Help with MPPT ans array

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slim1962
slim1962 Registered Users Posts: 5 ✭
in Solar Beginners Corner #1
I have 12x 24v 245w st solar panels.

Maximum Power 245w
Short Circuit Current 8.83A
Open Circuit Voltage 37.4V
MPP Current 8.22 A
MPP Voltage 29.8V

What would be the best and cheapest charge controller to us with 12 x 12v 230Ah batteries.

I have a samil 3kw inverter.

Any help would be great.
Paul
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #2
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    Re: Help with MPPT ans array

    Do you have a link to the samil inverter or it's full model name? (Doesn't look like they make battery inverters). If it is a battery inverter, what voltage does it use?
    No matter which way you configure them, those panels will need an MPPT type charge controller to down convert their voltage to either 12, 24 or 48V which ever your inverter supports. Again depending on your battery voltage you'll either need 3 x 80A charge controllers for a 12V battery, 2 x 60A controller for a 24V battery or 1 x 60A for a 48V battery.

    Do you already have those batteries?
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  • slim1962
    slim1962 Registered Users Posts: 5 ✭
    #3
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    Re: Help with MPPT ans array

    Hi
    its a Samil inverter 3000TL

    Have not got the batteries yet.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Help with MPPT ans array

    If this is the unit: http://www.samilpower.com/product_detail.php?product_id=22
    It is not a battery powered inverter.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #5
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    Re: Help with MPPT ans array

    Hi Paul,

    The bad news is that's a solar grid tie inverter meant to connect your solar panels to the grid. It can't be used with batteries. The good news is that you haven't got those batteries yet, because they are faaaar too many so you'll need lots of parallel strings which are not ideal.
    You'll find a wealth of collective knowledge on this forum, but to get the best out of it, it would help if you provided more information. In which country are you, and what are you looking for? a pure off-grid system? Grid tie with battery backup? Why do you want this system? Do you have grid power available, do you have a secondary charging source available (wind, diesel, hydro) ?
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  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
    #6
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    Re: Help with MPPT ans array

    Best/cheapest,, sort of an of an oxymoron.

    Avoid "ready, fire, aim!". Consider your loads, and then work backwards for battery sizing PV sizing, and indeed inverter sizing. A 3 kw inverter on 12 vdc is a HUGE inverter! 3 kw at 12 vdc is close to 300 amps net/net. You are going to need a very large battery bank to support such a large inverter. WHy do you need such a large inverter?

    Tony
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  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
    #7
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    Re: Help with MPPT ans array

    So we need more information...

    What do you want to do?
    Be grid connected, but have battery backup?
    Be off grid with a battery based system?

    If off grid, what are your loads, or how much electric do you need?
    This would be the mount of Watt hours you will use?
    If your currently on the grid you can read this off of the bill!
    At this point we always point out that conservation is cheaper than capacity.

    Your first consideration will be the voltage your system will run at, the size of fuses, wiring, and inverter specs will all depend on this.
    Generally if your using under 1500 watt hours a day, and need an array of 1000-1200 watts a 12 volt system will work.
    Systems using 2000 to 5000 watt hours, and need an array of 1000-3500 watts work best at 24 volts.
    Above this you'll want to look into a 48 volt system.

    These aren't firm rules, but it tends to work out best in these ranges.

    It's good you gave us the specs on the panels, Please don't call them 24V panels, they are NOT! if someone sold them to you as 24V panels they should be drawn and quartered, or hung by their big toes. 24V panels infer that they can properly charge a 24V battery bank with out the need of an MPPT type charge controller, they can Not.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • slim1962
    slim1962 Registered Users Posts: 5 ✭
    #8
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    Re: Help with MPPT ans array
    Photowhit wrote: »
    So we need more information...

    What do you want to do?
    Be grid connected, but have battery backup?
    Be off grid with a battery based system?

    If off grid, what are your loads, or how much electric do you need?
    This would be the mount of Watt hours you will use?
    If your currently on the grid you can read this off of the bill!
    At this point we always point out that conservation is cheaper than capacity.

    Your first consideration will be the voltage your system will run at, the size of fuses, wiring, and inverter specs will all depend on this.
    Generally if your using under 1500 watt hours a day, and need an array of 1000-1200 watts a 12 volt system will work.
    Systems using 2000 to 5000 watt hours, and need an array of 1000-3500 watts work best at 24 volts.
    Above this you'll want to look into a 48 volt system.

