What is the best combine with different watt panel

Majlis
Majlis Registered Users Posts: 8
I m beginner and in the middle of setting up a solar project for my home. I m looking for best setup in series or parallel combine for the solar panel in different watt. The panel consist of

4pcs 136watt, 33v, 4.1A
2pcs 144watt, 33v, 4.4A

I m using 45A mppt charge controller and intend run on 24v system. The wire that I need to run from the panel to the charge controller is about 20m.

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What is the best combine with different watt panel

    Do you have a link to the brand/model of MPPT charge controller you are planning on using?

    Basically, Vmp~33 volts is a bit on the low side for charging a 24 volt battery bank. Vmp falls as the panels get hot--I assume you are in Malaysia and don't have a lot of cold weather?

    So, you are really looking at two panels in series for Vmp~66 volts. Which would be great... Place the two 4.1 amps panels in series, and place the two 4.4 amp panel in series, then connect the two string in parallel for Vmp~66 volts and 8.5 amps total for the Array.

    In the US, the common 45 amp MPPT charge controller is a MorningStar TS 45 amp MPPT charge controller--Which would be perfect for the application.

    If you don't have a MorningStar MPPT controller--Then you may have issues with the MPPT controller you are using--Too low of input voltage from array and/or some inexpensive charge controllers that claim to be MPPT are not really.

    A 20 meter (~66 feet) is a fairly long wire run... Using a generic voltage drop calculator for 66' one way run, 8.5 amps, 3% or 1.98 volt maximum drop--You should be using: 12 AWG @ 66 feet = 1.21 volt drop or ~3.0 mm2 wire size...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Majlis
    Majlis Registered Users Posts: 8
    Re: What is the best combine with different watt panel
    BB. wrote: »
    Do you have a link to the brand/model of MPPT charge controller you are planning on using?

    Basically, Vmp~33 volts is a bit on the low side for charging a 24 volt battery bank. Vmp falls as the panels get hot--I assume you are in Malaysia and don't have a lot of cold weather?

    So, you are really looking at two panels in series for Vmp~66 volts. Which would be great... Place the two 4.1 amps panels in series, and place the two 4.4 amp panel in series, then connect the two string in parallel for Vmp~66 volts and 8.5 amps total for the Array.

    In the US, the common 45 amp MPPT charge controller is a MorningStar TS 45 amp MPPT charge controller--Which would be perfect for the application.

    If you don't have a MorningStar MPPT controller--Then you may have issues with the MPPT controller you are using--Too low of input voltage from array and/or some inexpensive charge controllers that claim to be MPPT are not really.

    A 20 meter (~66 feet) is a fairly long wire run... Using a generic voltage drop calculator for 66' one way run, 8.5 amps, 3% or 1.98 volt maximum drop--You should be using: 12 AWG @ 66 feet = 1.21 volt drop or ~3.0 mm2 wire size...

    -Bill

    Thanks for your reply. After I read back the panel spec, here is the following spec:

    For the 136w nominal operating cell temperature (NOCT) is 105w, 30.8v, 3.4A
    For the 144W nominal operating cell temperature (NOCT) is 111w, 30.8v, 3.6A

    It is a thin film panel which I guess not much effect on the hot weather. (unisolar panel) I m using Morningstar MPPT 45A charge controller. All the items already brought and waiting to be instal.

    If in this case, should I go for 12V system or still good in 24V system?

    So 3 string in (2 in 136W series) and (1 in 144W series) setup is the best? Total combine would give me a 61.6v, 10.4A in NOCT. Is this correct?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What is the best combine with different watt panel

    Sorry, missed you had 4 panels of one type and 2 of the other...

    Normally, I would suggest that you match Vmp to within 10% (or better) for parallel connections and Imp to within 10% for series connections.

    In your case, the panels are close enough to be virtually identical. (Vmp is identical, Imp is less than 10% apart).

    You could put the them in 2 series x 3 parallel:
    • 4pcs 136watt, 33v, 4.1A
    • 2pcs 144watt, 33v, 4.4A
    • Vmp~33 volts and Imp-array~12.6 amps; 1.98 volt max drop -> 66'/20m, 10 awg/~5 mm2 wire, 2 volt drop

    You also have the option of placing the panels in 3 series x 2 parallel (4.1 amp + 4.1 amp + 4.4 amp in series; then in parallel with second string). That would give you a Vmp-array~99 volts and ~8.2 amps:
    • 3%/2.97 voltage drop; 66'/20m -> 12 awg/~3.0 mm2 wire with 2.1 volt drop

    I assume you have "warm winters" -- So Vmp~99 volts should be OK... But really need to know your low temps so we can calculate the Voc-cold of the array and make sure it does not exceed the Vpanel maximum input voltage for the controller (around 140-150 VDC).

