June 18, 2004
Structures In United States Cover Area Equal To Ohio

No wonder Chrissie Hynde was upset about the shopping malls covering Ohio.

WASHINGTON - If all the highways, streets, buildings, parking lots and other solid structures in the 48 contiguous United States were pieced together like a giant jigsaw puzzle, they would almost cover the state of Ohio. That is the result of a study by Christopher Elvidge of the National Oceanic and Atmospheric Administration's National Geophysical Data Center in Boulder, Colorado, who along with colleagues from several universities and agencies produced the first national map and inventory of impervious surface areas (ISA) in the United States.

As calculated by the researchers, the total impervious surface area of the 48 states and District of Columbia is approximately 112,610 square kilometers [43,480 square miles], and, for comparison, the total area of the state of Ohio is 116,534 square kilometers [44,994 square miles].

The new map is important, because impervious surface areas affect the environment The qualities of impervious materials that make them ideal for construction also create urban heat islands, by reducing heat transfer from Earth's surface to the atmosphere. The replacement of heavily vegetated areas by ISA reduces sequestration of carbon, which plants absorb from the atmosphere, Elvidge says in the 15 June issue of Eos, published by the American Geophysical Union. Both of these effects can play a role in climate change.

In watersheds, impervious surface areas alter the shape of stream channels, raise the water temperature, and sweep urban debris and pollutants into aquatic environments. These effects are measurable once ten percent of a watershed's surface area is covered by ISA, Elvidge writes. The consequences of increased ISA include fewer fish and fewer species of fish and aquatic insects, as well as a general degradation of wetlands and river valleys. The impervious surface area of the contiguous United States is already slightly larger than that of its wetlands, which is 98,460 square kilometers [38,020 square miles].

Some argue that the use of photovoltaics as a power source will require the covering of too much surface area. Well, lets start with that area, 112,610 square kilometers [43,480 square miles], which is currently covered by human structures and look at what we would need to get enough power to use photovoltaics as our sole power source.

To put those numbers in perspective recall a previous post where I reported on a calculation by Dr. David Goodstein, Vice Provost and Professor of Physics and Applied Physics at Caltech about the surface area needed to be covered by 10% efficient photovoltaics to provide enough energy for the whole world at current consumption rates.

Goodstein says that at current photovoltaic conversion efficiencies it would take an area of land 300 by 300 miles to get as much energy as we get from fossil fuels.

Solar energy will be an important component, an important part of the solution. If you want to gather enough solar energy to replace the fossil fuel that we’re burning today—and remember we’re going to need more fossil fuel in the future- using current technology, then you would have to cover something like 220,000 square kilometers with solar cells. That’s far more than all the rooftops in the country. It would be a piece of land about 300 miles on a side, which is big but not unthinkable.

Dr. Goodstein was kind enough to provide me with some of the basic facts that went into those figures. The energy that would be collected by 300 by 300 mile area is for the whole world and he's assuming a current world total fossil fuel burn of 10 TW (ten trillion watts). He's also assuming a 10% conversion efficiency for the photovoltaics.

We would need an area not quite twice the size of Ohio to get enough power for the entire human race at current rates of energy consumption. Of course, energy consumption is growing and so the area needed is going to grow. But the 10% conversion efficiency assumption is rather low. Groups at Lawrence Berkeley and Los Alamos National Laboratories are pursuing two different methods for boosting photovoltaic conversion efficiency to over 50%. The development of very high conversion efficiency photovoltaics is a matter of when not if. So the surface area that needed for collecting energy for photovoltaic electric power for the whole world is likely to be less than two Ohios.

A related interesting question is just how much of the surface areas covered by human structures will be available to be converted to solar power collectors? That depends on what types of materials can be made to be photovoltaics. If we could discover photovoltaic materials strong enough to use as road covering then roads could be made into energy collectors. While the development of such materials may be a more distant prospect there are lots of other areas covered by human activities aside from the obvious rooftoops that could be covered by solar collectors. Take, for example, train tracks. All the train weight comes down on the rails, not on most of the surface of the railroad ties or the gaps between the railroad ties. So one could imagine railroad track lengths turned into solar power collectors.

