which typically last for hours at a time, underscore how Chancellor Angela Merkel’s plan to replace atomic power with renewable energy within a decade is gaining ground at the expense of profit at utilities from RWE to EON SE.”

She concludes that Merkel’s Energiewende is viable based on records set during brief periods at the height of summer – the only time when solar energy is cost-effective. This is absurd, and contradicts the big picture which shows German carbon output increasing with no end in sight. With such a miserable outcome and so much money invested, it’s not surprising that many Germans are in denial, although that doesn’t change realities one iota.

Have you seen these reports?

German greenhouse gas emissions rose in 2012

Anti-nuke move sends Germany’s emissions higher

The dirty coal behind Germany’s clean energy

Carbon Capture technology loses out in Germany

Germany blocks EU carbon cap to protect automakers

If I don’t feel inclined to indulge Germany for the environmental destruction it’s wreaking to provide a (false) sense of security for its populace, maybe now you understand why. Am I asserting Germany is “in the process of purposely destroying her own economy for no reason whatsoever?” Of course not. I’m asserting Germany is chasing an expensive and ideologically-motivated agenda with scant basis in science or engineering, it’s harming the environment, and there’s no evidence the situation won’t only get worse.

Bob Meinetz's picture
Bob Meinetz on August 9, 2013

Thomas, as Willem accurately points out above, this is the tip of the iceberg.

What is the cost for installation?

What are the costs and inefficiencies required to transmit this power from the American Southwest to the Northeast?

How many gas peaking plants must be installed to back up this system?

How many Li-Ion batteries are required for storage, and how much will that cost?

If “nobody is suggesting a 100% PV-Solar energy system”, why do renewables advocates repeatedly cite total terrestrial solar irradiance to justifiy PV technology?

These costs could easily extend the expense of widespread solar generation by an order of magnitude. It will never, ever happen.

Robert Bernal's picture
Robert Bernal on August 9, 2013

That is an old definition. Ever heard of excess CO2 and excess carbonic acid on a global (and proven) scale?

I was reluctant to believe, so I found out for my self. The ppm CO2 has risen by 80 in just my lifetime alone. Thus, by burning dead plants and animals on an increasingly global scale, we are altering the biosphere of an entire planet.

If you are already against the use of FF’s, you should know that renewables are intermittant and less power dense and that nuclear is subject to “society’s approval”. Therefore, the need to develop the least costly and safe approach.

If that requires a lot of powerlines, them so be it!

Clayton Handleman's picture
Clayton Handleman on August 9, 2013

I am confused by your post.  A few suburban wind turbines will really not address the issue ot providing power for cities so it seems rather off topic.  The scale required to make a dent in NYC or even Boston’s requirements is GW scale and that requires windfarms not endless battles in communities over onesy twosy turbines.  Power of that scale can be piped in from the Great Plains or Great Lakes or Off Shore.  I am not sure how a discussion of residential setbacks really brings anything to the authors point.  He is already saying that to solve the problem you need to get it out of populated areas.  There is a great deal of work being done to get wind from utility scale wind farms in places that don’t have the problems you allude to to the high density usage areas – see discussion and references at

Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013

Please estimate when the first gW of LFTR power will come on line?  2035? 2045? This is a very important question.

Clayton Handleman's picture
Clayton Handleman on August 9, 2013


Robert, I thnk you do a great job of making the point that an urban species cannot be run on local energy.  However I do not agree that it follows that we are therefore relegated to centralized power sources.  The only conclusion I can draw from your work is that power for a city needs to be obtained from outside of that city.  Certainly nothing in your work suggests to me that it has to be fossil fuel.  Here are a few points that jumped out at me:

1) Utility scale wind is not a centralized power source.  It involves placing turbines, spaced apart, throughout massive geograpic areas.  For example, the Palm Desert wind farm has roughly 15 miles of exent Same is also true for utility scale solar.  Here is a solar thermal plant that is about 4 miles wide and provides under 400 MW

2) Utility scale aggregation of low power density wind and solar can be accomplished through a supergrid that is now on the drawing boards.  It appears that the research is incomplete as to how well the supergrid will smooth out intermittency but there is work showing that it will have a substantial impact.  See

3) The suggestion that fossil fuels are the way we are headed seems flawed.  Fossil fuels, particularly coal are quite costly.  Those who are in favor of market driven economies should be vociferously pushing for mechanisms to assure that the externalities of fossil fuels are monetized.     While in the short term, the fracking boom is leading to a build out of natural gas capacity, Wind and solar are also expanding at a comparable rate.

