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A guide to the logic of giant kites

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  • roderickjosephread
    I have written and published an article http://kitepowercoop.org/kite-power-coop-news/40-new-online-guide-to-aweexplaining the reasoning of giant arch kites.
    Message 1 of 15 , Oct 9, 2013
      I have written and published an article explaining the reasoning of giant arch kites.
      This is your chance for editorial before the article gets distributed more broadly.

      The logic of giant kites

      Wind power is viable, only, without towers.

      Wind carries hundreds of times the total human energy demand. To mine it, standard turbines would require impossible amounts of steel and concrete.

      A new power race has begun.

      Squadrons of kite machines prepare to battle for dominance in air power.



      Kites to harvest the sustainable power we crave.

      Kites are powerful. So powerful that Americas Cup yachting banned them. Pulling one yacht is easy. How can you pull enough power for cities and cars?

      Wind power comes from how much air you move through. Large, fast wings are the design goal for airborne wind energy (AWE) engineers.

      Mechanical power is how quick, hard and far you move things. Link a strong fast pull to a generator that gives you power.

      Some proposed designs are over 1km wide. Others have flying turbines whose tips travel at close to the speed of sound. The power is all there.

      Large, fast, lightweight AWE machines have really arrived.



      The battleground

      Contenders for AWE dominance face obvious challenges. Kites are hard to control. Large air-plane wings are expensive and heavy. Land and airspace is limited. The standard rules of aviation airspace apply.

      The appeal of AWE lead engineering teams to surprisingly varied solutions.

      As well as the design war, a propaganda war has now begun. Well resourced government and corporate teams spar against university spin off's, charities and open network teams.

      Weaker designs will fall on the way. Gentlemen (and lady financiers), it's time to place your bets on the winning architecture.



      Scoring

      Successful engineering is measured by growth rate and return on investment. History is littered with dead engineering ventures that came so far and so close. Previous lessons make this battle all the more intriguing.

      Adrian Gambier (Frauhofer Institute of Wind Energy) says that complexity grids and RAMS (Reliability, Availability, Maintainability, Safety) dependability studies are key to spotting winners early.



      The teams

      Small networked teams like Kpower and Kite Power Cooperative, claim to hit these dependability metrics square on using new massive soft kite forms. But they seem committed to testing novel ideas before seeking funding.

      Makani Power, sponsored by Google and ARPA-e may seem the riskiest design of the bunch. A robotic rigid wing with dual mode propeller / turbine blades generates at altitude. But the Makani wing only flies in circles to generate.

      Ampyx Power from The Netherlands also use a fast rigid wing. Ampyx have grown beyond initial funding stages. They now raise capital on their own website. Sleek control and generation demonstrations have helped.

      Many more design teams are competing, and like Ampyx using the “yo-yo” method. In yo-yo standard kites fly across the wind pulling their tether from a generator drum on the ground. After generation the kite is wound back in.



      Why do they risk it?

      It's certainly not all money and power.

      Existing turbine dynamics were already highly optimised but barely touched at atmospheric energy. Radical changes were needed to reach the stronger high altitude wind energy. Oddly kite power has ancient history.

      Kites are also fun of course, but now, maybe even necessary.

      The winning design can hopefully save the world from an energy and global warming crisis.



      Coming clean

      That was my best objective view of AWE. I admit, I am heavily involved in Kite Power Cooperative. Generally speaking AWE scientists and engineers are a friendly lot. We recently shared research data at conference.

      But business is business. Get it right first time.

      My job is; hopefully save the world from an energy and global warming crisis. It's an odd remit. So I'm going to tell you exactly how I intend to go about it.

      It's new, it's scary and web-like. That description applies to the machine solutions and the team dynamic.

      Open Hardware

      All Kite Power Cooperative IP & designs are available as open source hardware. This way, designs are open to scrutiny and continuously improved by expert online forums. Anybody can use our designs under the creative commons 3.0 license. We ask that you feedback and care for the community you affect.

      Our designs are simple, fail-safe, scalable, inherently self controlled, with low embodied energy. They are insurable, locally empowering and beautiful.

      If I do say so myself...

      Cooperative teams

      Cooperatives are uncompromising in aspiration. We have a common goal. Environmentally and ethically sound energy security. Our design motives are pure, untouched by shareholder concerns.

      Members are eager to do their bit. Please feel welcome to join.

      This article is in part, a call to anyone who can help create better solutions.

      Giant kites are scary.

      Absolutely they are. Our designs are primarily crafted for safety.