There are other ways that road and parking lot surfaces could be made more usable for photovoltaics. One obvious way would be to develop devices for moving cars to parking spaces in ways that allowed most of the surface area not be untouched by car tires. Then less a less strong photovoltaic material could cover all the areas aside from the tracks that the car moving devices used and where the car tires would be placed in parking spaces.

One obvious point about parking lots: If a parking lot is covered and the top is not itself a parking lot then the roof of the parking lot could be covered with photovoltaics. Though I'm not optimistic about the economics of covering Walmart parking lots with roofs to convert them into solar collectors. Still, advances in the development of cheaper materials might make this economically justifiable at some point in the future.

One esthetic problem with high conversion efficiency photovoltaics is that they will likely be dark in color since they will capture most of the photons that hit them. So roofs and sidings of houses covered with layered nanotube photovoltaics would be dark. Most people would probably find that acceptable for roofs but perhaps less so for sidings. One solution might be the development of less efficient photovoltaics that absorb only some colors of light. Such selective frequency absorbing photovoltaics will then allow houses to be different colors. This is not as far-fetched as it sounds. A physicist at Virginia Polytechnic Institute (sorry, no cite, this is from a couple year old memory) has argued that by controlling the spacing between nanotubes it is possible to control what light frequencies they aborb. To take this even further imagine nanotubes that are repositionable. One could perhaps send a pulsed current through them to order them to change their spacing to change their color. This might even provide a way to absorb more photons to provide more electricity during peak periods.

The lesson I'd like you to take away from this post is pretty simple: There is enough surface area already being used by humans that if we just use that surface area for photovoltaics we can get enough power for the human race's needs for many years to come.

Share |      Randall Parker, 2004 June 18 02:01 PM  Energy Solar

Paul N. said at June 18, 2004 3:30 PM:

True, we have more than enough area to house photo-voltaics. What we don't have is enough money - photovoltaics cost roughly 20 times as much per unit energy as current technologies. According to the Commission of the European Communities, "Green Paper Towards a European Strategy for the Security of Energy Supply" (2000), these are the Euro costs per kilowatt-hour of major energy production techniques:

Coal .034
GTCC .031
Nuclear .040
Wind .071
Bio-energy .048
Solar Photovoltaic .655

If Solar PV power were anywhere near realistic to implement (like wind power is) perhaps this type of discussion would be relevant. The utter disregard for the economics of the energy problem (of which the Kyoto Protocol is another sign) is really infuriating to me.

Randall Parker said at June 18, 2004 3:38 PM:


I'm quite aware of the current economics. I'm also aware that there is only approximately $30 million per year spent on basic photovoltaic materials research (see down in the comments where I add in some House conference committee report from 2001). Some day photovoltaics will be cheaper. I'd rather that day come sooner rather than later. Hence I favor much more research funding for photovoltaics.

Paul N said at June 18, 2004 4:17 PM:

There are lots of uses for photovoltaics other than wholesale energy production, so perhaps diverting research funding towards them is a good idea. I certainly prefer that to spending the big bucks on manned space missions. One thing PV has going for it is that it provides energy at the most useful time, i.e. when it's sunny and energy demand is highest. Still, what I know of the underlying physics and the economics (is a 20-fold reduction in cost likely, even imagining the rosiest advanced-materials scenarios? I'm a technological optimist but we have to be realistic) makes me feel that it's unlikely that PV will ever compete with other methods for large-scale energy production. But I'd be pleased to turn out wrong.

If we do somehow trend towards some solar-based power source, I think the economies of scale would favor putting big arrays in low land-value areas (Nevada?) over the distributed suburban model you propose. Although many would probably oppose "desecrating" the desert, and would prefer if we were surrounded by PV. I guess my point is: land is not the limiting factor, money is (and land is cheap, except in cities).

