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Advice: Battery backup system for new house
I’m in the final stages of wiring our house and wondering if I should add anything more then a 50amp generator plug on the exterior of the house.

I will have:
6.5kw rooftop solar with Sunnyboy inverter grid-tied
2.5Kw ground mount with outback FX80 and a 3.5KW inverter running off a 18650 powerwalll.

I would like the powerwall to be my battery back for the house to run the well pump and lighting.

Any recommendations for wires to run to my load enter inside the house before closing up the walls?
It would have been nice if my house was pre-wired for solar....   so maybe figure out the kind of PV system you plan and see about putting in some wiring for it?.  

For example,  IF you plan off-grid solar (like mine) and IF you know where your battery bank would be (maybe in a small steel container in the back yard?),  THEN you would be more like my case where....

I wound up running several 50a@240v wires (e.g. 3 x 6AWG Red/Black/White/Grd THNN) from the battery bank/inverter to ATSs around the hosue - 1 ATS at the main panel, another near the outdoor heat pump unit, another at a 50amp sub-panel at a workshop area.     Take a look at my build thread -  2nd post with all the pictures...  and near the bottom of the pictures you'll see an ATS/MTS combination at the main panel to illustrate what I'm talking about.

While were on this subject...  The PV arrays required several runs of 6AWG Red/Black/Grd in EMT conduit (DC wiring must be red + black and in conduit in my jurisdiction) under the house from the panel location(s)/combiner-boxes to the battery bank / inverter area - e.g. 'off-grid control areal' Smile

I’m running grid-tie with the power company so on grid is for 99% uptime. We do live on a road that seems to loose power a few times a year. So my thought was a 18650 powerwall in a “power shed” to run just the lights, and well pump.

I already own everything for the setup, I’m just trying to figure out the best option to prewire the load center which is on the center of the house.

It doesn’t need to be auto switching, but that would be nice!
For such a large system, why not use Li-Ion EV modules or large format LiFePO4? You will probably end up saving money and getting better performance.
(08-10-2020, 06:21 PM)Crimp Daddy Wrote: For such a large system, why not use Li-Ion EV modules or large format LiFePO4?  You will probably end up saving money and getting better performance.

If you already own all the off-grid stuff then pre-wire the shed. Have a subpanel installed next to your main panel where all your critical loads will go into. Or you can get one of those manual transfer load centers from Reliance. Put your critical loads on this subpanel. That means lights, fridges, hot water and the well pump.

Then get the wire from your shed to this panel wired up. Your shed will house the Outback inverter because it has to be close to the batteries. You need two sets, one from the main panel to the outback, and one from the outback to the subpanel. Then run the wire from your ground mount to the shed. If it isn't a cost factor, run extra lines just incase you decide to expand. [url=][/url]

Did you test to see if the Outback will run the well pump? Is the well pump 120 or 240V? That's the problem I am facing right now as my well pump is too much for my current 2.4kw inverter.

Just fyi, when the power goes out, your grid-tied inverters will be pretty much useless. It'll take a lot of planning to have that part of the system working.
I would be fine with going with better batteries, yet this is only a system i would add to over time from harvested cells. They are free and expandable over the years.

- A subpanel would be tricky as the load center is in the middle of the house with limited wall space.
- The well pump is a soft start 240V 3/4hp pump yet I do have a transformer to step up to 240V yet with startup surge and inefficiency of the transformer, that 3.5KW Outback would be close.
- If I go with a SunnyBoy inverter I could draw off the 2Kw "secure power" outlet, IF I disconnect the rapid shutdowns which wouldnt be legal.

Are there any good grid-tie inverters with battery back-up inputs?

Or I just feed a 50amp breaker and do a manual interlock with the main breaker and call it a day. Which makes it a pain if power goes out when we are away.
(08-12-2020, 10:16 PM)keaton85 Wrote: Are there any good grid-tie inverters with battery back-up inputs?

I chose the Outback for just that reason... 8 different modes, so lots of flexibility.

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