      Arch kite systems connect to the earth at multiple points. This prevents catastrophic single point failures.

      Huge power is implicit in our designs, so we use proven principles from harsh marine environments. Many of our arch designs resemble trawler fishing nets. These designs can be inverted to work in tidal flows.

      Water is 800 times denser than air. Rope and fishing nets, have survived and evolved through centuries of marine testing.

      Arch kites can be launched with strict multi stage control bridling. This way gusts are not able to move huge architectures beyond human control.

      Working with the earth

      We are the only team using the earth itself as a main component. By staking arch kites to the ground in multiple locations we can be confident of yaw stability and fail-safe modes of our kites.

      Leading edge integrity is another advantage of multiple ground contact points. Tensioned crosswind load lines ensure that our sails present a smooth profile.

      Tensioned arch systems are material efficient. So we can build giant kites with low flying weight. This returns the best power to weight ratio of any design.

      Arches only “fly” multi tethered lightweight tensile ropes and fabrics. Arch kites are therefore more dependable and safer in the air. That's important for certification and insurance.

      Efficient land and air use

      Arch kites are held across the wind. They fill an area of sky with sails. An arch kite therefore engages with more moving air in any given second than faster designs. So for the same land footprint an arch kite can generate more power than a standard kite.

      Arches are low-complexity devices and use off the shelf materials.

      Modern Dyneema® rope has amazing strength. It floats on water. Ropes can transmit power more efficiently than electricity lines and oil pipelines.

      Generators are more efficient when they are big. And less deadly when they are on the land. Arch ropes, bridles and load-paths have been ganged to work together. Pulling generators round in both flight phases unlike yo-yo designs.



      Team flexibility

      How many TED talks, tell you to do what you love?

      Kite Power Cooperative and other open source teams do just that. Business development works are discussed and issued openly and cooperatively, but personal motivations and inspiration usually take top priority.

      I've been playing in the wind ever since I was born in a storm on the equinox.

      We'll get around to raising cash soon.

      One current group priority is redressing publication bias. A book on AWE by Airborne Wind Energy Consortium (AWEC) was published by springer. The book made no mention of low-complexity or open source architectures.

      So today I'm working on that. The forum will edit this article for me tonight.



      Ahead of the curve

      Open source hardware (like software) relies on being better. It is built with passion for an optimum outcome. Being open from the start allows us to prioritise our IP artworks and openly find support networks.

      Cooperatives are some of the biggest businesses on the planet. Businesses with a social structure survive market fluctuation.

      Keep your eye out for giant kite structures.

      Coming soon.



      Roderick Read,

      Windswept and Interesting Ltd

      for Kite Power Coop

    • roderickjosephread
      I have one concern about the article that definitely needs a group edit.... Bob S may have caught me spouting BS... not his initial intent (gedit?) But I may
      Message 2 of 15 , Oct 9, 2013
        I have one concern about the article that definitely needs a group edit....
        Bob S may have caught me spouting BS... not his initial intent (gedit?)
        But I may have wrong information, where I wrote the wooly statement "Generators are more efficient when they are big."  
        It's certainly the case
        with coal when building steam pressure for turbine generators...
        But to what extent does it hold for generalised electrical generators? Or even for that matter differing pumps or devices which could be considered the output transducer of a rope pull?
        Sorry this seems a bit basic a this stage and I thought we had it covered before now.
        Is a bigger generator better?
      • dave santos
        Roddy, It has been true that the largest generators are the cheapest to operate; a textbook case of economy-of-scale. The trend of automated manufacturing is
        Message 3 of 15 , Oct 10, 2013
          Roddy,

          It has been true that the largest generators are the cheapest to operate; a textbook case of economy-of-scale. The trend of automated manufacturing is eroding this advantage, as it becomes increasingly practical to create a flood of smaller units with ever less labor (esp. for wind-wall-of-turbines)Heat dissipation is a key issue for flygens, which must be super lightweight, so smaller is better in this niche. A big fixed industrial generator is so massive that its a huge effective heatsink. Large units generally run cooler with greater thermal stability using this mass advantage. Lifetime cost and capital costs complicate the choice question. Its safe to say that generators at all scales find large markets.

          Please include in your manifesto the CC cooperative idea that existing power plants, even at the largest scales, can be incrementally converted into kite-hybrids. kPower is actively proposing this AWE bootstrap concept to its utility partner, Austin Energy, to offset coal consumption driving .5 GW gens,

          daveS





        • Harry Valentine
          Very valid points raised here . . . weight and heat dissipation capability of high-powered electric generators. I ve encountered an epidemic of failures of
          Message 4 of 15 , Oct 10, 2013
            Very valid points raised here .  .  .  weight and heat dissipation capability of high-powered electric generators. I've encountered an epidemic of failures of small, lightweight electric generators that are required to deliver high output, in different applications.