    The choice between 12 volts vs 24 volt battery bank--The typical maximum (cost effective) solar array for a 45 amp output 12/24/48 volt controller would be:
    • 45 amps * 14.5 volts charging * 0.77 panel+controller derating = 653 watt "cost effective" maximum array @ 12 volt bank
    • 45 amps * 29 volts charging * 0.77 panel+controller derating = 1,305 watt max array @ 24 volt bank
    • 45 amps * 58 volts charging * 0.77 panel+controller derating = 2,610 watt max array @ 48 volt bank

    So, you array is ~832 watts... Your controller will current limit to 45 amps (probably) for a while during the middle of the day. It will not hurt anything (MPPT controllers are designed to current limit)--But you will not be able to reliably obtain 100% of the power during parts of the day.

    If you choose a higher voltage battery bank, you can process more energy from the array with the same controller.

    One question we like to ask is "what is your peak continuous wattage" you expect your loads to draw... Generally, around 1,200 watts maximum for a 12 volt bank, 2,400 watts maximum for a 24 volt bank, and anything larger--pick 48 volts.

    For example, a 1,500 watt Inverter would need wiring to be rated on a 12 volt battery bank:
    • 1,500 watts * 1/10.5 volts cutoff * 1/0.85 inverter losses * 1.25 fuse/wiring derating = ~210 amp fuse/breaker/rated wiring

    Do you have any specific 12 VDC loads or will this be an inverter based system (230 VAC at 50 Hz)?

    -Bill

    PS: it is late here--so double check my math.:roll:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Majlis
    Majlis Registered Users Posts: 8
    Re: What is the best combine with different watt panel

    I guess the 2 series x 3 parallel is good to combine. (total 66v, 25.2A) But the wire size is in 8awg/10mm with 2% drop using this site http://www.solar-wind.co.uk/cable-sizing-DC-cables.html The combine should give me the lowest wire cost since I need to run 20m long. I stay in 2storey house and the panel is at the back of the roof which facing the south. While the charge controller would be at the front of the house. That is why the wire is long.

    The combination of 3 series x 2 parrallel won't be scarify the 144w panel which will cause total effeciency drop? (4.1 amp + 4.1 amp + 4.4 amp in series) Since in series voltage add up and Amp take from the lowest?

    The weather here lowest in the morning sun is 29c till max 34c in the afternoon. Is it all year hot summer here in Malaysia with 4.5hr sun for array.

    I have a flexible load that later to be decide. It is very much depend on max output Watt the battery bank can be suit for the panel output. What is battery bank size I can buy for this array output? I intend to using seal AGM battery. 2 backup cloudy day should be enough I guess. I probably combine of using direct DC load output and inverter 240VAC 50Hz output.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: What is the best combine with different watt panel
    Majlis wrote: »
    I have a flexible load that later to be decide. It is very much depend on max output Watt the battery bank can be suit for the panel output. What is battery bank size I can buy for this array output? I intend to using seal AGM battery. 2 backup cloudy day should be enough I guess. I probably combine of using direct DC load output and inverter 240VAC 50Hz output.

    I think three parallel strings of two panels is good. Don't forget that with three strings you must put fuses or circuit breakers in each of the three strings. If you only have two strings you do not need the fuses/breakers.

    Your battery bank should be 24 volts. How large a capacity? That depends on your weather (how much sun do you get?) and your loads. I will guess that your array is capable of supporting 250-350 AH of battery at 24 volt.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Majlis
    Majlis Registered Users Posts: 8
    Re: What is the best combine with different watt panel
    vtmaps wrote: »
    I think three parallel strings of two panels is good. Don't forget that with three strings you must put fuses or circuit breakers in each of the three strings. If you only have two strings you do not need the fuses/breakers.

    Your battery bank should be 24 volts. How large a capacity? That depends on your weather (how much sun do you get?) and your loads. I will guess that your array is capable of supporting 250-350 AH of battery at 24 volt.

    --vtMaps
    Thanks vtmaps. I design to put a 30A breaker at the main wire before to mppt. As a protection and switch for maintainance. What is the reason to have fuse/breaker for each string?
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: What is the best combine with different watt panel
    Majlis wrote: »
    What is the reason to have fuse/breaker for each string?

