# help. 16 24v panels, outback mppt... math...

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Registered Users Posts: 9
ok so here is my problem, i am using an outback mppt 80 and trying to hook up 16 24 volt 150 watt panels. so far i have linked 8 panels 2 by 2 by 2 by 2 for open volts reading at 75.5. when i hook these 8 panels to the charge controller the read out says 60 volts coming in and its saying its receiving around 600 watts.

now here is where i am stumps, one i am really new to a system this big, my friend died and i got left this awesome system... so my math says i should be getting 1200 watts from 8 24v 150 watt panels. and the charge controller os telling me other wise and i missing something? i know with out a fact the wiring is sound and every thing is hooked up right.

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Re: help. 16 24v panels, outback mppt... math...

The Vmp-array sounds like it might be a little low... Vmp-array should be > 70 volts (STC) to ensure that Vmp-array>62 volts on hot days.

I am guessing you need to put 3 panels in series to get Vmp>~70 volts.

What are the Voc/Vmp/Imp ratings of these panels?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 9
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Re: help. 16 24v panels, outback mppt... math...

Maximum power (Pmax)2 150W
Voltage at Pmax (Vmp) 34.5V
Current at Pmax (Imp) 4.35A
Warranted minimum Pmax 140W
Short-circuit current (Isc) 4.75A
Open-circuit voltage (Voc) 43.5V
Temperature coefficient of Isc (0.065±0.015)%/°C
Temperature coefficient of voltage -(160±20)mV/°C
Temperature coefficient of power -(0.5±0.05)%/°C
NOCT3 47±2°C
Maximum series fuse rating 15A
Maximum system voltage 600V (U.S. NEC rating)
1000V (TÜV Rheinland rating)

right now, i have 4 2 panels series, paralleled together
• Banned Posts: 17,615 ✭✭✭
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Re: help. 16 24v panels, outback mppt... math...

Your configuration would seem to be correct: four parallel strings of two in series. Each string should have a 7.5 Amp fuse on it, btw.

The total array Wattage is 1200. You will not see this except on a few occasions. More likely you will see an average output of 900 Watts or so. You will not see this unless the sun is right, the panels aren't too hot, and the batteries need the power. Unlike with GT systems that always have some place for the panel power to go, off grid systems will not register Watts that can't go anywhere. If the battery and loads do not need the full panel capacity, it just doesn't show up on the meter (because it isn't being produced). Getting the angle to the sun right is important too.

Fire up the inverter. Turn on everything you've got at midday. See what the Outback's meter reads then.
• Registered Users Posts: 9
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Re: help. 16 24v panels, outback mppt... math...

thanks for the input every one, i got the other 8 hooked back in today, and i will test every thing out tomorrow and see what i get in full sun
• Solar Expert Posts: 5,183 ✭✭✭✭
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Re: help. 16 24v panels, outback mppt... math...

Kat, looking at your other post it is clear why you are not getting 'full ' production....you need to get some air movement under those panels in order to cool them, the hotter they are the less production you will get.
It looks like you are in the dessert...

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
• Solar Expert Posts: 6,003 ✭✭✭✭✭
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Re: help. 16 24v panels, outback mppt... math...
Each string should have a 7.5 Amp fuse on it, btw..

??? Anything up to 15 amps shopuld be fine by my reading...
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.
• Banned Posts: 17,615 ✭✭✭
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Re: help. 16 24v panels, outback mppt... math...
Photowhit wrote: »
??? Anything up to 15 amps shopuld be fine by my reading...

Nit-picking: Isc 4.75 * 1.25 (as per NEC spec) = 5.9375 round up to nearest size: 7.5 Amp.
Can't find that? Use a 10.
• Registered Users Posts: 9
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Re: help. 16 24v panels, outback mppt... math...
westbranch wrote: »
Kat, looking at your other post it is clear why you are not getting 'full ' production....you need to get some air movement under those panels in order to cool them, the hotter they are the less production you will get.
It looks like you are in the dessert...

we are in the desert here, but the highs are mid 70's and lows are upper 30's. even in the dead of summer we where pulling better then what we are right now. when i was given this system is was a mess and now i am trying to rewire and make it better. as soon as we can afford i and going to tilt the panels and give them more air and angle
• Registered Users Posts: 9
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Re: help. 16 24v panels, outback mppt... math...
Nit-picking: Isc 4.75 * 1.25 (as per NEC spec) = 5.9375 round up to nearest size: 7.5 Amp.
Can't find that? Use a 10.

why the fuse? and where should i put them?
inline between each panel?
• Solar Expert Posts: 334 ✭✭
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Re: help. 16 24v panels, outback mppt... math...

If the tilt is off that would make a pretty big difference in output this time of year, and much less so in the summer months. Any idea what the tilt angle is on them currently? We just leave ours set for the winter tilt angle (latitude plus 15 degrees), since during the summer months we really don't need any more power, but we can always use a bit more during the shorter darker days of winter.
• Solar Expert Posts: 5,183 ✭✭✭✭
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Re: help. 16 24v panels, outback mppt... math...
katbastard wrote: »
why the fuse? and where should i put them?
inline between each panel?

Yes they are needed to protect each panel in parallel...so 2 panels in parallel need 2 fuses, one for each line, generally at the combiner where the PV wires are combined.

On my small system I used car audio fuse blocks with "stab in" type fuses. your install needs a more robust fusing solution IMO. Like this http://www.midnitesolar.com/pdfs/MidNite%20PV%20Combiners%20explained%20w%20diagrams.pdf

cheers

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
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Re: help. 16 24v panels, outback mppt... math...

In theory (and per code), you only need 1 series fuse/breaker per paralleled string when you have 3 or more parallel connections (2 parallel strings pump current into 1 shorted string--causing the shorted string to exceed Isc/Series Fuse rating).

Two parallel strings (or one string) do not need a series fuse.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 5,183 ✭✭✭✭
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Re: help. 16 24v panels, outback mppt... math...

Bill, what are your thoughts about the implications to fusing as this system is at 150V DC? (from sig line)

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
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Re: help. 16 24v panels, outback mppt... math...

WB,

I am not following... You have two systems in your signature.

Are you asking about the array side or the dc battery/inverter wiring?

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 22
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Re: help. 16 24v panels, outback mppt... math...

BB- I think WB is refering to OP's sig.

WB- 150 vdc refers to cc's rated capacity.
• Solar Expert Posts: 5,183 ✭✭✭✭
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Re: help. 16 24v panels, outback mppt... math...

rbtrrer, OK got it, I re-read post #1 and saw the 150V as you said , in the description of his system.

I see he states PV input at 75.5 V and doubled that mistakenly.. parallel not series.

I believe his Vmp should be 69.0 V ( 2 x 34.5v) the 75.5v he indicates, is probably what he has observed.

Sorry for the confusion Bill, just asking about fusing on high-er voltage systems (anything above 24 V)

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep