# Very Large Scale Wind Generator

by Fish4Fun
Tags: generator, scale, wind
 P: 247 Renewable Energy (RE) Sources are a hot topic, but careful study of the solutions thus far offered make realizing RE as more than a tiny percentage of demand unrealistic. I have been thinking on an idea for a very large scale wind generator that I think is a potential solution for many of the current limitations of RE. I am going to outline the idea here along with some merits and potential pitfalls. Cost and output projections are just guestimates; the actual costs of a system this large would depend a lot on location and the details of actual construction. I am going to focus on the general concept and use specific numbers only to demonstrate a possible scale to help clarify the idea. In the event this is not an original idea, I would love any links to specifications or details of a similar system, but I have not been able to locate any. Imagine 100 miles of railroad track connected in a closed loop, for now, just imagine a 32 mile diameter circular track. On this track are flatbed rail cars 75ft in length connected one to the next. There are enough cars on the track so that the last car and the first car are connected together creating a closed loop of rail cars all the way around the track. Some or all of the cars on the track are fitted with a mast and sail that can be hoisted, furled and adjusted like the rigging on a sailboat. The sum of the force captured from the wind by the hoisted sails will push the cars around the track. Let's quantify the above example. The power in wind is defined as: Power = 1/2 * (Air Density) * Area * (Wind Speed)^3 * CP Where CP is the Coefficient of Power with an upper limit of 0.5926 (Betz Limit), and a realistic value of ~0.30. (100 miles * 5280ft/mile)/75ft/Car => 7040 Cars. If we assume every car is equipped with a 100ft mast and a triangular sail with an area of 3500sqft and that 90% of the sails are hoisted and capturing energy we have a swept area of 0.90 * 7040 * 3500 = 22,176,000sqft. If every third car has a sail then the sail area would be 1/3rd this figure, 7,392,000sqft. Alternately, we might consider the swept area to be 100ft height * 32 mile diameter = 16,896,000sqft. There are many things to consider when calculating the actual collection area in this large scale case, not the least of which is "shading", for the purpose of demonstrating my idea, having the right order of magnitude is close enough. Assuming the generator is located in an area with 20mph prevailing winds the available wind energy is: .5 * rho * 15,000,000sqft * 20mph => 609.6MW Assuming a CP of 0.30 this gives us 182.88MW of captured energy (about 1/3 the capacity of a small nuclear power plant). (Note: I used 15,000,000sqft as a "low-ball" of the above square foot calculations.) Obviously a project of this magnitude would require teams of engineers, including Electrical Engineers, who are far more likely to determine the best method of converting the mechanical energy into electricity than I am; however, my thought would be to locate stator coils in the the track and the rotor coils on the cars themselves. Obviously this would require the train to maintain a constant speed regardless of the wind speed to allow direct coupling to the Grid. Achieving a constant train velocity in varying wind speeds is easily achieved above some minimum "cut-in" wind speed. Designing the generator to achieve 60hz at some fixed train car speed is fairly straight-forward engineering. More on this later. ***************************************************** Following are some thoughts about the system including how it might be implemented, design advantages to more conventional RE, pitfalls and challenges. Obviously the physical size of this project presents some engineering challenges and the cost/benefit ratio would need to be carefully considered. Rather than figure out how much rail track, cars, et al might cost, I will focus on what the value of such a system might be. Assuming from our above example that the output @ 20mph wind speed is roughly 1.8MW/Mile, and assuming that RE needs to cost less than $3/installed watt to be viable, this gives us a maximum project cost of$3/W * 1,800,000W/Mile = $5,400,000/Mile. @ 10mph average wind speed$3/W * 228,600W/Mile = $685,800/Mile, and @ 30mph average wind speed$3/W * 6,172,200 = $18,516,600/Mile. Obviously a great deal depends on the site location. Why$3/Watt? Current wholesale power sells for $0.04/kWh, or$0.00004/Wh. A year is 24 * 365 = 8760 hours. Each Average Watt of output @ $0.00004/Wh => 8760 * 0.00004 =$0.3504/Year. This roughly represents the annual load on an 8% 10 year loan of $3. If a longer payback is acceptable then a slightly higher cost figure could be used; for a shorter payback period a lower cost per Watt could be used, but$3/W is good middle of the road figure. New nuclear reactors in the US are expected to have construction costs ~$3.50/W, so again,$3/W