Author Topic: controversy in windpower part 1  (Read 3302 times)

0 Members and 1 Guest are viewing this topic.

jacquesm

  • Sr. Member
  • ****
  • Posts: 467
controversy in windpower part 1
« on: January 05, 2005, 08:52:03 PM »
In windpower, as well as any other field of technology, there seem to be a whole lot of religious factions. The reason I call them religious is because most of the issues could be debated on merits, but are usually clothed in terms of who supports what without actual data supporting or disputing either side.



So, being somewhat new to windpower I'm trying to get a handle on these 'controversial' subjects, and I've tried to figure out the various pros and cons and I'd like to ask your help in finding more relevant data (and corrections in case I'm talking nonsense) with respect to the following, and if you're aware of other controversial issues to map them out:





  • Axial vs Radial alternators



    • axial+: no 'core', so easier startup

    • axial+: airgap is adjustable

    • axial+: ultra simple construction, fairly light weight

    • radial+: easy, use an existing industrial motor and add some magnets

    • radial+: small cross section

    • radial+: high power levels achievable



  • rotating case vs stationary case (radial alternators only)



    • rotating case+: centrifugal force keeps magnets in place instead of tossing them off the rotor

    • rotating case+: lots of space for copper

    • rotating case+: closest approach of magnets is where field is densest

    • stationary case+: more rugged construction (bearings on both sides of the main shaft)

    • stationary case+: cheaper laminations, and easier to get

    • stationary case+: use existing industrial motor frame



  • fixed pitch vs variable pitch



    • fixed pitch+: much simpler hub construction

    • fixed pitch+: cheaper to construct

    • variable pitch+: in theory a higher efficiency

    • variable pitch+: less wind loading in very high winds

    • variable pitch+: higher survival winds

    • variable pitch+: does not need a dumpload



  • upwind vs downwind



    • upwind+: no tower thump

    • downwind+: doesn't need a tail

    • downwind+: can use 'umbrella' feathering of the blades



  • HAWT vs VAWT



    • HAWT+: better vibration stability than VAWT

    • HAWT+: self starting

    • HAWT+: well understood, lots of time & money invested

    • HAWT+: easier to put on a tower to get into 'good' winds (most VAWT's sit on the ground)

    • VAWT+: does not need to be 'aimed' at the wind

    • VAWT+: does not need a tail

    • VAWT+: in theory very high efficiency

    • VAWT+: has it's alternator low to the ground



  • AC machines vs DC machines



    • AC+: power is easily transformable

    • AC+: longer distance between machine & consumer possible

    • DC+: does not need a rectifier, so no power lost there



  • permanent magnet vs excited field alternators



    • permanent magnet+: does not need field current or a mechanism to switch it on/off

    • permanent magnet+: cheaper to construct (most of the times, for a certain size it becomes cheaper to do a wound field, but that's usually no longer 'hobby' or 'semi pro' stuff, but big stuff, say 20 KW +)

    • excited field+: field strength - and thus alternator output - can be simply controlled



  • high voltage vs low voltage systems



    • high voltage+: less line loss

    • low voltage+: safer



  • two bladers vs three bladers



    • two bladers+: cheaper to make

    • two bladers+: easier to balance

    • three bladers+: no yaw rattle

    • three bladers+: usually longer living



« Last Edit: January 05, 2005, 08:52:03 PM by (unknown) »

bob golding

  • Hero Member
  • *****
  • Posts: 691
  • Country: gb
Re: controversy in windpower part 1
« Reply #1 on: January 05, 2005, 02:29:45 PM »
very good list. you seem to have come up with somethibg to keep all  factions happy.


well done.


bob golding

« Last Edit: January 05, 2005, 02:29:45 PM by bob golding »
if i cant fix it i can fix it so it cant be fixed.

RP

  • Hero Member
  • *****
  • Posts: 722
  • A dog with novelty teeth. What could go wrong?
Re: controversy in windpower part 1
« Reply #2 on: January 05, 2005, 03:31:46 PM »
A few comments:


variable pitch+: does not need a dumpload.  

