300w Wind Turbine producing 500w!

[Shay]

I have my Navitron 300watt Wind Turbine operating about a week now. Its on the standard 6m tower on a slight hill which gives it about a overall 8m height above the surrounding area.

Its rated at 300w at 7 m/s.  Taking the current wind speed from nearby weather stations (via http://www.xcweather.co.uk/) which would be located in relatively similar terrain but at a height of 10m the wind speed this morning was around 5m/s. The turbine was producing 500watts. 
Wind speed currently is around 7-8 m/s and its reaching 720 watts for short periods.
I'm not complaining for this over performance, I'm just curious as of the reason.

[martin]

which one have you got? - the "new" style with the droopy tail, or the older straight tail job?

[Shay]

The straight tailed 2.5m diameter whirlie one.

[martin]

off the record, they were grossly underrated..........if you've got 2.5 metres of blade, in comparison a Swift teapot is rated as 1.5kw with 2.12 metres.........

[billi]

Shay nice to hear

its blowing mad here in co.cork  , our washinmashine is on all day 

Billi

[Shay]

All that wind makes the doo-doo weather a bit more tolerable 

[billi]

 

Have to get a hydro turbine then as well to enjoy all weather (sun,wind,rain) 

I did my decidion on the windturbine on comparing models output at about 4-5 m/s 
Mine is rated 1000 watt at 9 m/s  and did 1500 watt sometimes allready 


But i act  like a lunatic and even stand up at night with a big torch in my hand to see if all is ok

Its good to have it up and learn befor the winter comes  to trust it
But think i will lower it or put the brake in on realy tough conditions

Billi

[RichieC]

But i act  like a lunatic and even stand up at night with a big torch in my hand to see if all is ok


Billi

 I'm glad I'm not the only one that does that! 

Rich

[oliver90owner]

they were grossly underrated..........if you've got 2.5 metres of blade

It's not the blades you should be worrying about.  It is the I²R losses.  Assuming it has the same output voltage the internally produced heat will be over twice the amount for the rating plate value.  In fact yours is nearly 3 times as much.

Your windings may well be overrated, as well as the blades, but they may overheat - especially if you were to operate at 700W for long periods (now over 5 times the thermal energy going into the windings).

Navitron will know the absolute maximum output it will accommodate.  It may well be much higher than the rating plate.

Regards, RAB

[martin]

There would appear to be some people who will raise some esoteric figure about bicycle wheels when a question about the price of fish raises it's head!
If someone remarks that they are getting more than the quoted wattage of a turbine, and asks "why?", I am under the impression that to tell them it's because they were underrated in comparison to many other manufacturers is entirely reasonable, and needs no reference to fish (nor bicycles)
To go a little deeper into it - there has grown up the habit amongst many western turbine manufacturers of "rating" their turbines at the ludicrously high windspeed of 12 m/s (eg 300w), in an effort to make their underpowered offerings look far more powerful than they actually are, whereas the Chinese manufacturers are in the habit of quoting a far lower windspeed (often, in the case of the earlier Navitron turbines as low as 7 m/s). SO, if someone is getting a wind of say 8 or more m/s, with a turbine that is nominally a "300 watter" (rated at 7m/s), it is entirely reasonable to expect that the "curve" carries on upwards way above the "rated 300w" (and it does!)...........I have yet to hear of one of this type of turbines burning out it's windings (so although a related matter, the question was not "will it break?, the question was "why?") - I answered that question....
SO, you may capitalise in disbelief all you like, the main reason why the turbine in question is "overperforming" is a function of the swept area of the blades, and the method used to rate it - simple physics, and clutter all to do with fish or bicycles!

[oliver90owner]

bicycle wheels......... the price of fish

While on the cost of a loaf of bread, please go ahead and tell the guy, and everyone else, the absolute maximum befiore I²R losses become over-burdening.  Or is it a secret?

I said:
It may well be much higher than the rating plate.

Lets be knowing - what is the safe limit.

Some generators are designed to turn away from the wind when overload is likely.  Does this happen with said generator?  Or does the power increase continually forever?

RAB

[martin]

 "befiore I2R losses become over-burdening" (sic) - not quite sure what that means, but it furls (turns the rotor out of the wind) before anything untoward happens...........
"rating plate"? - quoi?

[oliver90owner]

 Martin,

you say: it furls before anything untoward happens.....

OK, it is fairly obvious that it doesn't occur at or around 300W,  by my calculations (and they may be incorrectly used in an inappropriate manner) if 720W is seen before furling the rating (whether it is a plate like an electric motor or whatever) means the wind speed at, or perhaps before, furling is somewhat above this magical 7ms^-1 (9.5ms^-1).

