interfacing 3 phase w/ the grid.

[JerryFlyGuy]

Well I'm sure it will be obvious that I'm a newby at all of this, however I guess I have to start somewhere. I've purchased several books on the subject and impatiently awaiting their arrival. I'm wondering if someone could help me with a couple fast and dirty question/answers.

I'm looking at going all out and building a large wind generation system. I've a supplier that can provide me with a 208v 3 phase generator rated at 25kW. I've built many model airplanes in the past and like the way a hot wire can make wings very quickly [ not to mention accuratly]. I plan on building a fairly large 3 blade setup to operate this generator[ or something of similar capacity]. My question is, is this the best way to set up to connect to the grid and sell them my extra power? I live in an area w/ a fairly steady wind rated at 275-325W/M^2 on average. I'm also really lucky it would appear, to be able to sell my excess power to the grid. I've been thinking that maybe there is a better way to put out power than three phase and then have to re-phase it to match the grid. Would I have to rectify it down to DC and then pass it through an inverter back up to match the 60Hz of the grid? Are there off the self components that will do this in one step.. is this a 'backward' way of doing this? Are there systems of this sort out there that could have multiple turbines attached to the same 'inverter'?

Is it possible to install several smaller generators [ or alternators] onto one turbine and engage them to a main drive shaft as additional 'wind power' becomes available? Or just stick with one large generator/alternator?

 It's a huge project but I figure if I'm going to spend a bit.. I might as well spend what I need and do it right. I'm waiting to find out all the spec's I need to meet for my utility to allow me to connect to the grid. One thing that I've already learned is they frown on home-made equipment [ or so I've been told] this is why I'm looking at off the shelf generation hardware to use in my system.  Any advice that can be offered would be GREATLY appreciated. Website links would also be a great help. I've been reading lots, however sometimes you don't know if what you are reading is crap or golden.. so..  

Thanks in Advance!

JerryFlyGuy

EDITORS NOTE:

It is the opinion of this Editor that Do it yourself GRID TIE is extremely Dangerous as well as illegal without proper approval so discussing it further is pretty pointless. Comments disabled for that reason. If the poster had done the least bit of research he would have discovered that early on.

[wdyasq]

How you tie back into the grid is a discusion between you, the electrical company and the state regulating officials.

You may be able to wire cut model airplane wind with a hot-wire.  I have done so.  I have yet to figure out how to develop the twist needed for a proper windturbine with such a setup.  

Developing a proper laminate schedule is another problem you will need to address.  Fiberglass and carbon-fiber have fatigue problems not found in wood.

One would think any inverter hooked to the 'grid' would need to be approved by a major labratory and approved by the associated orginizations.  I contend putting a windturbine on the grid is like giving your wife to a pimp.  They take all she can put out and you get to buy what you care to use.  

I have never personally seen a successful private hookup of power to grid.  I'm not about to say it doesn't ahppen but - like a UFO, want to see one before I invest in the technology.

Ron

[Nando]

THIS MESSAGE I SENT, some days back, to somebody that may have the same thought that you have at the moment.