            Groundgen allows for heavy, liquid-cooled (if necessary) electric generators that will offer greatly extended service life .  .  . also easy and ready access for regular maintenance.


            Harry


            To: AirborneWindEnergy@yahoogroups.com
            From: santos137@...
            Date: Thu, 10 Oct 2013 08:38:04 -0700
            Subject: Generator economy of scale //Re: [AWES] RE: A guide to the logic of giant kites

             

            Roddy,

            It has been true that the largest generators are the cheapest to operate; a textbook case of economy-of-scale. The trend of automated manufacturing is eroding this advantage, as it becomes increasingly practical to create a flood of smaller units with ever less labor (esp. for wind-wall-of-turbines)Heat dissipation is a key issue for flygens, which must be super lightweight, so smaller is better in this niche. A big fixed industrial generator is so massive that its a huge effective heatsink. Large units generally run cooler with greater thermal stability using this mass advantage. Lifetime cost and capital costs complicate the choice question. Its safe to say that generators at all scales find large markets.

            Please include in your manifesto the CC cooperative idea that existing power plants, even at the largest scales, can be incrementally converted into kite-hybrids. kPower is actively proposing this AWE bootstrap concept to its utility partner, Austin Energy, to offset coal consumption driving .5 GW gens,

            daveS






          • Bob Stuart
            Heat Sink has acquired two different meanings. Classically, it is something that can rapidly absorb heat, such as a metal clamp used to isolate the heat of
            Message 5 of 15 , Oct 10, 2013
              "Heat Sink" has acquired two different meanings.  Classically, it is something that can rapidly absorb heat, such as a metal clamp used to isolate the heat of soldering to one section of wire.  For continuous use, a pure sink does no good at all; it needs to cool itself, usually with fins to heat air.  On electronics, a finned plate applied to a chip has little thermal mass, but is still called a sink, instead of a radiator or exchanger.  

              I've seen minor finning on the outside of explosion-proof motors, but I've gotten the impression that large generators are often designed with extravagant amounts of copper to increase efficiency, and no particular attention to cooling.  For continuous duty, mass means nothing; only area helps, and the square-cube law favors small units.  There is more than an order of magnitude difference in the weight of common motors in the fractional hp range, with those on model aircraft leading the pack.  

              Smaller generators with less thermal mass are more vulnerable to transient overloads or high ambient temperatures, but I don't think they are inherently unreliable.  I'd like to see the per-watt cost of automotive alternators compared to the larger competition.  They are presumably reasonably well optimized for automated production, which is an advantage if what we really need to buy is a given weight of wire and iron per watt.  How have better permanent magnets changed the options?  Can the better cooling of small units reduce the weight needed?  We know that turbine blades are on the wrong end of the square-cube law, with each added pound giving less length and power than the previous one.  Would even standard wind towers do better supporting dozens of small generators instead of one big one?  

              Bob Stuart

              On 10-Oct-13, at 9:46 AM, Harry Valentine wrote:


              Very valid points raised here .  .  .  weight and heat dissipation capability of high-powered electric generators. I've encountered an epidemic of failures of small, lightweight electric generators that are required to deliver high output, in different applications.

              Groundgen allows for heavy, liquid-cooled (if necessary) electric generators that will offer greatly extended service life .  .  . also easy and ready access for regular maintenance.


              Harry


              To: AirborneWindEnergy@yahoogroups.com
              From: santos137@...
              Date: Thu, 10 Oct 2013 08:38:04 -0700
              Subject: Generator economy of scale //Re: [AWES] RE: A guide to the logic of giant kites

               

              Roddy,

              It has been true that the largest generators are the cheapest to operate; a textbook case of economy-of-scale. The trend of automated manufacturing is eroding this advantage, as it becomes increasingly practical to create a flood of smaller units with ever less labor (esp. for wind-wall-of-turbines)Heat dissipation is a key issue for flygens, which must be super lightweight, so smaller is better in this niche. A big fixed industrial generator is so massive that its a huge effective heatsink. Large units generally run cooler with greater thermal stability using this mass advantage. Lifetime cost and capital costs complicate the choice question. Its safe to say that generators at all scales find large markets.

