System Sizing questions

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System Sizing questions

Postby pariahsmile on Fri Oct 13, 2017 2:01 am

I am trying to size a new system I'm thinking of building, it will be 500ah NiFe, 24v battery (trying to see if it can be had as a 48v system, but I don't see how... it's 20 cells of about 1.2v each in series). In selecting an inverter, I didn't know the Outbacks came with or without the charger until just now. I would want a charger built in, and I think the FX2524 would be fine for my needs; but it comes as a sealed unit in that size, or else I can get a similar one in vented configuration at 3524... another kilowatt. But the idle watts are the same, about 20w so seem to be very similar otherwise. I doubt I would need the extra kw but it would be nice to have since there seems to be no efficiency tax when idling. Both models have max 30A input for gen charging, which suits me just fine (2x Ryobi 2200 gensets in parallel will just about max out the 30A rating AC input, I'll probably get lazy and just run one of them at around 15A for twice as long).

Question is, has anyone noticed an improved longevity with the sealed vs vented outbacks? I live in a somewhat dusty area in Hawaii so a sealed unit is probably a good idea (unit will be outdoors on exterior wall, with a roof providing shade). The cc will be a Midnite Classic, and I have been playing with their sizing tool; wanted to go with 4 strings of 3 each 285w (3420w) Trina panels (Vmp = 35.6v, Voc=44.7v, Imp=8.02A and it never gets cold enough in Hawaii for Ioc to matter), but the sizing tool says that is possible only at 48v. At 24v, I would have to run 3 strings of 3 panels for a 2565w system. I am told the max charging amps for the 500ah NiFe battery is around 100A but it can take 125A periodically, although it looks like the Classic will max at around 84A in bright sun, comfortably within the battery's limits although I doubt it will reach that current often.

I am currently on-grid and have a very small 'trial' system of 3x 285w Trina panels with Midnite Kid and 1.5kw Cotek inverter, which have served well to illustrate that I am under-batteried (4x6v GC2, around 210ah @24v has been running about the past 10 months to specific appliances in my home to get just those appliances off grid. My normal daily draw from the Kid seems to be near 2.5kwh in the summer. In the winter I have to unplug one of the appliances to go nearer 1.5kwh or less as there isn't enough sun to support that much load.
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