Inverter Question

[DRJensen]

Hello, I currently producing some of my electricity with my yanmar/st genset thru a generator transfer panel. I am interested in solar grid tie and well as running my genset in grid tie as I currently run it with used ATF. I need to understand how to tie this to the grid with an invertor that will accept a DC input from PV panels and a 240 AC input from my genset. My genset is not big enough to run the whole house but with grid tie it would cut my consumtion quite a bit. What type of inverter would I need? I understand that I would also need a auto disconnect if the grid goes down as not to back feed the grid. I could also use an alternator setup for DC power generation but that is a cat of another color and not really and option because I currently produce AC power. Would I need a net power meter from my local power company? What regulates the output of the genset say a constant 5000 watts, the inverter size? Any help and guidance would be appreciated.

Regards Dave

[Tom Reed]

I am not aware of any inverter that will allow you to feed your generated AC into the grid. The best option is to rectify the AC to DC and then the inverter will not know or care where the DC came from.

[mike90045]

If you can convert 3 phase AC to DC, that's the easiest. Otherwise, you will need to build a high Voltage (50-500V) DC supply that is low ripple, and then feed the clean DC to a Grid Tie inverter - the GT inverter and your power supply have to have matching/overlapping voltage ranges.

[glort]

I built a 3 phase rectifier and run the power from an AC motor set up as a generator through that to produce DC current I thn backfeed through a normal solar panel inverter.
That takes care of the disconnect, quality, syncing etc.  You could run the same setup from a 240V generator. Still not exactly sure how your wacky US power works, here 240 Is single phase, 3 phase is 415. Shouldn't matter, just use the single phase from the genny if that's what it is through one rectifier instead of 3 of if it is 3 phase, still should be fine.

Don't know if you could have the panels and the Genny connected at the same time though on the same circuit however one of my inverters has Dual inputs which can be run singularly or paired so with this type of inverter I believe you could have the panels hooked in and run the genny at the same time.

Converting the AC to DC is easy and cheap. Some bridge rectifiers and a heat sink and you are good to go.

As for a DC alternator, make sure it outputs a high enough voltage. IE< the ones I have won't kick in till greater than 90V so you can't just hook up a std car alt.

As far as net metering, Up to you but I wouldn't bother. My setup just feeds back into a couple of power circuits. This supplies what ever is in use in the home to that wattage firstly and is supplemented by the grid over that. If there is excess being generated over what is being consumed, the meter spins backwards giving me some " credit" for when the draw is above what is being generated ( if anything at all is) .
From what I have read they make it impossible to do a proper net metering setup from a genny and if things are the same wherever you are like where I am, Currently they pay .6C KWH GENERATED and CHARGE .20C KWH for what you USE.

By just backfeeding, you get a perfectly fair return for any excess you generate and offset your bill from your own generation as well.
Hard enough to make this worthwhile even with free fuel let alone getting less than half back.  That said, check your rates but I think that you are going to be up against it unless you have a proper solar system to start with.

With the inverters I have, they regulate the output to their rated capacity. I can pump in 10 KW but on the 2KW units, thats all they will feed back.  All I have to do is make sure the voltage stays under 600V ( a lot harder than it sounds!) and any excess current is ignored. I could pair up multiple units though off the same source and that will work providing i'm feeding into a circuit rated to take the Output.  On the setup I have, I feed into 2 Different circuits to prevent supplying too much power to one and causing a Reverse overload if you will.  Again, I don't know what the std US circuit is but for power here it's 3600W on a circuit and a std outlet is rated at 2400W.

So to specifically answer your questions, A solar inverter would do fine, no need for a disconnect, it should be built in, DC alt has to be of sufficient voltage and clean enough, Net metering, Probably not, just backfeed into an existing circuit, Inverter regulates output up to its rated power and therefore load on generator.