              Please include in your manifesto the CC cooperative idea that existing power plants, even at the largest scales, can be incrementally converted into kite-hybrids. kPower is actively proposing this AWE bootstrap concept to its utility partner, Austin Energy, to offset coal consumption driving .5 GW gens,

              daveS








            • Harry Valentine
              How would you propose to increase cooling capability of lightweight airborne generators carried by kites? Is it worth the cost of using balloons to carry such
              Message 6 of 15 , Oct 10, 2013
                How would you propose to increase cooling capability of lightweight airborne generators carried by kites? 

                Is it worth the cost of using balloons to carry such technology?

                How do the short-term (capital & installation) cost and long-term cost (maintenance & spare parts) of conventional generators (air-cooled or water-cooled) installed at ground level compare with the cost of small, lightweight (air-cooled) airborne generators? 


                Harry



                To: AirborneWindEnergy@yahoogroups.com
                From: bobstuart@...
                Date: Thu, 10 Oct 2013 10:42:22 -0600
                Subject: Re: Generator economy of scale //Re: [AWES] RE: A guide to the logic of giant kites

                 
                "Heat Sink" has acquired two different meanings.  Classically, it is something that can rapidly absorb heat, such as a metal clamp used to isolate the heat of soldering to one section of wire.  For continuous use, a pure sink does no good at all; it needs to cool itself, usually with fins to heat air.  On electronics, a finned plate applied to a chip has little thermal mass, but is still called a sink, instead of a radiator or exchanger.  

                I've seen minor finning on the outside of explosion-proof motors, but I've gotten the impression that large generators are often designed with extravagant amounts of copper to increase efficiency, and no particular attention to cooling.  For continuous duty, mass means nothing; only area helps, and the square-cube law favors small units.  There is more than an order of magnitude difference in the weight of common motors in the fractional hp range, with those on model aircraft leading the pack.  

                Smaller generators with less thermal mass are more vulnerable to transient overloads or high ambient temperatures, but I don't think they are inherently unreliable.  I'd like to see the per-watt cost of automotive alternators compared to the larger competition.  They are presumably reasonably well optimized for automated production, which is an advantage if what we really need to buy is a given weight of wire and iron per watt.  How have better permanent magnets changed the options?  Can the better cooling of small units reduce the weight needed?  We know that turbine blades are on the wrong end of the square-cube law, with each added pound giving less length and power than the previous one.  Would even standard wind towers do better supporting dozens of small generators instead of one big one?  

                Bob Stuart

                On 10-Oct-13, at 9:46 AM, Harry Valentine wrote:


                Very valid points raised here .  .  .  weight and heat dissipation capability of high-powered electric generators. I've encountered an epidemic of failures of small, lightweight electric generators that are required to deliver high output, in different applications.

                Groundgen allows for heavy, liquid-cooled (if necessary) electric generators that will offer greatly extended service life .  .  . also easy and ready access for regular maintenance.


                Harry


                To: AirborneWindEnergy@yahoogroups.com
                From: santos137@...
                Date: Thu, 10 Oct 2013 08:38:04 -0700
                Subject: Generator economy of scale //Re: [AWES] RE: A guide to the logic of giant kites

                 

                Roddy,

                It has been true that the largest generators are the cheapest to operate; a textbook case of economy-of-scale. The trend of automated manufacturing is eroding this advantage, as it becomes increasingly practical to create a flood of smaller units with ever less labor (esp. for wind-wall-of-turbines)Heat dissipation is a key issue for flygens, which must be super lightweight, so smaller is better in this niche. A big fixed industrial generator is so massive that its a huge effective heatsink. Large units generally run cooler with greater thermal stability using this mass advantage. Lifetime cost and capital costs complicate the choice question. Its safe to say that generators at all scales find large markets.

                Please include in your manifesto the CC cooperative idea that existing power plants, even at the largest scales, can be incrementally converted into kite-hybrids. kPower is actively proposing this AWE bootstrap concept to its utility partner, Austin Energy, to offset coal consumption driving .5 GW gens,

                daveS









              • Baptiste Labat
                Here are my thoughts on the question of bigger generators are better . I think it all depends on the ressource. I will take the example of wave energy
                Message 7 of 15 , Oct 10, 2013
                  Here are my thoughts on the question of "bigger generators are better".

                  I think it all depends on the ressource. I will take the example of wave energy extraction. If it is too small it will not be able to retrieve the energy from the biggest waves. If it is too large, it will filter the waves out and not move at all. A good design has to be at the scale of the perturbations (modal wavelength, corresponding to peak of energy spectrum).
                  If you take the mega offshore wind turbine, bigger enables to go higher and to catch more wind that several smaller ones. As well bigger means they will resist better to huge waves. But such a big turbine might not be efficient because the wind is not uniform. That's why the blades are separatedly control to allow optimization of the angle of attack (pitch control) for the one at the top which has more wind, and the one at the bottom which has less wind (due to the shear layer).

