Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

Sharp230
Sharp230 Registered Users Posts: 22
Hi Everyone,

I have installed (4) Sharp 230 watt panels (Vpmax 29.3V and Ipmax 7.85A) in the back of my house and bought all of the necessary equipment such as the Morningstar TriStar MPPT 60A Controller, Prowatt SW 2000 Inverter, Trimetric battery monitor and (4)UBGC2 AMG 6v (200Ah@20hrs) Golf Cart batteries, but electrician I hired to put everything together couldn't figure out certain Fuse Amp calculations and wire size from the batteries to inverter, and Controller to batteries. Was also unsure of wire sizes to use on batteries and equipment. I still had to pay, and job is not complete!

(4) sharp panels (230 watts each =920 watts) in parallel to disconnect box on back of house (15ft). Wire size is (#10 AWG )
Through house wall to Charge Controller 6ft, wire size (#6 AWG)
From Controller to batteries 6ft, wire size (#4 AWG)

How do I put it all together?
Wire sizes where needed, Fuse & Breaker size in Amps etc!...........Also, would it be safe to keep the AMG batteries inside?

Thanks for any and all help in advance!!!!!
Sharp230

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

    Welcome to the forum Sharp!

    Yea, it is not unusual for electricians to be thrown for a loop when dealing with low voltage DC... They just do not seem to realize that Power=Voltage*Current... So, when they deal with 120 VAC circuits carrying 10 amps (1,200 watts), that is "nominally" 100 amps at 12 volts (also 1,200 watts). That is, roughly 11x heavier wire (i.e., a 14 awg 120 VAC wire should be ~3 awg at 12 VDC).

    Anyway, back to your questions. Starting with the array... How did you wire it up? (4 panels in series, 2x2 panels in series/parallel, or 4 panels in parallel)? All are "valid" configurations, but require different size wiring and possible fuse/breaker/combiner box.

    Next, the wiring from the Morningstar TS MPPT 60a controller... The manual should tell you what you need, but, from the math it would look something like (assuming a 12 volt battery bank):
    • 4x230 watt panels * 1/14.5 volts = ~63 amps best case available

    So, you are looking at designing a 60 amp controller to battery bank circuit (MPPT controllers will limit their output current to rated value, 60 amps in your case). Very simply, NEC uses a 1.25 "safety factor" for fuses/breaker/wiring:
    • 60 amps * 1.25 NEC = 75 amp branch wiring

    So, rounding up to 80 amps, the minimum wire size would be from this NEC Table (note the are other factors, cable in conduit? Ambient temperatures, and such. But, in general, the NEC table is very conservative so a good place to start with--And your electrician should be comfortable with using it):
    • ~6-4 AWG minimum copper wire awg (depending on insulation, etc.)

    Which is all fine, but battery banks are very sensitive to input charging voltage. And AGM batteries tend to be even more sensitive... So, my rule of thumb is ~14.2 volt for AGM charging (again, check the manual) and a maximum of 0.10 to 0.05 volt drop. So, we need to also know the length of the wiring. Assume for the moment 60amps, 4 awg and 0.05/0.10 volt maximum drop. Using this generic voltage drop calculator:
    • 1.0' one way run, 60 amps, 4 awg wiring -> 0.04 volt drop
    • 2.5' one way run, 60 amps, 4 awg wiring -> 0.09 volt drop

    So, you can see that a lot of current on a "relatively" small diameter copper wire has significant voltage drop. And, in general, you want to install the charge controller close to the battery bank.

    Now, in your case, you have one of the few charge controller that has Remote Voltage Sense Leads... you use a pair of small AWG wires from the controller sense terminals directly to the battery +/- bus or battery terminals. This allows you to use smaller AWG main wiring since voltage drop is not near as much of a problem (you will still need to check the manual for limits on wire length).

    But, if you assume a 1-3% maximum voltage drop:
    • 14.2 volts * 0.03 = 0.426 volt drop @ 3%
    • 14.2 volts * 0.01 = 0.142 volt drop @ 1%
    • Voltage drop 60 amps, 4 awg -> 10' @ 0.4 volt drop
    • Voltage drop 60 amps, 4 awg -> 4' @ 0.14 volt drop

    Now, the inverter calculations are similar... Assuming this is a 2,000 watt 12 volt inverter:
    • 2,000 watts * 1/0.85 inverter efficiency * 1/10.5 volts = 224 Amp continuous
    • 2,000 watts * 1/0.85 inverter efficiency * 1/10.5 volts * 1.25 NEC factor = 280 Amp continuous

    So, you are looking at fuses/breakers/wiring that will carry ~300 amps:

    CFB-300T 300 amp fuse with holder, Cut Cable Connection
    250 Amp Panel Mount DC Circuit Breaker, 125 VDC (note, this is a bit smaller than the 280 amp required--but probably would work for your system)

    Also note for your electrician, DC ratings usually require larger (physical size) of contacts and fusing elements vs a similar AC breaker/fuse. DC arcs are much easier to start and sustain--So don't just throw an AC fuse/breaker in a DC application.