Nathan Wilson's picture
Nathan Wilson on August 9, 2013

is anybody really saying that population dense urban areas have to or should have to get their power locally?

Yes! One of the biggest obstacles that the renewable energy movement faces is cost escalation due to non-optimal choice of technology.  Rooftop solar has a strong lobby that is trying to convince the world that it is the best choice, and advocating pricing schemes (net-metering) that make it look more economical than other renewable options like wind and desert CSP with storage, which not only have much lower total cost to society but also are more compatible with deep reductions in fossil fuel use.

According to the US solar trade group SEIA, utility scale solar PV costs about half of what residential does.  So not only is the resource potential of rooftop tiny compared to what is available from rural imports, the cost is higher too.  Net-metering pricing schemes hide the extra cost, and pass it on to other ratepayers.

I’m not saying that future breakthroughs in energy storage won’t make desert PV a competitive option, I don’t know.  But rooftop CSP will never be big, and PV without energy storage just produces fossil fuel lock-in.

Robert Wilson's picture
Robert Wilson on August 9, 2013


Your remark that after maximising local power generation “we fall back on whatever else is needed” is false advertising. If the majority of power is coming from non-local sources how exactly are we falling back on it? It’s very bizarre language.

Nathan Wilson's picture
Nathan Wilson on August 9, 2013

I live in a the central US, an area, sometimes called the Saudi Arabia of wind, which would easily supply all of the nation’s energy (electricity and syn-fuel).

We’ve all heard the story of how France, Sweden, and Switzerland replaced nearly all of their fossil fuel-fired electricial plants with nuclear plants in the space of a few decades.  In the US today, wind power is cheaper than nuclear and coal, and wind power has widespread puplic support, yet the build rates for wind farms are tiny (only about 4% of our electricity comes from wind).  What’s more, we just had are 2nd quarter in a row of zero wind farm development (see AWEA).

Why haven’t we switched to wind?

Three reasons:

1) a preference for local energy.  Local power plants boost local economies.  As discussed in Robert’s article, nukes can be local, but large scale renewables for most people will not be.

2) wind variability and the high cost of energy storage.  This means that instead of approaching 80% of electricity in a few decades, wind is working its way toward 20% of electricity;  even if we succeed, the dispatchable energy (hydro or fossil fuel) will provide most of our electricity. [Ammonia made from off-peak wind power could be a sustainable, non-polluting, but pricey transportation fuel, but it has not been accepted yet.]

3) the environment movement burned all of their political capital fighting nuclear (emission-free) power, as well as taking fossil fuel money in the process.  Now their clean energy efforts are doomed to only work the edges, and pose no real threat to the fossil fuel industry.

With these problem in the US, what are the prospects of more densely populated countries, where wind farm siting is more problematic?  Solar is more dense, but much more costly.

Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013

“The point is that solar is not a significant source of energy generation”

– currently, i agree

“it won’t be for decades”

– I disagree based industry growth patterns and improving technology

“and may never be. The numbers prove it. “

– I certainly disagree. “Never” is an extrodinary claim and requires numbers that aproach infinity.

“Again, if I’ve made unrealistic assumptions or errors please point them out.”

– $500 trillion was extrodinarily unrealistic. $4/watt solar panels was unrealistic with current tech and certainly with future tech and as Wright’s law becomes more a factor.

German carbon output increasing with no end in sight.”

– The Germans assure us that this increase in emmissions is a blip and based on advances in both solar and energy storage tech I’m seeing almost every day, I tend to agree.  Cheap energy storage, solar fuels and artificial photosynthesis are the keys. If they are achieved, alternatives to solar will be unable to compete. All of the above are making remarkable strides almost daily.

I agree with your point about “gilding the lily”. People do tend to hype the things they prefer. Perhaps i too am guilty of it with solar. But in a like vein, keep an eye out for articles gilding nuclear’s lilly. I see them every day. Also take care with your own biases. 

You are an excellent debater.
Robert Wilson's picture
Robert Wilson on August 9, 2013


I’m not sure if anyone would call Palm Desert Wind Farm distributed energy. 

My suggestion that fossil fuels are the way we are headed is simply a reflection of reality. Not one I want to be true. Show me a country that is moving away from fossil fuels quickly. The realities are sobering.