                  Hope it might be of help even if i am not strictly speaking of generators.

                  ++
                  Baptiste


                  On Thu, Oct 10, 2013 at 6:53 PM, Harry Valentine <harrycv@...> wrote:
                   

                  How would you propose to increase cooling capability of lightweight airborne generators carried by kites? 

                  Is it worth the cost of using balloons to carry such technology?

                  How do the short-term (capital & installation) cost and long-term cost (maintenance & spare parts) of conventional generators (air-cooled or water-cooled) installed at ground level compare with the cost of small, lightweight (air-cooled) airborne generators? 


                  Harry



                  To: AirborneWindEnergy@yahoogroups.com
                  From: bobstuart@...
                  Date: Thu, 10 Oct 2013 10:42:22 -0600
                  Subject: Re: Generator economy of scale //Re: [AWES] RE: A guide to the logic of giant kites

                   
                  "Heat Sink" has acquired two different meanings.  Classically, it is something that can rapidly absorb heat, such as a metal clamp used to isolate the heat of soldering to one section of wire.  For continuous use, a pure sink does no good at all; it needs to cool itself, usually with fins to heat air.  On electronics, a finned plate applied to a chip has little thermal mass, but is still called a sink, instead of a radiator or exchanger.  

                  I've seen minor finning on the outside of explosion-proof motors, but I've gotten the impression that large generators are often designed with extravagant amounts of copper to increase efficiency, and no particular attention to cooling.  For continuous duty, mass means nothing; only area helps, and the square-cube law favors small units.  There is more than an order of magnitude difference in the weight of common motors in the fractional hp range, with those on model aircraft leading the pack.  

                  Smaller generators with less thermal mass are more vulnerable to transient overloads or high ambient temperatures, but I don't think they are inherently unreliable.  I'd like to see the per-watt cost of automotive alternators compared to the larger competition.  They are presumably reasonably well optimized for automated production, which is an advantage if what we really need to buy is a given weight of wire and iron per watt.  How have better permanent magnets changed the options?  Can the better cooling of small units reduce the weight needed?  We know that turbine blades are on the wrong end of the square-cube law, with each added pound giving less length and power than the previous one.  Would even standard wind towers do better supporting dozens of small generators instead of one big one?  

                  Bob Stuart

                  On 10-Oct-13, at 9:46 AM, Harry Valentine wrote:


                  Very valid points raised here .  .  .  weight and heat dissipation capability of high-powered electric generators. I've encountered an epidemic of failures of small, lightweight electric generators that are required to deliver high output, in different applications.

                  Groundgen allows for heavy, liquid-cooled (if necessary) electric generators that will offer greatly extended service life .  .  . also easy and ready access for regular maintenance.


                  Harry


                  To: AirborneWindEnergy@yahoogroups.com
                  From: santos137@...
                  Date: Thu, 10 Oct 2013 08:38:04 -0700
                  Subject: Generator economy of scale //Re: [AWES] RE: A guide to the logic of giant kites

                   

                  Roddy,

                  It has been true that the largest generators are the cheapest to operate; a textbook case of economy-of-scale. The trend of automated manufacturing is eroding this advantage, as it becomes increasingly practical to create a flood of smaller units with ever less labor (esp. for wind-wall-of-turbines)Heat dissipation is a key issue for flygens, which must be super lightweight, so smaller is better in this niche. A big fixed industrial generator is so massive that its a huge effective heatsink. Large units generally run cooler with greater thermal stability using this mass advantage. Lifetime cost and capital costs complicate the choice question. Its safe to say that generators at all scales find large markets.

                  Please include in your manifesto the CC cooperative idea that existing power plants, even at the largest scales, can be incrementally converted into kite-hybrids. kPower is actively proposing this AWE bootstrap concept to its utility partner, Austin Energy, to offset coal consumption driving .5 GW gens,

                  daveS










                • dave santos
                  ...   ... We are considering thermodynamically open systems, and sinks so large that no runaway overheating occurs (like a power plant using ocean water
                  Message 8 of 15 , Oct 10, 2013
                    > (Bob's comments)
                     
                    >"Heat Sink" has acquired two different meanings.  Classically, it is something that can rapidly absorb heat, such as a metal clamp used to isolate the heat of soldering to one section of wire.  For continuous use, a pure sink does no good at all; it needs to cool itself, usually with fins to heat air. 
                    We are considering thermodynamically open systems, and sinks so large that no runaway overheating
                    occurs (like a power plant using ocean water cooling). Increased thermal resistance with temperature is the runway generator-killing effect, and a cool-running giant generator is clearly operating well below its heat-sink limit.
                    > I've gotten the impression that large generators are often designed with extravagant amounts of copper to increase efficiency, and no particular attention to cooling. 

