Hi, and these are my thoughts on a turbine

[Ben Colla]

We are on grid, and that isn't going to change.

I've thought about solar, but proximity to a mountain means, lots of cloudy days. We'll make more kWh from Wind than solar per year. But solar is pretty much set & forget.

We already pay $0.25/kWh and that is increasing 10 - 20% every year and will continue until we hit a currently undefined price point. But at least $0.60 / kWh. So I'm looking to protect us from future significant price rises. We do have a net feed in tariff, which pays us retail price.

So, that is why I'm looking at a home turbine, from the following parts :

(No links, to prove I'm not spamming in my first post).

5kw Exmork turbine with their controller and dump load
6kW Power-One inverter
the f-n.cn 16 meter hydrualic tower.
Sundry bits and pieces.

I've chosen what my reading says, are decent quality bits and pieces. Maybe not the best, but decent enough and I can afford it.
I've read the post regarding issues with the f-n.cn company, and the failings of their turbines. But it seems to me that it is the electronics or turbinethat fail, which then pound into the tower, which isn't designed to cope with it. Am I wrong in this thought? It seems to me, that now the chinese have reasonably simple engineering done, it's the delicate bits that have issues with.

As a saftey setup I'm thinking a system to machanicly activate the brake included in the Exmork, when the grid fails would be a good idea. I'd like it to be a simple and fail safe as possible. My first thought was a grid powered electro magnet holding up a 20kg weight. grid fails, magnet goes off, weight falls and pulls on the brake. Not much can go wrong with that. Except it doesn't self prime again when the grid comes back. I'd like that. Suggestions? I'm reluctant to rely solely on the electronics & dump load for protection.

finally, I'd love to say "this will all happen next month". But it won't. But I will keep you all posted if/when it happens.

So, Any thoughts, suggestions, ideas or comments?

[Rob Beckers]

Hi Ben,

Welcome to Green Power Talk!
I don't know the Exmork up close and personally, so I'll leave that to others. I assume the inverter is meant to read "Power One" as the brand name. Those I do know very well. No significant issues with them, other than the absolute voltage rating of 600V DC. Go over and the inverter will blow. Guaranteed.

With that in mind I'm a big fan of using a voltage measurement relay such as an Omron K8AB-VS3 and a contactor to provide a fail-safe in case the voltage gets too high, and when the grid is down. It's relatively little money (probably $200 in all), and provides a very reliable additional line of defense to keep the inverter alive.

-RoB-

[Ben Colla]

Yes, Aurora power one 6kW inverter. I've edited my original post to reflect that.


I've been wrestling in my head, with what I see as a bit of a problem. The best place for a turbine on our block is 200 meters away (600 feet or so) from the house. At 240v that means I need something along the lines of 400 meters of 35mm cable (2 AWG) which is (freaking) expensive. I've only found one place so far that lists a price and it's $5.00/meter or $2000 just for the copper.

Is there a problem with running the controller at the base of the tower, and the inverter at the house, 200 meters away? I believe I could get away with running the higher raw voltage coming from the turbine through 16mm cable that distance, and invert at the house. 16mm cable is nearly 1/2 the price, so that is my thinking. (drawback ... no 240v power at the turbine itself, but I'm prepared to cope with that, for an extra $1000 in my pocket).

On the gripping hand, $1000 just isn't really that much. Maybe it's better to do it right the first time.

[Rob Beckers]

Ben, for such a distance don't use copper, use aluminum. While you need a larger gauge (I don't have the conversions to get the same losses handy, my electrician deals with that stuff), it is still much cheaper than copper. Just make sure that the terminals on both sides where you convert from copper to alu and back are rated for aluminum, and use lots of anti-corrosion paste.

It shouldn't make much if any difference in cost to put the wire on the 3-phase side, or the DC side. The DC current is somewhat higher than the AC current (which has 3 wires to transport power through, vs. 2 wires for DC). With that in mind it may be more convenient to have the controller somewhere near the inverter.

-RoB-

[Ben Colla]

Hi Rob,
Thanks for the suggestion on Aluminium. I hadn't thought of it.
I asked for a RPM/Volts/Watts chart. I was sent

RPM VDC WATT Amps
100 150 900 6
130 180 1764 10
150 200 2420 12
175 260 2505 10
195 330 2700 8
215 340 3600 11
235 360 5100 14
255 390 5500 14
275 410 6500 16
295 440 7200 16
315 470 7650 16
335 500 8000 16

I stuck the Amps on the end, because it was easy, and I wanted to see what I had to cope with.