I am an Electronic Design Engineer with large power experience.

~~~~~~~~~~~~~~~~~~~~

Why one needs a GRID rated inverter for GRID connection of a wind mill.

The GRID has a fixed frequency that could be 50 or 60 Hertz.

A national GRID, that has several o many generating power plants across the country, requires a very accurate frequency standard with periodic resetting to insure Zero power phase differences, consideration of distance and energy velocity in the transmission lines are as well in check, so each of the many power plants has its frequency set to a phase angle difference such that the arrival of the others power plants energy does not have a contention angle that may generate a big equivalent short circuit to the local and remotes power sources.

An inverter that can be TIED to the GRID has to have additional circuitry to insure that the inverter energy can be applied to the GRID following the GRID frequency, a very small frequency difference between the GRID and the Inverter frequencies will cause a short circuit when the phase difference between both frequencies is becoming greater than the power that can be transferred to the GRID.

The small inverters, designed for GRID tied conditions, have circuitry that read the incoming GRID AC Voltage and apply current following the AC sine wave to present the GRID as a resistive current Source and some as well have additional circuitry to read the current that the local load is presenting to the GRID and if it is at different angle ( Inductive or capacitive = Power Factor not 1) the inverter circuitry tries to correct the power factor toward one and if successful the additional energy available is dumped into the GRID in phase = power factor of 1.

SIMPLE INVERTERS sine wave do not have such external phases synchronization capabilities and the sine wave generator is too loose to keep phase with the GRID Sine Wave.

Inverters MSW ( Modified Sine Wave) have a squared AC output that by definition will short circuit the GRID, even if in phase, and the inverter will, of course, NOT win that short circuit battle.

Regards

Nando

[anders]

im in Holland over here we have a system that lets us pay the difference between what you used and supplied
i think it would be possible to use a small solar grid inverter to deliver back to the net

regards anders   

[tecker]

 There are so many things you can do with extra Wattage in a Rural setting Like  small scale fish or crayfish, tooling ,metal reclamation, Greenhouse farming the list goes on and on . I don't think the EMCS really want the power and a surge could set you back.

[tanner0441]

Hi

Your talking 25KW so your blades have to be a fairly big set up, and to match a set of blades to that power will need careful design.  Then what hapens when you don't need 25KW how do you stabilise the speed? 1KW or so can soon get lost in the area if the grid goes down and you keep feeding into it.  25KW on the otherhand could fry anyone working on the overheads.  Also your talking of rectifying the 3 phase then re inverting it up to the grid voltage, do you realise the size of the cables required to handle that amount of power, not to mention the cost of the inverter. Plus what do you do if the grid does go down how will you control your turbine when the load suddenly disappears, or before they work on the lines they short the overheads out and ground them?

I would love to read the reply you get from the grid company when you tell them what you want to do. I imagine it could be delivered by hand...

I feel you would be better off building a smaller unit yourself, see how that performs and how you keep it under control in your wind area.  I could save you from spending a lot of money and falling foul of your energy supplyer.

Brian.

[Mary B]

Solar and wind grid tie are fairly common here. There are 6 large systems within 20 miles of where I live. One is a nice solar setup on 3 trackers with 1.8kw per tracker.

How you tie back into the grid is a discusion between you, the electrical company and the state regulating officials.<p>
You may be able to wire cut model airplane wind with a hot-wire.  I have done so.  I have yet to figure out how to develop the twist needed for a proper windturbine with such a setup.  <p>
Developing a proper laminate schedule is another problem you will need to address.  Fiberglass and carbon-fiber have fatigue problems not found in wood.<p>
One would think any inverter hooked to the 'grid' would need to be approved by a major labratory and approved by the associated orginizations.  I contend putting a windturbine on the grid is like giving your wife to a pimp.  They take all she can put out and you get to buy what you care to use.  <p>
I have never personally seen a successful private hookup of power to grid.  I'm not about to say it doesn't ahppen but - like a UFO, want to see one before I invest in the technology.<p>
Ron

[fabricator]

Wow, on a post like this you just don't know where to start, first that 3 phase generator is likely making 208 at 1725 or 3600 rpms, that is gonna take a pretty fancy gear train because a machine the size you propose would have something like a 30 foot rotor (15' blades). Max rpm for a direct drive machine that size would be around 200 rpms.
There is a world of difference between a 3 foot wing span and a 30 foot wing span, you would be talking a LOT of fiberglass and a LOT of resin and layups this size should be vacuum bagged, that is how the big boys do it, you would need several layers of cloth with alternating fiber directions, big job good luck.
Then we have the tower, if you want a machine like this to be all it can be you need a TALL tower, 80-100 feet, that is an expensive tower with a LOT of concrete at the bottom.
Wind aint easy man and it aint cheap either and BTW as a general rule grid tie is a scam, if you are planning to do this as a hobby or because you love wind turbines good on ya, if you are planning on doing this to lower your electric bill a little it might do that, but do know this. unless you are 5 years old you will never see an ROI, wind turbines are machines and they need regular maintenance.
If you want plug, play and forget, estimate how much you would have in this project and buy solar panels, just a ball park estimate from somebody who has been there, you would have $25-30K in this project, you can buy one hell of a pile of solar for $30K.

[ghurd]

"November 15, 2005"

G-