Randall Parker said at June 18, 2004 4:34 PM:


Photovoltaic costs have already fallen by two or three orders of magnitude over the last few decades. I think another couple of orders of magnitude is not impossible. The biggest problem now is the use of highly pure silicon crystals. One can make the processing of those crystals cheaper. But the starter material is so expensive that there is a real limit to how much improvements in current fabrication techniques can drive down costs. As a result of this fact a lot of researchers are exploring the use of materials that have a much greater potential to be made more cheaply.

As for locations for collectors and peak demand: If battery costs can also be lowered by orders of magnitude then that will reduce the problem of the daily sun cycle. MIT battery researcher Donald Sadoway thinks that lithium polymer batteries can be developed that are an order of magnitude higher in power per weight than lead acid batteries. If they have long half lifes they could be used to make electric cars feasible.

Also, another idea that I rarely see talked about but which I think holds a lot of promise is the use of photons to drive the artificial fixing of carbon to hydrogen to produce liquid or gaseous hydrocarbons. Liquid hydrocarbons are an especially convenient way to store energy. Liquid hydrocarbons would be made during sunny days to be used the rest of the time.

Fly said at June 18, 2004 7:43 PM:

“Also, another idea that I rarely see talked about but which I think holds a lot of promise is the use of photons to drive the artificial fixing of carbon to hydrogen to produce liquid or gaseous hydrocarbons. Liquid hydrocarbons are an especially convenient way to store energy. Liquid hydrocarbons would be made during sunny days to be used the rest of the time.”

This is an idea I find promising. Craig Ventor is working on an artificial cell specialized for this purpose. Imagine a genitically engineered fuel farm plant floating in the ocean “desert” regions that only required a little iron fertilizer. Engineer the plants to accumulate the fuel in bladders that could be tapped through vines. Well I can dream, can’t I?

gmoke said at June 19, 2004 9:36 PM:

According to what I've read, the electricity that comes out of the socket in your house is about a third of the electricity that's generated. One third is lost through transmission and another third is lost in generation. If we have PV electricity on our roofs and all over our neighborhoods then transmission losses will be greatly reduced and the professor's numbers are as much as one third higher than they have to be.

High efficiency appliances and lighting are other ways to reduce loads so that the generation capacity necessary is lessened and thus PV conversion becomes more affordable.

Bob Badour said at June 22, 2004 7:43 AM:


I would really be surprised if it is as much as a third. Assuming matched impedance from the generation to the transmission (a good assumption), only half the energy will get transmitted. Assumming matched impedance from the transmission to the electric device (not necessarily a bad assumption), only half the energy transmitted will get used.

That's a very simple model. It doesn't take into account losses at step-up and step-down transformers etc.

peter said at February 7, 2006 10:05 AM:

Dear All,

A few points about solar / renewables...
1. Cost of production - what one has to consider is that manufacturing solar panels for such massive projects would dramatically reduce costs, simply on a basis of economies of scale. I don't know how old some of these comments are (I'm posting in Feb 2006) but we've already seen drastic reductions in cost over the last couple of years (sources including gov't papers, energy companies themselves, and so on).
2. Land area required - according to the NREL (National Resource Environment Laboratory, I think), the land area of the US required for solar panels at 'x' efficiency (don't have the number handy) to generate 100% of US 2004 electricty demand would be roughly 2% of the land area of the US, roughly 1/2 of Nevada. I'm glad to see the calculation of the land area covered in structures above as I was looking for that. But a few things to keep in mind is how much land is already covered in the southwest (best generating area), including California...such as rooftops and parking lots that could be covered (above the cars) with solar panels, and that used for testing grounds or old military bases? The gov't is talking about giving over these lands (as brown to black sites, environmentally) to oil companies (like the one I work for) for refineries to help fill the current 'gap' in refining capability for the US. You could imagine that a lot of that land would be viable as areas for solar generation (agreed that transmission is an issue, though storage in fuels cells on site could help...I'm not a physicist, so I defer on that one!).
3. Cost - a few back of an envelope calculations come out around $100 billion to build such a 'monster' solar generation capacity, assuming the gov't pays for it outright and doesn't recover any of the cost via charging for the electricity generated (hardly likely). When looking at the revenue that the electricity could generate, you'd see that the payback period from a pure DCF (discounted cash flow) perspective is not collosal...and that doesn't include the environmental savings, national security benefit, etc. Agreed that it is an enormous number, but when put in to context (Iraq / Afghanistan have already cost the US taxpayer over $150 billion in INCREMENTAL military spending, above and beyond the currently proposed $420billion + per year. Hurricane Katrina relief 'promised' by Bush is circa $85 billion (according to his 2006 State of the Union address). It's not a million miles away from the National Missle Defense pork-barrel project that Bush has been pushing through. Etc, etc, etc...just helps put in to context how achievable such a project really is.
4. Efficiencies in usage - agree that this is the 'no brainer' of energy independence. However, one thing to keep in mind is that, as we've improved energy efficiency of cars, appliances, homes, etc., we have simply taken that 'conversation dividend' and 'reinvested' in more energy use. In other words, refrigerators are signifantly more efficient than in the 70s, now there are just more of them, and they're bigger. Car engines have become more efficient than before, but now we just make them bigger and more powerful with the savings we've made. The average size of a US home has gone through the roof over the last 20 years as it's easier to heat / cool them, etc. Conversation is going to be key, but what to do with the 'savings' may also be an issue for regulation. Just a thought.
5. Alternative Energy cocktail - I've seen similar estimates for the capacity of wind power in the midwest to generate all of the US electricty demand, and one might wonder whether a cocktail of these resources (as well as geothermal, tidal, etc) could be combined to not only generate the electricty we need (as well as continuing growth), but also enough to perform electrolysis of water (or other materials) for the production of hydrogen to produce liquid fuels for transport. Does anyone know how much energy it would take to produce enough hydrogen (from water...as coal is HIGHLY problematic, as are natural gas and other fossil fuels) to replace all ground transport fuels in the US? I've never seen anything on this...

Just some general thoughts that I'd be curious to hear your views on.
Oh, and Kyoto...if the US were part of it, or some other similar scheme, and did do the above in terms of investing in massive renewable schemes, the US could then starting selling back 'carbon credits' to the rest of the world. As electricty generation accounts for something like 40% of our carbon emissions, the savings would be enormous and we'd go from a net buyer of emissions credit to the massive provider of them...

Randall Parker said at February 7, 2006 4:23 PM:


Your post would be a lot more helpful if you included the numbers you used for your starting point for calculations and also links to where you got the numbers to start with.

Your $100 billion figure does not include what the resulting generating capacity would be or the average output and percent utilization. So this is a useless figure.

Bruce Wayne Henion said at September 16, 2006 9:25 PM:

How many acres would it take if 400 areas = 64 megawatts broken down by industry, i.e., coal, nuclear, oil plus solar cell contribution, moderate windmill, etc.

The largest PV array in the world - 400-acres = 64 megawatts

Morning Edition, August 30, 2006 • When the price of oil is high, talk turns to alternative forms of energy, including wind, biofuels and solar. One kind of solar energy isn't getting much publicity. But solar thermal power is quietly becoming a significant source of electricity in the Southwest.

In the desert south of Las Vegas, crews working on a project called Nevada Solar One are assembling a parabolic trough of curved mirrors connected in a huge array.

At the center, a closed-loop tube will be filled with oil that will be heated by the sun. The hot oil will flow around the 400-acre project and into a building where it will turn water into steam. It, in turn, will turn a steam turbine, which will make electricity.

Solar PV, or photovoltaics -- panels on roofs -- are what most people think of when they think of solar power. The largest PV array in the world, located in Germany, produces 10 megawatts of electricity. But Nevada Solar One will produce 64 megawatts -- enough to power 40,000 homes in the Las Vegas area during the hottest part of the day.





