String Sizing Tool for MX and FM Charge Controllers

OutBack's newest innovation in balance-of-system components

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Re: String Sizing Tool for MX and FM Charge Controllers

Postby SandyP on Sun Oct 25, 2015 8:35 pm

Raj174 wrote:..... yielding over 70 amps of charging amperage. Considering the size of the battery bank (170 AHs) which needs a max charging rate of about 22 amps, you will be seriously over paneled. This size array needs the battery bank to be a little over 600 amp HRs.......


Another option, until you get a bigger battery bank or if you do not really need battery storage and want power from the panels to run your equipment during the day, is to set the maximum charging amps on the FM80 to ~22 amps.

Go to the FM80 Charger Set Up screen and you can then reduce the charging current limit to something appropriate for your battery bank.

From the manual :

From the MAIN screen, press or < > to move
the " “ to the left of the Charger function and then
press the <GO> soft key. This will open the Charger
Set-Up screen.

The default charger output Current Limit setting is 80 amps for the FM80 and 60 amps for the FM60.
This setting is adjustable from 5-80 amps
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby manfrommaryville on Tue Oct 27, 2015 5:23 am

That sounds perfect since I don't need a lot of battery power for now! Thank you all for all of the help!
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby manfrommaryville on Tue Nov 03, 2015 6:03 am

It's me again - one factor that I forgot to mention is that the PV array is about 650feet away from my utility shed. If I'm running the numbers correctly it looks like if I have the combiner box near the PV array I would need a wire bigger than 4/0 to cover that distance with a < 3% loss. Instead of 3Serial/5Parallel is there a higher voltage/lower amperage config that I should consider to save on wiring costs or should I run 5 smaller cables and actually do the combining at the shed (or some combination in between combining some near the PV panels and the final combining at the shed).

Also, let me make sure I'm using the correct numbers. When I use MidNite Solar's sizing tool I get the following:
Rated PV Array Power: 4200W
Anticipated Array Power at 88F: 4095W
Rated PV Array Current: 45.35A
Battery Charging Current @57.6V: 72.9A
VMP: 93.6V
VOC: 118.5V
VMP @ 0F: 110.1V
VOC @ 0F: 133.8V

Which Amps & Volts should I use to determine wiring needs?

Thanks Again,
Scott
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My RE system: Off-Grid
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-SolarWorld SW280 modules (x15)
http://www.solarworld-usa.com/~/media/w ... asheet.pdf
-Trojan T875 8V Flooded Batteries (x6) http://www.trojanbattery.com/pdf/datash ... Sheets.pdf
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-MC 4 Solar Cables 50' (x4)
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby Raj174 on Tue Nov 03, 2015 2:41 pm

Hi Scott,
The array voltage is 93 volts. Running the numbers through a voltage drop calculator, it looks like three in series by five strings is the best set up. Five by three strings would produce too high a voltage for your FM80 controller (VOC). Normally, you want to have a voltage drop of less than 3 percent, however, in the case of extreme runs you can have 10 to 15 percent voltage drop depending on how much you are willing to pay for the wire run. You mentioned 4/0 awg, that would cost upwards of $2500 per wire. You could run #2 awg with a voltage drop of 9 volts giving you 84.4 volts at 45 amps, the equivalent PV at the controller would be a little over 3800 watts. That's a loss of about 375 watts, however, cost of the cable is about $700 per wire. 4 AWG is 500 bucks cheaper, but would bring the PV array down to about 3500 watts.You can play with the calculator and cable costs and power production to see what kind of time is involved in recouping initial higher cable costs. It's just up to you as to how much you want to spend up front. You can do the calculations on multiple smaller cable runs, but I think that you will see greater losses there.

That's how I see it anyway,

Rick

addendum;
Take a look at aluminum URD direct burial cable. It has two 1/0 AWG and one 2 AWG in the casing at about 1.50 per foot.
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby manfrommaryville on Fri Nov 06, 2015 5:37 am

Here's another twist - For phase 2 of this project I'm planning on adding 2 Radian 8048As (which will be in addition to the 4084A I already have) for a total of 20KW. I plan on using the same make/model of solar panels. Since it looks like I'll be starting phase 2 in the spring it makes sense for me to go ahead and run the wires for the 650ft stretch between the combiner box and the utility shed. For consistency I'll probably stay with the 280W Solar World panels but if I'm shooting for 20KW total what PV sizes do you suggest and what wiring should I use for the 650ft run?

