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Forum Index : Windmills : Grid Tied Micro-Inverter Use Concept - Wind Turbines - Efficient Legal

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Technophiliac

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Joined: 18/12/2020
Location: New Zealand
Posts: 80
Posted: 09:02am 02 Nov 2021
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Some objectives of alternative energy systems at least for me include:
1) Reduce the grid cost as much as possible
2) Be able to run independently should the grid go down for an extended period
3) Get the most bang for my bucks.
4) Keep it legal if at all possible. Life is simple and easy with legal systems. (Sort of -Why do Australasian power standards have to be tighter and more expensive than the rest of the World? Surely CE, RoHS etc could have been good enough?!)

To my mind, when the grid is up, a grid tied inverter is the most efficient way to go, over the alternatives. Returns from selling excess power to the grid are pathetic, one is better to retain and use as much power as possible ones own green power in an efficient economic sense. Even if it means charging your battery from the mains drawing the excess green power (when excess is available to do that!)

Plainly a grid forming inverter is helpful when the grid is down (or not connected - storage capacities becomes a significant requirement in that case)

But show me a legal grid tied inverter for a wind turbine in Australasia....?

I have a 3 phase generator, expected to be good for 800W with power peaks well in excess of that. Currently it has the 3 wires exiting it. How to legally connect to a grid tied inverter in Australasia? One approach that has occurred to me is to use a multi channel solar micro-inverter that is certified to meet Australasian standards. They can take say four sets of 400W solar panels. So if I can match the power from each phase of the generator I can run 3 channels of the micro-inverter legally....and efficiently.

How to do that? I could maybe run 3 x isolating transformers, one on each phase, rectify / capacitate the 3 isolated DC outputs and feed each phase into 3 of the micro-inverters channels.... Probably need custom made transformers for that - with matching high current coils....

But then if the 3 phase coils can be separated within the generator with six leads coming out of the generator they will (it seems to me) already be isolated and avoid the transformer step just described.

Plainly the turbine needs to be speed managed when the power exceeds the micro-inverter draw, so dump loads needs to be flicked in and out when required.

I also think I read somewhere, but cannot find it now, that part of the NZS4777 standard includes the grid being able to turn off / reduce the power exported to the grid during times of excess generation over load to maintain grid power standards. (Does this ever happen in practice?) Plainly a turbine running full song needs a good dump load available to cover the grid turning the inverter off at its pleasure...!

Also sustainably switching AC is preferable to DC (Say 48V @ > 20 amps) so one can switch in dump loads on the AC side of things more cheaply than on the DC side with relatively standard relays. (Or some power electronics is desirable avoiding relays clicking)

If the grid goes down significantly the wind generator can be rewired to run into a controller / battery / gird forming inverter. The generator coils can be joined into the three wire config easy enough as a part of that.

Is this thinking missing something? Or is this a reasonable direction to run up?
Davo, Wellington. You can have it perfect, on time, and at the best price. Choose any two.
 
pollenface

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Joined: 01/09/2020
Location: Australia
Posts: 31
Posted: 10:38am 21 Nov 2021
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How do you isolate and rectify each phase? I thought you need at least 2 phases to rectify to DC current.
Off grid man caver
 
Technophiliac

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Joined: 18/12/2020
Location: New Zealand
Posts: 80
Posted: 11:46am 21 Nov 2021
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Thanks for the question. Short answer: No.

How? Easy: Wire a full bridge rectifier across each phase - schematically uses 12 diodes rather than the more common approach of 6 diodes to form a single DC from 3 phases.

3 bridges sub-divides the three phases into 3 DC supplies but I am not sure whether they are isolated, probably not, but I am not sure if the bridge rectifiers in effect achieve isolation. Maybe someone here can get their head around the question of isolation, and whether its necessary. I'd need to run it up and see if the three DC supplies had a voltage relationship to each other, I would have thought they would, but thinking about it as I type converting to DC what is the relationship to each DC supply? There may be a voltage difference of some relationship between the three DC outputs, which might then be important....  

FWIW only 2 isolation transformers would probably be enough to isolate all 3 - if done that way.

Isolation could be done using transformers (on the AC side before rectification) with matching coils but probably more simply and cheaply simply separating the three phase coils should do it.