Bruce Wayne Henion said at September 16, 2006 10:51 PM:

How many acres would it take if 400 areas = 64 megawatts broken down by industry, i.e., coal, nuclear, oil plus solar cell contribution, moderate windmill, etc. The total US capacity is 9971 megawatts divided by 64 = 155.80 x 400 acres = 62,320 acres. Without knowing all energy production by source or fuel, the exact acres necessary utilizing PV array Renewable Energy Technologies is unknown, but it makes you stop and think for a minute.

Bruce Wayne Henion said at September 17, 2006 9:12 PM:

Maybe it’s time to start setting the example to Iran by illuminating the fact, that as a nation of “We The People, By The People”, that we ourselves don’t need to construct new Nuclear Energy Power Plants, replacing 30-year old Plants with PV Arrays, Trough Solar Systems, Solar Towers/Thermal Solar Powers, Dish/Engine Concentrating Solar Power Systems, Thermal Solar Collectors for your House and other Renewable Energy Technologies just waiting to expand exploitation, to include Ocean Geo Thermal to Wind Generation to Hydrogen Fuel Cells etc. There is absolutely no need for further Nuclear Energy Power Plants any where in the world yet many Nuclear Power Plants are on the drawing board in various countries presently using Nuclear Energy.

With only one out of ten shipping containers actually searched entering the U. S. and our boarders insecure between Mexico, Canada and the U. S., it’s inevitable that a Dirty Bomb, Chemical or Biological weapon of mass destruction will end up on our sovereign soil. A 50 gallon drum of MTBE dropped in one of our Lakes or reservoirs will not be environmentally sound. Yet MTBE is still used in gasoline.

The Iran President doesn’t want to destroy Jerusalem, as there are holy places sacred to all Muslims, just the Jewish people, so when he says a Nuclear Bomb is old technology, you better believe it and once those shipments to Russia of thermally hot and highly radioactive pollutants involved in nuclear energy from spent uranium fuel or reprocess this fuel and or sludge's originated as a result of the manufacturing of specialty metals and chemicals, used in energy production, chemical and mineral processing, aerospace, medical, research and consumer products are high jacked or for that matter, if Iran prevails and begins Uranium enrichment, soon after they will have their Dirty Bomb ingredients, Nuclear Fuel, etc. yet as a nation were some what divided on what to do. It is clear to me, that if Iraq under Saddam with Uranium enrichment and Nuclear Fuel, nuclear energy was a threat, even though none was found, surely another tyrant with the goals of his and his followers in mind need not be allowed access to technologies allowing for Uranium enrichment and Nuclear Fuel.

While we here at home suggest that our President should have open discussions with Iran’s President, I would ask to what end? The Iran’s President has made his case pretty clear. He’s upset Israel exist and England and the U. S. is his chief focus as he sees us as aggressors determined to establish democracy in the Middle East and from the beginning until now, without the support of England and the U. S. in his view, the State of Israel could not have evolved into the Country it is now. Amazingly Germany has agreed to provide more Nuclear Submarines to Israel, yet Iran only shouts “Death to Israel, Death to America”, while France was recently reunited with terrorism and the world stands by in total disregard for overall world safety as if countries in various regions are setting idle, waiting to see the resolve of the U. S. weaken, hoping diversity within our own democratic system will challenge our present Administration’s policies; which by the way will happen if we don’t fight the war on terror with all our might like Iran is willing to do for their holly crusade.

I have struggled with the notion of appeasement and it is beyond me why our country would even consider working with Iran’s Nuclear Energy Programs provided they allow for International Atomic Energy Agency Inspectors to make random inspections and transport the spent fuel to Russia.

