Upgrading small off-grid system

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SolMan
SolMan Registered Users Posts: 15
A client of mine purchased a cabin in the mountains (~6,000') with an off-grid system that is too small for his needs (Outback FX 2500, 12 HL-16 batteries @ 24V, and 2 small arrays: 300W into a C40 and 360W into an MX60).
We think he will pull 5,000Wh/day and might hit 3,000W if his wife uses the hairdryer while he's microwaving breakfast and surfing the internet.

The first thing we want to address is backup power. He has a 1,000gal propane tank, so I'm thinking about a 7-8kW propane generator wired into the (already existing) inverter bypass switch. I don't know much about Outback FX's or their ability to auto start a generator, but that would be good.

The batteries are 4 yrs old and done. I want to replace with 16 new HL-16's @ 24V (1,600ah).
I want to move the existing 660 watts of PV to power a new Grunfos DC well pump, and install a new array about 2,000 watts to charge the battery bank.
Not sure if we should reuse the MX60 and C40, since neither one alone will be enough to handle the new array, or splurge on a new FM80 or MN Classic.

The inverter may eventually prove to be too small, but we are going to work with it for now.

Any thoughts or suggestions on anything? Am I off-base?

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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Upgrading small off-grid system

    Oh boy! A retrofit-upgrade! Which do you prefer: dynamite or bulldozer? :p

    Let's see, #1 their off-grid power demands are ridiculously high. 5 kW hours per day? Sounds like too much electric heating elements like coffee makers and hair dryers.

    #2, those batteries are probably toast as it looks like they've been short on panel all along. 660 Watts isn't much. Even I've got more than that.

    #3, need more panels. This is typical of almost every system we get inquiries about around here. Obviously you can't supply 5 kW hours per day off 660 Watts of panels. I don't even have to check the math on that one: nobody gets that much sunlight per day!

    It also sounds like it's time to consider 48 Volt, if that's the kind of power they need.
    5000 Watt hours on 24 Volts = 208 Amp hours @ 24 Volts 50% DOD for 416 Amp hour battery bank.
    5000 Watt hours on 48 Volts = 104 Amp hours @ 48 Volts 25% DOD for 416 Amp hour battery bank.

    Where's the need for 1600 Amp hours of battery here? Forget the "three days without sun" stuff. You could run half that battery bank size at 25% DOD and get the power needs on a 24 Volt system, with one "extra" day's potential use before having to start the generator.

    To recharge that 800 Amp hour 24 Volt bank you could use an FM80 and about 3 kW of panels, but it would be at its limit. On 48 Volts the MX60 would do it but you'd need to change the inverter.

    As for the inverter, yes the FX2524 will auto-start a gen, providing the gen is compatible. You'd only need to to change the inverter if the loads will add up to more than 2000 Watts at any one time.

    So, the batteries need to go. The C40 doesn't integrate with the OB equipment so should be replaced. The old panels are probably not compatible with anything new out there. You could keep the inverter and the MX60, add an FM60, replace the panels with two matched arrays around 1500 Watts each (check PV Watts for year-round potential production) and install new batteries of about 800 Amp hours @ 24 Volts.

    Any of that helpful?
  • SolMan
    SolMan Registered Users Posts: 15
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    Re: Upgrading small off-grid system

    Very helpful, thanks!
    This is for a home-based businessperson running a few computers, monitors, HDD's, etc. although not everything all the time.

    A couple more questions:
    What does a gen need to be compatible with Outback inverter?
    Would you go with FM80 over Classic 150 or 200? We may discover we have to add panels down the road...
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Upgrading small off-grid system
    SolMan wrote: »
    Very helpful, thanks!
    This is for a home-based businessperson running a few computers, monitors, HDD's, etc. although not everything all the time.

    You mentioned running a microwave (1000+ Watts) and hair dryer (1500 +/- Watts) at the same time. There's the limit on the 2500 Watt inverter right there. If this level of use will exist you have to change out the inverter. At that point going up to a 48 Volt system becomes more attractive. Computers can chew up the Watts, and Watt hours, pretty fast too. Any chance of doing some real-world load evaluation with a Kill-A-Watt meter?
    A couple more questions:
    What does a gen need to be compatible with Outback inverter?
    Would you go with FM80 over Classic 150 or 200? We may discover we have to add panels down the road...

    Mostly it depends on how the generator is designed to start. Things like automatic choke and a simple start/stop wiring. You can check with the manufacturer to see if they have an autostart kit for the particular model. Inverters pretty much just close a relay or open it to start/stop the gen. There has to be a bit more wiring involved to turn on/off into: ignition on, activate starter, deactivate when engine starts/ignition off.

    I would go with the FM80 if the inverter and any addition charge controllers were also going to be Outback; that way you can link them all through a HUb and control each via the MATE. Makes for a nicely integrated system. I would go with one of the Midnight Classic series if high array Voc was likely and integration was not essential. There may be other circumstances that would point one way or the other which just don't spring to mind right now.