A few more questions.

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Seven
Seven Solar Expert Posts: 292 ✭✭
in Solar Beginners Corner #1
I am about to have 6x 210w panels in my possession and I am trying to decide between a 12v or 24v bank. Much of that decision comes from the inverter selection.

I am doing the math on watts/voltage and I get these answers.
1260w/14.8v=85.13
1260w/29v=43.4

derating the panels to 77% the numbers look like
970.2/14.8=65.55
970.2/29=33.45

Running a 24v bank of 370ah the derating of the panels would have me at a 9% charge.

Looking at the Magnum inverters, I am thinking of the 4000w models because the price difference between it and the 2000w ones is not much. The 4000w inverters are 24v.

I have it stuck in my head that you should run 2400w of panel for a 24v bank, but I don't remember where I read it. 1200 for 12v, and 4800w for 48v.

So my questions are:
Can I run a 24v bank with 1260w of panels?

Assuming 24v bank, is there any reason not to run the bigger inverter?

At this point I am planning on running 2 strings of three panels each for 90v and 8a per string. Kyocera 210gx-lpu(3) Kyocera 215gx-lpu(3) into a MS Classic 150.

How much am I missing here?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: A few more questions.

    Your going about it sort of sideways. The same amount of Watts divided up to either 12 Volt or 24 Volt is the same amount of power, just at different current rates. 24 Volts is slightly more efficient due to not as much power going to heat in the wires.

    What amount of load are you trying to supply? Do you need a 4 kW inverter to handle the maximum loads? How many Watt hours per day? These are the questions that find the answers.

    A 1260 Watt array @ 77% efficiency is 970 Watts.
    At 14.4 Volts charging that is 67 Amps, so for one thing you'd be maxing out a 60 Amp controller at times. This would support 670 Amp hours of 12 Volt battery, or about 4020 kW hours @ 50% DOD.
    At 28.8 Volts charging it is 33.5 Amps, easily handled by most controllers. This would support 335 Amp hours of 24 Volt battery, or about 4020 kW hours @ 50% DOD.

    If you have loads which will be drawing heavy Amps on the 12 Volt system it may be worthwhile to switch up to 24 Volt (don't forget about future needs/wants). The other question is: can you find batteries that fall within those charge parameters?

    That's why you size the battery bank to fit the loads and the array to recharge the batteries.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #3
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    Re: A few more questions.

    it would be fine to use either voltage, but many will cite that for every 1000w in pv then add 12v to the battery bank. you are over 1kw in pv, but i'm sure a 12v battery bank and matching inverter voltage would work even if higher amps flow providing the wires are big enough. the kicker in this decision might be if you expand on the system at all later on for then the 24v battery bank would be almost a certainty to be wanted. in light of being over the 1kw area already i'll add that the efficiency is not as good on the system the farther apart the input and output voltages are on the cc. going to 24v would improve the efficiency and between those 2 points would sway me to think 24v would be better to use than 12v for the batteries and inverter. there wouldn't be a problem in my mind either for going to 48v if you wished to.

    one of the advantages of higher voltages is the v drop diminishes percentage wise. you can still use very large wires if you wish and put your overall system % well below 1%. this too will help to accommodate future expansions. say for instance your total v drop % is at .85% (nice figure to have, but expensive on the wiring). now later on you decide to double your pv system as well as the battery capacity then the current will essentially double and cause the doubling of the v drop % to 1.7% which is still very acceptable. you wouldn't want to design at the edge with say 2.7% for the system v drop % and then decide to expand the system, with my double capacity example, and that would push the v drop % unacceptably to 5.4% and necessitate changing the wire to a larger one.

    planning is everything and as some of our offgridders around here often say, expansion is almost a certainty so you might as well plan for it now.
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #4
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    Re: A few more questions.

    I am doing what everyone says not to do. I am growing the system as I go. The initial loads on the array will be minimum. However it will be used as backup power when the grid goes down. 4-5 times a year.
    The actual loads on the system will vary depending on the situation. A few things will be running on solar only, all of the time. LED lights, and modem to begin with. I want to buy bigger than I need now so that I have useable backup and I can add to it. If we get hit with the rolling blackouts like last year, I want my fridge and some fans to run as well as a computer(laptop)
    The loads will grow. I'm planning that very thing. I plan to add about 1000w of panel a year for the next few years. My backyard faces South and there is almost no shading on it or my roof. When I have the equipment required I will go grid tie and keep the batteries for backup power

    I will be installing outlets in the house that will run from solar only for now. This may sound silly to some of you, but it is the best way I can think of to do it. It will be harder to do with 24" on insulation in the attic, so I may place the outlets and run the wires first. Again, not a big deal.

