Grid tie inverter 110 ac input for generator?

Entra7798 · September 2017

Hello everyone, Im having a little trouble finding what I need for a project in working an and thought maybe a few of you could point me in the right direction. I have a generator I've been experimenting with running on wood gas from a gassifier. I'd like to tie my generator into my house using a grid tie inverter but I can't seem to find one that will work. I've been looking at grid tie units made to work with ac wind turbines but I can't find any that the input is rated for more than 110 volts. The highest I can find is an input of 90 volts. I guess my first question is will a grid tie unit made for alternating current of a wind turbine work with the ac of a generator? If so does anyone know of where I cant find a a grid tie big enough to do the job? I have both a 1000w and 5500w generators

mvas · September 2017

No, but ...
I think there are Grid-Tie Inverters that "Sell" excess battery power to the Grid, like the Outback VFXR3048E, 3KW @ 48V DC.
Then use your Generator to "charge" the battery bank.
Since the battery bank will always be 100% SOC, all power will be "sold" to the Grid.
Not the most efficient design but it is a solution.

mike95490 · September 2017

You may need a Hybrid Inverter. Your wood gas genset will not have grid-stable AC, and so it can only be used for powering a battery charger, and you let the Hybrid Grid Tie Inverter steer the power where it's needed (house or grid)

The Conext XW6848 would do that, but the internal relays are only rated 60A @ 240VAC

Entra7798 · September 2017

From what I remember reading, most standard grid tie inverters will let you sell back to the grid as long as you have the right meter. That why there called grid tie. Because they let you tie into the grid. And if you happen to produce more electricity than you consumed the meter allowed the excess electricity to be pumped back into the grid. That's what I had read somewhere, but if misread let me know. I don't have any battery bank at the moment due to a lack of funds. So at the moment my plan is to go from the generator to the grid tie to the house. I've seen a few setups with wind turbines that work this way. No battery bank. The house is connected to the grid. The house uses both the grid and turbine power. If the wind stops only grid power and if no one is home and the turbine is producing more than the house is consuming the extra electricity pumps back into the grid as long as you have the proper meter

mvas · September 2017

Yes, we understand what you WANT.
We are trying to explain to you, what is available for your AC Generator.
You cannot SYNC your generator directly to the Commercial Grid and
your AC Generator does not behave like a Wind Turbine, nor like a PV Panel Array.
Most inverters are designed for PV Panel Input and/or WInd Turbine Input.
You have neither and there is your problem.
That is why I suggested using a Hybrid Grid Tied Inverter that uses 48 Volts DC (a small battery bank), with an AC Generator Input.

You do not need a large battery bank with a Hybrid Inverter, since the Inverter is not really running off the battery bank.

There may be a NET ZERO Hybrid System that will generate just enough watts to offset your House Loads,
such that, the Inverter will not push any Watts out into the Commercial Grid.

If you do not have NET METER, then you need to very careful installing any AC Grid-Tied Inverter.

Did you actually research the ... Outback VFXR3048E 3KW @ 48V DC or similar?
This one actually has an a AC Generator input !

There are not very many people who can run an AC Generator cheaper than buying Commercial Grid Power
therefore what you want to do is very unique.

BB. · September 2017

First, the warnings. There are several major issues with Grid Tied installations and utility power.

Many of the import GT inverters are not UL/NRTL Listed devices. And are "illegal" to install in North America and connect to utility power.
Many of the "inexpensive" import GT inverters are not very well designed. They tend to overheat/fail when operated anywhere near their rated load (and a proper solar or wind/water turbine system will run for hours per day, or longer, near rated load).
You need to install the GT inverter on a dedicated AC circuit. You should not install on an existing shared AC branch circuit. You now have two sources of energy into the wiring. If you have (for example) a couple of electric room heaters, you can draw (for example) 1,500 watts (12.5 amps) from the circuit breaker panel (the utility) and 12.5 amps from a gt inverter at the same time--That will overheat the house wiring/wall outlet and cause smoke/fire (if you have two heaters and/or a failed home appliance that is drawing too much current). There are more GT wiring issues, but they all revolve around this issue of "multiple power sources" on a single circuit--That is why dedicated branch circuit (from main panel to GT inverter directly, no other loads) is important.
In the "olden days", AC utility power meters did run backwards if you generated more power in the home and fed it back out into the grid. Today, many (some, most, all?) utility meters have been redesigned to not do that. A common method to steal power was to flip the meter upside down for ~10 days a month to run the meter backwards, and the balance of month forward to run the meter forwards. Or disconnect meter and run a second meter/jumpers to steal energy (or even pull the meter and jumper the socket). Modern meters will flag when they have been pulled from the socket, and many will still "run forward" if the power flow is reversed (Revenue Guard).
Utilities have their rules. They are looking for meters that can or will report illegal GT inverter installations. They do not like solar/other GT installations. It costs them money. And many (smaller/rural) utilities do not allow GT installations at all. They can disconnect your service if they find you using GT solar/wind and it has not been permitted.

There are large generator installations that can sync to the grid and feed back power. For example, hospitals with emergency backup power will run their weekly/monthly power tests doing exactly that... They use the AC grid as a "load" on their generator systems for the test (coordinated with the local utility--of course).

For your installation... There are several options. One is to simply put a relay that switches your home (or some circuits for your home) between generator and AC mains power. That is really cheap and easy (and sort of close to legal). Fire up your genset, those circuits run on genset power. Genset turns off, relay switches over to utility power. If you have some circuits that you would not like to see a power cut on (TV, computer, etc.). You can use a cheap computer UPS to protect those devices that you want "clean power" to. Note that small AC generator power is not always frequency (and sometime voltage) stable. A UPS may switch over if the AC power is 55/65 Hz if your genset is not stable.

