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Grid Tie to Generator or UPS


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I haven't done such a thing. But... 🙂

I know that they will not tie with a small petrol generator. I don't know if you've ever listened to those things running, but it always sounds like every few seconds there's just a small misfire or stuttering. I mean, just listen to it ... generator.mp3.

It will tie with a larger (usually Diesel-driven) generator, usually, especially the older style where the engine will speed up if the load drops, therefore naturally causing the grid tied inverter to limit.

It won't tie with a "modified" sine wave. I sometimes wonder why people even came up with that term. It must have been someone in marketing who wanted to make it sound better. It's not a sine wave at all. It's a square wave with some dead time in the middle and a modified duty cycle. No grid-tied inverter with any sort of grid-code compliance is going to tie with that. Even if it did, it would be an exceedingly bad idea if that UPS was not designed to accept energy on its output. In all likelihood you'll blow up the UPS, perhaps not immediately, but the first time you have less loads than PV generation... it's bye bye UPS.

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Definitely stay away from anything without a pure sinewave! 

As Plonkster said, NO! to try to synchronise with any generator that doesn't have a constant speed with or without load.

Anyway, if you grid tie with a diesel generator, your inverter should never be capable to generate more power than the diesel gen does, because it will "see" the generator as a synchronous motor and would attempt to push power into it. This may seem like a good idea to save fuel, but with a diesel engine it won't. A diesel engine has its optimum efficiency when it does the work by itself (the work it was designed to do). Any power input from the outside (inverter feeding in), will just result in heating of the windings of the generator and is counterproductive. 

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