If we can build a 64 Megawatt PV Array, then so can Iran, so why do they need Nuclear Energy Power Plants to generate electricity? They have allot of sun, deserts and wind, although they do have pretty tough san storms, so they might have to design a cover for the system to be placed on tracks that can slide over the PV Array, powered by engines above the wheels, the cover like a long train setting idle on another set of tracks until needed, entering through a removal section.

Technologies are awaiting exploitation, but we must marry ourselves to a better and brighter future through the use of available Renewable Energy Technologies, alternate methods of exploiting non renewable fossil fuels and better improved devices and products requiring less energy to run such as LED lighting and the like rather then florescent.

If were to continue relying on oil as a bases for our energy requirements domestically, then pollutants in our atmosphere will continue to increase and our reliance on Middle Eat Oil will find our nation continually embroiled in the affairs of other nations or seeking to exploit every drop of oil within the United States Of America. Alaska up for crabs I guess. With underwater thermal activity discovered under the Ice Caps and in the deep Atlantic, and many other areas of oceans and seas throughout the world, the Cascade Subduction Zone, Pacific Ring of Fire, Volcanic activity, recent devastating earthquakes and Tsunamis, it’s time to rethink exploitation of oil in areas that are sensitive for various reasons. With these worrisome events lurking in the future, we must now, like generations before contemplate a nuclear threat.



Bruce Henion said at September 19, 2006 4:07 PM:

64 Megawatt PV Array

Great technology but out to protect it from mother nature.

One idea:

Design a cover for the system to be placed on tracks that can slide over the PV Array, powered by engines above the wheels, the cover like a long train setting idle on another set of tracks until needed, entering through a removal section.


Unless protected, it's not as practical as even I dream it could be.

Then there’s NUTS with guns. 400-acre facility. How far can a sniper shoot?

Should it have a slide on roof for hail storms, although Nevada is pretty safe, there is always lighting storms. We can't put all our eggs in one basket, can we now?

captbilly said at November 20, 2008 4:53 PM:

This thread is one of the most interesting I have seen in a long time. I am a 50 year old physicist and engineer (Columbia) and I ran an alternative energy company for a few years befor Reagan pulled all the money out. It seems that we may be finally ready to do some serious work on alternate energy sources, although the recent decrease in oil prices is causing some to lose their memory again.

I heard someone on NPR pushing Gen 4 nuclear reactors as the solution and I can only pray that we don't go down that road. He argued that at present efficiency it would take 30,000 mi sq. of solar collectors to produce America's energy needs, and therefor it was totally impractical. First of all even ignoring for the time being the validity of his numbers it would appear that we already have more than that area of the US covered in structures. Secondly many people forget that much of the energy use in the US (as well as other countries) is for space heating and cooling as well as water heating. I saw some numbers on the DOE site that showed that about 75% of energy used in homes is used for simple heat and cooling. Industry and commercial buildings also use more low quality heat than electricity. Modern solar thermal collector designs that I (and others) are working on can achieve yearly efficiences of better than 50%, even in cold climates.

The yearly energy cost of heating homes in the US is over $200,000,000,000. This does not include the cost of installing and servicing the heating equipment, just the energy burned. I estimate that an average home could be heated and cooled 80% by solar(including hot water) for about $10,000 (if produced in very large numbers). Lifespan of a good system would be in the 50 year range (with some maintenance along the way) so energy cost would be quite low. THere are about 120,000,000 homes in the US so the total cost to solar heat and cool all of them would be 2.4 trillion dollars. That sounds like a huge number but it is about the same as the Iraq war will ultimately cost the US and about the same as what the financial bailout will probably cost. Imagine being able to save the equivalent of 4-5 billion barrels of oil per year, using simple technology. And keep in mind how much carbon would not be released as a result of this energy (over a trillion pounds).

By the way, I took a detour in life and flew B-52 bombers for 6 years, and I have contemplated the destruction that would result in just a single nuclear weapon in a major city. The idea of ever more massive amounts of nuclear materials (bomb grade or just highly radioactive) floating around as a result of massive numbers of nuclear power plants is terrifying.

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