Another method is to run an 1,800 or 3,600 RPM AC induction motor (assuming 60 Hz) as an AC Alternator on your wood gas engine. Turns out that if you drive the induction motor faster (i.e., ~1,875 or ~3,750 RPM), the induction motor turns into a phase synchronized AC alternator. You will have the ability to feed power backwards into your home (and potentially out to the grid) using this method.

However, you will have to ensure that all is safe using this method. If there is a power cut from the utility, the AC motor may continue to supply power to the AC mains (residual magnetism in the rotor), and if there is sufficient capacitor storage on the mains, you can get very high voltage spikes as the power is cut (inductor/stator windings in motor, capacitors on AC mains = oscillator/self exciting alternator).

You will probably find fewer (if any?) large companies that make small wind AC capable GT inverters--A few years ago, the small wind GT power market collapsed and (at least one) major vendor exited the market:

http://www.smainverted.com/sma-to-part-ways-with-windy-boy-inverters/

-Bill

bill von novak · September 2017

Entra7798 said:

From what I remember reading, most standard grid tie inverters will let you sell back to the grid as long as you have the right meter. That why there called grid tie. Because they let you tie into the grid. And if you happen to produce more electricity than you consumed the meter allowed the excess electricity to be pumped back into the grid. That's what I had read somewhere, but if misread let me know. I don't have any battery bank at the moment due to a lack of funds.

You did not misread; that is correct. All such systems need batteries.

I don't have any battery bank at the moment due to a lack of funds.

OK, so you will not be able to do that.

I've seen a few setups with wind turbines that work this way. No battery bank.

That's a bit different. Here's how that works:

1) A large wind turbine is spun up with AC power, and settles at a speed that is close to or at a multiple of the power line period. (i.e. a 60Hz, 100 pole machine might run at .6Hz or 36RPM.)
2) The blade pitch is adjusted so that the wind tries to push the rotor faster than the driven speed.
3) As the torque on the rotor tries to push the RPM higher, the EMF in the rotor starts to resist - and the torque is converted into electrical energy which is fed back to the grid.

To get this to work, the system has to be designed with that mode of operation in mind.

You can do this with a generator; indeed, that's how many power stations operate. They do NOT use inverters and again must be designed to do just that. Trying to do this on your own is extremely dangerous; if the power goes out, the generator will happily try to backfeed the grid and electrocute the utility workers who are working to restore power.

If you want to get some backup power for your small system, buy some batteries.

mvas · September 2017

Bill,
I think the OP is talking about the Small Scale Chinese Wind Turbines ( for Residential use ), that do have the Grid-Tie inverter, not the Commercial Scale Wind Turbine that you are describing.

BB. · September 2017

I looked through Ebay for small GT wind turbine inverters--And they seem to peak out around 60-90 VAC input--I did not find any 120-240 VAC input (there may be some, but I did not find any).

I assume that what the OP was looking for--A cheap and easy way to couple his wood gas powered AC generator to the Utility Grid to reduce his power costs.

-Bill

Lincoln88 · August 2020

Entra7798,
I just came across this discussion and was interested in doing a similar set up. As this post was from a couple years ago, I'm interested to see what you came up with if you could share

RCinFLA · August 2020

First, a couple of definition of terms. When someone refers to ''Grid-Tie inverter' they usually mean a battery-less grid tied inverter where PV panels are tied to an inverter that syncronizes and pushes current to grid. There are no batteries involved and when grid goes down no power is taken from PV array.

The term 'Hybrid inverter' or 'Hybrid grid tied inverter' is normally applied to a battery based inverter that can syncronize its inverter to the grid or a connected generator. Many 'Hybrid inverters' have two AC inputs, for Grid and Generator, but only one can be used at a time and grid present usually takes priority if both are present.

To push to grid in U.S. the system has to be 'official' where 'official' means U.L./CE certitified equipment, permitted and inspected install, usually by a licensed installer. And lastly but not the least, the approval can require the signoff by local utility. This may include a second meter, a smart meter, and registry in their system that you have an approved system that will be pushing power to grid. There may be some special local requirements in a given utility area.

With the widespread rollout of 'smart meters' the utilities now get near realtime information about your power consumption INCLUDING if you are pushing power to the grid. If you push power to grid without an approved system and the utilities find out they can disconnect you from the grid until the 'issue' is addressed.

In the least retribution case, an old style meter will just interpret power you push to grid as your consumption and you will be charged for the power as if you consumed it.

Now to heart of your question. A regular generator cannot directly push to grid. The grid frequency and phase is very concise, your generator is not and it does not have a way to intitially syncronize frequency and phase to match the grid and keep it matched.

A 'hybrid inverter' can synchronize to the grid and push power from your batteries to the grid. It cannot synchronized to the grid and also to an applied generator as there is only one inverter and therefore it can only synchronize to grid OR generator, not both.

Some folks run PV panels into a battery charge controller to feed batteries which is drawn from by hybrid inverter to push power to grid through the grid synchronized hybrid inverter. This is called 'selling mode' in hybrid inverters.

So the only way to do what you want to do is to use the generator or any other power generation source to feed power to battery node so it can be picked up by hybrid inverter to sell to grid. You will have to put a battery charger on output of generator. The hybrid inverter is setup to sell based on battery voltage. When it rises above a set voltage it will sell to grid.

If all you want to do is consume your own generator power and not push to grid you can set the hybrid inverter to not allow any power push back into grid. Only your loads will use battery and/or grid power. The hybrid inverter can be set to use battery power (based on battery voltage) first before dipping into grid power to suppliment any additional needed by your loads.

Grid tie inverter 110 ac input for generator?

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