It’s also very clear that natural gas is growing far more quickly in absolute terms than wind and solar in the US.


Randy Voges's picture
Randy Voges on August 9, 2013

Anybody know the record for comments on an Energy Collective post?  Just wondering.

Clayton Handleman's picture
Clayton Handleman on August 9, 2013

Point taken. 

Strictly speaking distributed generation would be small power sources.  Based on looking around the web a bit, it looks like there are two components to distrbitued generation, scale and proximity.  Seems like a reasonable definition would be:

Distributed generation = primary load is sufficiently proximal that the bulk of the power used never goes beyond the distribution system.


Central Power = Generation for loads at a distance.  Power from these plants must go through the transmission grid.


However, since your article was about density I bent the definition a bit. 
Treating centralized as high density power sources and low density as distributed. 


But I am in agreement with you, Westinghouse and Tesla, gotta get the generation out of the city.





Robert Bernal's picture
Robert Bernal on August 9, 2013

Depends on when we educate ourselves (that would be me) and then the public. Greater ambitions have been achieved within a decade. A molten salt nuclear plant was up and running from concept to criticallity in about seven years (way back then). I assume we would have to do it all over again,  and that it takes a few years to build factories for modularization.

But, I could be wrong about assuming that machinery could deal with high radiation within a sealed, meltdown proof unit. If so, then we need to install hundreds of thousands of square miles of concentrated solar thermal power across the world’s deserts complete with molten salt heat storage to power the world’s growing needs, electric cars (and batteries factories) and to be able to “clean up our excess CO2 mess” with even more energy needed for mineral sequestration via automated machinery or extinsive mining operations.

Robert Wilson's picture
Robert Wilson on August 9, 2013


I frankly could not care less if an individual wind farm could produce 100 W/m2. It is the average that matters here, not power densities for individual wind farms that you have both cherry picked and calculated incorrectly.

Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013

You recently stated that other than the two options above “currently, there is no other way to prevent biofry.”

I agree, but the key word there is currently.

Desserts do not only exist on land. It is also the vast deserts in our oceans that will become the source of our sustainable liquid fuels

Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013

Large scale MSR will not be proven for decades.

But hybrid CSR / PV systems are very much on the horizon

Clayton Handleman's picture
Clayton Handleman on August 9, 2013


overall what you have posted looks very interesting but it also appears to have a good deal of bias.  What jumped out immediately, many of the capacity factor robbing statistics, such as the distribution losses, are the same as for any other power source. 

As far as the HVDC goes, easy to snow folks on that one with handwaiving numbers.  You come up with 11% loss in the DC connection, is that really right.  What happens if you take all those 1% and 2% and carry them out to another decimal place or 2?

I hope that Roger Faulkner weighs in as he clearly has expertise on the HVDC transmission whereas I am new to it.

Also, you offer a .38 capacity factor.  Looking at turbines that are 5 year old designs is problematic as they will not be used in this build out.  Lets say that the .4 – .45 CF being quoted now is optimistic.  Given the rate of improvment in CF, isn’t it pretty safe that those numbers will be pretty good as the primary number in a build-out of this magnitude.  In other words, these aren’t going in next year.  And even the most wild optimist would not suggest that much of a 20% build-out is going to get very far in the next 5 years.  First they have to get those 7 HVDC lines in after all.  And we move off shore for a lot of the capacity, after all the NREL EWIT report is mostly based upon Great Plains resources but now we are looking at a likely rapid build-out of off-shore given the recent leases.  So I think you need to move your CF back to at least .43 average and you need to account for the fact that sometimes things don’t go just the way NREL predicts ; )  Already many of the projections that NREL has been cranking out have proven to be extraordinarily conservative.  For example their predictions of solar build-out.

So I think you offer a good cautionary tale as absolute worst case.  But you have a long way to go to convince me that your comments represent a likely scenario.

Lewis Perelman's picture
Lewis Perelman on August 9, 2013

Gail Tverberg has a detailed discussion of per capita energy consumption trend here:

The dominant trend has been toward rising per capita energy consumptin for a long time. This seems to be driven by countries where both population and GDP have been rising.

She usefully notes too that there is a general correlation of per capita energy consumption with employment rate.

