Dabble with wind.

[Andy Rhody]

Hi, Andy from central Pennsylvania, USA. and have hung out on a few wind boards for a few years. I've seen Rob out there and read some of his posts. The guy seems to have both feet on the ground. I'm not always sure where the ground really is.

I've made a few small prototype windmills and carve 4 foot wooden blades but eventually wanted to go grid tie so around this September I pulled the "trigger" on a 2000 watt Chinese windmill for 900 USD and then scored a 2000 watt Ginlong inverter both from ebay. My goal is to grid-tie without batteries. The Ginlong's voltage range is 30 volts to 750 volts and since the windmill is 72 volts, I figured that it was quite within the range. Aparently it doesn't work that way. 72 volts into 2000 watts equals around 27 amps and the Ginlong is only rated at 9 amps. I emailed Ginlong and they confirmed that the windmill's voltage is not high enough for their inverter and suggested that it was made to charge batteries so I guess I'm gonna be stuck for a while.

It appears to me that most of the popular grid-tie inverter companies like Outback, Auroa, SMA, and most others only manufacture higher voltage and lower amp inverters which would not work for my windmill of 72 volts. The Chinese Sun G inverters that are all over ebay which start around 250 watt and go up to 1000 watts have higher amp ratings and do seem to work well but they are in a different class for what I need.

I searched a lot of inverters and found a Chinese inverter company named "Tanfon" that makes a 2000 watt 48 volt grid-tie inverter and they insist that with their controler, will handle my 72 volt windmill with no problems so that's what I'm thinking about right now but I need more info before I go out and "dance" on the ice.

Thanks,
Andy

[Rob Beckers]

Andy, welcome!
When it comes to wind turbines and 100' towers, "ground" is relative as far as the feet go...

Is 72V DC the rated voltage for 2kW out for this turbine? Or is this the starting voltage?

With most Chinese inverters (besides Ginlong, which actually has a good reputation) you have to watch out. Few are UL listed, and most are therefore illegal in the US. Those that are listed have a reputation of self-destructing on the slightest provocation. So, try to get some feedback from others about quality before you commit.

-RoB-

[Rob Beckers]

One more thing: Just looking at the specs of the 3kW Power-One wind inverters that we carry. They will do 20A maximum on their input, so you could get 1.4kW out at 72V DC. If it's 72V 3-phase AC, that work out to around 95V DC, giving around 1.9kW.

Also, you can make the turbine run at a somewhat higher RPM than 'ideal', and get a higher voltage out of it that way. This won't work in running it twice as fast, but, say, 30% more should not be a problem. It's all a matter of the MPPT table you put in the inverter.

-RoB-

[Andy Rhody]

Thanks Rob, on the plate it says 72 volts and 320 rpms. It is 3 phase AC. Here's a picture of the plate.

http://http://i41.photobucket.com/albums/e295/andy47bottles/Science/NOV-11011.jpg

I looked at the Power One's but thought 20 amps would be too low and also the 7200 interface box doesn't dump until it reached 530 volts so I didn't think it would be good for me.


The higher RPM thing sounds interesting. I'll post a photo of a chart I made with the blue line being "open volts" and the red line being the load of the Ginlong. I powered it with my bicycle so I couldn't get it to go too high.

http://i41.photobucket.com/albums/e295/andy47bottles/Scie1.jpg
nce/Ginlongvoltchart-

[Andy Rhody]

Thanks Rob, it says 72 volts on the plate and yes it is 3 phase AC. Here's a photo of the plate.

http://i41.photobucket.com/albums/e295/andy47bottles/Science/NOV-11011.jpg

The higher RPM thing sounds interesting. Here's a photo of a chart I made with the blue line being the "open Voltage" and the red line being the voltage with the Ginlong hooked up as the load. I powered it with my bicycle so It doesn't go up too high.

http://i41.photobucket.com/albums/e295/andy47bottles/Science/Ginlongvoltchart-1.jpg

I had looked at the Power One inverter but thought that 20 amps would be too low and also, it's 7200 interface box doesn't brake or dump until 530 Volts DC so I thought it wouldn't work for me.