    The cable size would be around 4/O or heavier (this is heavy cable). Also, you need to worry about voltage drop. If this is a 12 volt bank, then the rough minimum battery voltage will be ~11.5 volts, and the inverter cutoff will be ~10.5 volts. That gives you 1.0 volt of "head room"--and you should be looking at ~0.5 volt drop maximum is you expect the inverter to operate at 2,000 watts or 3,000 watt surge. Using the voltage drop calculator with 4/O wiring, we get:
    • 224 Amp 0.5 volt drop -> 4/O wiring, 2 feet -> 0.5 volt drop

    When connecting the batteries together, I would plan on wiring with around 4/O wiring too (basically, each battery string should be able to carry near full rated current).

    Anyway, before I go any deeper--That is the basics of what I see.

    Note, I usually recommend around a 1,200 watt maximum inverter (~168 amp NEC branch circuit/fuse) rating because sending a lot of current around 12 volt circuits require A LOT OF COPPER and $$$ to do that.

    If your power needs are much more modest than the inverter indicates... You can use smaller awg wiring. And/or you can even use a smaller inverter... For your system, a 300 watt to 1,200 watt inverter would be a better fit.

    In some cases, people will use two inverters. One small one to run the laptop, a few LED/CFL lights, and a TV/Radio (MorningStar 300 TSW 12 volt inverter / 600 watts for 10 minutes is a wonderful unit) for the 24x7 loads, and a second/larger inverter for the occasional tools/microwave use (heating with a battery system is usually not really a good fit--Battery and PV systems just don't output a lot of power to boil water, etc.).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Sharp230
    Sharp230 Registered Users Posts: 22
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

    Thank you so very, very much Bill. It is so amazing how you guys can just spit these answers out so fast! You guys are so, so GOOD!
    Thanks again for all of your help!!!!!!
  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

    Heres my pic of my setup. it has a Morningstar TS-45 (PWM) Controller.. so your breakers in/out of it will be 75/80 amp and not the the 60 I used for mine..

    Update2.jpg

    Solar panels combiner box (with 10 amp breakers for each panel) to charge controller is 6 AWG and a 60 amp breaker..

    From charge controller down to the battery bank (with another 60 amp breaker) is 6 AWG

    From the battery bank back up toward the inverter is 3/0 wire.. and a 250 AMP ANL fuse in a holder.. (HD sells 3/0 compression lugs for $4.59/2 they go from 3/0 wire to 4 AWG wire gauge)

    I have a Bluesea battery switch on the 3/0 positive lead to the inverter so I can hook everything up and not get a shock (also good for maintanence of system and battery)..

    The inverter was supposed to be a Xantrex ProWatt SW2000 (same as yours)..

    Heres a video I did on the setup as shown above..

    [video=youtube_share;ET_6vCwCUsc]http://youtu.be/ET_6vCwCUsc[/video]
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!
    Sharp230 wrote: »
    Thank you so very, very much Bill. It is so amazing how you guys can just spit these answers out so fast! You guys are so, so GOOD!
    Thanks again for all of your help!!!!!!
    You are very welcome... After 13,000+ shots at "giving answers"--Hopefully I have gotten a bit better at it :p.

    Anyway, this is all a starting point. Feel free to ask questions and discuss the suggested solutions. I know I ain't perfect (as my wife and kids keep telling me).

    Also, need to know the solar/PV array configuration and confirm you are looking at a 12 volt battery bank.

    And, I like to know your loads (watts, watt*hours per day, where the system will be installed--roughly), so we can make sure everything is well balanced. Having too big of battery bank can be as bad (or worse) than having too small of battery bank, etc...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

    I'm going to drop a Helpful Household Hint here about fuses and wire sizes.

    Most equipment (inverters, charge controllers) comes with an instruction manual. Usually you can even look them up on line. Almost always it will contain the manufacturer's recommendations for wire size and circuit protection under various installation situations (i.e. length of wire, system Voltage, expected current). You usually can't do better than that and it's less of a headache than having to do the math yourself. :D
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

    I see from the OP that the panels are four in parallel, and that the distance from combiner to Controller is 6 ft. The wire size looks OK. You do need to make sure that you have a DC rated fuse or breaker in series with each of the four panels.

    I see from the OP that the distance between Controller and batteries is 6 ft of #4 AWG. The wire could be beefed up a bit, but I won't say much more about that without knowing the battery configuration... 12 or 24 volts? If its 12 volts, you also need to know something about the battery interconnections, best spelled out at smartgauge.com.

    Everything attached to the battery (inverter and charge controller) needs appropriate DC fuses or breakers. Need to know battery voltage to specify.

    To meet code you will need a DC GFP device.

    Trimetric monitor will need a shunt.

    Do you have a generator? If so, we can talk about transfer switch.

    One solution is to buy a Midnite E-panel. Comes with all bus bars, breakers, transfer switch, GFP, shunt, lightning protectors, etc. and has EXCELLENT directions and wiring diagrams. Should be no problem for your electrician to follow.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • Sharp230
    Sharp230 Registered Users Posts: 22
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

    Bill!
    This is just a quick note to let you know how much I appreciate all of your helpful information pertaining to my solar project. You truly are the MAN!!!!
    Thanks again!!!...and God Bless You!
    Sharp230
  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

    Um.. is my 6 AWG wire too lite to bring that 45 amps (max) @ 12v to the battery from the controller?? its about 5' in length (though it will be shortened to about 4 by the time I'm done)??