                    This is changing as engineers design more carefully.

                    >For continuous duty, mass means nothing;

                    Excepting flywheel-mass, which has key uses. A larger mass also has more area and a cooler equilibrium temperature for equivalent specific heat.

                    >Smaller generators with less thermal mass are more vulnerable to transient overloads or high ambient temperatures, but I don't think they are inherently unreliable. 

                    Cosmic Ray bombardment over eons :) 

                    >I'd like to see the per-watt cost of automotive alternators compared to the larger competition.  

                     We should see an asymptotic trend toward cost scale-equality.

                    >How have better permanent magnets changed the options?

                    Best performance, but preloads capital cost.  

                    >Can the better cooling of small units reduce the weight needed? 

                    Yes, and advanced liquid-air thermodynamic cycles may figure

                    >Would even standard wind towers do better supporting dozens of small generators instead of one big one? 

                    Its partly a packaging perception, since a large "single" generator is the integrated aggregation of "many" coils and magnets. Many small units might help in many interesting ways, like fast precise load-matching.



                    On Thursday, October 10, 2013 9:53 AM, Harry Valentine <harrycv@...> wrote:
                     
                    How would you propose to increase cooling capability of lightweight airborne generators carried by kites? 

                    Is it worth the cost of using balloons to carry such technology?

                    How do the short-term (capital & installation) cost and long-term cost (maintenance & spare parts) of conventional generators (air-cooled or water-cooled) installed at ground level compare with the cost of small, lightweight (air-cooled) airborne generators? 


                    Harry



                    To: AirborneWindEnergy@yahoogroups.com
                    From: bobstuart@...
                    Date: Thu, 10 Oct 2013 10:42:22 -0600
                    Subject: Re: Generator economy of scale //Re: [AWES] RE: A guide to the logic of giant kites

                     
                    "Heat Sink" has acquired two different meanings.  Classically, it is something that can rapidly absorb heat, such as a metal clamp used to isolate the heat of soldering to one section of wire.  For continuous use, a pure sink does no good at all; it needs to cool itself, usually with fins to heat air.  On electronics, a finned plate applied to a chip has little thermal mass, but is still called a sink, instead of a radiator or exchanger.  

                    I've seen minor finning on the outside of explosion-proof motors, but I've gotten the impression that large generators are often designed with extravagant amounts of copper to increase efficiency, and no particular attention to cooling.  For continuous duty, mass means nothing; only area helps, and the square-cube law favors small units.  There is more than an order of magnitude difference in the weight of common motors in the fractional hp range, with those on model aircraft leading the pack.  

                    Smaller generators with less thermal mass are more vulnerable to transient overloads or high ambient temperatures, but I don't think they are inherently unreliable.  I'd like to see the per-watt cost of automotive alternators compared to the larger competition.  They are presumably reasonably well optimized for automated production, which is an advantage if what we really need to buy is a given weight of wire and iron per watt.  How have better permanent magnets changed the options?  Can the better cooling of small units reduce the weight needed?  We know that turbine blades are on the wrong end of the square-cube law, with each added pound giving less length and power than the previous one.  Would even standard wind towers do better supporting dozens of small generators instead of one big one?  

                    Bob Stuart

                    On 10-Oct-13, at 9:46 AM, Harry Valentine wrote:


                    Very valid points raised here .  .  .  weight and heat dissipation capability of high-powered electric generators. I've encountered an epidemic of failures of small, lightweight electric generators that are required to deliver high output, in different applications.

                    Groundgen allows for heavy, liquid-cooled (if necessary) electric generators that will offer greatly extended service life .  .  . also easy and ready access for regular maintenance.