Clearly, an Aurora 6kW aint going to be big enough. So I guess 2x 4.2kW's would be the way to go. But that adds quite a lot to the $$$.

Is it possible to redirect everything over 340v/3600w to a dump load? That way I could buy one 4.2kW intverter now and a 2nd in a year or so. After all, most of the time I'll be generating less than that.

[Rob Beckers]

Hi Ben,

Looking at the Exmork Web site (not much info there): Seems you have the 350V model. Taking their rotor diameter (5.0 m), rated wind speed (12 m/s), rated power (5000 Watt), and rated DC voltage under load (350V DC), the following MPPT table should be more appropriate:


Wind RPM VDC Watt
2.5 53 90 0
3 64 110 50
3.5 75 127 100
4 86 144 180
4.5 96 162 270
5 107 178 380
6 128 211 680
7 150 243 1100
8 171 274 1650
9 193 305 2350
10 214 334 3200
11 235 362 4300
12 257 390 5500
12.5 266 402 6200


This actually assumes a very low efficiency of the rotor. Normally I would raise power a bit, but I don't know if the alternator can deliver more at those RPMs. The TSR of the rotor clocks in at a very low 5.6. Should be a quiet turbine at those low RPMs.

There is not much point in going beyond a 6kW inverter (which will safely do 6.2kW). Those higher power levels only occur at high wind speeds, which for most locales happen so rarely that they do not contribute much at all to overall energy production. Instead, focus on keeping the rotor under control in the high winds, make sure the dumpload comes on beyond 410V DC. Keep in mind that it is not the inverter that should keep the turbine under control; even when the grid is gone (and the inverter switched off) the turbine should not overspeed.

In terms of current, you're looking at a maximum of 16.4 Amp on the DC side. On the 3-phase AC side the theoretical current is 12.8 Amp per phase, in practice it's a bit more than that due to the very poor power factor of a bridge rectifier.

For your wiring distance (700 feet), you're looking at 8 AWG in case you use copper (that's for the AC side, 3-phase, 300V AC). With that the losses would work out to around 3.3% at full power, most of the time less since high winds don't happen that often or that long. For aluminum the resistance is about 1.6x that of copper for the same wire gauge. To get about the same losses as you would for copper, you're looking at 6 AWG in aluminum.

-RoB-

[Steven Fahey]

I figured I could chime in with some indirect experience with an Exmork 5kW turbine, since Rob says he hasn't seen one himself.

A neighbour of mine had an Exmork installed a couple of years ago. Itcame with a diversion load controller but no instructions about how to install that. The WT also did not come with assembly instructions, therefore in both parts of the system, mistakes were made and many serviceability issues came up that delayed the useful production of the turbine for MORE than a year. It was compounded by an absense of certifications, things taken for granted in North America which pave the way for grid-connection.

A storm blew through in April and it tore the tail and all 3 blades off. I can't say which went first, tail or blades, but the owner is fed up and will have the whole thing dismantled and removed. The company that originally installed it still hasn't taken it down either, so my neighbour has been looking at the broken monstrosity for 6 months.

If Exmork was going to replace the WT tail and blades under warranty, they would have by now. The company did honour warranty on the controller when it fried early on. Small comfort, now.

Selecting an Exmork is much like a do-it-yourself project, but without the fun of actually building a wind turbine yourself. It seems all risk is assumed by the user.

[Steven Fahey]

...now the chinese have reasonably simple engineering done...

It's not that you're wrong, or even that I know any better (I don't) but that statement does sound naive. Design and construction of anything is a starting point. Service and testing are another, and long term dependability is even more elusive!

No Exmork that I know of has been subjected to long-duration performance testing and monitoring. If such a task was under way or successfully completed, it would be a major accomplishment for a chinese company, and we would know about it from the product literature on the website, advertising, and distributors. Well, it just ain't so.

Very few wind turbine products have a "guarantee". It's not even a good guideline to "buy american" or some such patriotic tripe - just look at the Windspire. If you were to ask about how it fared in performance testing, Mariah would sheepishly have to admit their test unit didn't last 9 months before the testing facility gave up on it!