George Stevens's picture
George Stevens on August 9, 2013


good piece but I question this part:

“Future improvements in panel production will hopefully see significant improvements in panel efficiency”

Knowing a thing or two about PV physics  and research being done in that area it is rather safe to assume ‘significant’ gains will not be made in a efficiency of commercial panels. In fact i think it is much more likely that much cheaper substrates with lower efficiencies become more economical. Doing away with glass and aluminum would go a long way to making PV more viable. PV efficiency gains will especially be modest in light of the energy density of other energy sources.

Lewis Perelman's picture
Lewis Perelman on August 9, 2013

I have been somewhat surprised at the extent of argument that Robert’s essay provoked here.

Power density is indeed important, and too often overlooked, especially by proponents of renewable energy fixes that, for the most part, are still not sufficiently cost-effective or reliable to provide a credible replacement for fossil fuels or other conventional sources.

I thought Robert did a good job of documenting at length a rather focused but significant point: Urbanized regions cannot harvest enough energy from renewable sources *locally* to meet more than a fraction of their power needs. The corollary point was that if cities are going to rely more extensively on renewable energy sources it would have to be by importing most of it from elsewhere.

One key criticism of Robert’s analysis was that he seemed not to account for forthcoming improvements in the efficiency of renewable energy production and/or of the overall economic efficiency of energy use — yielding more dollars of GDP for each BTU consumed. But until those breakthroughs actually become commercially feasible and available, it does not seem unreasonable to consider the functional implication of energy technology as it exists now or in the imminent future.

BTW, Robert: I did think you may have been a little too cheeky in reponding impatiently to comments that seemed to misconstrue your argument or that went off on unrelated tangents that you had not addressed. But given the sheer volume of comments that continue to accumulate, I can imagine why you came to feel ‘tired’. Still, polite dismissal of what may well seem like distractions — “I disagree,” “You may have missed this; please read the article again,” “Asked and answered,” or just “[nothing]” — may serve your cause better.

I look forward to seeing further anlyses of this sort from you.

Robert Wilson's picture
Robert Wilson on August 9, 2013


This may be true, but can you please back up these assertions with some evidence?

Clayton Handleman's picture
Clayton Handleman on August 10, 2013

“”is anybody really saying that population dense urban areas have to or should have to get their power locally?

And to add to your point, there is another group that HATES the idea of making the transmission infrastructure more robust.  And they seem to not be too good at math.  I participated in a thread some time ago with folks of that mindset and wish I had had access to Robert’s post at that time as it might have helped the thread see the point of adding transmission resources.  These folks were convinced it was a big conspiracy and that the need for adding transmission all about creating an excuse to build coal plants in the midwest. 

They thought that renewables at point of use would solve everything.  Not only were they unwilling or unable to come to terms with the density issue, they also did not consider the issue of intermittency and storage.

Thomas Gerke's picture
Thomas Gerke on August 9, 2013

Robert, this behaviour is exactly the point. 

The fact that you choose to ignore technological improvements and declare the average of the past to be state of the art is troubling. It undermines your credibility and your credentials as an analyst. 

You claim to discuss the future of energy, but all you did is reiterate a 5 year old book with all it’s merrits and flaws. 

You say that I cherry pick, but I simply presented you with the findings of David MacKays 4 year old analysis of UK wind farms.

Is it so difficult to accept that on the basis of the state of the art of wind turbine technology the future average will move up into the area of 4 W/m² instead of 2.2W/m² ?

You could then still turn around and claim that “it doesn’t matter anyways”, but at least you would not be obviously ignorant of reality.

Mike Barnard's picture
Mike Barnard on August 9, 2013

For context, I provided a referenced list of the 50 most commonly cited pieces of research, literature reviews, governmental reports and consultancy reports, with analysis and reliability assessment to support my perspective.

Mr Post provides a link to an article from an anti-wind webzine hosted on an anti-wind campaign site.

You be the judge.

Robert Bernal's picture
Robert Bernal on August 9, 2013

I just made up “biofry”… Which to me would mean the ruin of everything caused by excess co2

Robert Bernal's picture
Robert Bernal on August 9, 2013

I know, I should stay away from words like “only”, because it might not be so long until some crazy improvement in efficiency is achieved, but I’m sure there is an upper limit to artificial photosynthesis.

Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013

I know – good, accurate way of putting it

Bob Meinetz's picture
Bob Meinetz on August 9, 2013

The first LFTR GW could come online in five years with $10B in development money. There are materials problems that have to be dealt with and some chemical separation issues; none of them are deal breakers. The MSRE at Oak Ridge in the 1960s ran for four years, generating 8MW with a reactor vessel about the size of five bathtubs. The concept works. Right now the politics doesn’t however, and for that it helps to review some history.