seems like a good place to begin. I am NOT stating this system could be built for \$3/W, I am simply stating this would be a good place to initial cost analysis. Obviously standard rail track and cars are not the optimal candidates for such a system. The lateral loads introduced by the sails would cause frequent de-railings. Similarly, the cars and track do not need to be designed to carry 170,000#s of payload. Design of a suitable rail system and "cars" would be a large part of any initial viability study. In conventional wind turbines "Tip to Speed Ratio" (TSR) is an important factor relating the speed of the turbine's tips to the wind speed. Typical values of TSR range from 0.5 to >12. Turbines with a TSR over 1.0 are considered "lift" type turbines while those with a TSR < 1.0 are considered "drag" type turbines. Sail powered ice boats achieve speeds as much as 5X the wind speed. Sail boats regularly achieve speeds faster than the wind. The design of this system should take into account the prevailing wind speeds, maximum wind speed and a "cut-in" wind speed that maximizes annual power production for a particular location. The fixed speed of the cars and the aerodynamics of the sails should be chosen to maximize annual power production. Unlike most existing commercial RE systems, this system could utilize land resources near large population centers. For instance, if the train speed chosen was 30mph, and a city with suitable wind resources were chosen that had a "belt-line" going around the city, it might be possible to elevate the track above the "belt-line". While adding considerable cost to the project, the elevated track would be exposed to higher winds than a ground based system. Transmission losses would be minimized by the proximity to the city. A 30mph train speed would pose little threat to catastrophic failure in a well designed system. Additionally this type of system could easily be placed over water where wind resources are frequently considerably higher than near-by inland areas. If you have followed along this far then you are likely a wind enthusiast, and as such, you might realize that sails are not necessarily the best means of capturing the wind's energy. If the sails were replaced with wings, it may be possible to increase performance and reduce system costs, but this decision would require a carefully selected airfoil for the particular site's wind characteristics. Because the distance from one side of the track to the other side is very large compared to the height of sails/wings (100ft to 32 miles), it is likely the "downwind" wings/sails that might generally be considered "shaded" by the "upwind" wings/sails would in fact contribute significantly to the energy captured. ******************************************************* I have been thinking on this system for a few months, and it seems very viable to me. What I would love is some feedback in the form of criticism or suggestions. I certainly do not have the resources to undertake such a project, even on a prototype scale, but I think the general idea has merit and might be feasible for a large corporation or government entity. It may well prove that the cost of construction would exceed any reasonable return on investment. I hope some people with experience might help define what the costs might be. I hope that some engineers here can help refine the production capacity/mile. If this idea does prove viable, and it is uniquely mine (both doubtful), I would happily offer it up under the GNU licensing agreement and simply expect recognition for the concept. I am not looking to make money, only investigate RE solutions that might actually make a contribution. Fish
 P: 475 The major problems that I see are, on the downwind section of the track the downwind cars will be shielded by the up wind cars and produce a lot less power then you anticipate, on the upwind section of the track you will have no motive power and on the cross wind sections of the track you will have enourmous overturning forces on the trucks.
 Mentor P: 22,244 How is this better than just installing 150 5MW wind turbines?
Engineering
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Thanks
P: 6,959
 Quote by Fish4Fun 1) While I used "75ft flat cars" as an example, the "cars" themselves really need to be little more than a tube or I-Beam with wheels and mounting platform for a mast or wing. For the mast/wing itself I suggested 100ft height; however, it may well be possible to engineer these in two parts, or it may prove more economical to actually set up a fabrication facility on site. Remember, the "cars" all travel around the track. If the masts/wings are in fact fabricated on site, then the output could be doubled or tripled by going with 200ft or 300ft height.
I think you are missing something here. The reason that a 100ft high "tall ship" sailing boat doesn't blow over sideways is because it has a deep keel to resist the overturning moment of the wind.