    The inverters I am looking at have built in chargers and the Classic will supply enough juice for 900ah of battery, so even if I stay with 12v I can go to 740ah of battery using the L16-s from Interstate. Only problem with that is right now I would only have about 65a for charging from my panels. When I get to 1800 watts, no problem. Another issue here is that I remember reading, or seeing here, that with a 12v bank you are only able to realize around 900w of panel. Or that the CC will only accept so much from panels for a 12v bank.

    I am sorry for the vague memory and answers. I have tried to take all of this in too fast and sometimes the numbers get jumbled up in my head.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #5
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    Re: A few more questions.

    Forcast how large you are going to "grow" the system, and build it there.

    4,000w inverter screams 48V

    You could start with 4 ,12V marine batteries, and when they become insufficient, step up to 200A 6V and ..... as your array and loads grow.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
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    Re: A few more questions.

    yes, the controller's output current limit could be hit at times using 12v for the battery system so i'd opt for going with a higher voltage for that reason too. let your thoughts take the steps to see where it is you are going and what that might entail and put that to paper to see if you've thought it out well enough to say to yourself this is what i need now to make it easier later. the real key is what you want to see at the end of all of your possible expansions and what it is you need in place now to make the transition easier.

    now in the case of having a built-in charger, the utility electric could press that charger into handling the normal charging requirements should the pvs fail to supply enough. the current supplied by the charger could add to the current from the pvs to meet higher charging % requirements. even inverter generators of the proper rating are possible to feed the inverter with to allow running of loads and charging. as a back ups system this would be automatic to engage the batteries to power the loads. it's no big deal to turn off the utility ac to use the solar power stored in the batteries too. in fact, i would encourage running off of the batteries at least once every week or so for a back ups system, as my batteries seem to like that, and it confirms things are still operating properly.
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #7
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    Re: A few more questions.

    Thanks for all of the replies. I hope to end up with around 5000w of panels. That is all I can envision having room for. About 24 of the 215w panels. The battery bank will change during this time and I have no problem with that. Old batteries will either go to a different system, or find another home somewhere. I imagine the final setup will be two 24v systems in order to keep using the initial equipment.

    12 panels, 215w each, 760ah of 24v battery should be the max of the first system. It will start with only 380ah of battery and 6 panels. This is where the inverter question comes up. Do I get the 4000w one and grow into it, or do I buy the 2000w with plans on doubling them up later. I didn't see a magnum 2000w in 24v, so that would lead me to an Exeltech or other brand. I am really leaning towards the 4000w one because in an extended outage I wouldn't have to worry about surge loads as much. Only drawback it it uses more power. I am going to have a smaller inverter to power little things so the big one would only come on when needed, or my array was big enough for it to permently power things.
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #8
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    Re: A few more questions.

    none for 48v? really?:confused:
    how about this?
    http://www.magnumenergy.com/Literature/Data%20Sheets/Inverters/MS-AE%20Series%20Data%20Sheet%20%2864-0250%20Rev%20C%29.pdf

    or this?

    http://www.magnumenergy.com/Literature/Data%20Sheets/Inverters/64-0275%20Rev%20A%20%28MS-PAE%20Series%20Data%20Sheet%29.pdf
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #9
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    Re: A few more questions.

    2000w 24v is the one I couldn't find. I do not have enough panel for 48v
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #10
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    Re: A few more questions.

    sorry about that as i don't know what went through my head even though i read it.:cry:
    outback also has 2kw and 24v. not sure of inverter/charger for xantrex at 2kw and 24v.
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #11
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    Re: A few more questions.

    Niel,
    No problem. Like I said, the numbers are all bouncing around in my head anyway. You pretty much answered my question with your first post.

    I can run a 24v system from 1200w of panel.

    With that being answered, now the decision goes to 4000w or 2000w inverter. I was focused on the Magnum inverters, but as I look I see a Samlex 1500w for less than $600. This could be the easy solution, if there is such a thing. Get the Samlex1500 for now, save more money and get the 4000 later. I could go the Epanel route with the magnum 4K.

    I have been hard researching for over a year and I really need to get going on this system. I prefer to "do" rather than learn most of the time, but with the expense of solar, I have had to change my process. That is, for the most part, due to this forum. This forum is why I buy my components from NAWS. I tell them that on every order.

    So thanks again to everyone here.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #12
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    Re: A few more questions.

    Before you buy a Samlex inverter read the caution on NAWS' Samlex page:
    "Note: We do not recommend Samlex for use with heavy startup loads, such as refrigerators or any other motor driven appliance that might have a large starting surge."

    Also the Samlex does not have a built-in charger.

    For full-size "I expect it to run everything" power you're better off with the Magnum.

    Consider also the Outback FX2524 - slightly better on power consumption than the Magnum, a bit less money, and "stackable" should you need more power capacity in the future.
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  • Seven
    Seven Solar Expert Posts: 292 ✭✭
    #13
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    Re: A few more questions.

    I did not see that. Thanks.
    I would still like a small 24v inverter and if I keep the loads light, the samlex may still work. It is inexpensive
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