    A defective string may become a short circuit to the other parallel strings. If you have two equal strings one string cannot exceed the capacity of the defective string. If you have three (or more) strings the good strings have enough current to cause a fire in the defective string. If you use DC circuit breakers and they are polarized, pay careful attention to the polarity. The load (minus) side of the breaker goes to the Plus side of the solar panel string. This is because when a panel becomes defective it becomes the load. This is the opposite way of wiring the breaker if you were to use the breaker as way to disconnect the string.
    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: What is the best combine with different watt panel

    System sizing...

    Assume a minimum (average) of 4 hours of sun per day for 9 months of the year, an 832 Watt array would produce around:
    • 832 watts * 0.61 typical DC system derating * 4 hours of sun per day = 2,030 Watt*Hours per day for DC system
    • 2,030 WH per day / 24 volt battery bank = 85 AH per day @ 24 volt battery bank

    If you were doing the same thing with an AC inverter, the typical system derating would be ~0.52 (adding 85% efficient inverter) ....:
    • 832 watts * 0.52 typical DC system derating * 4 hours of sun per day = 1,7031 Watt*Hours per day for AC system

    Battery bank size--Typically we recommend 5% to 13% rate of charge for off grid systems. For systems that are heavily used, you might want to go towards 10% to 13% rate of charge. For a 24 volt system:
    • 832 Watts * 0.77 panel+charger derating * 1/29 volt charge * 1/0.05 rate of charge = 442 AH @ 24 volt maximum sized battery bank
    • 832 Watts * 0.77 panel+charger derating * 1/29 volt charge * 1/0.10 rate of charge = 221 AH @ 24 volt nominal sized battery bank
    • 832 Watts * 0.77 panel+charger derating * 1/29 volt charge * 1/0.13 rate of charge = 170 AH @ 24 volt minimum sized battery bank

    To size your battery bank, we like between 1-3 days of "no sun" and 50% maximum discharge... So the equation would look like--for a 2,000 Watt*Hour per day load with 2 days of "no sun" and using an AC inverter:
    • 2,000 WH * 1/24 volt battery bank * 1/0.85 inverter eff * 2 days of no sun * 1/0.50 max discharge = 392 AH @ 24 volt battery bank

    The are the basic rules of thumbs and assumptions. You should never plan on using 100% of the system's estimated daily production as there are some days that will be better and some days that will be worse.

    In general, the old assumption was to add battery capacity to an off grid system to "add capability"... Today, we (or at least I), like to recommend a "balanced" system between load/battery capacity/generation capacity. A too large battery bank tends to run undercharged (early sulfation) and are very expensive to replace every 5-10 years or so...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: What is the best combine with different watt panel

    While it is the rule here, it was written into code in 1998 (I believe) before that many arrays were wired using distribution blocks.

    Even today, I might worry about fusing if the panels were roof mounted, where there is some possibility of a fire. But with standard glass panels,mounted with a tedar backing and aluminum frames, even if you had a fire, in a ground mounted system, it has nowhere to go.

    You can still find Distribution Blocks in stock at solar retailers who have been around for a while
    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.
  • Majlis
    Majlis Registered Users Posts: 8
    Re: What is the best combine with different watt panel
    vtmaps wrote: »
    A defective string may become a short circuit to the other parallel strings. If you have two equal strings one string cannot exceed the capacity of the defective string. If you have three (or more) strings the good strings have enough current to cause a fire in the defective string. If you use DC circuit breakers and they are polarized, pay careful attention to the polarity. The load (minus) side of the breaker goes to the Plus side of the solar panel string. This is because when a panel becomes defective it becomes the load. This is the opposite way of wiring the breaker if you were to use the breaker as way to disconnect the string.
    --vtMaps
    I will follow your advise. Will use a fuse over breaker on each string. Since the wire will expose outside which not suitable for the breaker. Lower cost too.
  • Majlis
    Majlis Registered Users Posts: 8
    Re: What is the best combine with different watt panel
    BB. wrote: »
    System sizing...