    I got 2 sets of rating numbers

    6AWG
    Chassis Wiring Amps: 101 amps
    Power Transmission: 37 amps

    I plan on going 24V and I will be only at 24 AMPS from the panels with that..

    For 4 AWG it shows
    Chassis Wiring Amps: 135 amps
    Power Transmission: 60 amps

    I'd hate to have to go buy more wire again..
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!
    ywhic wrote: »
    Um.. is my 6 AWG wire too lite to bring that 45 amps (max) @ 12v to the battery from the controller?? its about 5' in length (though it will be shortened to about 4 by the time I'm done)??

    OK--here we go:
    I got 2 sets of rating numbers

    6AWG
    Chassis Wiring Amps: 101 amps
    Power Transmission: 37 amps

    For our needs, we have two concerns. One is how much heat (power=I2R) the wire will generate, how much can be dissapated, and will the insulation withstand the ambient+thermal rise.

    Using the NEC code book, using their numbers will give you very concervative and relatively "safe" recommendations/requirements. May be on the "expensive" side (lots of copper).

    If you are running exposed wire, it cools much better--but is easier to damage and if it overheats/melts, can start a fire easier, etc...

    Wire Current
    Ampacities NEC Table 310-16


    For example, just using the above table (and I believe 3 wires in conduit), 6 awg wire has a "safe" rating of 55-75 amps in "typical" installations.

    Since NEC requires a 1.25x derating (you can only run at 80% of rated wiring/fusing for continuous current):
    • 45 amps * 1.25 = 56.25 amp minimum branch circuit rating

    So, technically, depending on insulation/conditions, 6 awg is right on the edge (no, your cabin is not going to burn down)--but that is the black and white of "code".
    I plan on going 24V and I will be only at 24 AMPS from the panels with that..

    For 4 AWG it shows
    Chassis Wiring Amps: 135 amps
    Power Transmission: 60 amps

    I'd hate to have to go buy more wire again..

    The other thing we care about is voltage drop... When working with low voltages (i.e., 12 volt), the voltage drop to the battery is critical (running at 120 VAC, the voltage drop is 1/10th "the problem" or even less).

    So, for a 12 volt battery, charging at ~14.2 to 14.5 volts (typical) and I would suggest your wiring drop from controller to battery bank is a maximum of 0.05 to 0.10 volt drop (at rated current and length).

    Using the generic voltage drop calculator with 45 amps and 0.05 and 0.10 volt drop with 4 awg copper wiring, the maximum "recommend by -Bill" length would be:
    • 45 amps, 0.05 volt drop, 4 awg wire -> 2 feet
    • 45 amps, 0.11 volt drop, 4 awg wire -> 4 feet

    Now, you have a MorningStar TS family (PWM and MPPT) which is one of the few controllers (Rogue is another that I know of--remember, I am not in the solar biz--so there may be others too) that support a remote voltage sense connection (current carrying voltage drop is bypassed with separate "meter" wiring)...

    So, in this case, I would use our 1% to 3% maximum voltage drop instead. For example, here is the 3% loss calculation:
    • 14.5 volts * 0.03 = 0.435 volt drop
    • Voltage drop calc: 45 amps, 4 awg copper wire, 0.435 volt drop -> 16 feet (one way run) gives 0.43 volt drop

    And the 1% drop would be 1/3rd that length (just over 5 feet).


    So--that is how I look at the problem, with remote sense, you can run longer wiring with higher losses--make your choices. And as Marc/Cariboocoot reminds, you can read through the installation manual and see what the mfg says.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

    I'll be at 4-5 feet with 6 AWG (tinned) Copper.. which the calc I used says .183 Voltage Drop (1.53%) on 12 v system & 45 amps..

    If I change to 4-5 feet of 6 AWG (tinned) Copper.. with 24v system.. it says.. .097 Voltage Drop (0.4%) on the 24v system with 24 amps..

    So for 12v I am on the EDGE for amps at 45 amps, with 24v and ony 24 amps (8 VMP *3 panels) I'd be much better..

    I did actually plan on getting the voltage sense wire put on the bank and the battery temp sensor as well..

    Overall the 24v system pays off again for me..

    I'd hate to have to throw out or try to sell the 6 AWG wire and buy 4 AWG..

    Thanks BB.. got nervous for a minute..

    I was so focused on the V drop and not the amps so much when I was planning this thing out..

    I'll have to find a different calc the one at powerstream is ok.. but the chart up top is confusing..
  • Sharp230
    Sharp230 Registered Users Posts: 22
    Re: Newbie! Where do I go from here? 920 Watts Solar Panels, Need help Please!!!

    Just don't won't to leave anyone out, however, I want to thank all of you guys for all of your support and helpful information which I am certainly able to use!!
    Thanks again and God Bless You!!
    Sharp230