# Wind turbine energy harvesting

1. Jul 17, 2009

### Nick Bruno

Hi all,
I just looked at a thread involving a wind turbine on a car or something of that sort and I have a similar idea... but it does not involve a car. It is similar in the aspect of something creates energy , and you add something else to it to get more energy, but I'm not sure if the system would be more efficient.

The idea:

A wind turbine rotates which rotates a shaft, which is conected to the generator. (typical)
Now what if small rods were embedded into the rotating shaft in the outward normal direction, lets say 3 rods on one plane, separated by 120 degrees.

Now if pvdf's or piezoelectric strips were added to an outer housing, such that these strips were deflected by the rotating rods, how would it effect the efficiency of the system?

Of course, these strips will add friction, but most of the time they are very very thin, and also smooth. They are easily deflected, but at higher Rpm's im sure more of an effect would be seen. I think decent voltage can be aqcuired through these pvdf's but compaired to the generator I think it is minimal. You would need a lot of these strips in order to get a noticable difference.

Im not normally apt to sharing ideas of this nature on forums due to a fear of someone stealing my idea, but I dont plan on doing anything with this idea in the near future. (got other stuff on my plate) but if someone developed this it would be really neat. I would like to see how it would effect the efficiency of the wind turbine.

2. Jul 17, 2009

### Staff: Mentor

Piezoelectric devices are extremely inefficient at generating energy, single digit percentages I think. So you wouldn't want to use one to steal energy from a 95% efficient generator.

Please accept the reality of conservation of energy: You can't take energy from the shaft without taking energy from the shaft.

Also, you're not really using the word "efficiency" correctly. Connecting another load to the shaft does not really reduce the efficiency of the generator, it just reduces the available input power.

Last edited: Jul 17, 2009
3. Jul 17, 2009

### Danger

Aside from introducing more friction (heat loss), you would also lose energy that would be converted to sound and to the additional electrical resistance between the strips and the end use.

4. Jul 17, 2009

### Nick Bruno

Now, I think this is actually a debatable topic.

Efficiency is defined as power out over power in. I would assume that a generator has a limited efficiency (max value) and after that you will not get any more due to the inherent mechanical properties of the device. This may be due to gear friction, sound, heat, etc.

But if you install a small pzt device on the shaft you really don’t think the output power, or the efficiency of the system as a whole, would be greater? Keep in mind the size of these pzt devices are very small. See the attached tech data for the pzt strips. They are less than 1 mm thick and the flexural modulus of them is almost negligible.

I took a class on smart material systems so I have acquired some articles over a period of time and some of these articles study the efficiency of the pzt strips (the same ones with the presented technical data. Their efficiencies can reach up to 20-35 percent. Of course this is electric energy over mechanical.

The question, in my opinion, would be do the pzt devices create more power output than the generator would lose due to their friction, noise, heat, etc. (which would most likely be very very small)

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5. Jul 17, 2009

### Staff: Mentor

Whatever power is extracted by the piezo elements is taken away from the generator path. What is the mechanical-to-electrical efficiency of the generators? Compare that to the piezo efficiency... Then calculate the overall efficiency of the generator system alone, versus the generator and piezos combined. Remember, the mechanical energy input to both systems is the same, so the total electrical energy you get out is the most for which system...?

6. Jul 17, 2009

### Staff: Mentor

Yeah, you're right, you didn't misuse it. I was thinking about the issue after I posted and added that part later without rereading your post. You defined your system as the entire system.

In any case, that means yes, the efficiency of the system is reduced by adding the piezo generator parts.
The efficiency of a good generator is around 95% and is not very sensitive to load. Ie, a generator running at half it's design power isn't much less efficient than one running at full power.
Absolutely not. It will be lower.
So that just means they won't take much power from the shaft and therefore won't generate much power themselves. But any power they generate is still taken from the shaft and therefore from the generator.
That's surprising to me, but ehh - I could be wrong about that.
No, at 35% efficient, a piezo generator is much less efficient than a regular generator at 95%.

Here's how the math works:

Assume a wind turbine produces 1000 W of mechanical power at the drive shaft.

Case 1: Turbine connected to generator.
1000*.95 = 950 W (input * efficiency = output)

Case 2: Piezo generators on shaft.
Figure you add piezo generators that take 10 W of mechanical power from the shaft at an efficiency of 35%:

990*.95+10*.35=944 W

7. Jul 17, 2009

### Nick Bruno

So I think in order for this idea to work, I would have to harvest energy from a difference source from a wind turbine. Instead of sharing the energy from the wind on the main shaft, possibly you could design I turbine column to vibrate close to resonance due to eddies that form from the wind! (dangerous but its just an example lol) Then you could implement pzt's in a different plane, but they wouldnt take away from the generator input.

8. Jul 17, 2009

### Staff: Mentor

There are lots of things that vibrate that shouldn't and piezos are a good way to dampen the vibration. I have a pair of skiis with piezo cells in them and an led imbedded in each ski to show it working. Wrap your knuckles against the ski and it'll light the led. I doubt that there is much power to be generated that way, but that is certainly a potential application.

9. Jul 17, 2009

### Nick Bruno

haha! thats really cool. A couple projects Ive heard of are back pack straps with piezo's in them that charge batteries as you walk, shoes containing them, and dance floors as well. Smart material systems is just a very interesting field and always makes good conversation.

I think Ill be writing my thesis on magnetic shape memory alloys in uses for energy harvesting.

10. Jul 18, 2009

### Danger

I'm not familiar with magnetic memory metals, but NiTiNOL (and most spectacularly BioMetal) are intensely cool.

11. Sep 21, 2009