Update on EnviroMission’s Arizona Solar Tower Project

June 27th, 2013 by Roy W. Spencer, Ph. D.

Yesterday I spoke with EnviroMission President Chris Davey to get an update on the progress of the first, large-scale solar tower (aka solar updraft tower, or solar chimney). EnviroMission is progressing through the permitting process and plans to start construction late next year in La Paz County, Arizona.

Billed as a 200 MW electrical generation facility, its towering hot air chimney will be about 2,600 ft tall, making it the second tallest manmade structure in the world, and about twice as high as the Empire State Building.


What has always captured my imagination about the concept is that it uses the daily generation of warm air at the surface by the sun to generate electricity. It takes the familiar principle of a chimney filled with buoyant, hot air to the extreme. The taller and wider the tower, and the hotter the air it contains, the greater the potential for energy generation. The solar heated air in the tower continuously draws air into the 2.5+ mile wide glass/plastic canopy and through approximately 32 wind turbines, each rated at 6.25 MW, circling the base of the tower.

Now, all of this hot air would have been generated anyway, without the solar tower there. But it would have driven turbulently mixed thermals as pockets of buoyant hot air rise and gradually warm the lower troposphere during the daytime. The solar tower simply organizes all of this buoyant energy into a single updraft, which will drive a fairly continuous 30 knot wind through the 32 turbines.

One advantage of this design over conventional solar is since the ground will absorb much of the heat, electricity generation will continue at night as the ground gives up that heat, and the outside ambient air temperature cools by about 30 deg. F, helping to maintain buoyancy in the tower.

Design details are still being optimized by industry leader Arup Engineering, based in the UK. Mr. Davey mentioned a couple of the remaining design uncertainties, such as what material to use for the canopy (tempered glass or some kind of plastic); easy servicing of the clear panels is very important.

The facility requires no water for cooling, a significant advantage, and is designed to last for decades. I forgot to ask about the anticipated effects of wind loading on a tower that tall, but Mr. Davey said there are no major design problems with the facility.

Here’s a pretty cool computer animation video which was made back when the tower height was anticipated to be 1,000 m, rather than 800 m. From what I understand, EnviroMission is also negotiating solar tower projects in Texas, and a few foreign countries, as well.

(Any errors, misrepresentations, or misrememberings in the above are my own.)

160 Responses to “Update on EnviroMission’s Arizona Solar Tower Project”

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  1. This is how to do solar right–large scale powerplants in desert locations hooked up to the grid. It must be many times more efficient than photovoltaic panels installed in urban areas. Alas, what we have in the U.S. for an energy policy rewards the very least meritorious. It is what gave us such fiascoes as Solyndra–$500M that ultimately produced nothing but vast quantities of pulverized glass carted away in dumpsters.

    • Austin says:

      It is way less efficient than photovoltaic panels in urban areas. The solar tower pays off because over it’s lifetime it is cheaper per MWh and uses land not used for other things. Both Solar Updraft Towers and photovoltaic panels in urban ares are good ideas.

  2. Myron Mesecke says:

    No water for cooling but how much will they use cleaning the glass? And how difficult will it be to constantly sweep sand from the glass? How will large concentrated columns of hot air affect the local climate? It has already been proven that wind turbine farms create localized changes to the climate. What will a concentrated blast of hot air entering the atmosphere at 2600 ft do?

    Lot’s of unknowns that can only be answered after the fact.

    • You probably wouldn’t want to fly a Cessna right over the top of the tower. But it won’t be as much turbulence as a thunderstorm updraft.

      What people don’t realize about wind turbines is that all of that wind energy is constantly being dissipated through friction anyway. Wind towers just extract a little before it is dissipated as heat, anyway.

      • Manfred says:

        Actually Roy, it could provide the glider pilot an entirely new option, ‘solar tower gliding’, in addition to the usual ridge, thermal and wave scenarios.

        • Kasuha says:

          I seriously doubt they’ll let gliders anywhere near.

          • Fred says:

            They don’t “let” skydivers near skyscrapers but they end up there anyway!

            This will be a magnet for adventurous glider pilots.

          • Manfred says:

            Oh that’s even more exciting then. They’ll scramble an F-35 Raptor every time a glider breaches the airspace around a solar tower. Can’t wait.

          • Kasuha says:

            They don’t let aviation near nuclear plants as well. Try flying there and see what’ll happen.

    • Mark says:

      Not a drop of water required. Think about it, all that is required is the Sun’s UV radiation to pass through the glass…it is not a photovoltaic transfer of energy. It is a greenhouse! Just crank up delta t and let nature do the work. Day or night!

      Shame, there was supposed to be just such a plant built north east of Mildura.

      • John Silver says:

        All they have to do is fill the greenhouse with CO2 and it will go nuclear.

      • crakar24 says:

        Day and night!!!!!!!!!!!

        Are you sure? Lets assume power output peaks in the afternoon, as soon as the heat begins to wane so does the draft ergo so does the power. As nightfalls there is no more heat therefore the power will drop off to zero at some point.

        As i am originally from Victoria i know the type of weather you get in Mildura (i assume you are referring to the one in Oz) and i do believe you get days when it is very cloudy and cold so how would it work then?

        Any alternative energy that requires gas/coal/uranium as a backup when the sun dont shine or the wind dont blow is just another green money scam, i would have thought after all these years and all these collapsed scams we would be much smarter at this type of thing.

        • Geo says:

          At night, the ground under the glass will still be quite warm (especially if there is a black surface or maybe lava rock at the base). All the while (in a desert) temps outside the glass will cool more rapidly, thus maintaining a temperature gradient (although, I’m sure the delta T will at some point toward morning begin to diminish a good deal….but that would be the point of the day of lowest demand.)

          • crakar24 says:

            Thanks Geo,

            So over a 24 hour period it will not produce 200Mwh it will be less than this lets say it would be closer to 100Mwh and at what cost? Also note it will be located in a desert which means the cabling for the power to where it is required will be long even DC would suffer some losses and once again i ask at what cost?

            This is just another green utopian dream that is only been made possible by some numpty government subsidising the whole thing.

            When will we ever learn?

      • michael says:

        not UV. mostly Infrared:

        from wiki:
        At zenith, sunlight provides an irradiance of just over 1 kilowatts per square meter at sea level. Of this energy, 527 watts is infrared radiation, 445 watts is visible light, and 32 watts is ultraviolet radiation.

  3. Skeptikal says:

    Have you got any idea on the build cost?

    • Jim Traynor says:

      Looks expensive. With natural gas at $4, and likely not to exceed $6 for quite some time, why on Earth would you allocate scarce engineering resources to this unless it can compete free of government subs.

  4. Sounds most interesting-have you seen any economic analysis over the life of the project including construction ,maintainence and transmission costs?
    What is estimated price/kwh at point of use without susidies?

  5. delurking says:

    Why glass? Why not just make the top surface black sheet metal? It would be far cheaper and more robust, and would lose somewhat less than half of the thermal energy to the air above the surface (a lot less if heat-pipes into the ground are used). The glass will reflect ~7% of the incident light to begin with, and is a terrible insulator, so a lot of the heat would get lost anyway.

    • Robert Austin says:

      Which would you chose to take shelter from the heat under? A glass roof or a black steel roof? No contest.
      The glass roof allows the earth below to act as a substantial short wave isolation absorber and heat sink. A black steel roof radiate much of the heat upward as long wave radiation and the air below would mostly be heated by contact and not by local convection as would be the case for the working air being above a hot surface.

  6. Svend Ferdinandsen says:

    Optimistic it can deliver 200MW times 5000hours, that’s 1000GWh in a year. At 50$ for a MWh (hope its close to the real price) it earns $50million each year, but can it pay for the construction and maintenance. The turbines alone costs most likely 1mill. each.
    I hope the best for the project, but fear it is an other green castle in the air.

  7. Kasuha says:

    I have serious doubts about this idea. It sure sounds great first but on second thought things stop looking easy. I would definitely like to know how they’re going to handle weather events such as heavy rain, thunderstorms or strong winds. The whole structure is basically large sail stretched horizontally just above the surface. If you let the wind below, it may lift it easily and destroy it. And if you don’t let it below, it may press it down and destroy it from above by pressure difference.
    Agricultural usage of the land below it is a question as well as any evaporation will reduce efficiency (more vapor = less heat). The soil won’t get any direct rain, too, so 12.5 square kilometers of irrigation systems would be necessary.
    Power production divided by area also totals on 15 W per square meter. Peak production.
    I’m definitely curious whether they’ll succeed building it and how will it look in 20 years.

    • contrary to the video, there won’t be anything grown under the canopy.

      The canopy is anchored at literally thousands of points, its a basic engineering exercise. It’s just a roof open at the edges, approximately 10 ft off the ground near the periphery.

      The available solar I’m guessing approaches a daily average of maybe 350 W/m2 at most in this location, but you will extract only a small fraction of that due to inefficiencies (solar PV gets about 15% as I recall). Yes, as you say, 15 W/m2 or so.

      A 50kW prototype in Spain was operated for 8 years in the 1980s:

      • Kasuha says:

        The prototype was 122 meters in diameter, some 47,000 square meters. Yes, that is basic engineering exercise. But at 12.5 square kilometers of the area I’m afraid it’s not just matter of scaling up and we may experience a new instance of “Tacoma bridge” effect. But I don’t wish the project anything bad. If it turns unused land into cheap energy source, it’d be great. With the land usage, however, it’s not very usable for countries with dense population.

    • michael Hertel says:

      Hi, please contact me about this idea if interested.

      I would rather see a tower sloped on the ordinary land in hot mountainous areas where you could grow crops under the green house.
      Note if you evaporate water in your green house area it reduces the density of the air and might make it work better despite using up some heat so that the whole mass is not at a higher temperature.

  8. Martinitony says:

    There are thousands of miles of freeways and highways throughout the nation, many in the desserts and hotter parts of the country. With those highways goes thousands perhaps millions of acres of right of way. Can a concept such as this incorporate hot air moving along side our freeways and highways toward turbines. Major high powered electrical lines criss cross those roadways. Thoughts?

  9. John K says:

    Hi Roy,

    A few questions come to mind. Does EnviroMission receive state funding? If privately funded, that suggests the backers expect significant return on investment. Do you know if EnviroMission or any competitors plan further projects? Their exists a great amount of desert to build these things. What legal hurdles must be overcome simply to construct one of these towers? Which utility will buy the energy generated?

    Many more questions come to mind, but the project does appear interesting. Thanks for the information Roy.

  10. George DeBusk says:

    A 2.5 mile wide glass canopy would translate to about 1,800 hectares under glass. That would be 18,000,000 square meters of glass. Assuming a bulk cost of $50 per square meter for tempered glass that would be $900,000,000 just for glass. That does not include the cost of supporting frameworks or the tower. This must be a two billion dollar plus project. That is for 200 megawatts.

    A Nuclear plant costs about a billion dollars per gigawatt, or about 10 times less than this solar tower. The nearby Tonopah, AZ, nuclear plant has a capacity of 3.3 gigawatts. It covers less than 1,000 hectares. To equal the power output of the Tonopah plant would take 16 towers and 16,000 hectares of land (without counting associated roads, parking lots, buildings, and cooling ponds). The maintenance costs of 16,000 hectares of glass must be astronomical. One hailstorm (not unknown in southern Arizona) might cause hundreds of millions in damage.

    I also would object to converting over 40,000 acres of desert to sterile, empty greenhouses when you could get the same power capacity by converting only 2,000 acres to concrete an cooling ponds. Land may be plentiful in the southwest now, but there is no reason to waste it!

    This tower may be better from a cost and environmental impact standpoint than 3,300 giant wind turbines strewn across the desert, but it still does not touch nuclear or natural gas.

    • Oh, I’m all for nuclear. But even people I’ve met who work in the nuclear industry are not hopeful for the future, maily due to public perception. But I hope that changes.

      If the canopy is glass, I believe they are considering actually making it on-site.

      • John K says:

        Hi Roy,

        Public perception falls victim to technological and market ignorance. Most people simply do not understand new reactor designs that make many of the old assumptions regarding nuclear power obsolete. Molten Salt Reactors, IFR’s and other technologies can greatly expand the quantity of available fuel and in the case of Molten Salt Reactors greatly reduce terrorist threats compared to previous generation water reactors. Ignorance will prove to be a very dangerous affliction for this country and today’s education incentive system provides little opportunity for that to change. BTW I heard or read somewhere that China will be putting a Molten Salt Reactor on line before long. This will allow them to produce nuclear power from the Thorium fuel cycle and thus provide a technological edge over the U.S.. Of course I think the Russians tried that unsuccessfully in the past. Why hasn’t the U.S. seriously proceeded with this technology? Didn’t the U.S. have a successful trial one some decades back? Why ignore all that research?

        In any case, properly developed nuclear power and natural gas seems a great way to go.

      • Lars P. says:

        There is another lie with nuclear – that any level of radiation is damaging.

        It is like the bacteria/microbes fear. People needed to learn that an absolute sterile environment is not healthier then an environment where some bacteria exists.

        The same with ratdiation – there are certain levels of radiation that are not harmful, can be even beneficial. Until this change in perception and understanding people will still fear nuclear.

        Once they realise that they constantly live with radiation, that a certain level of background radiation is ok, it will be a big step forward.

        The other point will be to have better clean-up technologies. In case of a nuclear spill technologies can be developed to bind/collect radioactive elements, something like technologies developed to extract Uranium from oceans.

        In this respect, with time, better acceptance for nuclear will come.

    • David Gray says:

      Shame on you George for actually bringing up those nasty facts and economic realities. They are not to be used with environmentalists. Nuclear (especially reprocessed options and breeder technology options) are the answer for the next 50 to 100 years(still waiting for fusion), but the environmental lobby is not really interested in solutions, it is interested in control.

      Given that we are on some kind of inexorable path to push more solar and wind, this is at least an interesting project.

      All the problems you point out are real, not the least of which is extremely high cost, but when “the people” start noticing their electricity bills being a factor of ten higher, perhaps they’ll start asking what happened?

      Nuclear is the obvious solution to most any nation’s energy needs, though for a few decades natural gas can provide a solution as well.

    • Fred says:

      Gaia is watching you George.

      Gaia does like not numbers, facts and common sense.

      Gaia likes emotion, taxpayer subsidies and sad pictures of lonely polar bears.

      Gaia might have to report you to the IRS for a “Flat Earther Audit”

    • Daniel Reppion says:

      Thats a little simplistic, given the assumption of build cost per metre, and the fact that your estimate seems fairly vague in regards to the running costs of a nuclear facility. This includes the costs of mining, processing/transporting/storing the fuel, as well as processing and storing the waste material.

      Even minus running costs the plant at Tonopah cost 5.9 billion ( http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5486744 ) to build in the 1980s, more like 12 billion in today’s money. Either way it makes the start up costs for this new form of generation comparable with that of Nuclear, by then an established and presumably relatively efficient (construction costs wise) type of technology.

      Directly comparing developmental technology to existing infrastructure cost wise isn’t necessarily indicative of it’s actual costs were it common place, nor is it unlikely that materials can be used capable of mitigating weather damage.

      • George DeBusk says:

        Nuclear does have running costs, but so will an 1,800 hectare glass (or plastic) canopy and a 2,000 foot tower. Any structure, regardless of the material of which it is constructed, will require maintenance. My tiny house (2,000 square feet) requires several thousand dollars a decade to maintain. Multiply that by 1,800 hectares and a 2,000 foot tower and the running costs must be in the hundreds of millions per decade. Turbines would also require servicing. I can but guess how much it would cost to clean up after one sand storm or do repairs after a hail storm. I am not building the thing, so it is not my responsibility to estimate that, but any investor would be ill-advised to sink their money into this seeming boondoggle without estimating both the realistic constriction costs and the running costs.

        I still find it hard to believe they intend to make a 2.5 mile wide glass (or plastic) canopy. I wondered if that was a typo. Even the cheapest two ply polycarbonate sheet would run over $10 per square meter, without even accounting for supporting infrastructure – and its survival time in the desert sun would be less than a decade. Tempered glass would last longer, but still not forever and at a much higher price. I cannot see how a project on that scale could be in any way economically feasible. Maybe a 100 hectare canopy, but not 1,800.

        As for nuclear, I am very bullish on nuclear, but the analysis is the same if you look at natural gas or hydroelectric. The price as described would be just too great. 18 million square meters of anything held 10 feet off the ground would be prohibitively expensive.

  11. Bret says:

    So I can see the upside to the fact that power generation will extend into the night (all night?).

    I’m concerned with what it takes to knock the towers down. Seems like a major terrorist opportunity to me. In some sense that’s true for any large power generation facility, but the tower looks particularly frail. Contrast that with an array of photovoltaics that covered an equivalent area. It would both generate more total electricity (though exclusively during the day) and be less susceptible to attack (a well placed bomb would only damage a small fraction of the array).

    I’m afraid the political future will require us to move away from large scale power generation and towards a safer, more distributed approach.

    • Kasuha says:

      Any reasonable power generation technology is the more effective the larger scale you use. Excpetions are large scale generators built of large numbers of small scale ones, such as wind farms and solar arrays – but even for these you often get some quantity bonus. Small distributed sources are usually expensive and inefficient. The only thing that may make small distributed sources viable would be if the generation became so cheap that the price would not matter.

  12. KTWO says:

    About two years ago a somewhat similar project was being planned for the Australian Outback. Haven’t heard of it since. Someone noted a pilot plant is Spain, thanks, I hadn’t heard about it.

    Other things being equal, the closer to the Equator the better for solar. If Europe is so darned determined about solar they should fund test facilities in the North African deserts.

    Nothing beats reality but virtually free land comes close.

  13. ROM says:

    The same outfit Enviromission had a big propaganda campaign here in Australia up to 3 or 4 years years ago on how they were going to build the same Solar Tower system some tens of kilometres north west of Mildura which is located on the Murray River in the south east of Australia.
    They even bought a station property, Tapio Station [ “Station”; a large as in tens or usually in hundreds of square kilometres, outback livestock grazing property ] to build the first of a proposed 30 or 40 towers that were to stretch across Australia on about the same latitude. A latitude where it was claimed that the cloud cover was lowest for the whole continent.
    At one point it was claimed that these 30 or 40 Enviromission solar towers would be able to supply all of Australia’s electrical needs.

    I think it all fell down around the fact that the Australian government refused to pony up a fair lump of the finance required to build the first Solar Tower.
    So the whole Enviromission outfit packed up and headed for the USA where they probably hoped the taxpayer’s pockets might be a little easier to pick.

    There were also reports in the media that the power concentration output was so inferior per dollar and per area that the whole thing was completely uneconomic.
    Measured against the current wind and solar energy performance and costs, if true, thats really saying something about the solar tower’s potential economic viability.

    The other unknown which was never mentioned except amongst glider pilots was the very strong likelihood that with the very fast, concentrated updraught from the tower ie a massively strong thermal updraught source, there was likely to be cloud formation from the updraught of varying and quite possibly large extent directly over the tower and it’s surrounding glass covered, heat generating areas for long periods whenever the normal atmospheric conditions were suitable for even quite limited cumulous cloud formation.

    The higher the Solar Tower and the stronger the air flow of the updraught up and out of the tower, the more likely such a tower and energy absorber would generate this semi permanent cloud cover formation directly over the entire tower and the critical to the entire operation of the system, the surrounding heat absorbing areas.

    A smaller version such as was operating in Spain for those eight years would not suffer the cloud problem but the energy output would also be a few magnitudes lower in output as well

    As an old glider pilot, all of us glider pilots were busting our backsides to see it built and have a go at soaring the Tower’s thermal updraught as Dr Spencer mentioned.
    Probably would have been a bit like trying to soar in a stubble fire and that sort of shatters the teeth on occasions and it sometimes almost needs a change of underwear after a rough one.
    Getting too damn old for that sort of teeth shattering excitement nowadays, unfortunately.

    Enviromission’s web site has been toned down a heck of a lot from it’s Australian heyday of a few years back but here it is.

    • In a dry environment like the desert, I predict there will actually be cloud suppression from the tower. Temperatures will be so high in the updraft where it exits the tower that it would have to continue to ascend to a very great height before condensation of what little vapor exists will occur. I’ll be on days with some cumulus cloud development, the tower will actually clear the clouds in the immediate vicinity.

      • Manfred says:

        A ‘thermal’ pump of this nature might on a hot day with reasonable humidity kick start a Cb. That would be exciting. Fix the tower up with conductors and capture the lightening while you’re at it.

        Can’t see the anthro ‘climate change’ brigade going for this. I know they overlook the bat and bird killing windmills, but what of this massive solar driven stationary vacuum cleaner? It’ll suck god knows what to god knows where, not to mention the dust.

  14. John Silver says:

    Typical megalomania. Have they done any testing?
    Is there a pilot plant?

  15. John Silver says:

    Furthermore, Arup is a danish name. Danes are bondfangere (cons in danish), like Vestas and Fisker to name a few.

  16. Dan Pangburn says:

    I wonder how much the power output would be increased by flooding the area under the transparent (to let the sunlight in) cover with water. Maybe spray for better control of relative humidity. The increased humidity would increase capture of long-wave radiation from the surface and decrease the air density. A back-of-envelope calculation indicates that a unit of energy reduces the density of the atmosphere about 3 times as much by evaporating water into it as it would by raising the temperature of the dry air. Stay below 50% RH at the bottom to prevent a cloud forming at the top of the 2600 foot tower. (Reduce the water at night?) Sounds like a way to create a synthetic hurricane and tap its power. Be sure to account for and possibly exploit conservation of rotational momentum. Trade off with cost of doing. Looks like a place for some serious economic, thermodynamic and structural (i.e. engineering) modeling.

    Double wall plastic (like greenhouses use) may be cost effective, particularly near the center of the covered area, to reduce heat loss if the temperature under the cover exceeds ambient there.

    If sea water is used there could be a side production of sea salt and/or maybe production of magnesium, lithium, etc.

    • I’ve thought a lot about how water phase change might be used, but I don’t see how it would help for any realistic tower configurations. First, you would need a continuous abundant source of surface water, because most water evaporated under the canopy would be exhausted out the top of the tower before most condensation would ever occur. If you had a tall enough tower (unrealistically tall) you could extract energy from the condensation of water, which could enhance the updraft and then fall back to the surface as rain and run back under the canopy…basically simulating what happens in nature with rain storms. But tower heights of 10,000+ feet would probably be required.

  17. RichardLH says:

    Hmm. So with a plot of land, a set of polytunnels, a tall chimney and a big fan we can all live ‘off the grid’ 🙂

    Oh, and lots of sun and preferably a low outside air temperature.

  18. RichardLH says:

    This is all going to balance around wind speed to temperature rise that can be imparted to the moving air.

    As you get closer to the center, the wind speed will be rising but the area of collection and, therefore, the energy transfer available gets smaller.

    The balence point should be somewhere out from the base of the chimney I think. A ‘chill factor’?

    That will probably limit power output.

  19. Dale Hartz says:

    Did I miss part of the technology? Des it only work in the daylight hours?

  20. Massimo PORZIO says:

    Dear Dr. Spncer.

    I’ve a little doubt, maybe I’m wrong because I’m not skilled in thermodynamics applied to air movement.
    In my opinion the turbines could oppose a force proportional to the energy “sucked” by the grid. This force should limit the the air flow, which otherwise would enter the chimney freely. That could reduce the air input from the border because the air under the “greenhouse collector” is hotter than the outside so this could produce a radial outgoing flux from the center to the border of the “collector”, which could induce a depression there under and a reduction of the turbine efficiency.
    In my opinion to avoid that backward “reflow” the inclination of the “collector” should be much more than the one shown in the pictures.
    But as I said before, maybe I’m wrong and the guys at EnviroMission already taken account of that.

    Have a nice day.


    • John K says:

      Hi Massimo Porzio,

      You had the same impression I did when I first read the post. However, as you pointed out I figured the upward inclination of the plate (or whatever you call it) toward the center tower would help direct the hot air to the tower. Assuming the engineers calculations prove accurate, the 30 knot air speed should provide sufficient force to drive the turbines and prevent blockage and air-flow restriction. Thanks for the post.

      • Massimo PORZIO says:

        Hi John K,
        yes, as said mine was just an opinion, or better an impression.
        One other doubt I have is about the efficiency by night, because in that case the only thing which make the difference between the outside and the inside of the system is the thermal insulation of the “greenhouse” roof.
        Since energy can’t be created or destroyed, the only possibility I can imagine to make it working by night such as by day, is that they designed the system to store in the ground below a lot of energy during the day, but this should mean that they had to oversize by a factor of two the design to get the same energy by night too.

        Have a nice day.


  21. LarryG says:

    1. – this is exactly why the gov does “pilots”. some fail. some succeed.

    2. – in terms of structure – have folks seen the cooling towers for Nukes?

    3. – in terms of weather changes. Have folks seen the smokestacks from coal or cooling towers for Nukes?

    4. – in terms of Nukes – what would be interesting – given the economics of Nukes – would be to compare them to wind and solar – rather than coal-burning generation.

  22. RichardLH says:

    I suspect the governing factor in all this will be heat transfer from the ‘hot’ ground into the air. That and the air density difference, from temperature or moisture, inside and outside the tower.

    With simple flat ground the transfer and storage will be poor. With correctly aligned heat storage/heat transfer ‘fins’ the transfer from surface to air could probably be improved. Water (in bags) used as a heat storage mechanism is mentioned on their site to help power through the evenings at least.

    Think of it needing to be like a big radial radiator trying to heat in inward flow of air.

    As I said above, I think that the limits to if this works well or not will fall in this ground/air energy transfer requirement. The ratio of available input power to wind speed is great at the edges, but falls off the closer you get to the center. Rising wind speed, falling input area.

    The prototype seems to have worked, but there is surprisingly little other ongoing work – which is odd given the low maintenance requirements.

  23. Greg says:

    I think there is another similar plant is Spain. Not the one Roy linked.

    I recall seeing a video walk around and the canopy was like a plastic tarp, pegged down a regular intervals (not glass). This caused the condensation off the underside to pour off and watered the ground under the canopy. It ended up having much more vegetation under the canopy than in the surrounding semi-desert area.

    Condensation was presumably a night-time effect.

    I love the simplicity of the concept. I don’t know why people start getting into “energy dencity”. There’s plenty of hot arid land in most continents that currently worthless and has an energy density of zero. It really is a non argument.

    Just have to hope the EPA don’t find a mating pair of tortoise on the land otherwise the whole project will have to wait until they die, so as not to disturb thier habitat.

  24. Noblesse Oblige says:

    Slightly off topic. I did a back of the envelope calulation of the fraction of terrestrial wind energy currently extracted as electricity. It is suprisingly large: a few tenths of a percent of the wind energy present in the troposphere. I hope someone else will do an independent estimate.

    I have no idea what this will mean for the climate.

  25. Greg says:


    It was the site Roy linked. Indeed plastic sheeting as I recalled.

  26. Ronald says:

    From an engineering standpoint wind loads are factored into the design. The bigger issue will probably be from vibrations due to the turbines,hear and other stresses.

    As for cost instead of glass plexiglass maybe a better option and go for a much lower cost than normal glass. Lowes sells these for about 27 dollars per square meter and if you include bulk those prices go down as much as half to one third. I just do not know about durability in the desert for the sun.

    Typical prices for energy are around 10 cents a kwh to the consumer figure half to a third is made by the producer. The cost of energy (due to demand) goes up during the day and lower at night so from an economic standpoint producing power during the day is most cost effective. So lets assume it makes 150mwh per hour at 5 cents per kwh. That is 7500 dollars an hour. Asssume 12 hours of usable energy for 330 days a year. Only looking at 30 million a year.

    Cost for land about 1000 per acre and you need 5000 acres. So the cost is not as exteme as one may think. The real cost is construction. I do not see them getting a return for at least 15 to 20 years and probably for 30 years.

    As for terrorism. Terrorists rarely target sites like these because the impact is minimal. Remember terrorists are different from military sabotage where the goal is impact infrastructure. Terrorists want news coverage. The bulding is a much harder target to destroy and you may kill 5 people assuming anyone even sees it. Note west had more people killed and was a much larger impact to the community, but the news focused on the boston bombings as a prime example.

    • michael Hertel says:

      Double or triple wall polycarbonate is a better option available in sheets 5 feet wide and 30 feet long.

      I would rather see construction on a mountain slope of 30 to 45 degrees on the sun facing side. Grow crops in the greenhouse and if possible recover some of the water evaporated at the start of the slope at the top.

      No prototype like I would build if I had the money has been built. Slope collector, no tower, air flows both up and then down again since at night water is cooled and that water is used to cool the air flowing down.

      The thing whatever its form must be multi use. A tower built as a hollow building with tenents might be much better than a simple tower. mghertel at execpc.com

  27. Thanks, Dr. Spencer. An interesting article.
    I think that the more diffuse the energy source is, the more invasive and extensive the energy plant becomes.

  28. Brane Jenko says:

    Hi everybody,

    I have checked few web pages about this project and found some facts about their business plan : they plan to invest 750 M$ for 200 MW capacity and ROI is planed for 11 yrs.

    To me it is a bit too high (3.75 $/W) and they also talk about “60% yield of energy harvesting” but don’t explain on what basis ? If 200 MW is peak power and if we asume that during night it should be less than I guess the 24h average power is lower, maybe 150 MW at best. As many of you said, it is a nice engeneering challange, the concept itself is much better than PV or wind turbines, but I would expect them first to make about 20-30 pilot plants because one in Spain almost 30 years ago is not enough. Because there are still a lot of engeneerings to resolve, such things are allways specific at particular location (weather, earthquakes, dust storms…).

    Anyway, for the night time decreasing of dT I think so a proper insulation of underground and installing a black color layer of “thermal capacitor” like brick should store and harvest some of the daylight sun’s energy for the night time.

    • Massimo PORZIO says:

      Hi Brane Jenko.
      “Anyway, for the night time decreasing of dT I think so a proper insulation of underground and installing a black color layer of thermal capacitor like brick should store and harvest some of the daylight suns energy for the night time.”

      IMHO the problem is that all the energy you store during the day, reduces the efficiency of the system. If you place anything under the canopy which stores energy the result will be a reduction of the wind there under.

      Have a nice day.


      • Brane Jenko says:

        Hi Massimo,

        thks for reply. I am much aware of this fact because the energy budget is fixed and limited, but I see some benefit in this “storage” just as advantage compared to PV which must be heavily backed up by conventional resources during the night time or cloudy weather. And insulation of the ground would surely increase total efficiency. Not to mention wind turbines. Winding usually don’t follow needs of the grid. Danish wind farms are almost 100% backed by Swedish nuclear power stations.

        I also think so that in worst case (thick clouds or night time) there is at least 8 K dT due to the 800 m height of “chimney” without any additional storage from day time.

        But anyway I remaind a little sceptic simply because there is lack of pilot scale projects. If we chemists would do this way, even I wouldn’t like to live near chemical plants.

        Wish you nice day to you too,


        • Massimo PORZIO says:

          Hi Brane,
          I fully agree with you.

          Anyways it seems that looking at the Dr.Spencer suggested link to the Manzanares prototype, the diurnal average power is all but flat.


          Click on the Operation item to get the performance graph.

          Of course it’s much better than a windmill, which (as you said about Denmark) is a good example of energy production inefficiency (let me say nothing about PV).

          Anyways, it seems to me that there was no energy storage in that experiment. Maybe they implemented it later since that experiment is dated 1987.
          The nighttime production was a tiny tenth or less of the maximum daily peak.
          Note that when the wind at the turbine dropped below 2.5m/s they disconnected the turbine from the grid, which is highlighted by the abrupt fall down to zero of the produced energy and the correlated little increase of the turbine speed.

          But that experiment was about a very little 200m tall chimney compared to the 800m tower of the new design, so maybe that your predicted 8 K dT could give some chances to produce something by night too.

          Have a nice day.


  29. Bert Walker says:

    The Dust.
    Yesterday I drove the I-10 through La Paz county Arizona. The visibly suspended dust appeared concentrated up to 15-30m from the ground. It will be interesting to see the effect of vacuuming this dust laden air from the desert floor and depositing it at least 800m high. (I presume the tower exhaust will rise even further, – any estimates?.) How much will it decrease solar transmittance? Perhaps seed clouds? Prolonged muddy rain, or brown hail?
    On another dust related note, I wonder how much water will be needed to clean the glass/plastic panels after a dust storm?

    • Massimo PORZIO says:

      Hi Bert,
      “I wonder how much water will be needed to clean the glass/plastic panels after a dust storm?”

      I also wonder how much last the transparency of a glass/plastic panel to the sand dust erosion.

      Have a nice day.


  30. RichardLH says:

    I still think that the reason that this will be poor in power output is one of design.

    With a circular radial pattern you will only achieve limited use of the available sunshine/power.

    Look at it in reverse. If this was a radiator and cooling air instead of the other way round what temperatures would the various parts of the circle reach as you move towards or out from the center?

    Given a constant input per area, then the air temp will rise but only to that where input = output for a give circular stip at some radius.

    I believe that the ‘rings’ (the circlar strips aranged raidaly around the center) will be higher in temp at the edges but lower in temp at the center.

    That will limit the power output.

    If this was arranged so that the air flow was constant across the gronnd or even slowing as it approached the center then the heat transfer would be better.

  31. Matthew L says:

    I have been interested in this type of project for some while. One thing that puzzles me is why do you need the large area of glass/plastic at all? The system works by exploiting the difference between the temperature at the bottom of the chimney from the top. Surely that exists anyway and all you need to do is direct the naturally already warm air at ground level through the turbines.

    It would probably mean it only works during daylight that way, but the cost saving would be massive.

    I hope at least one of these gets built as it is an elegant and imaginative idea that should at least be tested. An extreme version of this is the “superchimney” that generates clouds as well as energy. However to do that it needs to be over 3km tall!! It has a rather entertaining web site devoted to it. Probably a lot of hokum, but worth a peep:

  32. RichardLH says:

    And I have just thought that through to its logical design conclusion and suspect that the most efficient design would be one that would raise eyebrows from above and might have some planning restrictions!

    What would you get if you laid out the collectors as parallel rows (with constant cross sections – so constant air flow) feeding a set of larger concentrators tube to the center? Then, if you have 4 collector tubes, you get a reasonably efficient design and a nightmare!

  33. Dr. Strangelove says:

    Roy, tell them to first build a small-scale model to test the design. I think the full-scale tower will produce less than 200 MW. For small turbine to generate 6.25 MW, it has to rotate very fast. Note the giant wind turbines only generate 3 MW. To rotate fast, air speed must be fast. But that means less time to gather heat from the glass canopy. Lower temperature = lower energy = lower air speed

    To remedy this, create a funnel to increase air speed. But this will lower the air pressure (Venturi effect) hence no gain in energy (because energy is conserved). Worse, air flow to the large diameter chimney coming from a funnel will create turbulence and friction increasing energy loss. They have to model the aerodynamics of the design.

  34. Dr. Strangelove says:

    Something is wrong with their calculation. If the wind speed is only 30 knots, the turbine will not produce 6.25 MW. It will only produce 12 kW. Do the math. Turbine diameter looks like 3.3 m. About 9 m^3 of air will pass through the turbine every 0.7 sec. The kinetic energy of 1 m^3 of air at 30 knots is 100 J.

    9*100/0.7 = 12 kW

    They need a faster wind speed to generate 6.25 MW.

  35. coturnix19 says:

    Maybe they should build such a tower on a red sea coast of africa or a gulf coast of arabia. Make it twice taller though to pierce through the inversion and above the free convection levels. If we were to believe those noaa weather maps, those places get enormous (4kw/m2) amount of untapped cape during the summer (half a year or such). Not only would it generate electricity, it would/may also produce rain for local acgriculture and perhaps cool local climate a bit. And the updrafts, and constant lightning show will be spectacular. A man-made persistent thundercloud!

  36. A 2600 ft tall, self-supporting tower? That’s make it one of the tallest such structures in the world. I anticipate that the wind loading on the tower would be substantial; especially for a design life of 50 or 100 years.

    In a “past life”, I used to design tower structures. at 2600 ft, it’s not going to be cheap or easy to build. An artist’s impression of what it could look like is Sci-Fi.

    The up-draught to the tower is essentially sources by the radial inflow from all direction. Unless my mother’s been cleaning, there’ll be dust. Lots and lots of it. Probably several tons every day which I guess will be “plumed” directly under the tower, with only a little of it entrained well enough to take the 2600 ft elevator all the way to the spout at the top. The rest will try to settle in what would be the turbulent flow around the base of the tower.

    The 6.25MW turbine doesn’t make sense for the notional height below the tower. At a guess; each turbine would have to be at least 100 metres in diameter. If the turbine is too “efficient”, it’ll tend to reduce total flow as the air has to have enough kinetic energy left to become potential energy in order to leave the top of the tower (neglecting insolation via the tower).

    If I were you Dr Spencer, I’d be comparing the lengths of my legs because it seems to me that EnviroMission has been pulling your leg.

  37. Steve says:

    Enviromission has been trying to do this project in Australia for over a decade, and haven’t made any tangible progress, despite plenty of support for renewable energy in Australia.

    I’m not sure it is viable – too expensive and technically fraught to compete with cheaper and simpler (conventional solar thermal) and commercially more mature (photovoltaics) technologies.

    People tend to think there is no environmental impact from putting glass over huge swathes of desert, but obviously there is: the desert is an ecosystem, and this project would have a huge impact, for only 200 MW. Photovoltaic panels on buildings have a lower environmental impact, are easier to install and maintain, and are a proven technology.

    Enviromission frequently refers to a project in Spain from the 1980s as proof of concept:

  38. Dr. Strangelove says:


    I would agree on that leg pulling. Yes you need 100 m turbine diameter to produce 6.25 MW. But there’s no way you can fit 32 turbines in that solar tower. The chimney looks 100 to 200 m in diameter. You can fit at most 6 turbines.

    To fit 32 turbines, the chimney must have a circumference of at least 3.2 km and diameter of 1 km. That’s absurdly big and prohibitively expensive. The solar tower would be 8x longer and 3.5x taller than Hoover Dam.

    • Dr. Strangelove says:

      We can limit the turbine diameter to 10 m to limit the size of the solar tower. But this will increase wind speed since the wind is funneled to a smaller area. We can determine the wind speed by solving simultaneously the following equations:

      E = J As t
      E = 1/2 m v^2
      V/t = Ac v

      Where: E = energy; J = solar flux; As = canopy surface area; Ac = canopy cross-sectional area; t = time to travel canopy; m = mass of air; v = air velocity; V = volume of air

      Assuming the canopy is 3 m above the ground, J = 1 kw/m^2 (peak at noon time) and 50% of solar flux converted to kinetic energy. The wind speed inside the tower is over 140 mph. This is like an F2 tornado. But the wind speed outside is lower because its energy will be dissipated by the turbines, turbulence and friction. The conventional wind turbine will not work. At 140 mph, we need a design that resembles the jet engine turbine.

      • There still has to be enough energy remaining in the air *after* the turbine to make it to the top of the 2600 ft tower. Unless you’re banking on a chimney effect to clear the hurricane-like dust storm at the base.

        Structurally, a high velocity inside and low velocity outside would be “tricky”. Especially in the case of a small structural failure; that’d probably entrain shards of “roof” to wreak havoc with the turbines. A sudden stop to them (rotating inertia) has the potential to cause a structural failure of teh turbine supporting structure; unless that structure is built to withstand the worst-case scenarios.

        THe “proof of concept” tower in Spain was falling to pieces from exposure to sunlight after about 6 months of operation.

  39. Manny says:

    Dr Spencer, since you are interested in big solar projects, you might want to have a look at the Drake Landing solar community in Alberta, Canada. its design is more human-scaled then that monstrous tower you are reporting about here.

  40. MikeN says:

    How much are they paying for the land?

  41. Dr. Strangelove says:

    This solar tower is a bad idea. The structure is too big for 200 MW. The tower is almost as tall as Burj Dubai. Including the 4.9 sq. mile glass canopy and 32 turbines, it will probably cost as much as Burj at $1.5 billion. Note that a 200 MW wind farm costs only $400 million, this is almost the same for solar PV. And if you put solar panels in the same area, you can get 2,000 MW or 10x more than the solar tower.

  42. ansgarjohn says:

    Atmospheric Vortex Engine got a grant last year.

  43. David Springer says:

    Scam. Juat bilking investors. Nothing more.

  44. Steve says:

    Here is a 250MW (25% estimated capacity factor, 500GWh per year) solar PV project that, unlike Environmission, has actually been built. Estimated cost at $1.6billion:


    • Dr. Strangelove says:

      CVSR is overpriced at $1.6 billion for 250 MW. Somebody will make tons of money on that deal. More realistic cost is the deal made by Warren Buffett. He acquired two solar PV projects (579 MW) for $2 billion. That’s $3.45/watt. China-made PV costs less, 2 to $3.00/watt.

  45. JohnD says:

    I have given this a good deal of thought. Essentially it is an inefficient solar collector. The inefficiency would be fine it were inexpensive to construct, but it does not appear to be. I can not find any estimates of $/KWH for the tower. My guess would be that the tower $/KWH would twice that of a photovoltaic array. The additional benefit of having power generated after dark may somewhat offset the higher $/KWH, but that is speculative, and only of minor benefit. The updraft effect of the 800m tower may provide some additional efficiency, hard for me to say, I don’t know that they are making that claim. Unfortunately there is just no efficient way to collect energy from wind using classic wind turbines.

    • Dr. Strangelove says:

      This solar tower is really a heat engine not a wind farm. Air under the canopy is heated and mechanical energy is extracted from the temperature (& pressure) differential between air in canopy and at top of chimney. The structure is big because it uses air as working fluid. Other heat engines use water/steam as working fluid. The heat capacity of air is 4,000x less than water. So you need a larger machine (tower & turbines) to produce same amount of power. The draft effect doesnt give more efficiency because it is balanced by increase in potential energy of the air as it moves up.

      Thermal efficiency is determined by the air temperature under the canopy. If you raise it to 80
      C, efficiency is < 12%. The higher the temperature, the higher the efficiency. Solar thermal has higher efficiency since it is hotter. At 200 C you get < 25% efficiency. The wind turbine is even higher < 60% because its not a heat engine. It just extracts the winds kinetic energy. Solar PV is about 20% also not a heat engine. The solar tower is too big and inefficient compared to these.

      • RichardLH says:

        See my above for a constant air flow (and hence higher temperature) collector design.

        Me, I suspect I could do this very cheaply with black corregated iron constant section tunnels feading a set of velocity increasing concentrator tubes to the chimney.

        Low velocities require large diameter engines so this should be a large, edge driven fan in the chimney form a central engine house.

        Stil dont know if the cost/benefit ratio works though.

        • RichardLH says:

          Oh, and a glass ‘insulator roof’ only if the cost/benefit ratio shows it is worth it.

          • RichardLH says:

            Probably cheaper to lower the top of ‘collectors’ to below the ground line and/or make a ‘wind break’ around the edges to get the highest air temps.

            I am not sure I would want to pay for glass at those temps then!

  46. Werner Weber says:

    What is the efficiency of that power station?
    The glass roof ring around the tower has a diameter of 2.5 miles or 4 km, which gives an area of 12 square km (km**2) or 12 million square meters. Assuming the standard 1000 Watt/square meter solar irradiation, this gives a total solar irradiation of about 12 Gigawatt. Putting solar panels there, would yield 1.2 Gigawatt during maximum solar angle, when standard 10 % panel efficiency is assumed. This may be reduced by a factor of 2 as an average during the daytime, or 600 Megawatt. The turbines installed in the tower yield 180 Megawatt. Thus any solar panel field has three times the efficiency of the updraft power station, at a cost of about 2.4 Billion US $ for the solar panels (200 US $ per square meter). Or, for the same power yield as the updraft power station, the cost is 800 million US $.
    What is the prize for a 800 m updraft Tower, the tallest building under the sun? 10 billion US $, or more?
    There has been a German updraft project 20 years ago. It has been built in southern Spain – and was an enormous failure. It never lived up to its efficiency expectations. Finally, the tower has been blown away in a storm.

  47. B Parsons says:

    I thought I had found one website that was impartial but I see that the posts I logged here encouraging that the temperature data be presented raw and not differentiated have been removed. Shame on you Dr Spencer, you do not have the stones to either do that or allow it via a web site that I attached. Your bias is showing and it isn’t pretty.

    • Kasuha says:

      I think that post containing three or more links get automatically redacted as a measure against automatic spam. So if you tried to post a lot of links, the problem might be there.

      • RichardLH says:

        What you mean logic rather than opinion deleted the post.

        Now if we can just get that from both sides, logic and observation that is.

  48. Threepwood says:

    An impressive monument to stupidity, superstition, and a huge leap backwards to medieval reliance on the weather to determine productivity

    The entire industrial revolution & green revolution of farming, was founded on being able to generate as much power as we needed on demand, not wait for the weather gods to smile on us, rain to fill a stream, wind to blow a windmill. They should make it resemble a totem pole and perform sun dances around it when it’s cloudy.

    The whole game with power generation is being able to depend on meeting demand peaks, because that’s where we run out first and need to add capacity- inc/ one in the morning when the desert is very cold & this tower will be dormant. i.e. these pet projects can never replace a single real power plant, only waste resources for them.

    I’m all for wind and solar where it can compete without massive gov’t subsidy, i.e. garden ornaments

  49. RichardLH says:

    B Parsons says:
    July 5, 2013 at 6:17 AM

    “Your bias is showing and it isnt pretty.”

    Hardly a gibe to throw at a hard working and very diligent scientist.

    One who apparently looks at the science as a scientist not in a ‘believer’ or ‘non-believer’ view of things.

    • B Parsons says:

      Well I am a scientist too yet you deleted my previous posts perhaps you cd tell me why?

      • RichardLH says:

        Me I did nothing! I only looked in from outside and said that I considered it a poor choice of words to use when describing someone who has so clearly demonstrated lack of bais in his work so far.

        You obviously think differently.

  50. Threepwood says:

    This design could actually be quite viable with a few minor modifications.

    reduce, the height of the chimney and hence cost and ugliness to a small fraction of the current scale. Get rid of the entire base also, using a fraction of the land.

    Instead of waiting for the sun to warm air to blow turbines- here’s the clever part- Use the sun’s energy that has already been stored in natural gas to boil water! Far more energy density in a far smaller space, the real beauty though is that you can vary the amount of power generated to exactly meet demand at any time without ever falling short or wasting excess. This can be done at any time of day & no matter what the mood of the weather Gods.

    Believe it or not this miracle technology has been used all over the world with great success, the fuel is abundant and cheap.

    Finally; simply locate it on the grid not as far as possible from where the energy is actually needed.

  51. RichardLH says:

    Threepwood says:
    July 5, 2013 at 6:43 AM

    “Use the suns energy that has already been stored in natural gas to boil water!”

    Wait ‘n’ thousand years for the (finite) supply of gas to be restored. Repeat as required. Try to figure out how to survive in between.

  52. RichardLH says:

    Threepwood says:
    July 5, 2013 at 6:24 AM

    “Im all for wind and solar where it can compete without massive govt subsidy, i.e. garden ornaments”

    I’m all for getting as much useful enegry from the environment as we possibly can.

    Looked at in the long term, this all comes down to leveling out our use of the available sunshine, stored or otherwise. What level we finally settle at is the real question.

    Or go Thorium or such with no such input limits.

    • Threepwood says:

      “Im all for getting as much useful energy from the environment as we possibly can”

      As am I, where useful means economically viable, producing more value than we are consuming, for society, not just the direct beneficiaries of the project.

      For solar and wind, lighting the edges of your driveway for a few hours after dark and making a little man pedal his bike are economically viable uses, powering an industrialized nation not so much..

      • RichardLH says:

        I agree. But it rather depends on how long a term view you are prepared to live with.

        Short term solutions are always needed for the short term, but that should never prevent long term planning and design.

  53. Matthew L says:

    Great thread with lots of proper critical thought. Makes a change from sky dragon slayers!

    What I have gleaned from it is that the best systems are probably small scale, relatively low tech and close to where the energy is needed.

    This tower is huge scale, unproven tech and some distance from where the energy is needed. The killer blow is delivered by those that say a conventional, relatively well proven, PV system covering the same area would produce more energy and cost less.

    The trouble with all these large scale systems in remote locations is the cost of transmission and/or storage. That is the hurdle the big Sahara project (Desertec) couldn’t jump. Interestingly a couple of the Desertec plants will be built, but by Morocco to provide electricity for the Moroccan people. Much more sensible.

  54. RichardLH says:

    Matthew L says:
    July 5, 2013 at 8:12 AM

    “This tower is huge scale, unproven tech and some distance from where the energy is needed.”

    I also would agree with that. Hence my somewhat cheaper corregated iron alternative (see above) which I rather suspect would scale into the smaller end of production rather well and have a much improved cost/benefit ratio even at those small scales.

  55. RichardLH says:

    I mean, think. Where would you prefer to be on a hot summer day? Inside the greenhouse or the black corregated iron pig sty in the middle of the field? Air temperature wise that is.

  56. ansgarjohn says:

    TORNADO POWER The Atmospheric Vortex Engine site sponsored by PayPal founder Peter Thiel has a FAQ comparing using artificial tornadoes (vortexes) with the solar chimney.

  57. RichardLH says:

    Re-post to here as this where it first started.

    I have it:

    The latest in solar power launch systems.

    As you sit in your capsule floating on the bath of, soon to be made steam, propellant water charge below, you check all the seals to the launch tube around the capsule are tight. The solar power collectors are just about up to launch temperature now and soon it is time to go.

    The launch tube above has been pumped down to the air pressure at the top of the tube now and we are into the count down.


    The valves below open, the launch latches unlock and all that stored solar energy and hot air in the collectors vaporises the water almost instantly so, with the additional kick of the lower air pressure ahead, you start to rise. The accceration is gentle but persistent as more water is sprayed in below and behind you and the hot air/steam mixture pushes you upwards to the stars.

    We got the figures exactly right today and as we leave the top of the tube we are right on target for orbital insertion without having to use our safety/emergency backup rockets.

    Eko low Earth orbit? Depends on the tube length and the temps I suspect.

    Fig 1.

    Above, used as a power generator for small scale continuous power extraction rather than ‘pulse’, orbital launch use.

    When used in launch configuration, it only requires only the addition of capsule, water supply, air pump, latches and valves. (Oh and a very long, high precision, high temperature, launch tube and a lot of land in the sun!)

    • David Springer says:

      Not remotely feasible. Whole tube must be pumped down to below 1 millibar otherwise the craft will burn up from air friction. And God help you, the tube, and anything living above ground for miles in every direction if you touch a wall on the way up.

      Who comes up with crap like this?

      • David Springer says:

        Oh hey I know. How about we build a spring steel tower 50 kilometers high. We bend it so the top is touching the ground and put slingshot cradle on it holding a cargo headed to LEO.

        This stuff doesn’t even make decent science fiction. It’s not credible even on first blush.

        • RichardLH says:

          I am very sorry you get not get the humour implied in my suggestion. I do rather realise the engineering complications that it would require to overcome.

          It was just such a nice, elegant, idea. Almost free (after all water IS the ‘propellant’ and the sun is the ‘oxidiser’ ) and so like a giant steamm powered cataput that the thought just needed putting out there.

          I now have this wonderful image of a planet, gently rotating in the sun, and splitting out little ‘life seeds’ from a large low orbit blowpipe powered by solar energy sitting somewhere in the desert.

          Even as a cartoon it works for me.

      • RichardLH says:

        Well we are still allowed to think, consider, dream. The outlines are not always practical at first. But that dos not mean no merit.

        The concept of using what is in fact bouyancy (with a steam kicker) to launch spaceship is not one I have encountered before.

        Looking at the tower, the thought came to mind.

        Most continuous power machine can be turned into ‘pulse’ use.

        This is just one way of achieving that 🙂

        Now if we can just get some tension into it (by placing a ‘donut’ lifting craft at the top end of the pipe to make it taut and steerable as well?) and keep the ‘breech’ pressure low but continuous down the ‘tube’ so as to provide continuous pressure and figure out how to make the ‘tube’ empty quickly and this is probably more practical than the ‘space elevator’.

        At least the material sciences are close to being able to provide the required amaterials.

  58. Adam Gallon says:

    Another lovely subsidy harvester.

  59. michael hart says:

    Is the device expected to produce any kind of a thermal signature that could be observed by satellite? Maybe it might also provide some extra knowledge about the atmosphere.

    Also,I’ve seen some quite impressive photographs of wind farms apparently acting as condensation seeds in humid atmospheres. Might this have some local weather effects?

    • michael hart says:

      I see the local weather effect question has been addressed upthread.

      • RichardLH says:

        I think that blowing ‘smoke rings’ with my steam blowpipe unpthread also might rasie soem environmental concerns 🙂

        Could make a pretty pattern from space though.

  60. pochas says:

    If you have the opportunity, you might ask what effect water spray humidification might have on efficiency, applied either at the periphery of the collector or at the base of the tower, after the turbines. It should be easy for them to simulate this, and they probably already have done so.

    • RichardLH says:

      I think that water addition is a poor choice. Although it has greater capactity to absort heat there are much simpler and more effective efficiencies to be made I believe.

      Firstly let us describe what we are seeking (or so I believe). We are dealing with a low grade energy source (solar) which we need to collect as much of and use it as well as possible. The less energy interfaces there are (such as moving to water/steam etc.) with their consequent potential losses the better.

      So the ideal engine is one that operates on air and solar only. It should have a multi-stage layout with rising temperatures as we go though each stage towards the exhuast. The volume, velocity and pressure will remaim unchanged throughout the engine. Only temperature changes as we move through it.

      The first, pre-heat stage, is a flat black metal plate of relative thinness. Below it is an air cavity and it has insulated side and bottom. Air flows in at one end. The plate is angled so that it points at where the sun will be at noon on an equinox and runs directly West – East.

      The second, heat stage, is another flat plane, this time covered by an insulating sheet of high heat glass placed a few meters/centimeters above the plate. The same insulated sides and base continue and it too points at the exquinox.

      The third, or super-heat stage, is another flat box, this time standing vertically. There are cylindrical ‘mirrors’ concentrating the available sun light onto both sides of this, now fully metal, vertical box.

      At all times the volume and cross section of the various stages have remained the same and they are all connected in sequence with constant cross section areas. This allows us to ‘fix’ pressure, volumn and velocity as unchanged throughout the engine.

      The ‘chimney’ at the center does not have to be that tall now. We are dealing with air that will be in the 200+C hopefully and the hydro-static ballance we require is pivoting round the turbine now anyway.

      The air can expand out to loose the temperature and the work can be extracted by a fan or turbine in the resultant air stream in doing so. The exhaust velocity/temperature is controlled by how much air needs to move to from hot to cold to allow the required work to be done.

      A diffuser can be fitted to the top of the chimney (as the velocity is relatively low) and that may help prevent any unintended local ‘climate’ consequences. 🙂

      The important thing here is the cross section remains constant, except where we expand it out to get the energy.

      The addition of a forth, ‘hyper-heat’ section, with a ceramic tube at the center of a even larger cylindrical solar collector to allow even higher air temperatures will require a higher temperature turbine also.

      `Low tech version (which could just be single ‘burner’/stack) could be built with local materials if an edge driven fan is used instead of a turbine. Think of a lorry axle mounted vertically supporting a large horizontal fan and blades at the top. Generator takoff from where the prop shaft was. Wheel on the ground bolted to the floor.
      The fan can be as large as required and made out of local materials if the heat is kept low and larger air volumes used instead. Flywheel capabilty can still be included (see below) to allow for night time working even at small scale.

      Ultra large scale, storage added, versions would require a circular ‘ring’ filled with ballast, floating in a circular water canal and the ring retained by guidewheels to the bank. The top of the ring carries a set of turbine blades which interact with multiple fixed ‘heat towers’ in a similar fashion to a Whittle turbine laid out flat.
      The only difference is that this engine operates at constant pressure/volume/veloicty and the only variable is temperature.

      That gives an almost ‘free’ way to stored unneeded energy that is collected. As rotational energy in a very big flywheel. Big enough, who knows, to get through the Winter?

      Cheap enough and efficient enough you think?

      Anyone want to do the maths and work out the best cost/benefit/size ratios? From Kilowatt to GigaWatt. And who builds the first prototype? Race anyone?

  61. Dr. Strangelove says:

    You cannot keep pressure, volume and velocity constant. Air is a gas. It follows the ideal gas law and the Bernoulli equation. You have four variables: pressure, temperature, volume and velocity. You need at least four equations and solve them simultaneously.

