Boosting Secure Power Supply mode of SMA Sunny Boy

[ayrat]

I have an SMA Sunny Boy inverter (not hooked up to the grid), and only use its standalone (Secure Power Supply) mode during daytime (doesn't require batteries). But this SPS mode provides only up to 2000W 110V pure sine wave, which is not sufficient to start some motors (some requiring nearly 5000W to start up).
So, there are some simple no-name 1000W, 110V grid-tie inverters. I tried to hook one up with only one panel, and it seems to be able to synchronize with Sunny Boy's 110V output. I was contemplating if adding say, 3000W worth using few of these inverters (along with more panels) to the same line wouldn't damage Sunny Boy and give me a wattage boost to 5000W to start motors? I suppose that there is some input resistance with certain power dissipation to the Sunny Boy (from the 110V side), which I have no way of knowing, hence too scared to try, and would greatly appreciate any input first.

[Mike90250]

They are your inverters you bought and paid for, but I don't think they will last long wired up the way I'm understanding. (2 inverter outputs tied together?)

[SunEagle]

Those simple no-name "grid tie" inverters sound like the ones that are neither UL listed or legal to use in the US.

I understand the OP's desire to self generate power when the grid is down but please do not go about using equipment that may cause damage or injury just to save a few pennies.

[solarix]

The grid not only provides a signal for grid-tie inverters to synchronize with, but the grid has to be a load that can absorb the power. The add-on inverters need to push their power somewhere. The instant your actual load is less than what the combined inverters want to produce, the voltage will go up and they will shut down.
You could get a large uninterruptible power unit and charge it off the (slow but steady) SMA secure power outlet, then run your bigger load off the UPS.

[solardreamer]

This kind of questions seems to come up over and over and it seems one key issue is the lack of understanding of the function of the grid with a grid-tied solar system. Specifically, the grid functions as a power pool/buffer that provides and absorbs AC power to ensure stable power with grid-tied solar depending on the balance between power used by loads and power generated by solar/grid-tied inverters. I have looked and I am a bit surprised that there is still no easy to understand video that explains this.

OP, you need to have a power pool/buffer that can absorb extra solar power generated or enough power load to guarantee there is never extra solar power but also does not overload your inverters as solar power changes with sun position, clouds, etc. for your idea. to work. Otherwise, you will likely blow up your inverters when there is extra solar power.

[J.P.M.]

This kind of questions seems to come up over and over

Sort of off topic but for repeated questions I used to wonder why this forum doesn't have a FAQ section for those things that seem to come up from 1X/week to several times/year.

That way some other poster could respond: "Ok Mr. Fanork, your question seems to match Q# 69 of the FAQ section. See and understand that for initial guidance."

Might save some time and more importantly, keep things a bit more accurate.Then I thought about it from the cynical sniff test mode.

[ayrat]

Thanks for all of your answers gentlemen, from your responses, seems too risky. I'll probably end up going with some sort of batteries, which I hoped to avoid.
My logic was as follows. I imagined that engineers working on SMA Sunny Boy SPS thought to add good protection and thought of the following scenario.
Say, someone runs a smaller 2000W motor off of SPS (disregarding how they managed to start it), then turns the motor OFF. So, while the motor is slowing down, but still spinning, there is, potentially, up to 2000W of backfeed. So, whatever electronics is there, should be able to dissipate it. And since it's designed by Germans, they must have doubled it, so maybe it will be able to absorb 3000W from other inverters when there are no other loads. But cheaper grid-tie inverters on the same line, yeah, now I can see, they seem likely to break.