You guys are awesome. I really do appreciate all of the help! What started all of this is the electric company wanting to charge me $20K to run power to my build site including clearing a 40ft section of trees and running power lines (the ground is too rocky to bury the cable). The 4KW phase 1 is just for the farm. Phase 2 is for our future home and additional capacity for the farm.

Thanks,
Scott
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My RE system: Off-Grid
-Outback Radian 4048A
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-Outback FM80
-Outback MATE3
-SolarWorld SW280 modules (x15)
http://www.solarworld-usa.com/~/media/w ... asheet.pdf
-Trojan T875 8V Flooded Batteries (x6) http://www.trojanbattery.com/pdf/datash ... Sheets.pdf
-MidNite Solar SPD115-DC Surge Protection (x2)
-MidNite Solar Combiner Box (x2)
-UNIRAC Rails
-MC 4 Solar Cables 50' (x4)
-Generac 15Kw Ecogen Generator

Re: String Sizing Tool for MX and FM Charge Controllers

Postby Raj174 on Fri Nov 06, 2015 10:49 am

Hi Scott,
I'm sure that almost anyone on this forum would tell you that the $20,000 grid connection would be the best choice, way more cost saving and dependable. An additional 16Kw off grid install would cost over $40,000 plus maintenance time and future costs for battery replacement and equipment failure. Even though sunlight is free, grid power is still cheaper when all the costs are totaled. Unless your goal is to be self sufficient and not depend on the grid then it doesn't make economical sense to proceed with phase 2, just my honest opinion. Another reason would be that you can't resist the project because your already have a solar addiction which is expensive, but not unheard of among those of us on solar forums. LOL
Honestly, I am not trying to be presumptuous, many solar enthusiasts have found themselves making expensive mistakes and having to live with the consequences.
Do you still want to proceed?

Rick
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby manfrommaryville on Fri Nov 06, 2015 5:25 pm

I appreciate the sanity check. I probably don't pass it but I do want to proceed.
manfrommaryville
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Posts: 6
Joined: Wed Apr 29, 2015 4:19 am
My RE system: Off-Grid
-Outback Radian 4048A
-Outback Pre-wired Load Ctr GSLC175-PV-120/240 with 175A d/c
-Outback FM80
-Outback MATE3
-SolarWorld SW280 modules (x15)
http://www.solarworld-usa.com/~/media/w ... asheet.pdf
-Trojan T875 8V Flooded Batteries (x6) http://www.trojanbattery.com/pdf/datash ... Sheets.pdf
-MidNite Solar SPD115-DC Surge Protection (x2)
-MidNite Solar Combiner Box (x2)
-UNIRAC Rails
-MC 4 Solar Cables 50' (x4)
-Generac 15Kw Ecogen Generator

Re: String Sizing Tool for MX and FM Charge Controllers

Postby Vic on Fri Nov 06, 2015 7:39 pm

Hi manfrom..,

Completely agree with raj Rick. Your system is imbalanced now -- your battery bank is really too small, and does not match the rest of your system that well.

When you add more inverters, this TINY battery bank will be nothing but trouble.

Adding batteries to an existing system is often also problematic, as batteries of differing ages take and deliver current differently.

If you are seriously making the Phase II additions, you probably want to try to sell the existing battery bank, and find large Capacity batteries, probably 2 volt batteries with Capacity to match the rest of your system, and try to use ONLY a single string of batteries.

Also, you might want to consider High Voltage Charge Controllers, perhaps from Schneider, or, perhaps Midnite Solar, and run the PV String Voltage considerably higher than the envisioned strings of three SW PVs that you contemplate.

You envision a fairly large off-grid system. Designing a balanced system will make it easier to manage and maintain. It is an engineering project, and the numerous details DO matter.

Please proceed with reasonable caution.

Also, as Rick mentioned, Grid Power is far less expensive that is battery backed off-grid power. And, as system components, like batteries age, they will take more and more of your time to monitor and maintain them.

