Small wind turbines no longer worth it?

[Messier11]

I would like to get a wind turbine just to get maintenance power when I am not at the cabin over the winter when I litterary get zero sun production for at least 3 months. 100 watts per day on average if I am away for say 50 days in a row, is a heck of a lot better than zero.

What kind of gear would it take to get that? I have good wind conditions, the cabin is on an island right at the shore.

 

[OzSolar]

I would like to get a wind turbine just to get maintenance power when I am not at the cabin over the winter when I litterary get zero sun production for at least 3 months. 100 watts per day on average if I am away for say 50 days in a row, is a heck of a lot better than zero.

What kind of gear would it take to get that? I have good wind conditions, the cabin is on an island right at the shore.

Take a look at Hugh Piggott's blog. His plans will help you build a very solid turbine that will give you years of service.

If you want to buy a turbine "off the shelf" that might give a few watts here and there take a look at the Primus turbine which is based on a design from SWWP. Below is thier energy chart but cut that monthly production by at least 50% when making a decision about this. IE: the best that turbine will do at 6 m/s site is 15kWH per month.

 

[brandnewb]

I would like to get a wind turbine just to get maintenance power when I am not at the cabin over the winter when I litterary get zero sun production for at least 3 months. 100 watts per day on average if I am away for say 50 days in a row, is a heck of a lot better than zero.

What kind of gear would it take to get that? I have good wind conditions, the cabin is on an island right at the shore.

ok, you sound like you have favorable wind conditions.

My current status quo in terms of battle plan is like this;

* Check out local code and see the maximum allowed turbine diameter.
* Check out local avg wind conditions. One can try and find a near community station at for example windly.com. But the more nothern one gests it might get less populated with stations. In the worst case buy your own weather station. It's not too expensive.
* check out if there is anything reasonable to be expected here, in terms of power generation potential using the local code restrictions and the avg. wind speed.
*If favorable then plunge in, you can join me in this endeavor
* start with the turbine. Do measurements that I do not know about yet. I am learning as we speak.
* then design your alternator to match. I for one did it all wrong and started with the alternator out of some prestige thing. Have no fear though. If one needs a brutal alternator then I can be of service.

 

[upnorthandpersonal]

I posted the below in another thread, but I's probably worth repeating. In addition, since @Messier11 is in a cold climate with substantial snowfall/freezing temperatures you also have to deal with the turbine freezing up, getting locked because of all the snow. If this is all known and you still want a turbine, go with the numbers @OzSolar mentions.

Wind doesn't scale to small turbines. You're dealing with two fundamental issues:

- The Betz Limit
- The Power in Wind equation

The Betz Limit is basically a theoretical number of the maximum efficiency you can possibly get. At most, only 59.3% of the kinetic wind energy can be used to spin the turbine and generate electricity. Remember this is a theoretical limit; in practice, you're going to be closer to 40%.

The Power in Wind equation is given as:

P = 1/2 x ρ x A x V³

Where:
P = power in Watts
ρ = air density (kg/m³, at about 1.2 at sea level)
A = Swept area of the blades (m²)
V = Velocity of the wind

So, no matter how good your turbine is, you will get in practice at most 40% of the wind energy converted to electricity. To capture the wind energy in the first place, you have two variables to increase (one in your control, the other not): swept area and wind velocity. The smaller you make the turbine, the faster you need to spin to make any meaningful energy. The only variable you control is the swept area, which means making the blades as big as possible. Also notice that the velocity is cubed in that equation, so you'll generate much, much less power at low wind speeds; don't assume this is linear or even exponential!

In other words, it doesn't work because physics.

 

[brandnewb]

ok, I'll admit I have never taken into account yet freeze conditions yet. ;(

I am not giving up on turbines just yet though.

We here in the NL have not had a good freeze for a while. Last I remember was -20C that lasted for like 4 days. Since then it is getting less cold and less cold

 

[brandnewb]

In other words, it doesn't work because physics.

Yes that is indeed how it looks yes? But can you please apply a bit more nuance?

For example, from what diamater do the physics start to give hope? We are investing alot in wind parks after all so there must be some kind of a tipping point.