This is true only if the pitch can be controlled remotely from the ground.  I agree the dump load is not needed for high wind overspeed conditions but may still be needed to shed excess power when the battery's full.


HAWT+: self starting.  

A VAWT savonius is self starting.  I think only the darius style needs help to get going.


VAWT+: in theory very high efficiency.  

Again, I think this applies only to darius style rotors.  The savonius style are not particularly efficient.


I'd also suggest adding:  


VAWT+: may not require a tower.

AC+: no brushes to wear (usually)


I'm not trying to be picky.  Actually most of my thoughts derive from what I've read on this board over the past few months.


rp

« Last Edit: January 05, 2005, 03:31:46 PM by RP »

monte350c

  • Full Member
  • ***
  • Posts: 228
Re: controversy in windpower part 1
« Reply #3 on: January 05, 2005, 04:25:59 PM »
Hi Jacques,


Sounds like the trip was quite an adventure. Glad you made it in one piece.


That's a good list - here's an addition:


HAWT vs VAWT -


HAWT+ - use of blade material vs. swept area


(for example a 2-blade HAWT with 5 meter blades and 10 meter diameter will have a swept area of about 78 sq meters - a 2-blade Darrieus VAWT with the same blades - 3.2 meter diameter - only 7.9 sq meters or about 10%)

« Last Edit: January 05, 2005, 04:25:59 PM by monte350c »

jacquesm

  • Sr. Member
  • ****
  • Posts: 467
Re: controversy in windpower part 1
« Reply #4 on: January 05, 2005, 04:36:19 PM »
thank you Russ, good points !



Regarding the no need for a dumpload in variable pitch machines, you can disconnect the mill completely and it will not overspeed (assuming your feathering system works), so you do not need to be able to control the pitch from the ground.



I totally missed out on the savonius rotor, my bad !



« Last Edit: January 05, 2005, 04:36:19 PM by jacquesm »

DanB

  • Global Moderator
  • SuperHero Member
  • *****
  • Posts: 2151
  • Country: us
    • otherpower.com
Re: controversy in windpower part 1
« Reply #5 on: January 05, 2005, 05:33:56 PM »
Ahh.. controversy... I love it!

Great list - good points.  Very nice that you kept it all so positive!!  Although I would say that sometimes I don't veiw it quite as  simple.  Lots here for a good discussion though!  Perhaps Im just in the mood to ramble and state some of the obvious... but here are my thoughts...


"Axial vs Radial alternators"


Lets remember that both axial, and radial alternators could have laminates.. or air cores.  I actually saw a really neat 'brake drum' style wind turbine once that had a the coils cast in a cylender, with magnets on the outer diameter and a steel ring on the inner diameter to return the flux.  


    * axial+: no 'core', so easier startup


yes... this could apply either way though and an axial machine could have (and often does have) laminates.


    * axial+: airgap is adjustable


Yes.. I agree!  That is a handy feature!


    * axial+: ultra simple construction, fairly light weight


utra simple construction is nice, and I think often times the choice is based upon available resources.  I think just about anyone can build an axial flux machine and this is probably their most attractive feature.


    * radial+: easy, use an existing industrial motor and add some magnets


Yes, that is handy - although I think, to get good results and a good match for the prop you have to start with the 'right' motor... and like anything else, starting with something new thats not been done before may yield slightly unpredictable results.


    * radial+: small cross section


I would say that depends.  Some radial designs are still quite thin with large diameter to keep the magnets moving faster and fit more wire in.


    * radial+: high power levels achievable


hmm... Im not sure either has an advantage in this area.  There have been some very powerful axial flux alternators built in very large wind turbines.


