Need help on Battery Sizing/cost

WillWinston
WillWinston Solar Expert Posts: 45 ✭
in Off Grid Solar & Battery Systems #1
Here is what I am planning for my 48 V off grid system in Wisconsin

27 Evergreen 195's(3 strings of 9 X3 in series) into 3 XW60-150
12 Evergreen 205's (3 srings of 4 in series) into 1 XW60-150 (this is 48.5 Amps but I think it should be ok-- only .5 Amp over the recomended according to this

http://www.se-renbu.com/support/xwsizing/Default_SE.aspx

about 7600 watts (if I did the math right) or 150 Amps (and since I am on Vicodin for this morning's oral surgery math is a bit challenging -- but dreaming is good.....)

These will be tied into my Xantrex XW6048 inverter


now for the batteries

I currently have 8 Surrette (6 VOLT) CS 17-PS 546 A HR (new)

Do I buy 8 or 16 more of these for (another $6K or $12K)

OR

go with HuP solar One @ 1585 AHr ( *gulp* @ $16.2 K) (and get the free shipping :D)

The array should average about 900 Kw-Hr per month according to this link

http://www.wholesalesolar.com/StartHere/OFFGRID/OFFGRIDCalculator.html


TIA
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Comments

  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Need help on Battery Sizing/cost

    Okay, here we go again with the old saw. :p

    What are your loads?


    Off-grid systems are based on the amount of power you need to supply, not the amount of panels you have. The panels recharge the batteries.

    Right now your Surrettes are capable of a max of about 13 kW hours (not including conversion losses). Do you need more power than that?

    Your panel/controller configuration is a bit confusing too.
    Do you mean you have nine 195 Watt panels on each of three separate 60 Amp controllers?
    That's 1755 Watts per controller. Why is this configured this way?
    Add the 205 Watt panels and we get a total array of 7725, which is really large for an off-grid system.
    It should supply around 124 Amps of current maximum, enough for 1240 Amp hours @ 48 Volts. That's a Watt hour potential in the neighbourhood of 29,000. That is a lot of power.

    In terms of AC Watt hours out the door you could expect 15 kW hours with 4 hours of good sun.

    If your existing batteries are "old" then adding more of the same to it would be a bad idea. "Old" includes years, cycling depth/frequency, and less-than-perfect recharging.

    Were it me I'd pick some big 2 Volt cells for this.
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #3
    Re: Need help on Battery Sizing/cost

    not sure why one array is 3 in series, and the other is 4 ?? Aren't the Evergreens all about 18V P max ??

    Anyway, you need to aim for about 80- 100V at the array, to save amps in the wires (and the copper losses) and to have enough PV voltage, on a hot day, to be able to EQ if you want to. I use 5 in series on my array.

    And you have another choice (maybe) - if these are not on a fixed roof, but on pole mounts, you could have the arrays aimed in 10 degree steps, to spread your harvest peak, over a wider time frame. If all are due south, the arrays will be slow to "wake" in the AM, all reach full potential at noon, but the batteries won't be able to take it all, and then in the afternoon, when you use appliances - the arrays are winding down, and you are running off batteries..... Something to think about.


    And I'd go with the 1 monster string of batteries, less interconnects to maintain, less cells to water, less hassle all around, in my opinion.
    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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  • WillWinston
    WillWinston Solar Expert Posts: 45 ✭
    #4
    Re: Need help on Battery Sizing/cost

    Thanks for your quick response

    The solar panels were a terrific deal -- so yeah it probably is a lot of power

    this will be for a small farm -- a fair amount of water pumping, a reasonably big shop and freezers for food storage

    The power usage actually compares with our current suburb house with air and lots of electrical waste

    I also plan to use electric vehicles as much as possible -- maybe even an electric tractor

    http://www.renewables.com/Permaculture/ETractorSpecs.htm

    So more is more -- it sure beats waiting for the Fed to inflate my life savings into the toilet
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Need help on Battery Sizing/cost

    Do you happen to have the full specs on both panels?
    When I looked up the Evergreen 195's I got Voc of 32.9, which could not possibly be used in a string of nine on a Xantrex XW60 controller (9 * 32.9 = Voc 296.1). Could you mean a string of 3? That would be Voc 98.7.

    Sorry but I'm very confused about the array layout. :confused:
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  • WillWinston
    WillWinston Solar Expert Posts: 45 ✭
    #6
    Re: Need help on Battery Sizing/cost
    Cariboocoot wrote: »
    Do you happen to have the full specs on both panels?
    When I looked up the Evergreen 195's I got Voc of 32.9, which could not possibly be used in a string of nine on a Xantrex XW60 controller (9 * 32.9 = Voc 296.1). Could you mean a string of 3? That would be Voc 98.7.

    Sorry but I'm very confused about the array layout. :confused:


    the 205's 195's

    Vmp 18.4 27.1
    Imp 11.15 7.2
    Voc 22.8 32.9
    Ioc 12.1 14.5

    3 195's in series 9 panels total per XW60-150

    4 205's in series 12 panels total per XW60-150

    I have been using this tool

    http://www.se-renbu.com/support/xwsizing/Default_SE.aspx
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  • WillWinston
    WillWinston Solar Expert Posts: 45 ✭
    #7
    Re: Need help on Battery Sizing/cost
    mike90045 wrote: »
    not sure why one array is 3 in series, and the other is 4 ?? Aren't the Evergreens all about 18V P max ??

    Anyway, you need to aim for about 80- 100V at the array, to save amps in the wires (and the copper losses) and to have enough PV voltage, on a hot day, to be able to EQ if you want to. I use 5 in series on my array.

    And you have another choice (maybe) - if these are not on a fixed roof, but on pole mounts, you could have the arrays aimed in 10 degree steps, to spread your harvest peak, over a wider time frame. If all are due south, the arrays will be slow to "wake" in the AM, all reach full potential at noon, but the batteries won't be able to take it all, and then in the afternoon, when you use appliances - the arrays are winding down, and you are running off batteries..... Something to think about.


    And I'd go with the 1 monster string of batteries, less interconnects to maintain, less cells to water, less hassle all around, in my opinion.


    Mike these 195's are a bit higher in voltage so 3 in series works out well

    I am leaning towards the HuP Solar ones too

    Interesting ideas on the inclination/orientation
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #8
    Re: Need help on Battery Sizing/cost
    WillWinston wrote: »
    ... this will be for a small farm -- a fair amount of water pumping, a reasonably big shop and freezers for food storage.....

    For for the water, if you can pump daytimes, say 10am - 2pm, into elevated storage, you can effectively run the pump off the PV, and skip the losses associated (about 20-25%) in storing the power in the batteries.

    I'm using just a smallish 1/2 hp pump, at about 9 gpm / 165' lift, to get my water. That gives me about 2,000 gallons a day, and as days get longer & hotter, I run the pump a bit longer to keep up with the orchard's water needs ( about 300 trees so far, more next year)
    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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  • WillWinston
    WillWinston Solar Expert Posts: 45 ✭
    #9
    Re: Need help on Battery Sizing/cost

    Mike that is a great Idea

    I was thinking of making a water tank for the irrigation water

    one challenge at the farm is that it is a ridge top -- plenty of good water but it is 400 feet down

    I was looking into the Grundfos pumps for the new well -- quite efficient and low startup current loads
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