Your comment about, as you put it, the earlier Navitron turbines as low as 7 m/sdoesn't cut any ice .  This is a new turbine, not an earlier one?  Is The straight tailed 2.5m diameter whirlie one(sic) one of these 'earlier' ones you are referring to? Please quote actual and relevant figures.

Don't beat around the bush. Tell me, and Shay and the rest of the world that are reading this, how much power it will produce safely (without overburdening - that is overloading - the thermal capacity of the windings , ie approaching a temperature that may melt the insulation.  There will be a limit and Navitron and the manufacturer's should know that limit.  What is it?

More people are likely to go out and buy one of these if they know it is good value for money and likely to produce lots of power and is unlikely to fail early by not furling at an appropriate wind speed.

There is so much rubbish posted about specifications, with some quoting very high wind speeds, some quoting more sensible wind speeds etc. that the picture needs to be made  transparent, not hidden amongst any assumed data that could easily be used as sales hype for a product. 

Maximum safe output is one of the needed criteria to be able to assess the likelihood, or not, of the machine lasting it's designed lifetime (subject to normal maintenance schedules).  By the way what is the design lifetime for these Chinese machines? 

RAB

[martin]

ho hum!
There are two turbines which Shay may have been referring to, both rated at 300 watts, which is why I enquired as to which it was - the "older" (or possibly more correctly "original") straight tailed version, and the "newer" 300w with the droopy tail, so I knew which........
The "earlier" turbines were rated very differently to "western" turbines, and it IS entirely reasonable that they quoted an incredibly modest "300w" at 7m/s - this in no way suggested that once the windspeed reached 7m/s that they suddenly stopped producing power - the curve continued on up........which meant that when you applied the fairly accurate "rule of thumb" about the power possible from a turbine, these were incredibly conservatively rated compared to "western" machines.
I really am rather lost as to why you are getting somewhat foam-flecked about a machine that would appear to be performing better than you at first may have presumed it could........shock, horror, probe, it's giving more power than you think it dares to?
  At 7m/s it gives a good 300 watts, and at higher windspeeds it will give more - it is substantially built, and furls before overheating  - the "newer" droopy tail job uses a totally different system with an inbuilt brake (all the control gear is built into the turbine) - the "newer" turbine also has somewhat less swept area, bringing it more "in line" with Western ratings. THEY ARE  TWO VERY DIFFERENT MACHINES
So, as I said, they are not given to burning out their windings, as they furl in time to prevent it - having never had the privilege of gathering windspeed, voltage and amperage from one in the field, I am unable to give you figures of precisely just how good they are, I'm afraid you'll have to make do with the "Rolls Royce" answer - "Power sir? - sufficient!"
By the way, just for clarification, I am not a Navitron employee, and although I'm very happy to impart what knowledge I may have on a product (in this case gleaned from selling them, and in the case of the "newer" one, being on the verge of putting one up in my garden!), but am not here to be demanded of by self-appointed "experts"

"Maximum safe output is one of the needed criteria to be able to assess the likelihood, or not, of the machine lasting it's designed lifetime (subject to normal maintenance schedules)" - from this statement, do I presume that you have the in-depth knowledge of the minutiae of wind-turbine design to be able to make those judgements definitively, accurately and relevantly?

[longstroke]

I think I can see where you're both coming from and find myself in agreement with some of the points that each of you are making.

For a start I'd assumed that you (martin) worked at Navitron and that seeing as this is Navitrons forum presumed that it was a place for people to ask questions about the various products to which you seem to be able to provide in-depth answers.

But also when you goto a shop to buy an appliance in the same price range as a 300Watt turbine it has a huge long spec list so that whilst Joe Public forks over the cash and throws it in the car, a more particular person can study the spec to gain a better understanding of its capabilities.
So when I look at some of the products on the Navitron website I do notice that the amount of detail is minimal.

The droopy tail 300Watt says lightweight but doesn't explain whether it is refering to the weight, construction or life expectancy. Does this make the original one the better buy? Where would I find details for wind speeds, self furling, electrically braked etc.

Oliver90 was pointing out a basic rule of electrics to do with the the heating effect in the windings being proportional to the square of the current which strikes me as a reasonable concern if you buy a 300Watt turbine and find you get more than double the power at times, and which according the the heating rule equates to nearly 6 times the heat in the windings at 720 watts.

Having read the previous posts I have to say I am even more inclined to buy one of the straight tail ones so this thread has only been beneficial to Navitron so as far as I can see when you have a good product (even if its not yours - I have no idea of your relationship with Navitron but if you didn't support them you wouldn't be here on their forum answering questions and providing the large amount of info that you do) the more that is known about it the better as it will encourage even more people to buy.