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I still haven't decided what to do, but found this 1000VDC variable power supply on ebay for $50:

https://www.ebay.com/itm/334503593016

The specs say it can put out 1000V @ 0.4A which should be adequate for testing this. 

https://assets.ctfassets.net/ntf98c1thwoe/1AojVLJke9WasHhTvkaMS2/184f9df025c552959ed4360400e8e0be/labconcopowersuppliesmanual1992-2007.pdf

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I more or less understood something like that...
you must match the array and the possibilities of the inverter before digging and installing...
the easy move would be to change the inverter now to match the array then.
I don't know if your zener mods will work or not, but it's worth a try.

When I started the ground mount solar array in 2008, I did plan ahead to some degree, but did not imagine I would purchase equipment in 2025 that can only withstand 550V maximum open circuit voltage instead of the more typical 600V or 750V of the SMA TL series grid tie inverters I installed.  I had forgotten the details of my wiring and thought the wiring to the array was direct burial UF cable, but it turned out that I used 3/4" liquidtight metallic flexconduit.  Oddly, the wire in the conduit is only 14 gauge.  Presumably, that is what I had on hand or was available at a good price at the time, but I found 3 unused wires in the conduit so could split the array without pulling additional wiring. 

I got a Bluetti EP900 on/off grid battery system with 2 mppt solar inputs that are limited to 550V.  Since I only got the EP900 a couple weeks ago, I'm just setting it up now.  I'm planning to stay with the old SMA TL grid tie inverters when utility power is available, but want to configure the system so that I can easily switch the solar array to feed the EP900 during extended power failure. 

I suggested the zener voltage limiters to a friend many years ago who used it in his small hydropower system and that has worked well for nearly 25 years.  I haven't used them myself though.  After finding that I did run conduit and have  spare wires in the conduit, I may just split the array into 2.  Combining the 2 with diodes probably won't be the most efficient, but may suffice since it would be used in that configuration except during extended power failure which is not a frequent event. 

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[Country]

Country	Pakistan
Note	I am electrinic engineer. I want to use this website to get help.

@pickit2,

I was in no way critisizing you darling.

lets converge on a good solution

Mike

Relay was a quick response. as you could use the excess voltage, for whatever ie: charge a smaller battery. 
I would use a powered Test load, don't everyone have one in their tool box.

@pickit2,  good thought. dont like relays though

i would add a variable current source (load), big mosfet ( probably several in parallel, with equalising reistor in the Source, so the G-S voltages are the same), big heatsink and fan, and control loop to keep the voltage at 540V.

so the current is variable.

and fuses of course

aditionally,Vgs falls as the temperature increases, so you need the resistor to mitigate and equalise  this.

Aquick look, found a mcrochip part APT6011B2VRG, APT6011LVRG MOSFET MOS5 600 V ..., I am sure there are many others.

how about a comparator circuit with a relay to add a load if the voltage is above the say 540V.
you could even add it to the panel groups, so if a group is below the upper limit they still supply the full power.   

I more or less understood something like that...
you must match the array and the possibilities of the inverter before digging and installing...
the easy move would be to change the inverter now to match the array then.
I don't know if your zener mods will work or not, but it's worth a try.