Outback 80

Chris11 · December 2014

I'd like your help please.....

I bought 10 panels from Costco, 12 volts @ 100 watts each. They have a Voc of 21.9 volt each. My plans were to connect them in 5 strings of 24 volts each string. Tonight I was going to order an Outback Flex 80 and read that it can "only" handle 150 volts. Since I'd have 21.9 Voc from each panel that tells me that the Outback won't be able to handle 10 panels. Is this correct? Seems wrong to me for such an expensive controller but I'm fairly new at this so don't know if it's my interpretation or something else.

Thanks for all replies.

BB. · December 2014

Re: Outback 80

I think you have it confused...

Yes, two panels in series adds voltage (Vmp-array = 2* Vmp-panel = 2 * 18 volts = ~36 Volts Vmp for the array).

And when you put the strings in parallel, the current will add.

Guessing:

100 Watts / 18 volts Vmp = ~5.5 amps per panel
5 parallel strings * 5.56 amps = 27.8 amps total for the array @ ~36 volts Vmp

Now--The FM-80 can take around 140-150 Volts input from the array. For most places that works out to a Vmp-array of ~100 VDC maximum (due to temperatures and Voc maximum).

100 volts / 18 volts = 5.55 panels = ~5 panels in series maximum

So, you could also do an array with 5 panels in series and 2 parallel strings. (Vmp-array~90 volts; Imp-array~11.12 amps).

Now, what battery bank voltage are you looking at? For an FM-80, roughly the maximum array wattage recommended would be:

80 amps * 14.5 volts charging * 1/0.77 panel+array derating = 1,506 Watt array "cost effective" maximum @ 12 volt bank
80 amps * 29.0 volts charging * 1/0.77 panel+array derating = 3,013 Watt array "cost effective" maximum @ 24 volt bank
80 amps * 58.0 volts charging * 1/0.77 panel+array derating = 6,026 Watt array "cost effective" maximum @ 48 volt bank

And there are some other recommendations, minimum array voltages for 12/24/48 volt battery bank, optimum Vmp-array for a 12/24/48 volt battery bank and such.

Anyway, can you tell us a bit more about your needs (battery bank voltage/AH rating, where the system will be installed--roughly, your expectations for full time of grid/emergency power/etc.).

-Bill

Chris11 · December 2014

Re: Outback 80

Thanks.

I see my mistake was using Voc instead of Vmp for maximum total voltage. So my 10 panels will be OK with the FM-80. I also never thought of running 5 panels in series with two strings. That sounds better.

At the moment I have 2 Costco GC2 batteries. (Guess who loves Costco.) The amp hours on the GC2 battery with 107 Reserve Capacity minutes would be 208 amp hours at a 20 hour rating. They were mfg. in July of 2014. I plan on buying two more and initially connecting them in series for a total of 24 volts.

I know people on here suggest working backwards from needed power but at the moment that's not possible since I'm building a western town which will be expanding each year, final quantity of buildings depending on how long I live.

Again, thanks for taking the time to educate me.

Cariboocoot · December 2014

Re: Outback 80

Voc is what you use for maximum input Voltage. But Voltage only adds when panels are placed in series.

A series string of two panels with a Voc of 21.9 is a Voc of 43.8 for the string. It does not matter how many such strings are placed in parallel; Voc remains the same.

Current adds for parallel connections. In this case 5 time probably 5.7 Amps. This would make the total array current 28.5 Amps.

Your proposed battery bank of four 6 Volt 208 Amp hour batteries giving 208 Amp hours @ 24 Volts could be charged from this array.

Working from power requirements isn't backwards, it's forwards. Working from equipment you've already got and trying to make it meet the power demands - that can be difficult.

Outback 80

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