    Rotating flywheel on water is a poor way to store energy. Energy loss due to drag is very high. Magnetically levitated flywheel in a vacuum or hot molten salt insulated by vacuum and mirror are better energy storage.

  62. RichardLH says:

    Hmm. You can try to keep them constant until you wish to actually expand the gas out to recover the energy. Actually an ideal gas engine if it works.

    This has ideal forward characteristics with very small ‘drag’ and other parasitic losses.

    The point is to ‘pin’ the atmospheric centre point at the turbine. If ererything else is also balanced around that point we can extract energy.

    Whilst mag lev and other such things are brillant, they are somewhat more expensive than a water canal. This is trying for cheap, even local, materials. Oh, and try 10km/hour as a rotation speed and a few thousand tons as ballast. Fewer looses then and a LOT of energy.

  63. steve kettle says:

    what would happen if one of these things were built a few feet over a large body of warm water.

    would the heat from the ocean water travel up the stack ?

    • RichardLH says:

      I would suspect that it would work similar to putting a shaped lid above a warm pan of water on a stove.

      • michael hart says:

        Unless it was one of Kevin’s oceans, it which case the heat would disappear into the abyss. 🙂

  64. RichardLH says:

    Ok . so final workable design – I hope.

    Firstly let us describe what we are seeking (or so I believe). We are dealing with a low grade energy source (solar) which we need to collect as much of and use what we collect as well as possible. The less energy interfaces there are (such as moving to water/steam etc.) with their consequent potential losses the better. Also it must be cheap and easy to construct, locally if possible.

    So the ideal engine is one that operates on air and solar input only. It should have a multi-stage layout with rising temperatures imparted to the air as we go through each stage towards the power takeoff point and have a low temperature exhaust. The pressure will remain unchanged throughout the engine. Only temperature/velocity changes as we move through it.

    Single Solar Air Jet Pipe.

    Heat Stage 1.

    Long thin box open at one end to the outside air, roofed with a black, heat absorbing/conducting panel towards the sun. Bottom and sides of insulating and heat resistent materials and sealed air tight except at the entry point.

    Angled to the equinox noon sun for year round working and running West – East.

    Air entering (through an air filter as required?) through the open end of the box starts heating up. It wants to expand. Because of the sealed, constant cross section of the box, it does so by moving faster on down the tube. Towards the exhaust.

    Heat Stage 2.

    Another long thin box constructed as above but this time with an insulating ‘glass’ roof to achieve higher temperatures in the air. Same angles to the sun. Same heating/velocity effects on the air. This is now a mechanical thermal diode series pumping power into the air as both heat and hence velocity. The pressure is still constant. Well the ‘pressure/temperature/velocity = constant’ triple point is anyway. Higher air temperatures will mean higher velocities and because this point is higher up the temperature gradient, gives a self starting capability to the engine.
    On we go.

    Heat stage 3.

    Final box section, this time ‘on edge’ and now fully heat conductive. Cylindrical ‘mirrors’ concentrate the required power on each side. Highest air temperatures/velocity and a good top end to the input thermal gradient to get all this going fast in the morning.

    Cylindrical ‘mirrors’, and hence box rather than tube, rather than parabolic for cost reasons. Can also use a very large ‘flat plane’ mirror array in extreme setups.
    Now we are cooking. The air is now very hot and, because it is actually ‘pushing’ against the new outside ‘cold’ air now comming in to replace it at the entry point, it is now moving quite quickly.

    Stage 1 = Trevethic. Old steam.
    Stage 2 = Watt. Super-heat steam.
    Stage 3 = Whittle. Jet engine.

    Concentrator venturi/expander (similar to the compressor stages in the Whittle engine).

    Takes the now fast, hot air from the prior ‘heat’ stages and then converts some of it’s intertial energy as required to get to an even higher local velocity in the air stream and then reverse itagain and slow it down again to get to the air temps as required by the fan/turbine input. This is probably the high point, thermally, for the engine. Downhill from here. Classic turbine entry throat.

    Turbine/fan power extraction.

    We now have very hot fast air, still at the ‘pressure/temperature/velocity = constant’ triple point, at the face of a turbine which is also has its exhaust at the base of a hydro-statically balanced exhaust chimney. Air flow up the chimney is driven by the temperature difference to the outside air from the turbine/fan output face up to the top of the chimney only, in the ideal case.
    As the chimney/exhaust can be of any width as well as height, so final output velocities and hence temperatures can be kept as low as required to get reliable operation.
    We can allow the air to expand out (and hence cool it down to the required exhaust temperature) and do work using a full, multi-stage turbine, or get somwhat less energy out by using the simple interia of larger air volumes which are required by an edge driven fan. That should get better results in that setup even though it may give higher exhaust temperatures so higher losses.


    The height of the chimney now is really governed only by the need to keep sufficient air flow in the exhaust stream, not to extract power as such, so the height required is correspondingly less. Just enough to reliably not choke the turbine output.

    This is because we have kept to the ‘constant pressure point throughout’ requirement and kept that pinned right through even in the turbine. Even when we expand it out we are doing so at constant pressure to get the highest efficiences. Volume/temperature/velocity are what changes. Not pressure.

    The overall point is that this is cheap. I mean really, really cheap. And so simple to make. If you have the odd sheet of metal and glass around you can build one in your back garden.

    Do NOT allow children to get near the hot end!

    Now we have a working, individual ‘solar heat air jet pipe’ then all the classical multi chamber engines then follow, in whatever scale required.

    Low tech versions (which could just be single collector/concentrator stack) could be built with local materials if an edge driven fan is used instead of a turbine. Think of a lorry axle mounted vertically supporting a large horizontal fan and blades at the top. Generator takoff from where the prop shaft was. Wheel on the ground bolted to the floor.

    The fan can be as large as required and made out of local materials if the heat is kept low and larger air volumes used instead. Flywheel capability can still be included (see below) to allow for night time working even at smallest scales I think.

    The rest below may sound more exotic, even extreme. But I think still possibly plausible.

    Ultra large scale, or storage added, versions would require a circular ring filled with ballast, floating in a circular water canal and the ring retained by guide wheels to the bank. The top of the ring carries a set of turbine blades which interact with multiple fixed heat towers in a similar fashion to a Whittle turbine laid out flat.

    The only difference is that this engine operates at a constant pressure point and the only variables are thus velocity and temperature.

    That gives an almost free way to stored any unneeded energy that is collected. As rotational energy in a very big, slow flywheel. Big enough, who knows, to get through the Winter?

    Cheap enough and efficient enough you think? Even without the storage?

    Anyone want to do the maths and work out the best cost/benefit/size ratios? From Kilowatt to Gigawatt. And who builds the first prototype? Race anyone?

    Fig 1.
    Very basic 1.5 stage engine that started this all off.

  65. Dr. Strangelove says:

    You cant keep pressure, volume and velocity constant. As you heat a gas, it will expand. If you confine it, the pressure will increase. If the tube is open at one end, the gas will move there and increase its velocity. Stage 1 will not work. As you heat the air, it will exit the open end of the tube because outside pressure is lower.

    10 kph rotating flywheel will store little energy. Increase the weight to thousands of tons and you increase the drag, which is proportional to volume and surface area. Magnetic bearings are not experimental. They are commercially produced and used in power plant turbines. Use magnetic bearing on a flywheel shaft and you have a magnetically levitating flywheel. Hot molten salt is used to store energy in solar thermal plants.

    • RichardLH says:

      Consider that this is a thermal diode upslope. Forward is the only route possible. Backwards is down slope.

      • RichardLH says:

        Remember, the other end is hotter still. A lot hotter than the ouside air. So which way do you think it will run?

        • Dr. Strangelove says:

          All thermal diodes obey the 2nd law of thermodynamics. Heat will flow from hot to cold. The hot air will flow outside. Hot air has higher pressure than cool air outside. As hot air expands and flow outside, it will then cool.

          Moving an object in water wastes a lot of energy (drag) because water is a dense medium. If you want to conserve and store energy, use the least dense medium: vacuum and magnetic field.

  66. RichardLH says:

    You can squeeze a ‘pip’ of air between warm plates and see what happens though.

    Only pressure is held constant if you look.

  67. RichardLH says:

    And for the next project.

    Wind power for the future.

    The problem with wind is the air. Its too light in mass really. In order to get useful energy collection we need to think big.
    Victorian big I suspect.

    And it keeps coming from all directions and so erracticaly.

    So let’s start with a big flat field somewhere where the winds blow constantly enough to make this all worth while. Or a nice round hilltop which we can work with.

    Draw a big circle on the ground out to the limits of the property and give it a little ‘working’ space round the outside or somewhere down from the top of the round hill.

    Dig a circular canal inside the planning circle of whatever dimensions you wish. Make it a half circle in cross section.
    Construct a boat ‘ring’ that is suitably smaller to give needed clearancies and float inside the canal. To fill up the whole canal area. Load with as much ballast as required to bring it down to just a half cirle below the waterline.

    Place some sleepers round both inside and outside of the cannal and construct two rings of quide rails inside and outside the canal.
    Add wheels to the ‘ring’ to centre it in the canal.

    Add whatever friction reducing compounds you want to ‘hull’ and water.
    Cover to protect against frost, evaporation, accidents, etc.

    We now have a nice big, high mass, low speed, low friction bearing and flywheel to work with.

    Now to get it all moving.

    On the ‘ring’ add some fixed wing blades to whatever vertical dimensions local planning will allow you to get away with.
    Construct them so that this is running in the low speed, high torgue end of airfoils.
    Space round the ring as required to get the best overall air flow.

    Remove the protective covers on the blades and wait.

    Looked at from above, you now have a large vertical cross flow air turbine.
    At very low cost and speed. Slowly building to the local average wind speed if you don’t take power.

    Add power takoff by running some wheels off the ‘ring’ from the banks and……

    Victorian really. With AC.

    Will run for as long as there is wind to collect. Virtually zero maintenance and running costs.

    More complicated solutions will require computer controlled airfoils or ‘faster than the wind’ propellors driving the ‘ring’ onwards.
    Only for those who require the last word in efficiencies.

    P.S. The above should be ‘bird friendly’ as well.

  68. RichardLH says:

    And for the full set:

    Wave power for the future.

    Waves are big things. Lots of mass. Really lots of energy. Difficult things and they can get VERY big.

    Look at a cross section of a single wave though. It has a peak and a trough.
    If we can take all of the water than is in the peak and drop it into the following trough we will have recovered all of the energy of the wave. All bar turbulence anyway.

    So let’s create a mechanical diode circuit that can do just that.

    Construct a large flat ‘beach’ and make it float at ‘sea level’. As wide as you can sensibly build. Point at the waves.
    Add to ‘beach’, banks, in the form of an flat entry throat towards the turbines at the ‘back’.

    Drop the water through the distance of the RMS average height of waves collected, half above, half below, ‘sea level’ in some large horizontal water turbines.
    Take the outflow and return it to where the waves are collected as a slow ‘DC’ return to where the waves are breaking across the whole beach.

    A mechanical rectifier for waves.

    Build as large as required. Moor where needed.

    It is also possible to add the same large ‘flywheel slow storage concept’ to this as well to create energy harvestor ships that can collect far distance waves.
    Or build comunities in the oceans.

  69. Threepwood says:

    Now all we have to do is train the waves to rise and fall to meet our energy demand, especially in the evening when the wind dies down and in the morning before it gets up.

    All these ideas depend on some mythical massive & efficient storage device-

    consider this, any of these storage devices would be immensely useful for conventional power sources also to smooth supply/demand, it would mean max capacity could be reuduced, saving cost etc etc…. the reason they don’t do it is the same reason ‘alternative’ energy is still ‘alternative’ after so many decades. if it ever worked it wouldn’t be alternative anymore

    • RichardLH says:

      I assume you did not get the fact that these can be moored just off shore and thus provide continuous shore supply.

      And I rather suspect the cost/benefit ratio is quite good for this type of project.

  70. KTWO says:

    The mechanical engineering maths – constant pressure, etc – are beyond me.

    General comments.
    1) There seem to be no scaling problems with the various air chimney proposals. It should be cheap to test them. I could test some with the cooking utensils in my kitchen and the sunlight in my yard. Plus a sheet of glass, caulk, thermometers, etc. A few lbs. of ice cubes and an electric fan would also help. The little cooling fans in desktops can be used for little turbines.
    2) I don’t have to do (1). Most such schemes have been tried and abandoned. Sometimes repeatedly for over a century. That does not mean they must always fail but it certainly does not mean this time will be different.
    3) Wind and wave and tidal power have siting problems. Wave and tidal also have corrosion problems. Newer materials can reduce the corrosion problem. Mother Earth isn’t helping with the siting problems, nor will she.
    4) Coincidentally, siting is the problem with hydroelectric. We only need a thousand more rivers. Yet if we had them the cost of bridges might impoverish us. Problems can lead to solutions. Solutions can lead to problems.
    5) Beware of those who insist on starting big with a plan for years of construction. If proposals like Eniromissions will work there is no need to spend billions of $$ to prove it. Refer to (1).. Gradually increase the size of pilot plants.
    6) Follow the money. This has been, and still is, a major problem with alternative energies. Subsidies and governments involvement make it nearly impossible to find true costs. Government money buys the opinion of experts. The experts produce the opinions wanted. Every subsidy spawns a lobby devoted to continuing the subsidy.
    7) Have one main goal. The target that will not be eroded for any feel-good reason. If reducing CO2 emissions is that goal then reducing them somewhere in Africa is as good as reduction in Arizona. And it might be much cheaper or easier. OTOH, if you want cheaper electricity in Tucson then don’t concentrate on CO2, concentrate on $$$/KWH.

    • RichardLH says:

      All that is true. I just needed a place to stand to see it clearly (or so I hope). This blog was part of it.

      Never mind, The designs are out there now, free to use if anyone wants. No control EVER. Deliberately.

      And all so cheap.

      Appologies to Roy, but this did start here.

      Just a simple design exercise that got out of control. On a Global whiteboard, with everybody watching.

      Everyone will go on about the triple point. Standard classroom stuff. How you cannot do anything, or, if you do, pressure will change. A mantra driven into everybody so hard, any mention of getting round it or using it in someway different raises engieering hackles immediately.

      Lightning fast reply based on a couple of words read. No need to UNDERSTAND or even try to. This man is so obviously mad.

      Then during this toy design (I mean, it can NEVER work – that is just too crazy) the ‘lttle lemon pip of air’ is born.

      And now trouble comes in big.

      If this even looks looks like working it will become so hot (pun) it will burn all those who approach without care.

      I mean, cheap energy! Patent lawyers ahoy.

      So the rudness which which these deigns are splattered across the web. But they are out there. Maybe rubbish. Maybe not. We will see. But it IS public domain.

      Feel free to throw them away if you like.

      I will get round to the prototype as soon as I can. Should be simple. Just need to get the ‘engine’ running wihtout the fan/turbine which is the hard bit. Just heater and chimney will do at first.

      Two stages. If hooking them together produces a stream of hot air out one end we are done. Principle proved.

      The thermal wedge/diode, ‘little lemon pip of air’ works and the rest…..

      So, simple instaructions for test.

      Find long metal tube.
      Cut into three sections.
      Seal back together with insulating materials (to keep the heat supplies separate).
      Paint the top black.
      Add insulating roof above the middle section.
      Seal it to keep the wamm air in. MAke sure the cross section of the air flow does not alter. At all. That way this stays constant pressure. Just velocity/heat changes, just like the triple point says.

      Now we aae pushing warm air off the springboard of the cold air comming in through the entry port. At constant pressure. Expanding forward towards the exhaust.

      Up the thermal slope gaining energy as we go.
      So attach to a turbine throat and fan/turbine and Whittle’s work has been reborn as a constant pressure solar air heat engine.

      A toy, honest! A public toy at that!

  71. RichardLH says:

    Sorry, half way through, I changed from two to three stages in my decription. Third stage is the mirrors to keep the thermal diode pointing upslope.

  72. RichardLH says:

    Ok. Camping/hiking version. (Assuming the above works anyway).

    Make the three flat tubes aluminium. Fold at dotted lines. Chimney just another section.
    Allow fold out mirrors for the top heat stage.
    Turn the fan/turbine into a long, edge driven ‘air wheel’ across the chimney.

    Take power from that.

    Lightest thermal diode, portable power station!

  73. John Moore says:

    I wish I had seen this article sooner, as I live in the area.

    Some comments and questions for Roy.

    1) Temp drop at night of 30F. That’s at the surface due to rapid radiative cooling through dry desert air. I doubt that cooling will extend very far up, and if it doesn’t reach to the top of the tower, then it doesn’t affect the efficiency. However, advection of air into the area may dominate any local cooling. That air temperature would be lowered by mountains in its path or increased if it is advecting in from the Gulf of California (a not-uncommon “gulf surge” event). Hence the effective lapse rate (the critical parameter) is not easy to estimate without records of the atmosphere at 300m. Am I missing something?

    During the summer monsoon season, there will be less cooling due to higher water content in the atmospheric column. This is easily seen in the temperature records of the area.

    Those of us who fly (or flew, in my case) sailplanes in the area notice the effects of these phenomena because the morning air on dry days has many thermals since the lapse rate is rapidly increased by solar heating.

    2) Dust – the area is subject to dust storms during the monsoon season (about 2-3 months). They are not every day, but they do sometimes lay down quite a dust coating, so cleaning will be an issue, but not too often.

    3) Wind stress – the monsoon season routinely produces severe thunderstorms throughout the area. These have microbursts with surface winds not uncommonly in excess of 100mph, and large area macroburst outflow winds with gust velocities over 50mph. Where the microbursts happen is strongly influenced by topography, and I don’t know if the location of this tower is in a high or low likelihood area, but lower areas are typically at higher risk.

    There are also rare tornadoes, but the probability of a tornado hit, especially one with winds exceeding 100mph, is very small.

  74. RichardLH says:

    You do all realise that chimneys work either way up. It is Th – Tc * H.

    So why look for 5c air at xxx Km when it is just 2 meters below you in a cellar?

    And why not balence the flue (so that entry and exit are at the same atmosperic level) and… well I said all that before.

  75. AVE_fan says:

    A good summary of the Solar Tower concept followed by a comparison of it to the Atmospheric Vortex Engine is given in the FAQ section of the AVEtec website.


    It would be interesting to see what a “hybrid” of the two concepts might produce. If it could result in a tower 1/2 or 1/4 of the currently proposed 800 m height, it would tend toward becoming much more mechanically and economically viable.

    The covered area for *solar capture* could also be reduced considerably in size.

    Even in a steady wind of moderate velocity, *vortex shedding* from a tall tower would occur, creating stresses that would weaken it over time.

  76. Theophilus says:

    Bloggers – Where would we be if the Wright Brothers had listened to the likes of you? Whatever happened to the can-do attitude that saw a golden age of innovation throughout the 20th century? It’s about time all you prophets of doom got behind some ambitious projects like the solar tower and gave them your support rather than your damnation.

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