And... in favor of the 'laminated' machines, lets not forget that they do require a lot less magnetic material.  I think perhaps that is their greatest advantage.  There are also differences in the power  curve for laminated machines I think.  Once laminates start approaching saturation... then full power is reached.  I think this can prevent some laminated machines from stopping nicely when shorted out so in some cases some other type of brake might be required.  (some other type of brake is

probably not unwise on any wind turbine)


"rotating case vs stationary case (radial alternators only)"


    * rotating case+: centrifugal force keeps magnets in place instead of tossing them off the rotor

    * rotating case+: lots of space for copper

    * rotating case+: closest approach of magnets is where field is densest

    * stationary case+: more rugged construction (bearings on both sides of the main shaft)

    * stationary case+: cheaper laminations, and easier to get

    * stationary case+: use existing industrial motor frame


All good points.  I'd also think there is advantage to the rotating case in that the magnets are moving faster, and there is room for more magnetic material for a given alternator diameter.  Another advantage of a rotating case is the nice large rotating front of the alternator which makes a natural blade hub.  With a shaft - I think you probably wind up with a more expensive hub, but it's hard to say...


"fixed pitch vs variable pitch"


    * fixed pitch+: much simpler hub construction

    * fixed pitch+: cheaper to construct

    * variable pitch+: in theory a higher efficiency


I wonder if thats true...  I don't know from experience or anything, but it seems debatable.  Once it starts to feather.. or furl - of course it supposed to become inefficient, but till then... isnt your pitch angle fairly fixed in either case?  During normal operation I wouldnt think feathering the blades slightly one way or the other would affect efficiency that much.  But again - I dont really know about this from experience, just being a bit skeptical.


    * variable pitch+: less wind loading in very high winds


Do you mean on the tower?  I wonder if that's true as well...


    * variable pitch+: higher survival winds


I think that could be debated as well... again, I don't really know - but nowhere have I read that this is the case and don't really see why it should be.


    * variable pitch+: does not need a dumpload


Yes - you explained that to me, I can see the advantage of being able to let the machine free-spin.  I guess in theory a side furling machine protects itself too while free-spinning, but they do run much faster and it's scary.  According to Victor, Bergy claims their machines can be left free spinning  - again though, it seems scary, I wonder if its good practice to do that with any wind turbine, variable pitch hub or not.  I have no experience with variable pitch hubs, hopefully that will change one day.


To me, one other obvious issue with variable pitch machines - it's bound to cost a lot more to build, and there will be a lot more expensive moving parts to wear out.  There is surely an economy of scale here.  It would be fairly insane to build a variable pitch hub for a 8' machine, but perhaps on a 16' machine it starts making sense.   Maintenance and repair is bound to be expensive over time though in my opinion.


"HAWT vs VAWT"


... hmm - this one is so controversial Im not even sure I want to comment on it! ;=)


    * HAWT+: better vibration stability than VAWT

    * HAWT+: self starting


Some VAWT designs are self starting.


    * HAWT+: well understood, lots of time & money invested

(VAWT-: fairly well understood, gobs of time and money wasted) (sorry.. just kidding here  - actually, I think there has been lots of good research into vertical axes designs and there are some serious problems which seem difficult and complicated to overcome)


    * HAWT+: easier to put on a tower to get into 'good' winds (most VAWT's sit on the ground)

    * VAWT+: does not need to be 'aimed' at the wind

    * VAWT+: does not need a tail

    * VAWT+: in theory very high efficiency


If we stay on the positive side of looking at things - I think we should mention that that HAWT's are fairly easy (and there are several reliable approaches) to control in high winds.  VAWT's have a problem with this.  HAWT machines also suffer from much smaller fatigue forces on the blades.

    * VAWT+: has it's alternator low to the ground


"AC machines vs DC machines"


    * AC+: power is easily transformable


yes, that's the biggie.

    * AC+: longer distance between machine & consumer possible


Only because it's easily transformable though...  distance otherwise has only to do with voltage and if the voltage is equal, over distance.. then DC wins.  But it's the fact that we can transform AC that makes it desirable.


    * DC+: does not need a rectifier, so no power lost there


Yes - although at higher voltages than 12, I think thats almost a non-issue.

On the favorable side of AC also - we should remember it's a lot easier to build an alternator than it is a dynamo no matter how we do it.


