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I bought one, expensive retail, planning to use it with transformer, also transfer switch, for 10kW of Sunny boys on grid and grid backup.
Then picked up 3 more that had been used for development of battery support of grid, 3-phase.
Then 8 more on a pallet (Thanks, DC Solar and Warren Buffet!)
You can figure out how to use transformers with a protractor and compass. Voltage is length of a vector, and phase is angle. One vector off the end of another to see what it produces. Or Trigonometry and Pythagorean theorem. Excel calculations and graphs. You can draw static arrows, but they are really rotating in a circle in the "complex plane" at 60 Hz. One axis is real (voltage) and the other is "imaginary". Projection of a vector on the real axis is instantaneous voltage. But you can do the math without imaginary numbers (represented as "i" or "j").
Using a 480V PV inverter adds the expense and weight of transformers. I see plenty on eBay, but located half way across the country, today's elevated shipping cost makes them less attractive. So better off with single-phase 208V GT PV inverters.
I had 3x toroid transformers I picked up, was able to use them as 120 to 260V auto-transformers, close enough to 277V to be within limits.
I want to get a bunch of 10kVA 240/480 to 120/240V transformers. With that I can use each 120V leg to make a 480V leg, for floating delta, and they're not too heavy to move with an appliance dolly. Two of the same could be used to make 3-phase from 2x 120V inverters that are 120 degrees apart, so one DC Solar trailer could make three phase with addition of just transformers, although 3rd Sunny Island would be preferred.
I rely on the power company, at least while I have NEM 1.0, for most storage.
I had an old AGM bank, now degraded from 100 Ah to 40 Ah, which I used for the 3-phase setup. Don't know how much starting surge that could supply.
I have a mountain property I thought this setup could be used for, which is why I picked up the TriPower when I saw it. Best sun would be hundreds of feet up the hill, so 277Vrms from ground would cut IR losses, while still being OK for 600V wire.
But I'm kidding myself. I just assembled the system because I could. Now I need to find some 3-phase loads bigger than my pool pump. I keep seeing air compressors at local auctions ...