Furthermore, CONSERVATION is by far the least expensive watts that you can "produce".

FWIW, Good Luck, Vic
Last edited by Vic on Mon Nov 09, 2015 5:11 pm, edited 1 time in total.
4/20/08: 18 Shell SQ 175-106 Vmpp, Stacked 5548 SW+, 1350 AH Surrette 4KS25's, MX-60, Kubota SQ-3250 25 KVA Polyphase Diesel genset. Thanks OutBack for this Forum + the great Support and Service.
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby Raj174 on Sun Nov 08, 2015 7:08 pm

Hi Scott,
I think the next thing to consider is system loses. Power losses in most lead acid off-grid solar power systems are 45% to 50% and that's accounting for a 3% loss in wiring.
Even with MCM 500 aluminum cable, an additional 10% will be added to the losses in your proposed system due to the 650 foot cable run. So a 20,000 watt system will produce 8,000 to 10,000 watts average at the inverter output. If anyone thinks this has been over estimated please don't hesitate to add a correction.
Have you considered this?
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby Vic on Mon Nov 09, 2015 5:34 pm

Hi again Scott,

Couple more comments ...

Sometimes, if one needs to place the PV arrays relatively far from the point of greatest power consumption, one can choose to place the Charge Controllers (CCs), batteries and inverters near the PVs, and run the AC cables to the point of consumption. This can allow the use of AC transformers to step-up the voltage at from the inverters, and step it back down at the areas of consumption. Higher voltage means much smaller cable, and still have low cable losses, at some cost in losses in transformation.

As referred to in my earlier post, another approach is to use high PV string voltage for transmission from the PVs to CCs/batteries/inverters, located near the point of greatest AC power consumption. This requires specialized CCs that can efficiently deal with high PV String voltages. One can choose to run string voltages similar to those used in typical GT inverters -- on the order of 350 - 400 or VDC.

Am not aware of any Outback CCs that will handle string voltages this high. Believe that it will not be impolite to give several Links to some of these HV CCs.

Here is the Schneider Electric MPPT 80 - 600:
http://www.solar-electric.com/inverters ... 0amp6.html

This is a fairly new model from Morningstar:
http://www.solar-electric.com/inverters ... oller.html

Morningstar also makes one with a built-in Disconnect, if needed.

MidNite Solar's CCs can handle 180 - 200-ish volt string voltage, if the Classic 250 is chosen -- this may not be high enough string voltage to save enough in cable cost.

The Schneider and Morningstar HV CCs are expensive, and your cable costs might not be high enough to justify using HV CCs, as you would need more than one, with your envisioned large off-grid system.

Just a few more things to think about.

CONSERAVATION is your friend. Every watt of power that you do not have to produce will save greatly in system cost.

GRID power will generally be much less expensive than off grid power if you have a way to do that.

FWIW, Vic
4/20/08: 18 Shell SQ 175-106 Vmpp, Stacked 5548 SW+, 1350 AH Surrette 4KS25's, MX-60, Kubota SQ-3250 25 KVA Polyphase Diesel genset. Thanks OutBack for this Forum + the great Support and Service.
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby koalamotorsport on Sun Dec 27, 2015 9:40 pm

I see that OB has gone from hosting the string sizing applet to making it a download. Has anyone successfully downloaded and run it? It will not run for me.
Thanks!
Brett

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Wired to allow expansion up to 400amps
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby michaelkiera on Sun Apr 30, 2017 7:08 am

:grin: :grin: I see you have Astronergy listed as "Chint Solar" in string size tool . . . Drop down box is very small to read, I am half blind!! Way to fix that? Enlarge app/text?

(ps edit: What an idiot! See "Custom Tab" on tool but cannot decipher input parms! Could you plz list input parameters from left to right??. Am looking at:

Astronergy CHSM6612P-310 Solar Panel

THX!
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby cabin50 on Wed Sep 13, 2017 7:20 pm

how do I post things for overall feed back?
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Re: String Sizing Tool for MX and FM Charge Controllers

Postby Raj174 on Thu Sep 14, 2017 2:58 am

Just post in the category that refers to the equipment you are having issues with and everyone will see it in recent posts.
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