In the 1960s a nascent uranium mining industry and expertise gained from the U.S. weapons program favored going down a different path, that of pressurized water reactors (PWRs), and MSRs were abandoned after Nixon fired Alvin Weinberg from his directorship of Oak Ridge. They experienced a rebirth in 2005 after an influential paper by Ralph Moir and Edward Teller which revisited the idea, even suggesting it as a powerful weapon against global warming.

In 2007 the Yucca Mountain Nuclear Waste Repository was looking like a done deal, but the state of Nevada didn’t want it. At about this time Harry Reid learned that MSR technology would not require significant storage and could actually burn up existing waste. Utah was another state that was a potential target for a repository, and so in October 2008 Reid and Utah Senator Orrin Hatch co-sponsored the Thorium Energy Independence and Security Act of 2008, allocating $250 million for MSR research. The bill was referred to the Senate Energy and Natural Resources Committee, where it died.

Why? There are several possibilities, but the most credible ones involve the committee’s chairman, Jeff Bingaman (D-NM). MSR technology would only require minimal amounts of uranium to start the reactor – after that it could run indefinitely on abundant and cheap thorium – and New Mexico has the second largest known uranium reserves in the country. The state is home to several institutions which profit from traditional uranium fuel cycle research, including Sandia and Los Alamos National Laboratories. Also, New Mexico is more friendly to waste storage than either Nevada or Utah – the Waste Isolation Pilot Plant near Carlsbad is the source of almost $630 million in annual federal funding.

But the biggest stumbling block was a new addition to the New Mexico uranium industry – URENCO. The international consortium was formed by treaty in 1971 when Britain, West Germany and the Netherlands decided for strategic and business reasons to combine their uranium enrichment programs. It became a major U.S. player in 2004, when U.S. regulators began processing an application to construct a $1.8 billion plant in New Mexico. It had strong backing from powerful state and federal officials, including Republican Pete Domenici, who was then chairman of the Senate Energy Committee. But more importantly, it had the significant backing of “Louisiana Energy Services”, or LES, an alliance that includes the big American firms Exelon, Duke and Entergy, as well as Cameco, a uranium mining company, and Westinghouse, a nuclear fuel manufacturer.

The plant in New Mexico was built, and Exelon, Duke, and Entergy all got their piece of the uranium pie. With uranium fuel assemblies selling for about $4 million apiece and thorium constituting an existential threat to the industry, the fate of the MSR remains sealed to this day. Engineers I know who have communicated directly with the Dept. of Energy have been told the legislative process is so tainted that MSRs have very little chance of being developed here in the U.S., and will very likely be developed abroad. That seems to be playing out as predicted.

Stephen Nielsen's picture
Stephen Nielsen on August 9, 2013

Yes, in order to get the HUGE number of barrels of oil like fuel (methanol, etc) that would be needed to feed the worlds energy appetite, enormous portions of these ocean desserts would have to be covered by solar conversion mats.  So much so that you could see them from space.


The geography is FREE, it would produce very nearly zero polution, it has the very possible capacity to be carbon NEGATIVE (reversing climate change), and once they were set up they would produce a constant, predictable amount of fuel for 30 or more years without price fluctuations

Randy Voges's picture
Randy Voges on August 10, 2013

I’d counter that it’s not so surprising once you realize the wider context; that in practice (not in theory) there’s a fundamental contradiction between two branches of science.  Climate scientists and their supporters say the implications of the science require us to stop burning things, whereas the energy scientist (i.e., the engineer) disagrees, given that energy demand is really about power.  Because power is the rate at which energy is produced or consumed, you look for whatever produces energy quickly, and the simplest way to do that is to burn something (or more accurately, produce heat).  Power density then becomes extremely important, because it measures the extent to which power that can be produced with the least amount of physical space.

This contradiction can be resolved by nuclear power, which has enormous power density and produces no greenhouse gases during generation.  This is why the film Pandora’s Promise resonates right now.  The trouble is that in practice, environmentalists would have to rethink their longstanding opposition to it (as well as their overall policy approach), and this cognitive dissonance produces an emotional response that generates the sort of responses we see here, as well as in Schalk’s latest post.



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