2 Phase PV System Installation Approach ?

Coach Dad
Coach Dad Solar Expert Posts: 154 ✭✭
in Off Grid Solar & Battery Systems #1
Does anyone foresee any issues with the following plan?

I have a remote off-grid cabin that is normally used on weekends only. I’m currently running a 10 kw portable gas generator as my power source. I expect to install my complete PV system by the end of the summer.

I would like to install my PV system in 2 phases.
Phase 1) Install the Magnum Energy MS4024PAE inverter along with a 24 volt 305 AH battery bank (4-AGM 6v 305AH batteries wired in series)
Phase 2) Add the PV array and MPPT charge controller with all the other parts..

Since the MS4024PAE has a built in 5 stage battery charger, which can be wired to my generator I was planning on using the generator to charge the batteries during Phase 1 until I have the PV arrays installed. I expect the battery bank to only discharge to about 20% DOD over the course of a normal weekend.. So at the end of the weekend I would start up the generator and run it for a few hours to top them off before I leave for the week…
I would then turn everything off including the inverter so there is no drain on the battery bank.

My concern is… would the batteries be ok without a trickle charger running on them from Monday through Friday?

Are there any other concerns?

Thanks in advance
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: 2 Phase PV System Installation Approach ?

    Check with the battery manual, but if the battery is 100% charged, they can set for upwards of 6 months between recharging. If the battery is less charged, fewer months between recharging.

    Also, you could look at getting a 1% sized solar array with an inexpensive controller.
    • 305 AH * 35 Vmp (solar panel rating) * 0.01 rate of charge = 107 watt array
    So, you could probably get away with a 50-100 watt array (i.e., 2x 50 watt @ 17.5 volt panels in series = 100 watt array) and not ever worry about the battery (of course, you have to recharge the battery bank pretty well with the genset before you leave).

    Otherwise, if you are going to be there every 3 months or so, just plan on recharging with the genset (a much smaller genset would save lots of fuel and noise).

    In any case, with that size battery bank, if you have only the battery charger load--You would get away with a 1,600 watt genset pretty nicely (Honda eu2000i; Yamaha 2xxx inverter series, etc.). Only burn ~1.1 gallon of fuel for every 4 hours of runtime under rated 1,600 load (9+ hours per gallon with 400 watt load). A 10kW genset is probably a bit large and thirsty if its main use is recharging the battery bank.

    Here is a very nice thread on the ins and outs of picking the optimum small genest/battery charger setup. Kind of long and you can skip towards the end to find the answer if you are not interested in the details:

    Question about battery charger selection with EU2000 generator.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #3
    Re: 2 Phase PV System Installation Approach ?

    one other consideration: if you install everything at once (magnum ms4024pae, batteries, PV array, and controller) all of those items will be eligible for the 30% federal renewable energy tax credit. If you install the magnum and the batteries first, they are NOT eligible. The PV and controller will be eligible when you install them at a later date (but before 2016).
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: 2 Phase PV System Installation Approach ?

    sure, if they are charged up they can be left alone on a trickle charge. just don't try to bulk charge a battery bank with a trickle charge is all i'm saying. as a matter of fact a fully charged agm can be left without even the trickle or float charge left to it altogether for quite some time as their self discharge rates are low. (talking up to a month or so with no charger to maintain them on full batteries to start)

    in general speak your starting out with a basic backups design works, but the generator will need to be run for quite some time if the batteries are drawn on to insure they do not get deficit charged and that generator may need a higher capacity than you think due to power factors and other inefficiencies. it will be a pain to run the genny until your pv system is in place. i will recommend that you get the remote for the inverter as it will allow for the tailoring of the inverter settings to suit the agm batteries among other nice features. http://www.solar-electric.com/mameadrecofo.html

    also of note is that i must caution you not to have too small of a battery bank. many go with 100ah per kw capacity on the inverter, but also know, especially in the case of sunxtenders, that the temperature derating could also necessitate more capacity on top of that rule of thumb minimum. so if we were talking sunxtender batteries it would be 400ah x 1.43 derate factor = 572ah. now their largest 6v battery is the 405ah meaning that for 6v batteries you would have need to parallel another battery string to get the capacity. it may be better to use their 2v cells and place them all (12 of them) in series with the higher ah rating needed.

    we tend to think and advise more on an ideal level, but you are free to use or not to use our advice to whatever degree you'd like. i would think bigger than 305ah though.
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  • Coach Dad
    Coach Dad Solar Expert Posts: 154 ✭✭
    #5
    Re: 2 Phase PV System Installation Approach ?