                    Harry


                    To: AirborneWindEnergy@yahoogroups.com
                    From: santos137@...
                    Date: Thu, 10 Oct 2013 08:38:04 -0700
                    Subject: Generator economy of scale //Re: [AWES] RE: A guide to the logic of giant kites

                     

                    Roddy,

                    It has been true that the largest generators are the cheapest to operate; a textbook case of economy-of-scale. The trend of automated manufacturing is eroding this advantage, as it becomes increasingly practical to create a flood of smaller units with ever less labor (esp. for wind-wall-of-turbines)Heat dissipation is a key issue for flygens, which must be super lightweight, so smaller is better in this niche. A big fixed industrial generator is so massive that its a huge effective heatsink. Large units generally run cooler with greater thermal stability using this mass advantage. Lifetime cost and capital costs complicate the choice question. Its safe to say that generators at all scales find large markets.

                    Please include in your manifesto the CC cooperative idea that existing power plants, even at the largest scales, can be incrementally converted into kite-hybrids. kPower is actively proposing this AWE bootstrap concept to its utility partner, Austin Energy, to offset coal consumption driving .5 GW gens,

                    daveS











                  • Bob Stuart
                    ... Let s leave the flying flywheels out for now, unless they are dual- purpose. I m totally lost at trying to think of an example to match the second
                    Message 9 of 15 , Oct 10, 2013

                      On 10-Oct-13, at 11:52 AM, dave santos wrote:


                      >For continuous duty, mass means nothing;

                      Excepting flywheel-mass, which has key uses. A larger mass also has more area and a cooler equilibrium temperature for equivalent specific heat.

                      Let's leave the flying flywheels out for now, unless they are dual-purpose.  I'm totally lost at trying to think of an example to match the second statement.

                      Bob


                    • Bob Stuart
                      Presumably, generators can be designed with better inherent cooling. Even better ductwork can help, and wind is a handy resource. Astro- Flite motors just
                      Message 10 of 15 , Oct 10, 2013
                        Presumably, generators can be designed with better inherent cooling.  Even better ductwork can help, and wind is a handy resource.  Astro-Flite motors just have the usual little slots in the end plates to give circulation a chance, but no particular incentive.  Exhaust holes around the middle of the armature might take advantage of existing pressure differences.
                        I don't think it is ever worth the bulk of a lifting gas in a useful wind.  The lift to drag is worse than more kite.

                        I'd like to see a lot more comparative analyses being done, but I have not had the time to follow up all the leads to places I might find good simulation tools.  <sigh>

                        Bob

                        On 10-Oct-13, at 10:53 AM, Harry Valentine wrote:

                        How would you propose to increase cooling capability of lightweight airborne generators carried by kites? 

                        Is it worth the cost of using balloons to carry such technology?

                        How do the short-term (capital & installation) cost and long-term cost (maintenance & spare parts) of conventional generators (air-cooled or water-cooled) installed at ground level compare with the cost of small, lightweight (air-cooled) airborne generators? 


                        Harry


                      • dave santos
                        Bob, We can t disregard the inherently enhanced flywheel effect of bigger generators, if this helps compete against many small generators, by a smoother power
                        Message 11 of 15 , Oct 10, 2013

                          Bob,

                          We can't disregard the inherently enhanced flywheel effect of bigger generators, if this helps compete against many small generators, by a smoother power output.

                          An example of Thermal Mass effect, of greater mass being a system thermal advantage, is a power plant with a small cooling lake (a common design). The lake reaches a thermal equilibrium with the plant's nominal heat loss (the plant's specific-heat input) as a higher average water temperature, in proportion to water mass and associated higher surface area. A larger water mass with more surface area finds a lower equilibrium temperature. If the lake shrinks in drought, the lower water mass finds a higher equilibrium temperature. If the lake mass drops enough, the remaining cooling water even boils away in a thermal-runaway. A large heat-sink mass, like an ocean, is more robust against overheating than a small mass. Hope this example helped,

                          daveS





                          On Thursday, October 10, 2013 1:48 PM, Bob Stuart <bobstuart@...> wrote:
                           
                          Presumably, generators can be designed with better inherent cooling.  Even better ductwork can help, and wind is a handy resource.  Astro-Flite motors just have the usual little slots in the end plates to give circulation a chance, but no particular incentive.  Exhaust holes around the middle of the armature might take advantage of existing pressure differences.
                          I don't think it is ever worth the bulk of a lifting gas in a useful wind.  The lift to drag is worse than more kite.

                          I'd like to see a lot more comparative analyses being done, but I have not had the time to follow up all the leads to places I might find good simulation tools.  <sigh>

                          Bob

                          On 10-Oct-13, at 10:53 AM, Harry Valentine wrote:

                          How would you propose to increase cooling capability of lightweight airborne generators carried by kites? 

                          Is it worth the cost of using balloons to carry such technology?

