

I'm sorry that I don't have more time to go in depth on this, it is indeed a complex issue that I have and continue to deal with. A few comments -
Transformers can be killer if they mount in numbers much and I've found wire to be cheaper than tare losses. As a very rough rule of thumb figure on at least a 3% loss at each transformer and a 1% tare loss 24/7 even without a load. Large transformers can also give fits to inverters. Gensets have a limit to a backfeed from inverters and other sources. The rule of thumb on this one is 30% of genset rating. For your 60kW units this is only 20kW of PV.
AC coupling gensets w/PV is a tough nut on efficiency, they won't couple unless the genset is running or you have additional battery based inverters to couple to. If the genset is running as it seems it will be here, the battery based inverters with transfer and charge the batteries and in most cases fully charge them before the PV had much chance to do so because the genset is likely producing double the charge rate of the PV. It can be sickening to see the PV at Float by noon and the gensets running all morning!
The o-t-g world is in serious need of large battery based inverters THAT ARE EFFICIENT to tackle these challenges. As far as I know only Outback fills the bill with the key word "efficient". Outback is limited to 10 inverters in a single (120/240 split) phase for 36kW and 9 in 3 phase 208VAC for 32.4kW. The only way to make it work is as others have suggested - break up the loads and distribution, maybe point-of-use smaller systems. In addition, you should not connect more than 10 Outbacks to a single battery bank. 
Good industrial batteries are cheaper than diesel and pollute less while increasing the life of the gensets and holding them at optimum loading.
I'm 4 years into a 17,000 s.f. o-t-g "home" in Mexico, I'm using 28 Outback inverters on 3 battery banks and 3 seperate distribution lines and 3 66kW Whisperwatt gensets. The EE designed the original 400M distribution system w/transformers and 3 phase 480VAC like a good EE would, but when I demonstrated the economics of spending a small fortune on copper to save a massive fortune on solar he jumped on a transformerless distribution system! The project has tripled it's load since my original design a few years ago. I've spent 90% of these 4 years controlling loads, I've specified 98% of all appliances, motors and misc. loads and have given my blessings to the rest. I don't think we can make this palace any more efficient.
I'm echoing the others here and the Wreches Mantra - put most of your efforts into efficiency and controlling loads, THEN look at solar and other RE's.
Good luck and keep us posted....
-jeff o


>From the Solar, Wind and Hydro powered office of Jeff Oldham/Regenerative SOLutions



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