Sorry, kinda on a soap-box here. My point is there's nothing simple about wind-turbine engineering. I should offer some suggestions instead about where to look for helpful info and research, instead.

Try Home Power magazine. They review the WT's on the market every year. The Exmork is NOT on the list, for reasons they explain in the magazine. Home Power is glossy and flashy, and the systems they feature are anything but "shoe-string" budget projects, however.

Do research at the NREL's small wind turbine testing website. There are various models undergoing testing all the time (including the failed Windspire if you want to know how bad it can get).

A very comprehensive website about WT product quality is Paul Gipe's www.wind-works.org. By spending an afternoon or two reading through that you will learn everything you need to evaluate a WT for your needs and the site you have available. I can't recommend it enough.

Good luck! And yes we will be please to know what you learn and how you choose, when the time comes.

[Ben Colla]

I hear what you are saying.

I've looked into Rob's web site, and it seems the Scirocco is a well built, long lasting turbine. But I can buy 7 comlete turbines, with controllers, shipped, from Exmork for the cost of one Scirocco. Admittedly, the Scirocco MAY outlast all 7, but I'll never know, because I wouldn't buy 7. If the Exmork lasts 2 years and proves a wind turbine is well worth the effort for me, then fails, I'll look elsewhere.

[Dale Sheler]

Do you have a wind power ordinance where you live, and will you need a permit to erect the tower?

[Ben Colla]

Do you have a wind power ordinance where you live, and will you need a permit to erect the tower?

Our local government tagline, or logo is "Out envirronment, our future" So it should at least be friendly to the idea. I checked about 18 months ago, and there were no rules regarding towers and/or wind turbines. I'm about to ask them again, in writing if this is still true.

[Dale Sheler]

Our local government tagline, or logo is "Out envirronment, our future" So it should at least be friendly to the idea. I checked about 18 months ago, and there were no rules regarding towers and/or wind turbines. I'm about to ask them again, in writing if this is still true.

DO NOT do that! put your turbine together, get your tower and put it up, believe me I speak from experience, it is 1000 times easier to ask forgiveness that it is to get permission.
I went in and blindly took the high road and went to get a permit, turns out my township has a brand new ordinance, one of the most draconian in the country, the only tower that is allowed is a monopole, so I said fine I'll put up one of these Chinese monopoles, the building inspector requires a stamped drawing from a state licensed structural engineer on the tower and the turbine, you cannot get either from exmork or the Chinese tower factory.
To have a state licensed structural engineer do a structural analysis of the turbine and tower will cost upwards of ten thousand dollars and that does not include any guarantee that they will find it sound enough to actually certify either as being sound enough to put their stamp on it.
If I had known then what I know now my turbine would be standing here on a 16 meter tilt up tower, but now the powers that be will be on me like a chicken on a bug if I start anything, so please, just put your turbine up.
In the spring I'm going to do just that, I may become a poster boy for small wind, but I will not be subject to an imbecilic ordinance written by people who had not a single clue as to the physical or monetary realities of residential size wind power.

[Ben Colla]

I went in and blindly took the high road and went to get a permit, turns out my township has a brand new ordinance, one of the most draconian in the country, the only tower that is allowed is a monopole, so I said fine I'll put up one of these Chinese monopoles, the building inspector requires a stamped drawing from a state licensed structural engineer on the tower and the turbine, you cannot get either from exmork or the Chinese tower factory.

Well, that bites, doesn't it.

I wouldn't expect either Exmork or the tower company to supply you with what you want, and I wouldn't expect the state to accept it, even if you did get it.


I think I'll just put it up. I can honestly say I did ask, and that they said no problems, because I did. I was there and spoke with 3 different people from the planning department, for probably 30 minutes. They looked in books, and thought about it.

I just got a quote back for the chinese 16m hydraulic monopole tower. Looks like $5,500 AUD delivered, complete (tower, 2 big rams, electric hydraulic pump), with GST/Customs/duty, which I can't escape. Shipping from China to Melbourne, $156USD. Which, is basicly free. The thing weighs 2000kg. I don't see why the shipping is so cheap, but there ya go.

I'm going to have more problems moving it around the place than getting it here.

[Dale Sheler]

Excellent plan, the shipping to Chicago for the 16 meter tower for me was $550 USD which is also incredible, the one thing that is curious, the 16 meter tower they quoted me only needed one hydraulic cylinder, makes you wonder what the story is.