    These aren't firm rules, but it tends to work out best in these ranges.

    It's good you gave us the specs on the panels, Please don't call them 24V panels, they are NOT! if someone sold them to you as 24V panels they should be drawn and quartered, or hung by their big toes. 24V panels infer that they can properly charge a 24V battery bank with out the need of an MPPT type charge controller, they can Not.

    Hi thanks for reply,
    we are in spain and off grid,we need 4-5kw a day, I have been told on here I can not use the samil 3000TL, I wanted to wire the batteries for 48v they are 12 x deep cycle 230Ah 12v batteries. And the panels 12 x Maximum Power 245w
    Short Circuit Current 8.83A
    Open Circuit Voltage 37.4V
    MPP Current 8.22 A
    MPP Voltage 29.8V


    If you can help be grateful

    Paul
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  • slim1962
    slim1962 Registered Users Posts: 5 ✭
    #9
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    Re: Help with MPPT ans array

    Hi thanks for reply,
    we are in spain and off grid,we need 4-5kw a day, I have been told on here I can not use the samil 3000TL, I wanted to wire the batteries for 48v they are 12 x deep cycle 230Ah 12v batteries. And the panels 12 x Maximum Power 245w
    Short Circuit Current 8.83A
    Open Circuit Voltage 37.4V
    MPP Current 8.22 A
    MPP Voltage 29.8V


    If you can help be grateful

    Paul
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #10
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    Re: Help with MPPT ans array

    Four to five kW hours a day is large, but not impossible.
    Those batteries will require you to have four parallel strings of four in series to get 920 Amp hours @ 48 Volts. This is enough for up to about 22 kW hours per day! You could cut that battery bank in half to begin with: Two parallel strings of four would be 560 Amp hours @ 48 Volts. At only 25% DOD you'd still have about 6kW hours of power available.

    As Photowhit said, those panels can only be used with an MPPT type charge controller. On a system this size you'd want one anyway.
    If you go with the eight battery bank outlined above you'll want about 3500 Watts of panel, or 14 of those panels. You might do it on 12, but it won't be as good when conditions get less than ideal. (You would not be able to properly charge the 960 Amp hour bank from 12 of those panels, btw.)

    So let's see: twelve 245 Watts panels configured as four strings of three on a MidNite Classic 150. 2940 Watts, capable of about 47 Amps @ 48 Volts or 8% charge rate. Array Vmp would be 89.4 and Imp would be 32.88. So far so good.

    You are going to need to pick an off-grid inverter. You need to know your peak maximum load because the inverter has to handle this. You were looking at a 3kW unit based on what?
    Spain power is 230 Volt 50 Hz I think. We have a couple of forum members from Spain who will be best at advising you according to what you can get there.
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #11
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    Re: Help with MPPT ans array

    Another expat in Spain, welcome to the club :)

    12 x 245W panels, so 2940W- you'll do very well for a 5kWh daily demand. I have 2880W and didn't have to use the generator at all this year, and we have a 6-7kWh daily demand.
    For a 4kWh/day consumption and 3 days of backup power, that's 4000 * 3 days / 48V = 250Ah, and since you should try and keep them above 50% discharge, that's 500Ah @ 48V. Around here for this size of instalation the rolls royce of batteries are OPzS stationary batts, but they're very pricey. Next best is forklift batts at about 60% of the price of OPzS and then the flat plate batts like Trojans. With both the OPzS and forklift batts you can buy them in 2V cells of exactly the capacity you need so you don't need to put any in parallel, you can have a single 24 cell battery of 48V and 500Ah. This avoids a lot of charging problems with parallel batts.

    For a 48V battery you can wire those panels in 4 parallel strings of 3 in series, so each string will have a voltage of around 90V. You could fit the array into a single 60A MPPT charge controller. For a simple, no frills, low cost unit, the Morningstar tristar MPPT 60 is your best bet. Else for something more cutting edge with more features than you can shake a stick at, the midnite solar classic is a good choice and it'll support 90A so there's room for future expansion.

    As for the inverter there's a wide range to choose from, depending on what your peak power draw is. The Victron Multiplus range is pretty good and reliable, and if you're looking for a >5kW inverter then the SMA Sunny Island is a good choice. In fact I'm installing one for a mate tomorrow :)

    Then the ancilliary bits, string combiner, DC breakers, mounting system etc.
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