# Variable Output for Wind Turbine

#### Dawsonh4

Joined Apr 11, 2017
38
I am curious if it is possible to control the speed of the blades in a wind turbine by adjusting the energy load.

Apologies for the lack of detail around the question as I don't posses a lot of background on the subject.

I know the general setup for wind turbines have a cut-in and cut-out speed and the speed at which the blades turn can be adjusted via a gearbox.

My thought goes back to the high school science experiment that shows how it gets harder to turn a generator with the more light bulbs connected to it.

Using that theory would there be a way to replace the gearbox and simply adjust the load that the blades are seeing?

Joined Feb 20, 2016
3,940
Yes you can switch a load on to slow the turbine down. Or on extreme winds, short the terminals.

#### Dawsonh4

Joined Apr 11, 2017
38
In terms of a wind turbine supplying energy to the grid would is it possible to supply more/less energy to the grid based on wind speed?

For example: if there is significant wind could a method be put in place to increase the amount of energy going to the grid which would in turn put more resistance on the turbine and ensure the blades to not hit a maximum speeds. The opposite would be under low wind speed the turbine would be under less load and send less energy to the grid.

if it is possible why are gearboxes used over this method?

Joined Feb 20, 2016
3,940
Note. I have no real expertise in these fields but here is my penny's worth..
I think gear boxes would be used to match the propeller and generator efficiencies. In the big wind turbines, the prop rotates fairly slowly but the generators need to spin faster to generate the power. It all hinges on relative motion of the conductors in the magnetic field.
A MPPT electronic controller is easier to use for best efficiency on a small scale wind turbine.

#### wayneh

Joined Sep 9, 2010
17,155
if it is possible why are gearboxes used over this method?
As far as I know gearboxes are just that and are not used to absorb energy. The blade speed is adjusted by some combination of applying more load, changing the pitch of the blades, and rotating the axis of the blades away from the eye of the wind. The latter method is how the old farm windmills worked.

#### tcmtech

Joined Nov 4, 2013
2,867

#### Picbuster

Joined Dec 2, 2013
1,027
You need a gearbox to jack up the speed allowing the generator to do his work.
The prop pitch is adaptable to wind force and allows speed control.
Pitch is set in feathering when wind speed goes below a certain value and prop stops rotating.

Picbuster

#### Janis59

Joined Aug 21, 2017
1,357
1)Any gearbox is subject to elementary physics - if down-speeding gear power factor is going to be divided with gear coefficient, then up-speeding gears it must be multiplied with that factor. The result - more than 50% of energy loss what in extreme may be near to 99% of energy lost. Therefore wise people are building custom-made low-turns alternator instead of common use alternator with gear.

2)Theoretically it is possible to break off the wings with help of generator, but is is so costly that no-one not doing like that. See, one need to brake it exclusively for one reason, if wind blows too strong so the rpm of wings becomes over centripetal force may crush the wing inner structure. If the "normal" wind speed is 5...7 m/s then storm may have a 30...40 m/s, but no-one is cancelled the law of N~v^2.

Thus the power on blade will become the (40/5)^2=64-fold higher than power for what the generator is calculated thermally. It means the wires what are considered to survive a thermal stress for, I guess, 10 Amperes, will be loaded under 640 Amperes.

So the exitus letalis is unavoidable. But to apply the alternator what is 64-fold more powerful as optimally needed, that means at least 40 000 - fold larger funding for system building. Absolute nonsens.

3) Normally are three methods used to solve this problem. (a) computer measures everything and makes a solution what is executed by adequate servos. (b) something is measuring windspeed and if it is overstepped, applies a mechanical brakes (friction-band or disc-type, or drum type [may use sth from automobile industry] or just falling flag type as in bicycle carret) and (c) use a turbines TAIL.

4) Such combined turbine tail is mount on freewheel, on what the generator is mount, but with skew in axial plane. Yet tail may freely rotate on vertical axle, but is fixed about 22-25 grades in slope against horizon.

When wind is mild it steers turbine in-wind, but when it is too high, the tail steers wheel out-wind. To illustrate You may see wind energy basics course slides, what is one of themes I teach regularly, those You need is one of the most last inside there. Sorry You will not be able to read the explanations without of use the Google Translate, but the aim is to show the pictures, what all languages are identical (what a surprize .

https://www.dropbox.com/s/iggfjdc2t6wmxmm/WindEnergy_10kl.ppt?dl=0

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#### Dawsonh4

Joined Apr 11, 2017
38
This is all enormously helpful. Thank you all!

I have to catch up and do additional research, but will definitely have a few more questions.

#### GopherT

Joined Nov 23, 2012
8,012
This is all enormously helpful. Thank you all!

I have to catch up and do additional research, but will definitely have a few more questions.
Some wind turbine manufacturers avoid gearboxes because this is the single biggest maintenance expense. They convert to dc then use inverters to go to AC. Also, the high gear ratios required for low wind speeds result in a significantly higher minimum wind speed to get the blades moving if stopped. Gearbox-less (direct drive) turbines are cheaper to build, more efficient, and less maintenance.

#### Dawsonh4

Joined Apr 11, 2017
38
What about in compressed air storage. With the ability to spin the turbine very quickly there might not be a need to gearboxes, correct?

#### GopherT

Joined Nov 23, 2012
8,012
What about in compressed air storage. With the ability to spin the turbine very quickly there might not be a need to gearboxes, correct?
Eaton offered a hydraulic pump system where a hydraulic pump is on the turbine head, then the fluid is pumped to a ground-level generator (direct drive) or gearbox/generator. This simplified oil changes and and most mechanical wear items to be replaced at ground level with a little more up front costs. Still some debate on how often the oil needs to be changed and how much oil should be in the sump to limit oil change frequency.