 

[brandnewb]

to check out what could be a reasonable expectation one can check out this

Wind Turbine Calculator [HAWT and VAWT]

The wind turbine calculator finds the power output, efficiency, RPM, torque, and revenue of a wind turbine (either HAVT or VAWT).

www.omnicalculator.com

you\ll need your local code max diam and avg wind speed though

 

[brandnewb]

and that is why I am suggesting that people with large pieces of land with little to no local codes, given there is wind, can fully utilize it.

But then again I have never taken into account the freeze aspect yet

 

[upnorthandpersonal]

For example, from what diamater do the physics start to give hope? We are investing alot in wind parks after all so there must be some kind of a tipping point.

Of course - which is why I deliberately stated 'small wind turbines'. Wind makes sense on large scale, large turbines purely because it is the only variable you control in the formula. Let's do the math:

P = 1/2 x ρ x A x V³

Let's assume we have a constant 10mph (4.5 m/s, 16km/h) wind. The average in Sweden is 7 to 8 mph.

First, let's take a 'small' wind turbine with a blade length of 2 meters, swept area becomes r² x pi = 12.5 m². Putting the numbers in the formula this gives:

P = 1/2 x 1.2 x 12.5 x 4.5^3 = 683.5W -> this is the theoretical available wind power.

Now, from your link we can see that the actual efficiency μ is somewhere in the region of 30%. In every case, even a magical turbine, gives you an absolute maximum efficiency of 59.3% - the Betz limit. Let's assume we have the highest real efficiency of the very best turbines - 40%.

This means that our small turbine has a maximum output of around 274W.

Let's double the blade length to 4m. Thanks to the exponential in the area calculation, we get a swept area of 50m². Keeping everything else the same, we get a theoretical max power of 2734W, and a realistic output of 1100W. So, by doubling the blade length, we get a 4x power increase.

Now let's increase the wind speed slightly. Assume we have a decent pole to put it on, and put it where we get a 15mph wind (6.7m/s, 24km/h). For our small turbine, we now get a theoretical power output of 2256W, or 902W realistic. For our larger turbine, we get a theoretical power of 9023W, or 3609W realistic. So by just having an additional 2m/s wind speed, we increase the output by a factor of 3.

Now, to put this into perspective: one of the smallest commercial wind turbines you can get today has a blade length of 7.5 meters. A typical 1MW turbine sits around a blade length of 30 meters.

 

[brandnewb]

so, sorry to put is so bluntly, you are still 99.99988% convinced that my projects as wel as this thread\s premise is doomed to fail?

 

[brandnewb]

for all readers here. What our good friend is doing is correct.

Smacking some sense in our brains and expectations.

However, never stop thinking outside the box.

Imagine if Albert Einstein never did?

 

[upnorthandpersonal]

so, sorry to put is so bluntly, you are still 99.99988% convinced that my projects as wel as this thread\s premise is doomed to fail?

I'm following your progress and want to see what you come up with and what the results are. That's also why I'm not arguing against what you're doing in your thread, and I support your endeavor. This however is the thread "Small wind turbines no longer worth it?", and I'm just posting my arguments as I did in the very first reply to OP in this thread.

 

[brandnewb]

I am just a dumb ass. Which wishes I had a big piece of wind flud land in a rural area so >I could build a 10m diameter turbine.

Then things would start to change yes?

 

[brandnewb]

I'm following your progress and want to see what you come up with and what the results are. That's also why I'm not arguing against what you're doing in your thread, and I support your endeavor. This however is the thread "Small wind turbines no longer worth it?", and I'm just posting my arguments as I did in the very first reply to OP in this thread.

ugg. you are correct, point taken. totally the wrong thread for my rambling.

 

[OzSolar]

Yes that is indeed how it looks yes? But can you please apply a bit more nuance?

While were on the subject of rants. The big font is the point I'm trying to make and what follows is my own ramblings.

One nuance that is rarely if ever talked about with small wind is that you will get almost of all your monthly energy in a short period of time and if you're off grid your batteries will quickly be full and you'll end up wasting most of it.

