Big Offgrid System Request for Guidance [RE-wrenches]

[Jeff Oldham]

Hi Allen,
I'm sorry that I don't have the time to help you w/this but I've done several of these systems and can give you my thoughts and share w/the group:
Conventional EE thinking will get you into trouble!
3-ph is not going to have many inverter options above 10.8kW unless you can live w/monster inverter losses (NO!)
I go w/120/240 single and no transformers (have gone 350m) take a look at your transformer tare losses as well as efficiency, add it up as a kWh/day load and when you look at the cost of PV powering these losses even expensive copper looks like a bargain! In addition, the larger transformers can have quite an in-rush and can trip off your inverters.
The only viable inverter answer at this time is 10 stacks of Outback VFX3648 per circuit (36 kW per stack/circuit) . At this moment I'm expanding a RESIDENTIAL system from 3 circuits, each containing 10 VFX3648's, 12 HUP 1690Ah @ 12VDC and a 66kW genset to a 4th circuit of same but w/o the 4th genny. Yep, 144kW inverter, 975 kWh of battery, and 3) 66kW gensets on a freakin home! (17,000 s.f.). Sunny Island will probably not give you the power you need for each circuit. AC coupling is of no use if your night time loads require larger inverters, this has yet to be a solution for me to these projects as they always seem to need the inverter power and not only when the sun is shinning!
In a nut shell, the approach should be as many 10) inverter systems as required for the loads with as many distribution circuits. I also like a dedicated genny to each, with a DPDT transfer switch that allows me to pick any one of 2 gensets to a system for back up and genny maintenance. You may find it better to not have a common distribution point as each system can be indenpendant and closer to the loads, but this too has trade-offs. I also like HOMER as well.
Avoid absorbtion chillers or you will be haunted for life! Look at mini-splits in the SEER 20 or better range, do not spec these until the last minute as improvements are as fast as the computer world!
I'm very happy w/WattPlot for my remote monitoring.
Good luck!
 
-jeff o


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

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