Look at the great information on this site about the F@P motor re-wiring, the coils are joined together at one end of the coil runs, that is not necessary, the three coil series could be run out giving three independent matching power circuits.

I recall the Honda Inverter 2.0 Generators which have 3 phase coils joined together in the usual star pattern for the mains feed, but also have a separate 12V coil for the 12 V output, presumably rectified from a single phase too.

Most people will have things with a single phase rectified into DC..... whether their houses are supplied with single or 2 or 3 phase supplies. Not convinced? If you are running off grid you are probably running a single phase inverter and feeding appliances that convert and use DC. Routers. Phone chargers come to mind as examples.
Davo, Wellington. You can have it perfect, on time, and at the best price. Choose any two.
 
Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 94
Posted: 05:03am 24 Nov 2021
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Hi Techno.
Depends on what voltage the wind turbine puts out.
Most of the Grid tie inverters I have seen want at least 150 volts input to work, some  can run with up to 600 volts DC.
So if the wind turbine is 48 volt then you may need to use a transformer to step the voltage up, then use a 3 phase recifier ( I have seen them in one package that take up to 200 amps)
Feed that into a normal grid tie inverter and it should be legal.
That is of course as you come under the AS/NZ wiring rules that you get a sparky to connect it all up.
Have fun
Pete
 
Technophiliac

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Joined: 18/12/2020
Location: New Zealand
Posts: 80
Posted: 05:16am 24 Nov 2021
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  Godoh said  Hi Techno.
Depends on what voltage the wind turbine puts out.


"48V" AC - but no doubt voltage varies widely.....

  Godoh said  Most of the Grid tie inverters I have seen want at least 150 volts input to work, some  can run with up to 600 volts DC.


This is what I had in mind Pete:

https://www.enfsolar.com/pv/inverter-datasheet/13238 - the HME-1350-AU

I trust of interest, 4 inputs, voltages up to 60V, each pair of inputs I understand can be wired in parallel, I am seeking clarification if all 4 inputs can be paralleled, I suspect not.

Thanks for considering and replying.
Davo, Wellington. You can have it perfect, on time, and at the best price. Choose any two.
 
Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 94
Posted: 05:52am 24 Nov 2021
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The link doesn't take me to a datasheet. When I look on Gumtree here in oz there are heaps of grid tie inverters for sale cheaply.

Micro grid tie inverters could do the job fine. They are normally have all their outputs connected in parallel anyway.
The only problem I can see is that they will drop out when the wind drops off, but the solar panel connected ones do the same when night comes, so the inverters should be smart enough for what you are thinking about.
The rectifiers I was thinking about look like this one.
https://www.ebay.com.au/itm/232387047561?hash=item361b58f089:g:AbcAAOSwnK9ZUJ-i&frcectupt=true.
Sorry I haven't got the hang of getting links to work in this site, yet.
But there are plenty of them on ebay and they are pretty cheap.
Pete
 
Technophiliac

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Joined: 18/12/2020
Location: New Zealand
Posts: 80
Posted: 06:53am 24 Nov 2021
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Sorry I botched the URL.

try https://www.enfsolar.com/pv/inverter-datasheet/13238

and the pdf is https://cdn.enfsolar.com/Product/pdf/Inverter/5f58775643af4.pdf

  Godoh said  The rectifiers I was thinking about look like this one.
https://www.ebay.com.au/itm/232387047561?hash=item361b58f089:g:AbcAAOSwnK9ZUJ-i&frcectupt=true.


I describe those as standard 3 phase to DC using 6 diodes. If the inverter input will take all the power as DC they would be fine. I imagine a smoothing capacitor might assist, but not yet tried.

The micro-inverter I am looking at notionally has 4 inputs, not sure their relationship.
Davo, Wellington. You can have it perfect, on time, and at the best price. Choose any two.
 
Godoh
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Joined: 26/09/2020
Location: Australia
Posts: 94
Posted: 09:11pm 24 Nov 2021
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Hi Dave, they look good on paper.
They say that they can handle 4 panels so that is pretty useful
Better than having an inverter for every panel.
I did not see anything about paralleling the outputs but they would be pretty useless if they could not be paralleled.
Good luck
Pete
 
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