    Thank you for your feedback...
    BB- I'm normally there every weekend.... and I expect to get the panels installed during the early part of the summer. So I don't see the need for the small panels if the Battery Bank is fully charged when I leave at the end of the weekend.. Agree?

    vtmaps- I thought that the federal credit is only good if you are installing it into your "Primary Home"... I'm putting this system into a weekend cabin.. does it still qualify???


    niel- 305ah is all I can afford at this time. Money is one of the reasons I want to phase in the installation.
    The Magnum Energy Inverter has a 105A battery charger built into it... So It will do all the phases of the charging process using my generator as the power source. Yes I'm planning to install the MS-ARC....

    Based on my calculations.. I expect to have an average DOD of around 12.3% per day (900 watt usage from the 24v 305AH battery bank).
    If I’m at the cabin for 2 days I would drain the batteries down to about 25% DOD…

    The rating of the MS4024PAE charger is 105A… I was going to set it to 75A using the ME-ARC

    The Concord AGM batteries recommend using a charge rate anywhere from 0.2C all the way up to 5C.

    So if I set the charger to 75A,,, I calculate that the batteries can be charged fully within 3 hours for a 25% DOD and charged fully within 4 hours for a 50% DOD

    Time for Full Charge = [((DOD/100) x Rated Capacity AH)/Charger Output] + 2 hrs
    Time for Full Charge = [((50/100)x 305AH)/ 75A] + 2hrs = 4.0 hrs

    Is this calculation correct?
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #6
    Re: 2 Phase PV System Installation Approach ?
    Coach Dad wrote: »
    vtmaps- I thought that the federal credit is only good if you are installing it into your "Primary Home"... I'm putting this system into a weekend cabin.. does it still qualify???
    Yes. You want the Renewable Energy Tax Credit. See IRS Form #5695. The tax credit (30% of your cost) is non-refundable, which means it can only be used to pay your taxes. If you don't use it up in the year you file, you can carry it over to pay your taxes in future years (only up to the year 2016, unless it gets extended).
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Coach Dad
    Coach Dad Solar Expert Posts: 154 ✭✭
    #7
    Re: 2 Phase PV System Installation Approach ?

    Hi vtmaps- am I missing something? I went to the tax form and the first line asks the following.
    Were the qualified energy efficiency improvements or residential energy property costs for your
    main home located in the United States? (see instructions) . . . . . . . . . . . . ▶ 1a Yes No
    Caution: If you checked the “No” box, you cannot claim the nonbusiness energy property credit. Do not complete Part I.

    Since the cabin isn't my "main home" I can't claim them...
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  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    #8
    Re: 2 Phase PV System Installation Approach ?
    Coach Dad wrote: »
    Hi vtmaps- am I missing something?
    Yes, you are. Turn the form over and look at part 2. The instructions for part 2 state explicitly:
    Qualified solar electric property costs. Qualified solar electric property costs are costs for property that uses solar energy to generate electricity for use in your home located in the United States. No costs relating to a solar panel or other property installed as a roof (or portion thereof) will fail to qualify solely because the property constitutes a structural component of the structure on which it is installed. The home does not have to be your main home.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
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  • Coach Dad
    Coach Dad Solar Expert Posts: 154 ✭✭
    #9
    Re: 2 Phase PV System Installation Approach ?

    vtmaps
    you're right!
    THANKS!!!!!!! You saved be a bundle!!!! I can't thank you enough.
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