[Rob Beckers]

The Power-One wind interface box is just a glorified rectifier, and certainly not their finest work. Very few use it to control a dump load, since as you noted the voltage for that is way too high.

Did your wind turbine not come with a rectifier and dump load controller? If not, you can quite easily make your own, any 3-phase bridge rectifier of sufficient size will do (overkill is good for this). Dump loads can be controlled with a voltage-sensing relay and contactor, I can send you wiring diagrams with part numbers for those. That will leave you free to use whatever inverter you want without having to worry about the rectifier from the same manufacturer.

So, 72 Volt 3-phase will work out to very close to 100 Volt DC after rectifying. For 2kW that means a current of 20 Amp (a bit more given the losses). By tweaking the MPPT curve you can run the turbine at a somewhat higher RPM for the upper end of output power, and get the current down a bit more if needed.

Do you have a picture of it? What is the exact diameter of the turbine?

-RoB-

[Andy Rhody]

No I didn't get a rectifier or dump load controler with the windmill but I do have an 80 amp 3-phase bridge rectifier. The blade diameter is 10 feet 10 inches or just under 11 feet.

Here's some photos.

http://i41.photobucket.com/albums/e295/andy47bottles/Science/Sept2011006.jpg
The blade is sandwiched between the hub and that round plate.

The mount facing upwards.

http://i41.photobucket.com/albums/e295/andy47bottles/Science/Sept2011005.jpg

http://i41.photobucket.com/albums/e295/andy47bottles/Science/007.jpg

[Rob Beckers]

Is there a brochure or spec sheet for the turbine?

-RoB-

[Andy Rhody]

Just sent you an attachment in an email of the manual. Thanks.

[Rob Beckers]

Got it. Thanks Andy!
The manual is much more revealing: Your turbine was designed for direct battery charging, for a battery bank of 72 Volt (ie. 6x 12V batteries). That means, design wise, they had to make the alternator so it hits around 72V DC at a fairly low wind speed, the cut-in wind speed or start-up wind speed. That means there's a good chance the turbine will produce a much higher voltage (while running at the proper RPM) at rated power.

Trouble is they don't tell us what RPM the turbine is running at when it reaches cut-in. Do you have a way to run the alternator off an electric drill or some such thing, so you can measure RPM and the (unloaded) voltage of the alternator? The name plate value (320RPM/72V) is not very useful for grid-tie inverter purposes, since it was measured while clamping the alternator to a 72V battery bank.

Other parameters found in the manual that are useful:

The diameter is 3.2 meters. That's the best indicator for output power vs. wind speed. Using that, a reasonable output power value at 11 m/s wind speed is around 1.6kW (that assumes 30% overall efficiency). Not quite the 2kW they claim, but that is often the case (brochures and reality diverge).

The rated RPM of 320 works out to a TSR (tip-speed-ratio) of around 5. That's pretty typical for battery charging turbines that get clamped to the battery voltage (the batteries keep the turbine from speeding up as it normally would when the wind speed increases).

The latter means it's likely meant to push around 90V DC (full batteries) at that RPM. It also means the unit is likely meant to run at around a TSR of 7 if it wasn't constrained by the batteries (and run more efficiently). That puts a grid-tie RPM at around 460 @ 11 m/s wind speed, and the voltage would then be around 130 Volt DC. With 1.6kW that works out to approx. 12.3 Amp.

The alternator seems to be able to run up to 3kW output. That would be reached around 13.5 m/s wind speed. If I plot those values and voltages I get the following MPPT curve:

Wind RMP DC Volt Watt Out
4 167 50 0
4.5 188 57 80
5 209 65 130
6 251 75 240
7 292 86 400
8 334 97 600
9 376 108 880
10 418 118 1200
11 460 128 1600
12 501 138 2100
13.5 564 152 3000

This follows a TSR of 7 all the way. If you want to keep the RPM down a bit (noise) at the higher end, the last one or two points can be modified.