                          How do the short-term (capital & installation) cost and long-term cost (maintenance & spare parts) of conventional generators (air-cooled or water-cooled) installed at ground level compare with the cost of small, lightweight (air-cooled) airborne generators? 


                          Harry




                        • Bob Stuart
                          OK, that example of a remote sink, with extra variables makes perfect sense. I just couldn t tell what you were talking about, since the context for the
                          Message 12 of 15 , Oct 11, 2013
                            OK, that example of a remote sink, with extra variables makes perfect sense.  I just couldn't tell  what you were talking about, since the context for the discussion was the thermal mass of the generator itself.

                            Bob

                            On 10-Oct-13, at 8:01 PM, dave santos wrote:


                            Bob,

                            We can't disregard the inherently enhanced flywheel effect of bigger generators, if this helps compete against many small generators, by a smoother power output.

                            An example of Thermal Mass effect, of greater mass being a system thermal advantage, is a power plant with a small cooling lake (a common design). The lake reaches a thermal equilibrium with the plant's nominal heat loss (the plant's specific-heat input) as a higher average water temperature, in proportion to water mass and associated higher surface area. A larger water mass with more surface area finds a lower equilibrium temperature. If the lake shrinks in drought, the lower water mass finds a higher equilibrium temperature. If the lake mass drops enough, the remaining cooling water even boils away in a thermal-runaway. A large heat-sink mass, like an ocean, is more robust against overheating than a small mass. Hope this example helped,

                            daveS





                            On Thursday, October 10, 2013 1:48 PM, Bob Stuart <bobstuart@...> wrote:
                             
                            Presumably, generators can be designed with better inherent cooling.  Even better ductwork can help, and wind is a handy resource.  Astro-Flite motors just have the usual little slots in the end plates to give circulation a chance, but no particular incentive.  Exhaust holes around the middle of the armature might take advantage of existing pressure differences.
                            I don't think it is ever worth the bulk of a lifting gas in a useful wind.  The lift to drag is worse than more kite.

                            I'd like to see a lot more comparative analyses being done, but I have not had the time to follow up all the leads to places I might find good simulation tools.  <sigh>

                            Bob

                            On 10-Oct-13, at 10:53 AM, Harry Valentine wrote:

                            How would you propose to increase cooling capability of lightweight airborne generators carried by kites? 

                            Is it worth the cost of using balloons to carry such technology?

                            How do the short-term (capital & installation) cost and long-term cost (maintenance & spare parts) of conventional generators (air-cooled or water-cooled) installed at ground level compare with the cost of small, lightweight (air-cooled) airborne generators? 


                            Harry






                          • Gabor Dobos
                            Some further details to the topic of liquid air cooling of electric motors, generators: (By the way, if cooling proceeds with LE or LN2, superconductive
                            Message 13 of 15 , Oct 11, 2013
                              Some further details to the topic of liquid air cooling of electric motors, generators:
                              (By the way, if cooling proceeds with LE or LN2, superconductive technology is at hand.)

                              The limit of today’s technical state puts the power to weight ratio of a brushless electric motor at 6-10 kW/kg (  http://en.wikipedia.org/wiki/Power-to-weight_ratio ), but a superconducting device cooled with liquid nitrogen may reach even 20 kW/kg. There is extensive research in this field and a predicted value of 25-40 kW/kg in the case of motors and about 40-80 kW/kg in the case of generators may be found in the literature (Next Generation More-Electric Aircraft:  A Potential Application for HTS Superconductors Cesar A. Luongo, Senior Member, IEEE, Philippe J. Masson, Senior Member, IEEE, Taewoo Nam,  Dimitri Mavris, Hyun D. Kim, Gerald V. Brown, Mark Waters, David Hall ).

                               Gabor



                              On 2013-10-10 19:52, dave santos wrote:
                              >Can the better cooling of small units reduce the weight needed? 

                              Yes, and advanced liquid-air thermodynamic cycles may figure

                            • joe_f_90032
                              http://ewh.ieee.org/tc/csc/europe/newsforum/pdf/LuongoC_2AP01.pdf http://ewh.ieee.org/tc/csc/europe/newsforum/pdf/LuongoC_2AP01.pdf
                              Message 14 of 15 , Oct 11, 2013

                                http://ewh.ieee.org/tc/csc/europe/newsforum/pdf/LuongoC_2AP01.pdf

                              • joe_f_90032
                                https://medium.com/p/bb928aca0ab6 https://medium.com/p/bb928aca0ab6
                                Message 15 of 15 , Oct 15, 2013
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