Unless you plan to build some type of multi-rail track with rails at different heights, the only alternatives would be

1. A very wide track. I'm guessing, but if you wanted 100ft high sails that might mean say a 25 ft wide wheelbase, compared with normal railway engineering of less than 5ft, or

2. Cars that are insanely heavy, so the outside wheels don't lift into the air when the wind tries to blow them over.

Think about the geometry of a catamaran sailboat, not a railway truck - though racing catamarans often sail with one hull out of the water and rely on steering to stop them overturning completely, but steering is not an option on a fixed rail track.

Actually, the problem of transporting wind turbine blades is easy to solve. With a small airship you could take the blades direct to the site, on any type of terrain, anywhere on the planet. It's a pity that airships went out of fashion a long time ago, and the German "Cargolifter" project ran out of money before it had a product to sell.
 P: 247 AlephZero, I am aware of the keel on sailing vessels, and the disparity of height to base for a "standard" rail car and the mast/sail. The rail I envision would be a multiple contact system. Imagine a round rail with "wheels" @ 330 degrees and 150 degrees for the "outside" rail, and 30 degrees and 210 degrees for the "inside" track. That is one possible solution. Another would simply to have a third rail with the wheel 180 degrees out from the primary wheels. Honestly, modern roller coasters achieve far greater de-railing forces than this system would encounter. I think it is safe to assume a rail/car system could be designed that would negate the lateral forces exerted by the sails/wings. I appreciate this concern, but feel that it is not a major impediment to the overall system. Thank you for pointing out that lateral forces might be a problem if a standard rail car/track were used. It is fairly obvious to me that a system specific rail car/ track would need to be designed for this project to be viable. I appreciate you taking the time to read through my post and comment on it. Please continue to point out pitfalls and problems you see. Fish
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P: 3,081
One issue that jumps out at me, aside from cost comparisons, is land usage:
 4) The relatively large "footprint" of each turbine means spreading 150 turbines over a fairly large geographic area.
vs
 4) The footprint of my proposed system does not require it to be a circle, just a closed loop. This means that the track can follow natural geographic boundaries, roads, right-of-ways etc, etc.
While the boundaries of a traditional wind farm can be large, the actual dedicated land for wind turbines may be relatively very small, as the land can be dual use in, say, the present case of cotton farms in Texas. It seems to me this enclosed loop of track concept has lot of work to do to make the same claim. A rancher/farmer that signs up to lease land for 3-4 turbine towers barely misses it, and they certainly don't interfere with daily ranch/farm operations. I don't see how that can ever be so when enclosed by a continually moving solid wall of flatcars.
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P: 3,081
 Quote by Fish4Fun ...If we assume every car is equipped with a 100ft mast and ...
Note that the most common 1.5MW GE turbine has a tower height of 328ft w/ the blade radius reaching out another 116ft. This matters of course because:
 ... The wind blows faster at higher altitudes because of the drag of the surface (sea or land) and the viscosity of the air. The variation in velocity with altitude, called wind shear, is most pronounced near the surface. Typically, in daytime the variation follows the 1/7th power law, which predicts that wind speed rises proportionally to the seventh root of altitude. Doubling the altitude of a turbine, then, increases the expected wind speeds by 10% and the expected power by 34%. Doubling the tower height generally requires doubling the diameter as well, increasing the amount of material by a factor of eight. In night time, or better: when the atmosphere becomes stable, wind speed close to the ground usually subsides whereas at turbine hub altitude it does not decrease that much or may even increase. As a result the wind speed is higher and a turbine will produce more power than expected from the 1/7th power law: doubling the altitude may increase wind speed by 20% to 60%.
http://www.daviddarling.info/encyclo...er_height.html
 P: 363 Fist of all I would like to say that even if this idea doesn't work out I think it is cool that you came up with something original (at least I have never heard of this before) and have obviously put a lot of thought into it. I do have a few concerns though. What would happen if two cars try to move in opposite directions? Lets assume that the 32 mile diameter track was located in a huge open field with nothing around it. If the wind was blowing over this entire field in the same direction then the cars on one side of the track would be pushed in one direction while the cars on the other side of the track would be pushed in the other direction. I think a far more realistic scenario is the track being located in an area surrounded by hills and buildings so the wind at various sections of the track would be in opposite directions and various speeds. Obviously the cars and sails would be designed so that they are most efficiently propelled by wind blowing in a certain direction, but your idea calls for very large cars that will still have substantial drag. So wind blowing in the wrong direction would at the very least slow the whole train down. Have you considered how fast the wind would have to be blowing to get one car moving? I have no idea, and it is certainly design dependent. A lighter car would be better but more likely to get blown over. A considerable amount of work would probably have to go into reducing friction between the wheels and the track just so the wind could push the cars. A single car would likely have a minimum wind speed, below which it would not move. If there is a substantial area of the track where the wind is below this speed, even if it is in the right direction, the wind at the other portions of the track may not be sufficient get the entire train moving. This could be even more of an issue if the wind at some sections of the track is opposing the motion of the train. I could also see reliability being a problem. You are proposing using 7040 cars. What if a wheel breaks or one car gets blown over by hurricane force winds. If anything causes even one car to stop moving or derail it would probably cause a chain reaction that could potentially derail several cars maybe even hundreds. If the system is built off the ground then a derailing of one car would certainly take many more with it. Thats all I have come up with so far. I look forward to your response. Thanks for starting an interesting discussion!
P: 247
mheslep,

Thank you for reading my post and taking the time to make constructive comments. You bring up two interesting points.

 Quote by mheslep One issue that jumps out at me, aside from cost comparisons, is land usage: Traditional vs While the boundaries of a traditional wind farm can be large, the actual dedicated land for wind turbines may be relatively very small, as the land can be dual use in, say, the present case of cotton farms in Texas. It seems to me this enclosed loop of track concept has lot of work to do to make the same claim. A rancher/farmer that signs up to lease land for 3-4 turbine towers barely misses it, and they certainly don't interfere with daily ranch/farm operations. I don't see how that can ever be so when enclosed by a continually moving solid wall of flatcars.
I actually envision the track being elevated, though I certainly did not mention it, I did allude to it when I suggested placing the track over existing belt lines/highways. This brings up a point I am sort of surprised no one has pointed out: Dealing with uneven terrain & obstructions such as trees, hills etc. While theoretically in a closed loop there would always be an equal amount of weight going uphill as going downhill, there is certainly a good case for making the track level.

Conventional HAWTs are typically located in remote areas where land use costs are minimal, but the remote locations themselves add a fair amount of cost to the overall system. In many cases roads need to be purpose built to allow access for the materials, equipment, construction and maintenance crews. While the foot print of a 1.5MW turbine maybe small, this is not the only land requisite for the turbine construction and support. Power lines either need to be buried or elevated above ground, and in many cases these runs can be quite long. Obviously a plan for a wind field containing over 100 conventional HAWTs would include minimizing road construction and likely attempt to coordinate power lines with roads where possible, but the roads and power lines still add "nuisance costs" to the farmer and require land.

Assuming the span between supports for an elevated system were 50ft, 100 miles of track would require 10,560 supports. The amount of land taken up by these bases would depend a lot on the elevation, weight of track and anticipated forces on the track, but the space between supports should be available for farming or other uses. Obviously the construction of the bases would require some infrastructure construction similar to building roads for conventional HAWTs, unless a system were devised to use the track itself with special "construction cars" to erect bases and set the track.

I really do not have all the answers, a project of this magnitude would require careful engineering even in the feasibility stages.

 Quote by mheslep Note that the most common 1.5MW GE turbine has a tower height of 328ft w/ the blade radius reaching out another 116ft. This matters of course....
Of course! I am aware of the increased wind speeds at higher elevations, but I cannot imagine how a system as large as my proposed system could have a base height of more than 25ft-100ft and remain fiscally viable. It may be possible to elevate the track 50ft and utilize a 300ft mast/wing, but the torque on the track/wheels/cars would be phenomenal. I am NOT a structural engineer; I have NO IDEA what is practical or even possible, nor what the expected costs might be. I would love a structural/civil engineer to chime in with some thoughts on feasibility/cost estimates/design ideas. It may well be that elevating the track is what makes this idea a fiscal loser.