I'm of course biased (since I sell them), but a 3kW Power-One Aurora wind inverter would do this job quite nicely. It has a starting voltage of 50V and can handle 20A maximum on its input (the above works out to 19.7A @ 3kW). Note though that no matter what inverter you use, you have to install a dump load and a mechanism to switch on the dump load and protect the inverter at a certain voltage.

-RoB-

[Andy Rhody]

Rob asked:
"Do you have a way to run the alternator off an electric drill or some such thing, so you can measure RPM and the (unloaded) voltage of the alternator?"

Yes Rob, I've done that. It was a bit tough. My drill was taxed pretty hard but here are the RPM's and "open" volts that I got and I'd give or take about 10%.

RPM's Open Volts

25 10
50 20
75 30
100 45
125 60
150 65
175 75
200 86
225 100
250 110
275 125
300 130
325 140
--- ---
--- ---
--- ---
--- ---
600 380

[Rob Beckers]

So this is AC voltage, phase-to-phase, Andy?
It's a bit higher than I would have expected, then again, there are many sources of error in measuring this way. For the time being I would suggest trying the MPPT curve as listed before, and to see how that works out. If you believe that the turbine is spinning too slow vs. wind speed the curve can be modified later.

-RoB-

[Andy Rhody]

No Rob, It's not AC. It's DC after I ran it through a bridge rectifier.

[Rob Beckers]

Andy, just saw the picture you sent me: Looking good! You should post it on here...
How high is your tower? Since you're up there with scaffolding I suppose it's not very high.

I'm thinking about how to optimize the MPPT curve for your turbine, given that you don't know what the wind speed is at the turbine. For now, keep an eye on the maximum power that the inverter produces. It gets logged in memory. Wait for a decent storm (shouldn't take long this time of year) and let's see if it hits 2+ kW (before it furls).

Given what you've been saying about running it on the dumpload, with the higher voltage that you observe, and the higher open voltage you measured some time ago (see earlier posts in this thread), it may well be that the voltage in the MPPT curve needs to move up. However, you mention seeing a peak output of 600 Watt with just 10 mph wind speed (average wind), that is only 4.5 m/s, and the turbine would be doing no more than about 100 Watt (average) in those winds if all is working well. So maybe it's right on the money as it is!

-RoB-

[Andy Rhody]

Yes, it's not up very high. Only 23 feet. I don't like to admit that but here's a photo.

http://i41.photobucket.com/albums/e295/andy47bottles/Science/032.jpg

I'm happy that it seems to be woking but it also seem to furl too earily like in 11 MPH winds. Click on th photo below and watch it furl. This is 11MPH according to the Weather Channel.


http://i41.photobucket.com/albums/e295/andy47bottles/Science/th_002-2.jpg


Yeah, we'll wait for a storm or better wind. My goal right now is to keep the mill from self destructing and keeping the DC current below 20 amps to protect the inverter and,................ if the local utility company ever gets their arses down here and plugs in that additional meter in my new meter socket which they made me install, I'll really show ya but until then, I guess I'll just keep doing my testing illegally. LOL!

[Rob Beckers]

Just to clarify: There's no need to monitor the input current. The inverter will limit current by itself, as needed, to limit the output power and/or protect the inverter input.

23 feet is pretty close to the ground! I know you're in a very windy spot, but don't expect too much that close to the ground. The air tends to be turbulent close to the ground, and wind turbines can't make much from turbulent air.

Keep us posted!

-RoB-

[Andy Rhody]

Well the local power company put the meter in yesterday and I have only one more inspection to go and then I guess I'm done. Fired her up tonight with 10 MPH winds and everything was working. That Aurora 3KW inverter scared me a little bit. You know, I didn't want to blow anything up but when I turned everything on it started up right away and ran real sweet. Just turned on the power and it started in about 30 seconds. I didn't have to do anything but watch. I never imagined that it would be so easy. I peaked at 900 watts.

[Rob Beckers]

Congrats with the meter! So you're in business now...
What's left? Electrical inspection?

-RoB-

[Andy Rhody]

Yes, one more inspection for the building permit ane then the "Tweeking".