    Assume a minimum (average) of 4 hours of sun per day for 9 months of the year, an 832 Watt array would produce around:
    • 832 watts * 0.61 typical DC system derating * 4 hours of sun per day = 2,030 Watt*Hours per day for DC system
    • 2,030 WH per day / 24 volt battery bank = 85 AH per day @ 24 volt battery bank

    If you were doing the same thing with an AC inverter, the typical system derating would be ~0.52 (adding 85% efficient inverter) ....:
    • 832 watts * 0.52 typical DC system derating * 4 hours of sun per day = 1,7031 Watt*Hours per day for AC system

    Battery bank size--Typically we recommend 5% to 13% rate of charge for off grid systems. For systems that are heavily used, you might want to go towards 10% to 13% rate of charge. For a 24 volt system:
    • 832 Watts * 0.77 panel+charger derating * 1/29 volt charge * 1/0.05 rate of charge = 442 AH @ 24 volt maximum sized battery bank
    • 832 Watts * 0.77 panel+charger derating * 1/29 volt charge * 1/0.10 rate of charge = 221 AH @ 24 volt nominal sized battery bank
    • 832 Watts * 0.77 panel+charger derating * 1/29 volt charge * 1/0.13 rate of charge = 170 AH @ 24 volt minimum sized battery bank

    To size your battery bank, we like between 1-3 days of "no sun" and 50% maximum discharge... So the equation would look like--for a 2,000 Watt*Hour per day load with 2 days of "no sun" and using an AC inverter:
    • 2,000 WH * 1/24 volt battery bank * 1/0.85 inverter eff * 2 days of no sun * 1/0.50 max discharge = 392 AH @ 24 volt battery bank

    The are the basic rules of thumbs and assumptions. You should never plan on using 100% of the system's estimated daily production as there are some days that will be better and some days that will be worse.

    In general, the old assumption was to add battery capacity to an off grid system to "add capability"... Today, we (or at least I), like to recommend a "balanced" system between load/battery capacity/generation capacity. A too large battery bank tends to run undercharged (early sulfation) and are very expensive to replace every 5-10 years or so...

    -Bill
    Thanks for your calculation. I guess I need sometime to digest your calculation.

    To summarise out, my system will be in
    -3 string with 2 panel in series (136+136)(136+136)(144+144)=66V,12.6A which will produce total of 832W
    -Using 20m long 8awg/10mm gauge wire from panel to mppt
    -Each fuse of 6A in each string with final 30A breaker before into the MPPT.
    -A battery bank size of 400AH@24V in 4 string with 2 in series. 100AH, 12V Seal AGM battery. Or A grid tie inverter 2000W 240V.
    -An AC inverter 2000W 240V.

    For each day of usage, I cannot use more than 200AH@24v or 4.8Kwh from the battery bank. The less the better.
  • Majlis
    Majlis Registered Users Posts: 8
    Re: What is the best combine with different watt panel
    Photowhit wrote: »
    While it is the rule here, it was written into code in 1998 (I believe) before that many arrays were wired using distribution blocks.

    Even today, I might worry about fusing if the panels were roof mounted, where there is some possibility of a fire. But with standard glass panels,mounted with a tedar backing and aluminum frames, even if you had a fire, in a ground mounted system, it has nowhere to go.

    You can still find Distribution Blocks in stock at solar retailers who have been around for a while
    We call it terminal block at here. It is widely use in electrical wiring for industrial. But nowaday, the panel already come with a MC4 connector that joint directly to the main junction box.
  • Photowhit
    Photowhit Solar Expert Posts: 6,002 ✭✭✭✭✭
    Re: What is the best combine with different watt panel
    Majlis wrote: »
    We call it terminal block at here. It is widely use in electrical wiring for industrial. But nowaday, the panel already come with a MC4 connector that joint directly to the main junction box.

    "...Main Junction box" Is this what we call a combiner box? are the panels fused there? You didn't seem to know about fusing panel strings, perhaps we're both confused?

    I'm talking about skipping the combiner box and just combining the strings with out fusing using a distribution block. In my years I've seen a hand full of photos of fires I don't believe I've seen one that wasn't a homemade panel, with plastic where glass is normally. Don't know that I've even even seen one with the cells mounted on wood (not a smart design)
    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.
  • Majlis
    Majlis Registered Users Posts: 8
    Re: What is the best combine with different watt panel
    Photowhit wrote: »
    "...Main Junction box" Is this what we call a combiner box? are the panels fused there? You didn't seem to know about fusing panel strings, perhaps we're both confused?

    I'm talking about skipping the combiner box and just combining the strings with out fusing using a distribution block. In my years I've seen a hand full of photos of fires I don't believe I've seen one that wasn't a homemade panel, with plastic where glass is normally. Don't know that I've even even seen one with the cells mounted on wood (not a smart design)

    I guess it is same meaning with different name. "main junction box" is combine all the wire together for the outdoor. Inside have this we call distribution block where the wire all terminated. You can have fuse or breaker in the box provided it is waterproof..