In the end, if this idea does prove viable, it will likely be from economy of scale. Designing a 100MW to 10GW power plant always relies on prodigious engineering efforts to overcome challenges, a design based on this idea would be no different.

Thank you again for taking the time to consider my idea and post your thoughts and concerns.

Fish
P: 247
RandomGuy88,

Thank you for taking the time to read through my post and commenting. I will address your concerns in order:

 Quote by RandomGuy88 What would happen if two cars try to move in opposite directions?
Thank you for bringing this up, it will allow me to address a facet I only touched on in my initial post.

Regardless if sails or wings are used, "jibing" or altering the angle of attack is a critical part of the system. In sailing, a vessel can make headway in any direction from any wind direction by vectoring the force (ie adjusting the angle of the sail relative to the wind and vessel heading).

In this project knowing the wind direction and speed and communicating it to control mechanisms aboard each car equipped with a sail/wing would be critical. The project would require wind direction and speed sensors placed all around the track. I would guess at least one every mile of track, perhaps considerably closer. The cars would obviously have to know their relative position on the track.

 Quote by RandomGuy88 Have you considered how fast the wind would have to be blowing to get one car moving? I have no idea, and it is certainly design dependent. A lighter car would be better but more likely to get blown over. A considerable amount of work would probably have to go into reducing friction between the wheels and the track just so the wind could push the cars.....
I have considered this and feel that I have addressed it fairly well in my original post. In short, the power in the wind is a function of the affected area and the wind speed cubed (ws^3). The cars will begin moving when there is enough force to overcome static inertial friction and will continue to accelerate until they reach design speed (cut-in wind speed). Once the cars reach design speed, any increase in wind speed will result in power being generated, NOT a further increase in car velocity.

 Quote by RandomGuy88 I could also see reliability being a problem. You are proposing using 7040 cars. What if .....
Yes, careful attention to design and construction would be VERY IMPORTANT. Assuming a car speed of 30mph, roughly 4 continuous years of operation would equal slightly over 1 million miles of travel. Designing the system for durability AND maintenance would be a key consideration. It would be fairly easy to design the system so that during calm periods cars could be swapped out for maintenance. I have no idea what a reasonable car rotation rate might be, but 30mph is a fairly low stress speed, using multiple wheels per carriage might allow one or more wheels per carriage to fail w/o system failure allowing the offending wheel to be replaced during the next lull.

 Quote by RandomGuy88 Thanks for starting an interesting discussion!
I am glad that you have enjoyed it. Thank you for your interest and thank you for your input.

Fish
P: 247
In another forum, a member posted this information:

 Dear Mr Fish4Fun An interesting topic you mention - I believe that this specific idea was discussed in detail in the 1930's with the so-called Madaras power project at Burlington New Jersey USA - with tall rotor towers mounted on rail wagons running around a very large circular track I remember once reading an article in what I believe was a copy of the United States magazine "Practical Mechanics ? from the 1930's". and I also have an illustration in one of the books in my own library: "Energy - Survival Scrapbooks #3" by Stefan A. Szczelkun - New York 1974 - Lib of Congress Cat. Nr. 73-82211 This project in New Jersey USA - utilized the so-called Magnus effect - and was to a great degree influenced by the pioneering work done by Flettner in Germany mainly for ship propulsion. However I do consider that these technologies will have a great future importance - although not exactly for direct electrical power generation. I believe that this is clearly indicated by the present interesting work being done by Professor Salter from Edinburgh in Scotland with regard to the basic "Elsbett-Salter" technological approaches for introducing moisture into the off-shore atmosphere [off-shore sea winds blowing in-land towards arid-zone coastal areas]. With greetings and best wishes to all - JF
I responded with the following and thought I would do the same here as this pretty much resolves my initial questions:

THANK YOU. You have given me a wealth of information in your post! Using the information you gave me, I was able to locate an article from Popular Science, September 1978, page 75ff:

Further research took me to the full DOE study of the "Madaras Rotor Power Plant" in section 8 of this document:

http://www.nrel.gov/docs/legosti/old/469.pdf

For the casual readers I will outline the "Madaras Rotor Power Plant" concept, and DOE findings:

The general layout of the project is similar to my initial outline except in scale, the scales mentioned in the report included a 457m diameter closed track with 18 cable connected cars with an output of 18MW, and a 75 car, 100MW system. Further track size considerations ranged from 10.41km to 42.73km. Other figures:

Track/Cars:
track gauge = 11m
car height = 3.8m
car length = 19.2m
car width = 17.4m
gross car weight = 328,000kg

rotating cylinder:

aspect ratio = 8
e/d = 2
cylinder diameter = 4.9m
cylinder length = 38.1m
end-plate diameter = 9.8m
Rotation Speed = 186RPM

The "optimal car speed" (referred to as "track speed") was determined to be 13.4m/s. The mean wind speed used was 8.1m/s.

 Comparisons were made between Madaras plants and comparable arrays of horizontal axis wind turbines. Based upon assumptions employed, plant and energy costs of a racetrack-configured Madaras system were found to be similar to costs of an equally sized farm of conventional first generation wind turbines.
Furthermore, as many have pointed out:

 It is clear that the Madaras system composed of translating rotor cars is more complex than a stationary array of conventional wind systems. Thus, it is anticipated that the operation and maintenance cost for a Madaras system would probably be higher than that of conventional wind systems. Calculations based upon costs developed for the system indicated that the energy cost is similar to a conventional first generation system...

1) While my idea involved sails or wings, this project was based on rotating cylinders. The lift generated by a rotating cylinder (the Magnus Effect) is stated as being superior to sails or standard air foils by as much as a factor of 10. This assessment would seem to imply that the use of rotating cylinders is superior to sails/wings; however, while the same aerodynamic efficiency holds true for aircraft, the Magnus Effect has not proven viable in general aircraft design. This suggests that the most efficient airfoil is not always the most economically viable or mechanically reliable engineering solution.

2) The Madars system was considerably heavier than the system I envisioned. This was primarily due to the massive DC motors employed (450kW) to rotate the cylinders, the inclusion of 4 * 250kW generators on each car, and the notion of using a "conventional" railroad track which required a huge "base width" (11m). I am uncertain if using a narrower track gauge with over/under track wheels, lighter cars and an integrated car/track generator design would substantially impact the cost or efficiency and thus economic viability of such a system, but I suspect it would not.

3) The Madaras system proposed using a 457m diameter track with 27m cylinders and an estimated output of 18MW suggests an overall CP of 0.45 using the swept area = 457m * 27M = 12339m^2 and a rated output @ 8.1m/s wind speed. This lends some credence to my initial assumption that using exposed width * height is legitimate even for a very large scale VAWT. It also demonstrates that an initial CP of 0.30 is not unreasonable for a system this size. The more rigorous engineering methods employed in the DOE report stated that a "race car style track" with long straight sections normal to the prevailing winds would produce a considerably higher output than a simple circular track (assuming prevailing wind direction were predominant).

4) The DOE report proves 100% that my idea was NOT unique, furthermore, many of the precepts have been carefully studied and evaluated. While I have no memory of ever having read about the Madaras project, it is entirely possible I read the Popular Science article in 1978, perhaps seeding the notion.

*******************************************************************

In conclusion, while I still believe the concept is potentially viable, I do not have the engineering skills nor the resources to do more than outline the project, certainly not refine it past its current state. The DOE report, while slightly different than my thought, is proof that a rigorous scientific study of the concept has been completed, and the conclusion is that more conventional wind turbines hold at least a maintenance advantage over the Madaras concept.

I would like to thank everyone who has taken the time to read through my posts and respond. A special thanks to "JF" for helping me find the information to close the book on this line of thought. I hope others have enjoyed this exercise as much as I have!

I wish everyone a Happy Holiday Season!

Fish
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P: 3,081
 Quote by Fish4Fun In conclusion, while I still believe the concept is potentially viable,
'Viable' implies both technical and economic feasibility. To know the concept is viable you'd need to estimate some rough order magnitude of cost per unit of energy produced.