- #1
Fish4Fun
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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.
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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
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
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