And that's assuming you've got a wind turbine that's working to factory specs which you don't because there's never been one made that does.

If you've ever lived with a commercially made small wind turbine AND actually monitored it what you'd see is that your turbine might be spinning but it's making almost no usable energy most of the time. The real world cut in wind speed for most machines is a very STEADY 12 mph. I wish I still had all of that old data to show you but it was stunning. All of the Bergey 10's that I monitored averaged 5 to 10 kWh per day but could shoot up to a 120kWh on the windiest days. This is a wind turbine that is rated to do 13,000 KWH/year at a 12 mph site. That's 35 kWH/day.

I'll stop here but the short version of the story is that Bergey has been getting away with some very serious overstatements (flat out lies) going on 4 decades now and they are supposedly making the best turbine ever made. They've been the recipient of 10 of millions of dollar in grants and have had a small army of degreed engineers working on thier turbine for decades it still sucks.

 

[Hedges]

Turbulence is reportedly a major factor in small wind underperforming.
There was a study of many installations, with anemometers mounted to measure wind speed. Production from the turbines was always much less than what calculations said it should be based on wind speed and turbine performance graphs.

Small wind turbines on short towers receive wind with turbulence due to wind interaction with obstacles and the ground.
Turbine blades operate based on lift, like airplane wings. When you fly a light plane over hills, the ride is bumpy because turbulence changes wind velocity and angle, killing lift.

The anemometer is able to spin and measure velocity despite that, because it is a "drag" device, not a Bernoulli "lift' device.
Of course it is only trying to get RPM, not power, from the spinning cups. But I think power harvested from a drag device is relatively immune to turbulence.

You can build a drag device for power generation, e.g. split 50 gallon drum on a shaft, making "S shaped buckets. Second one at different angle so one bucket always cupped into the wind. This will harvest much less per unit area that a turbine, but could be a robust poor-weather generator. And won't need a de-icing system (as planes do) to maintain lift.



Very low RPM, and observe the skinny belt; obviously not meant for much power in this demo unit.
You can also place multiple half drums around a larger diameter circle. Same edge velocity, even lower RPM. Like a water wheel tilted so axis vertical. (If wind reliably came from one direction, could be vertical axis with return direction lower.)

Because turbulence is relatively irrelevant, perhaps walls channeling wind (as is done for water turbines) would work. It doesn't work for wind turbines because it creates turbulence and kills lift. But the boosted velocity may work for drag devices.

 

[OzSolar]

Vertical axis are the turbines of the future... and always will be.

 

[rhino]

The amount of available wind power is directly proportional to the height above ground level. That is why commercial turbines are both trying to increase diameter of swept area AND height above ground. That is why you will never see commercial VAWT farms.

 

[Messier11]

ok, you sound like you have favorable wind conditions.

My current status quo in terms of battle plan is like this;

* Check out local code and see the maximum allowed turbine diameter.
* Check out local avg wind conditions. One can try and find a near community station at for example windly.com. But the more nothern one gests it might get less populated with stations. In the worst case buy your own weather station. It's not too expensive.
* check out if there is anything reasonable to be expected here, in terms of power generation potential using the local code restrictions and the avg. wind speed.
*If favorable then plunge in, you can join me in this endeavor
* start with the turbine. Do measurements that I do not know about yet. I am learning as we speak.
* then design your alternator to match. I for one did it all wrong and started with the alternator out of some prestige thing. Have no fear though. If one needs a brutal alternator then I can be of service.

(a) Without seeking any permission, I can build a turbine with a wing span of 3 meters or app. 120 inches.

(b) This is information on my wind conditions:



With the following break down:


(c) Just for the fun of it, I am considering getting that book or just by some Chinese junk to experiment.

Just needs to find out what kind of gear I need to charge my 48v battery.

 

[rhino]

Just fyi, the smallest non "toy" turbine I know of is the 7m Bergey. They used to have a smaller one but I see they've gotten rid of that. There just isn't a lot of options below the 10kW range. There was another good one in the UK that had smaller ones from Proven Energy but they went bankrupt after a flaw was discovered in one of their turbine models.