"permanent magnet vs excited field alternators"


    * permanent magnet+: does not need field current or a mechanism to switch it on/off


Yes.. and for small wind turbines, I think the field current required by a machine with an electro-magnetic field would be a killer.  Perm. magnet machines will be much more efficient in low winds, especially small ones.


Fun post - brings up all the fun arguments we like to have ;-)

I can see this one might get 100 comments or more!!!

« Last Edit: January 05, 2005, 05:33:56 PM by DanB »
If I ever figure out what's in the box then maybe I can think outside of it.

jimjjnn

  • Hero Member
  • *****
  • Posts: 511
Re: controversy in windpower part 1
« Reply #6 on: January 05, 2005, 05:42:24 PM »
What were you doing up above Ft Collins that it caused this brain Hemmorage?

Air too thin? Golf in the pines?

Dan(s)and Matt bend your ear off? Poppy seed cake? Dans get the Band going for some good music?


Your list was excellent as you covered about all.


Enjoyed reading about the trip back to Canada. Real fun when you got to the icy part.

Be interesting to see the activity on the Dunlite.

« Last Edit: January 05, 2005, 05:42:24 PM by jimjjnn »

zubbly

  • Sr. Member
  • ****
  • Posts: 371
Re: controversy in windpower part 1
« Reply #7 on: January 05, 2005, 06:01:13 PM »
Hi Jacquesm!


just my comments and thoughts (no arguments intended with anyone)


"axial+: no 'core', so easier startup".    i think with the much experimentation that has been done with induction conversions decogging methods, we can put these two types of generators on an equal  base for easy start-up. Also, a converted induction motor i believe, has less drag with ball bearings than a tapered roller bearing does.

On the other hand, a tapered roller bearing has more load capability than a ball bearing. I have not heard of a roller bearing failure yet in a genny and believe that is because it is bigger than necessary.


"The reason I call them religious is because most of the issues could be debated on merits, but are usually clothed in terms of who supports what without actual data supporting or disputing either side". I think there are preferences to make a genny in one fashion or the other, solely based on ones knowlege, available tools and parts, and perhaps just the look of it.  My personal preference for a genny is a induction motor, but i really do prefer the (look) of a axial coreless. Don't no why, perhaps it just has more character and looks like more of an accomplishment.  lol


"high voltage vs low voltage systems"  I think we could add in the "cost" for the high volt versus the low volt. Aside from the safety issues, i think when it comes to cost for a small system, low volt still wins because of the price of the higher voltage inverters. (just speaking my thoughts here).


Jacquesm, i like the way you showed the pros and cons on all the different types of gennys and systems, and see little room for improvemnt or additions.  Its a great quick reference.


thanks for sharing your thoughts and efforts!


zubbly

« Last Edit: January 05, 2005, 06:01:13 PM by zubbly »

Ungrounded Lightning Rod

  • SuperHero Member
  • ******
  • Posts: 2865
Re: controversy in windpower part 1
« Reply #8 on: January 05, 2005, 08:04:02 PM »
Even a Darrius is not as efficient as a good HAWT.  HAWTs can approach the Betz limit very closely and VAWTs don't do so well.


HAWT+  Little blade flexing during cycle limits fatigue (vs HAWTs where the forces on the blades are constantly changing direction, leading to fatigue and breakage - one of the things that has made Darrius designs problematic.)

« Last Edit: January 05, 2005, 08:04:02 PM by Ungrounded Lightning Rod »

Flux

  • Super Hero Member Plus
  • *******
  • Posts: 6275
Re: controversy in windpower part 1
« Reply #9 on: January 06, 2005, 01:58:59 AM »
None of this is absolute, but in general this seems a well balanced summary.


The one thing that may be questionable as DanB hints at is the tower loading with  variable pitch.


If you pitch to stall the loading is high and this works best with down wind rotors.


If you pitch to feather I still suspect the loading is considerably higher than a furling machine in high winds.


Not a bad idea to collect thoughts occasionally as long as it is kept balanced as in this case.


Flux

« Last Edit: January 06, 2005, 01:58:59 AM by Flux »

rotornuts

  • Hero Member
  • *****
  • Posts: 537
Re: controversy in windpower part 1
« Reply #10 on: January 06, 2005, 10:08:21 PM »
From what I've learned so far I'd like to build a radial, stationary case, variable pitch, upwind, HAWT with an AC, permanent magnet, high voltage alt. and three or five blades. Whew!


Regarding variable pitch. I'm still undecided about variable pitch and induced stall on a non pitching unit. If I could achieve a good degree of control of the pitch angle as to maximize performance over the broadest range of rpm then that would be my preference. I'm very interested to see what jaquesm has in mind for the control system on the motor side of his newest endevour. Is it a servo, centifugal wieghts or something else? A servo would yield good fidelity.

« Last Edit: January 06, 2005, 10:08:21 PM by rotornuts »

Jerry

  • Hero Member
  • *****
  • Posts: 1519
Re: controversy in windpower part 1
« Reply #11 on: January 06, 2005, 11:00:41 PM »
Hi Zubbly & group.


I was directed to this board by Richard Pereze the chife at the Home Power magazine a # of years ago.


The first thing I saw as a wind generator was a converted ac motor that Dan B had built.


Back then there were plenty of the old # 29 curved NEO magnets. I started to do motor conversions also.


Shotly after my itroduction to the OP board it took another direction.


The disc alt. There was a couple years discusion on laminations. Then  the dual rotor no laminated alts apeared.


I feel the converted motor idea had very littel time or effort put into it compaired to disc alts.


It seems as though disc alt builders are the majority. Maybe 80% disc, 10% motor conversions and 10% others.


I'm not complaining but if as much enegy had been put into motor conversion it would be way addvanced beohned were it is now and there would most likely be a source for curved NEOs.


I suspect that most comercial small and large wind gennys look more like motor conversions than disc alts?


However I think the 10% of us motor converters will keep at it and not loose our enthusiazim. (SP?).


However I have sevearl disc alts just waiting to be built. My big enemy is time and motor conversions seem to be fast.


Us motor conversion folks may need our own section? I think I need a section 8?


                           JK TAS Jerry

« Last Edit: January 06, 2005, 11:00:41 PM by Jerry »

Nando

  • Hero Member
  • *****
  • Posts: 1058
Re: controversy in windpower part 1
« Reply #12 on: April 19, 2007, 09:14:15 AM »
RP:


YOU SAID:

variable pitch+: does not need a dump load.

This is true only if the pitch can be controlled remotely from the ground. I agree the dump load is not needed for high wind over speed conditions but may still be needed to shed excess power when the battery's full


I say:


No necessarily, the pitch does not need to be remotely controlled.

Also, we have two types of pitch control, one via fly weights and the other via Torque.

Fly weights if well designed will have a high RPM at any load, zero or maximum load and a brake maybe used to stop the mill to stand still.


Torque, if well designed, has the property of RPM reduction if the load is removed and the blades profile is the proper one ( pitch angle in essence reduces the "length" of the blades, plus the stalling of the "wing" effect.


Both types when unloaded do not have run away RPM and its problems.


Nando

« Last Edit: April 19, 2007, 09:14:15 AM by Nando »

RP

  • Hero Member
  • *****
  • Posts: 722
  • A dog with novelty teeth. What could go wrong?
Re: controversy in windpower part 1
« Reply #13 on: April 19, 2007, 09:47:52 PM »
Good points.  I forgot that the speed limiting would obviously take care of no load conditions.


Feel free to respond in less than 27 months next time.  :-)

« Last Edit: April 19, 2007, 09:47:52 PM by RP »

Nando

  • Hero Member
  • *****
  • Posts: 1058
Re: controversy in windpower part 1
« Reply #14 on: April 20, 2007, 09:22:18 AM »
I will try my "bestest" to improve the delivery time, though I think, I need. to read the date of the message, which I rarely do.


I do not why it was in front of me and just responded to it.


Nando

« Last Edit: April 20, 2007, 09:22:18 AM by Nando »