Grid tied SMA inverter with Generac Nexus ATS

System · August 2010

I've recently installed an 8kW Generac generator with their Nexus automatic transfer switch (ATS)at a residence with an SMA Sunny Boy 5000 grid tied inverter. Prior to the installation, I checked with tech support from both entities and they equally agreed that the units would interact with one another if the generator transfer switch was "installed on the other side of the inverter." I talked theory with both camps, yet neither had a white paper, nor a hard diagram for install. So, install for the ATS can only go one way: after the inverter...

I tested the gen set/ATS on automatic, with the PV inverter input breaker off. All good! Repeated the test with the inverter breaker on, and the generator started, the inverter Faulted: Disturbance Mode Ref: L1/L2) and shut down. Generator shut down, Faulted: Overspeed. I opened both input/output breakers, repeated the test without the inverter and the gen ran fine. No apparent damage (SIGH!) to any equipment.

I'm in process with both tech depts and have not yet been back to the site to check (transient?) voltage present at the main panel buss from the gen set. Also, could the sensing circuit at the ATS prompt the inverter? I have been told that when the grid drops out the Sunny Boy 5000 shuts off in 1/120 sec. The Nexus ATS waits 3-5 sec. WTF? Then, if I get this sorted for the start up, what about the other end of the cycle, Re: reestablished grid, gen sense (15 sec +,-) gen shut down and inverter start up?

Any suggestions, while I pound on tech support?

Thanks!

mike95490 · August 2010

Re: Grid tied SMA inverter with Generac Nexus ATS

Any suggestions, while I pound on tech support?

Too bad there is no way to get each support mailing each other, with you as BCC.

BB. · August 2010

Re: Grid tied SMA inverter with Generac Nexus ATS

CopperHawk,

Just to be clear...

[FONT=Fixedsys]Generator =======o\
                   \
                    o===Protected Load

Grid Power ===+==o
              I
              ======Solar GT Inverter[/FONT]

So, your GT+Grid Tied Inverter are tied together to the Grid Input on the ATS

Generator is typed to Gen Input on your transfer switch.

And your protected load is on the ATS load output.

Or are you trying something like this:

[FONT=Fixedsys]Generator =======o\
                   \
                    o===+==Protected Load
  [/FONT][FONT=Fixedsys]                      I
                        ======Solar GT Inverter[/FONT]
[FONT=Fixedsys] Grid Power =====o[/FONT]

From what it sounds like, you may be trying to do the above setup?

It could work--but for most gensets, we are under the assumption that the Protected Load is always higher than the output energy of the Solar GT Inverter.

If the GT inverter output is greater than the load, then the genset will be try to be back driven by the GT Inverter (not sure that any genset will "like" being back-driven by a GT inverter)--And, it would seem to me, to indicate some of the problems you are reporting.

If the Genset and the GT Inverter are ever connected together (off-grid mode) and operated--Most Gensets do not have stable enough frequency to meet the GT inverter's requires (approximately 60Hz +/- 1%).

There are a few "inverter generators" (they have electronic controlled output frequency/waveforms) that can be stable enough--but I don't think any of them will respond well to back feed of power (will it cause damage to the genset? Not Sure. The GT Inverter should be pretty immune to any damage in these setups unless voltage goes way high of its specification).

Otherwise--My other guess, if the first setup, then I would check the Neutral connections between the Grid, Genset, GT inverter, Loads, and ATS... It is possible that somewhere the Neutral(s) are not doing what they should be (parallel paths, Neutral open during some switching positions, etc.).

-Bill

Grid tied SMA inverter with Generac Nexus ATS

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