Pipe Dream or Viable Energy?

I’m a proponent of alternate energy sources, mostly to get us disengaged from Middle East Oil. Often there are schemes floated to produce alternate energy that just don’t balance out when you sum up the energy in versus energy out. Most corn based biofuel processes fall under that category now, so does nuclear fusion, but that may change someday.

So when something dropped in my inbox today called “cold energy” I was immediately skeptical, because it made me think of “cold fusion”, which was a hoax. This one however may be different and it’s concept is simplicity itself.

It’s another form of wind power, but this one has to do with high and low pressure systems on a synoptic scale. Basically the idea is to build open ended pipes between areas that often have strong pressure gradients, such as the Midwest. This map below gives you and idea of how High and Low pressure centers are often separated in the USA.


The pressure difference between the two pressure systems would push air down the pipe, and drive a turbine. The turbine would have reversible pitch blades to capture airflow no matter which direction the High to Low pressure gradient was.

A company called Cold Energy LLC is proposing building just such a system. The hold a patent on the concept, and call it Atmospheric Cold Megawatts (ACM). Here is some descriptive text from their website:

Utilizing a revolutionary new process, the ACM technology is capable of generating power at the scale of coal and hydro plants with virtually no environmental externalities. By leveraging the differences in atmospheric pressure at geographically separated locations, wind speeds approaching sonic levels can be generated within ACM pipelines. This energy may then be converted to a variety of desired forms using existing technology.

No fuel is required or consumed to produce the power. No pollutants are introduced into the atmosphere as the result of the generation process. The cost per KWh is a fraction of traditional (and alternative) generation methods. Because there are few moving parts, maintenance costs are minimal and the projected lifespan of installations is considerably longer than any other generation method.

They claim they can produce power at a cost of .03 to 1 cents per kilowatt/hour. Of course the advantages are huge, with there being no environmental impact other than long pipes either above or below ground. Here is how they say it would work out:

ACM is a system for the generation of energy based upon differences in the atmospheric pressure at geographically spaced sites, and comprises at least one long conduit – in the order of many miles long. In operation, the air flow in the conduit will accelerate to a high velocity wind without the consumption of any materials and without the use of any mechanical moving parts. A power converter, such as a wind turbine, in the conduit converts the high wind velocity generated by even small pressure differences into energy of any desired type.

The opposite open ends of the conduit are located at geographically spaced sites, selected on the basis of historical information indicating a useful difference in barometric pressure. A plurality of conduits, each having open ends in different geographically spaced sites, may be interconnected to maximize the existing pressure differences, and will produce higher and more consistent levels of energy production. The ACM conduit configuration of the invention can transform even barometric pressure differences in the order of one tenth pound per square inch into wind velocities in the sonic range.

I think its totally tubular. ;-) But will it work?

UPDATE: It’s a pipe dream, see reader comments, particularly Brendans.


46 thoughts on “Pipe Dream or Viable Energy?

  1. Just a couple of questions:

    How will the wind accelerate?
    How will the resistance in such long pipes be overcome?
    How do they stop the air from taking the way of the least resistance (open air) and to choose the way of more resistance (the pipes)?
    Why is this principle not used in gas-pipes, why need gas-pipes pumping stations to keep the gas flowing?

  2. I may be a bit out of my depth but I would guess that the pressure differential would drop across the entire length of the pipe and the difference at a particular point (where a turbine might be located) would be negligible.
    There aint no such thing as a free lunch.

  3. Do the calculations to determine how much energy it takes to move any fluid through a long tube. This is the same limitation the sea water temperature difference promoters ran into when they tried to build a practical system. The frictional losses are significant, to say the least.

    Here is a simple thought experiment: How much horsepower does it take to get sonic wind speeds in the short length of a wind tunnel?

  4. Wow, that does sound cool.

    Would be great to see some small-scale experiments. I would think something could be setup with a pressure tank and room pressure for proof of concept.

  5. Instead of large pipes that are hundreds of miles long and require covering or disturbing vast tracts of land, how about a series of very large poles to which large blades and an energy converter are affixed? They could be placed in remote or very windy areas where pressure differentials are irrelevant.

    Oh, wait, I think someone may have already tried that successfully. Of course, the energy produced doesn’t really cover the cost of building and maintaining those… shall we call them windmills… but they have worked for centuries for various applications.

    Another idea that has also worked are generators using tidal/wave power. Some think that you can generate electricity from solar power as well.

    The point is, the wind is free, the waves are free, and the sun is free, so why not use those free lunches, too? “Watt’s up with that?”

  6. Assuming a 10 meter (diameter) pipe and a 30 mph windspeed through the pipe the theoretical power available would be about 115.5 kw.

    Power varies with the cube of speed and square of the pipe diameter.

    Subtract from that the inefficiency of the turbine/generator and considerable friction losses from moving the air through a very long pipe.

  7. I would think it would be testable with a length of a natural gas pipeline that already exists. Run it during summer when usage is low. I’m leaning toward frictional loses being the spoiler.

  8. No experiments are necessary. This is a simple bernoulli problem. Not wanting to take a whole lot of time (and then spending way too much time), I used an online calculator. I assumed incompressible fluid and a steel pipe. Forget the 1 m pipe diameter, I used 10 to minimize pressure drops (the 1 m pipe diameter would get you about 7 km…). Try it yourself. I used the calculator at
    (Beware, you only have a few opportunities to use it before they want you to sign up) My inputs are 102.4 kPa, velocity, 2 m/s, D 10 m, pipe roughness, 0.0005 m/m, pipe length ~ 675 km, no elevation gain, fluid density 1.2 kg/m^3 and fluid viscosity 0.0182 cP. Your output is 99.6 kPa… If your pressure at point b is less than 99.6, you have a physics problem of trying to get water to flow uphill. This isn’t exact – I should have iterated around the mass flow rate, or changed the pipe diameter (I got the approximate intial velocity from the simple form of Bernoulli – for air it will change as you add pressure drop and changes in property along the line), but its good enough to show that you won’t get hardly any movement. I used your map, and found the great circle distance between austin, tx/kansas city, mo and chicago. 675 km is somewhere in between. Now try to put a turbine to get useful work out of it. Forget it. Anthony – feel free to email me about things like this if you have questions in the future…

  9. Thanks Brendan. That’s why I made the title “Pipe Dream or Viable Energy”. This had a flavor on par with a perpetual motion machine.

    No free lunch here, I wonder how they got this one past the patent office?

  10. Anthony –
    I forgot to mention. I love your site and what you are doing… I keep meaning to try to check out the Livermore site for you, but don’t have a good gps and haven’t found someone to borrow a good one from yet. Keep up the good work!

  11. One can patent practically anything in this country. The folks at the USPTO don’t check to see if the device works, their only concern is if it violates an existing patent. You could patent custom-fit left nostril inhalers if you wanted (unless someone already has).

    Regarding ocean thermal gradient systems: I remember reading (in an article by Jerry Pournelle about 25 years ago) about a prototype that generated a few hundred kilowatts off Puerto Rico about 80 years ago. The problem they had was corrosion, not friction losses.

  12. I think about it like this. There is an even greater pressure gradient between air two miles straight up and at sea level, so we just make a tower tube with intake nozzles at the ground floor, and the air should rush in at sonic speed then spill out of the top in the rarified upper atmosphere.
    Except for gravity.

  13. What about a solar chimney would it work? I first saw it in a SF book but seems like the idea would work.

    the start of chapter 2

    Carnifex-ARC by Tom Kratman – Baen Books – Chapter 2

    A solar chimney dominated the island’s skyline, rising several hundred meters above its highest elevation, the otherwise unnamed Hill 287. From the base of that chimney, a thick tube of reinforced concrete, ran an extension northward, toward the equator, along the side of the hill. This ended at one of the three largest greenhouses on the planet, the other two also being the foundations for solar chimneys. Fixed mirrors, sighted to reflect the maximum amount of sunlight into the greenhouse with the least expense and for the least effort, sparkled on the hillside.

    The greenhouse contained air heated by the local sun. The air escaped along the tube that ran along the ground and up the hill before making its final exit at the top of the chimney. Along the way, the wind thus created turned turbines that produced the electricity needed for the island’s twenty-one thousand legionary personnel and their families plus those of the thirteen thousand legionaries deployed to the war. Intended, eventually, to provide electricity almost twice that many, the chimney operated at less than half capacity.

  14. Cold fusion wasn’t a hoax. The Fleischmann/Pons experiment has been replicated hundreds of times. Whether there is a viable energy source there is anyone’s guess, but the possibility that there might be sent the crowd for whom cheap, plentiful, pollution and CO2 free energy would be a disaster into denial overdrive.

  15. They are trying to get a chimney going in austrailia but the cost of the structure makes its prospects grim.

  16. I am reminded of my youth in the Los Angeles basin plagued by smog–blamed at different times on the back-yard incinerators (which turned out to have been a source of life-saving activated charcoal, some said; the butadiene and other refineries, the Fontana steel mill, ….

    Among the solutions offered were tunnels through the mountains or fans atop them to blow the crude into the desert.

    Must have worked, it seems to be smog all the way across some days.

  17. Rube Goldberg would be proud.
    And as for America’s “dependence” on Arab oil, it is the dammed environmentalists keeping on us that path by blocking ANWR oil .

  18. Well how do you like that?

    Free lunch is back in play fellas.

    So the Spanish heat tower proves the theory, now lets refine it a bit and adapt it to the modern world.

    As Anthony has been steadily pointing out, NOAA and GISS are mostly measuring urban heat islands. We don’t need a fancy collection grid to heat the city air for a contraption such as this if it is set in an urban area.
    Suppose instead of just an ac/heating plelum, elevators, electrical bus, and plumbing;that all skyscrapers included their own heat tower as a core. All it needs is an unobstructed intake. Say maybe the floor just above the parking.

  19. They did this experiment on TV the other day in Japan where they attached a vacuum cleaner on one end of a long hose and suck a tissue paper. The goal was to find out at what length the suction of the vacuum cleaner loose out to friction. They also had three college professors theorize the limit via calculation.

    The estimate by the college professors were anywhere from 80m to about 900m.

    The result. At 2km they ran out of hose and the vacuum cleaner was still able to pull the tissue through the hose. The only “problem” was that longer the hose, longer it was taking for the suction to build up enough to make the draw on the tissue. At 2Km I believe it took almost a minute before sufficient pull was generated to suck in the tissue.

    From looking at this experiment, I think the biggest problem for this scheme would be the duration of time before sufficient pressure difference is built up and time it takes to create sufficient pull. It may take hours at the distance we are looking at…. By which time, the difference pressure may have reversed itself. Not a very reliable generator of power.

  20. The last question isn’t one about Bernoulli – its a matter of seal and your pump. If you have perfect seal, a pump will be able to create a “vacuum” on just about anything – minus the efficiency of the pump. (There are different levels of seals on pumps as well, and pumps reach a point where the removed gas is equal to the amount of gas that slips back in – real vacuum pumps for lab environments are very expensive, because of the engineering…) The professors probably tried to use Bernoulli’s eqn, but its the wrong application for this environment.

    The thermal tower may work – but its likely a matter of economics. There are lots of energy systems that one can build, but if they can’t meet marginal rate of return, then forget it. AS an example, wave based power systems (mentioned above) could possibly work in some of the more intense wave environments, but here its a matter of economics and durability – building something that meets the required roi and survives 20-40 years in one of the most brutal environments on the planet (the wild ocean) is pretty daunting. Check out http://www.oceanpd.com that has probably the best of these systems. Great for Europe, somewhat good in environments North of SF Bay and North of MA – there’s not enough wave action in the summer months when demand is high to justify (at current prices) a system like this south of those points…

  21. Oops. Missed the OTEC reference (the first one stated to be off Puerto Rico). Destroyed by a storm was probably a good excuse. DOE had an OTEC lab in HI in the 80’s that couldn’t, as I mentioned, meet ROI. The sheer cost of such systems, the thermal efficiency is oonly 8% – (299 K -277 K)/277 K is really bad, and that doesn’t take into account fricition losses (larger with water than air) and conversion losses (turning ke into electrical). DOE gave up on this as a bad job after spending oodles of money on it. I heard there was a new group out there trying again, using a different fluid, but they still can’t get around the efficiency issue, which is mud. I’d put OTEC in the more than pipe dreams, less than reality category.

  22. Hello,

    You really don’t need to do any calculations to understand the “pipe” idea.

    The atmosphere is nothing but a pipe of very large diameter. The air moves through the atmosphere – or pipe via the pressure differences mentioned in the article.

    Having a pipe of some diameter would decrease the air flow already available in the atmosphere – since its diameter is smaller than the atmosphere’s “diameter”. Thus you are bound to get a _LOT_ smaller velocity of air through the pipe than you already get via wind. And wind speed is fairly slow, which is why windmills have to be 50m in diameter to be cost effective.


  23. One idea I have had for many years would be to bore a hole through a West Coast mountain such as, say, one of the coastal mountains. We often get strong winds either offshore in the fall or onshore in the winter. Such a tunnel could be constricted in the center with a turbine that would work in either wind direction.

    In addition to providing wind, it would as a side benefit transport some unknown quantity of water inland as air would not be forced up over the mountain where it would drop its water content when the wind is onshore.

    Such a tunnel could also be used to carry infrastructure such as power, water, and data communications. An area such as San Jose to the coast near Capitola or from, say, Lake Elsinoire to San Juan Capistrano might be another place to try.

    I wouldn’t place transportation infrastructure in the tunnel. Its primary purpose would be energy production.

  24. in other words, it could work in areas that have a huge pressure difference over a short distance such as through a single mountain in California. Put one though that huge mountain in San Bernardino and you would not only get a huge amount of wind but it would clear out a lot of the air pollution that stacks up against that mountain too. Energy, water, cleaner air. Still probably too expensive to drill through that mountain, though.

  25. Crosspatch,
    Not far east of me is a place that nature made a “tunnel” through a mountain range. It’s called the Columbia River Gorge. East side is predominately high pressure; west side typically low.
    Makes for some great wind-surfing.
    Also makes for bizarre winter effects when the Canadian arctic air meets the wet Pacific air at the mouth.
    However, the wind direction isn’t constant. A forecast of “east AND west 40 mph winds” is not unusual.
    The trees look very confused.

  26. We have such a tunnel. Its called the Calducutt, and its a mile and half bore from the cool oakland side to the warm Contra Costa County side. It still needs fans to ventilate is.

    The problem with delta P in atmospheric pressure is that it depends on very low frictional pressure drop to work. Like or not, our best, most economical pressure driven power source is windmills, and the best areas are already being harvested. Building tunnels is an incredibly expensive engineering project, and you’ll never recover ROI, let alone have enough delta P to run an economically based system.

    Here are the technologies that will make a difference.

    Nuclear – this is the big boy, since if you make a nuclear plant that you can reprocess fuel, you reduce your wast by 90-95% – basically eliminating the need for a Yucca Mt (Yucca is designed to hold waste for 10k years – and if you reprocess fuel you only have to hold the waste for a few hundred… eliminating the need for a lot of the protections built into Yucca…) And one nuclear plant creates a very compact energy source that is easy to manage. Look for more nucs to come on line soon, especially the melt down proof pebble bed reactor types…

    Wind – this is rapidly being used. Most of the high quality windsites will soon be used up…

    Ocean wave – this is a future resource of great potential, but the engineering is still daunting.

    Geothermal – if we could find a way to creat good fracture zones, this would be a winner – but we don’t know how to do that, and so were stuck with the few good geothermal areas we have.

    Solar thermal – this is the most cost efficient of the thermal systems, but tends to get less attention because you need a big system to make it cost effective.

    Solar electric – these systems can be small, but are all really expensive. They survive through state subsidies… If nano based solar electric ever comes to fruition, this might be a winner…

    I didn’t mention hydro, since almost all the good hydro spots have been used – much like the best wind spots soon will be…

    I may have missed a few, but these are our best new generation type techs… Conservation and new efficiency can get us there as well, but don’t ask a new developing country to use them – when you produce no power, conservation doesn’t really help, and most of the new co2 will be coming from developing countries as there economies try to come up to speed with ours… (for example, China, India…)

  27. I got a C in Algebra 45 years ago and never took physics in high school or college, so this all sounded amazingly cool to me. I emailed the link to this post to a friend who has a much more scientific mind than I do, before all you math and physics whizzes weighed in. He concurred on the math, but sent me a link to this equally fascinating concept.

  28. Brendan

    tThere is a natural gradient between mountaintop air and valley air which doesn’t fluxuate or change direction. Most of the cost of the Spanish thermal tower would be due to making the thing structural and safely free standing.
    Instead of that we would run the pipe on the ground up the side of a mountain. It doesn’t have to be free standing or support it’s own weight so this gives us leeway over the materials used in the construction. It could be plastic, concrete, treated paper – whatever is most cost effective and weather survivable.
    And there are large areas particularly along the valley side of the California Coastal Range where the hill country is contaminated by asbestos, the EPA won’t approve the areas for human use or habitation. It’s just sitting there unused and unusable.
    Perfect for a heat pipe electrical generating plant.
    This heatpipe windmill design removes the hippy/greenpeace/save the butterflies lobby because the birds won’t be killed in the prop.

  29. Hi Brendan,

    As a mechanical engineer I appreciate you bringing folks back to reality with some of these wacky ideas. And thanks too for summarizing the most viable alternative energy sources we have at present. I am reminded that most of the ideas I see floated today are not new – in fact we have been researching alternative energy in this country for the better part of 30+ years! How long has NREL been around? Having said that, the fruits of that research have been improvements in materials and processes to the point that these technologies may now be economically viable.

    Unfortunately, we will be seeing more of these wacky ideas as the global warming industry continues the panic the public into funding these things via government subsidies or a “carbon tax”. And there appears to be no end to the scare tactics the global warming industry will employ. Just today I saw a “news” article on how someone is now blaming global warming for the “reduced intensity” of the fall colors! Well, I live in NH and the colors here are quite beautiful this year – very intense reds on the maple leaves.

  30. Heh, I can see the marketing campaign now:

    “To understand how this works, just remember your childhood summer days playing with the hose in the yard… What happens when you make a smaller hole by nearly plugging the hose with your thumb…. The water spurts out ten times faster and farther! Our technology works on the same scientific principles…by focusing a lot of wind through a very small hole, it just gets faster and faster!”

    Lol….. nevermind the disparity that the water in the hose has nowhere else to go, and the air has a billion better pathways, and unlike the water, the air could just reverse direction if it had to (ie by hitting a ‘plug’, it would rather turn around than exert enough pressure to get through)

  31. I’ve not worked out the math for thermal towers – its probably alright, The potential problem is that to get really good thermal gradients, you need a mirror array, and it may be better to use your solar mirrors to run a solar thermal plant. Like I said, I haven’t worked that math (and my background is thermal systems, so I could – but I’ve got a new job and that’s my priority…) I will say that a solar thermal system, like the planned solar 3, is much more land efficient – and by land efficient, I mean it not only is cheaper land wise, but gets more solar energy than the solar tower. By the way, covering the amount of land required for a 200 MW, 25,000 acre site, may not be a land cost problem, but it will be a huge environmental impact problem – i.e., many dead plants and desert tortaises (tongue in cheek, but not by much…). That’s 40 sq mile for a 250 MW site. Here’s the more realistic approach.


    Thanks for the kind words from Frank and the nice update by Mr. Watt.

    Don’t get disallusioned! Energy is a function of what the public will pay. There is a lot of potential energy out there. We will not run out – but we may have rough patches. What we will do is transition in such a way that our overall costs are minimized (I don’t believe solar electric is in that catagory, by the way – too damn expensive – check out this site… http://www.solarbuzz.com/SolarPrices.htm – By the way, don’t confuse their “Solar 3” with what I mentioned above – its a catagory…) Solar electric is mind boggling expensive…

    Solar thermal is much better from a cost perspective. That’s why you aren’t seeing plans for a 4500 acre solar electic site…

  32. The Caldecott tunnels are very near the summit and are only around 3500 feet long so they wouldn’t be a good example for what I am talking about. And while there are ventilation fans, there are times (probably today, for example) when the wind can be fairly strong (in the neighborhood of 50mph). But to get an idea of what I am talking about you would need to get on a boat and go out to the entrance of the Golden Gate. The air is only very rarely calm there.

    A tunnel from the Santa Cruz coast to the Santa Clara valley would pull in a large amount of coastal air during Summer when the valley temperatures would rise during the day causing a thermal low. Cooler (and wetter) air would then be pulled in through the tunnel from the coast. At night in Summer the flow would probably reverse by morning with cold air in the valley blowing toward the coast in a sort of “offshore” breeze.

    Two other side benefits would be an increase in moisture in the valley and a ventilation mechanism for air to circulate during a temperature inversion that would otherwise cap stagnant air in the valley. It wouldn’t even need to be one continuous tunnel, it could be a series of tunnels through the various ridges between the coast and the valley.

    To get an idea of what I mean, have a look some time in the evening driving along I-280 South of San Francisco at around SR92. The fog just crests the hills. If there were a tunnel through that mountain to the other side, Crystal Spring Reservoir might be covered a good bit of the time with a layer of fog that would cut down on evaporation saving a good amount of water. I think there could be lots of uses for strategically placed tunnels to get air to flow in certain ways with energy production being only one benefit. But I would say that the notion of long distance pipes is silly because the atmosphere already acts as a pipe connecting the two places together. It only works where the pipe provides a path that would otherwise be blocked, like with several thousand feet of mountain in the way. Then a short tunnel could have a great impact.

  33. It is sort of Rube Goldberg. But it’s not a perpetual engine machine. It’s solar power harnessed with minimum processing.

  34. This is the sort of mindless drivel that will occupy the minds of those who believe in free lunches. None of them want to solve the energy problem. If they did, they’d push for a couple of hundred new nuclear reactors and we’d all have cheaper energy.
    Instead, they’d rather chase fantasies that have no chance of working. It’s a spiritual problem. They hate us, and want us to pay ever more for ever less.

  35. Since no one else has yet, I’d just like to point out that reduction is definately a viable mitigating factor and can help immensly to get us through the rough patches. If you can afford it, it’s time to pony up and buy, at a minimum, compact flourescent lights (there are small amounts of mercury in them so please dispose of burnt bulbs accordingly), and if you have have the means, LED lighting is the way to go.
    Go Conservation!!!

  36. How about a “gas Turbine” that uses low pressure air heated by the sun. My original thought was a big, sealed plastic tent set up on a lava field (lots of those in Hawaii – lots of sun too). A fan/compressor would blow cool air in and then the heated air would exhaust through a turbine that would hopefully produce more power than it took to run the compressor. If it works at high temps it ought to work at lower temps – just a lower power density.

  37. Pivnic –
    I did mention conservation. But even conservation won’t supply the energy needs of 5 billion new customers who really don’t like living in poverty.

    Sorry, I was wrong on calducutt. But – your tunnel approach is like the an OTEC system, except you are using a delta T of maybe 15 Kelvin to drive the airflow – and all that is doing is creating a pressure differential. So its back to Bernoulli. You won’t be able to generate much electricity out of a single bore – and you have completely ignored the point of how expensive it is to bore that tunnel, crosspatch. You’re ROI is close to infinity. You’d be better off putting windmills on the santa clara hills, in the few areas you can actually get decent wind energy, or better yet, off the coast, where there is good wind power all the time.

  38. Don’t forget, windmills cause global warming. By slowing down the movement of the air, less heat is lost to outer space.
    Windmills are not only economically stupid (over a dollar a KWH, vs clean nuclear at under a nickle/KWH), but also, they actually do make the globe warmer.

  39. It fails and succeeds for another reason.

    There is a big difference in relative kinetic energy for the air in Chicago vs the air in Dallas due to the parcels being at different lattitudes on a spinning globe.

    This Delta-E is not insignificant.

    If the air in Chicago could displace to Dallas in a frictionless pipe, it would gain that net relative kinetic energy due to centripetal acceleration. It would then just depend on the orientation of the pipe as to the relative velocity of the air when it emerged in Dallas.

    Trying to send the air to Chicago from Dallas is a pipe dream, but going the other way could be a reality depending upon friction.

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