Solar Panel Advice

Discussion about OutBack Inverters in Off Grid Applications

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daverad1
Forum Junior Member
Posts: 1
Joined: Mon Jul 27, 2020 12:37 am
My RE system: Inverter: WZRELB 5000W Heavy Duty Pure Sine Wave Solar Power Inverter DC 48V
Solar Controller: Outback Flexmax 80 FM80 MPPT 80 AMP Solar Charge Controller
Batteries: VMAX SLR155 Vmaxtanks AGM Deep Cycle Batteries 12V 155Ah

Solar Panel Advice

Post by daverad1 » Mon Jul 27, 2020 12:46 am

Hi Folks,

I have a FlexMax 80 that will be charging a bank of 4 Vmaxtanks AGM Deep Cycle Batteries 12V 155Ah running in series for a total of 48 volts. Any recommendations of the best solar panel feed to the OutBack device? I was thinking of using solar panels in the 300 watt range. I assume I need to run the solar panels in series to the Outback to achieve the same 48 volts as well?

Best Wishes,
Dave

raysun
Forum Emperor
Posts: 2758
Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower One: FX3048T, (2) FM80, MATE3s, FlexNetDC
Outback 200NC batteries (8 @ 48v)
Outback IBR3 battery enclosure
Suniva 330 watt panels (12 - 6 strings of 2 in series)
Hyundai 355 watt panels (6 - 3 strings of 2 in series)
Honda EU7000is gas fuel generator

Re: Solar Panel Advice

Post by raysun » Mon Jul 27, 2020 6:03 pm

daverad1 wrote:
Mon Jul 27, 2020 12:46 am
Hi Folks,

I have a FlexMax 80 that will be charging a bank of 4 Vmaxtanks AGM Deep Cycle Batteries 12V 155Ah running in series for a total of 48 volts. Any recommendations of the best solar panel feed to the OutBack device? I was thinking of using solar panels in the 300 watt range. I assume I need to run the solar panels in series to the Outback to achieve the same 48 volts as well?

Best Wishes,
Dave
There's lots of brands out there that deliver good performance. Solar panels are becoming a bit of a commodity, so often the biggest determinant is cost/watt.

300W class panels can be either 60 cell or 72 cell, and hover around 30 - 40Voc. The panel voltage must be 1.5V above the battery voltage for the charge controller to operate. The maximum series panel voltage must never exceed 150V - the charge controller rated maximum. 2 panels in series will meet the minimum voltage requirements. Most panels and climates *may* permit 3 panels in series.

The FM80 charging a 48V battery can manage a total of 3840W, so 12 panels @ 300W would be easily accommodated.

However, the small battery capacity cannot handle that much charging power. The maximum charging current for the battery is 35A, or about 1.7kW of charging power. A larger array can be installed, of course, because PV arrays are rarely putting out 100%, but the output from the charge controller will need to be limited to 35A.

One other issue - the 5kW inverter is much too large for the battery capacity. If the Inverter is run anywhere near its rated output, the battery would be exhausted in less than 15 minutes. If run at a lower output (more in line with the battery's C20 capacity of 155AH) an average battery output of 375W can be sustained. That will be very low on the inverter's power curve, so it will be operating at low conversion efficiency. That battery wattage will yield 100 AC Watts or less output from the inverter. The system needs a much smaller Inverter (less than 1000W) or a much bigger battery.

Given the current battery type, a 2nd bank, bringing the total to 330AH, combined with an FM80 and 4kW PV Array would support a 2kW and possibly (a very high quality, not cheap Chinese) 3kW inverter if used for an average AC daily load consumption of approximately 6kWH.
Last edited by raysun on Tue Jul 28, 2020 5:58 am, edited 6 times in total.

Mike Curran
Forum Emperor
Posts: 1731
Joined: Sat Aug 28, 2004 6:28 pm
My RE system: Outback - Garage roof:
- 8 (2x4) Evergreen 180's into one FM80 (2007/2020 - replaced MX60)
- 6 (2×3) ALEO S79-300's into one FM80 (2017)
- 2 grid-tied GVFX3524's classic stacked for 120/240VAC (2007)
- 12 Surrette/Rolls 2V x 1766Ah (2007)
- Hub10.3, Mate3s, FNDC, RTS, OpticsRE. Tigo Energy ES maximizers on each PV module.

Westinghouse Solar - Barn roof: (2012)
- 30 (2x15) 235W panels with Enphase M215 microinverters, grid-tied

Outback Skybox - Barn roof: (2019)
- 14 (2x7) Talesun 275W (DC array input to SB charger)
- 3 SimpliPhi 3.8 batteries, 48V, 225Ah total
- AC coupled input (manual switch during grid outage only) from 14 Talesun 275W,
Enphase M215 microinverters, normally direct grid tied

All self-designed and self-installed
Location: Chagrin Falls, Ohio

Re: Solar Panel Advice

Post by Mike Curran » Mon Jul 27, 2020 6:16 pm

I assume I need to run the solar panels in series to the Outback to achieve the same 48 volts as well?
No need to match the panel voltage to the battery voltage. The FM80 will take any array (open circuit) voltage up to 150 volts, and will charge your 48 volt battery perfectly well. You just need to be careful not to exceed that 150 volt threshold else your FM80 will be toast. That means taking into account temperature effects on your panel output voltage, which will rise as temps fall.
http://www.tigoenergy.com/site.php?95b2dca2-ca6c
https://enlighten.enphaseenergy.com/public/systems/Hctc107221

provo
Forum Czar
Posts: 509
Joined: Thu Jul 27, 2006 4:34 pm
My RE system: Sixteen Evergreen EC-120
(4 strings, total 1920W)
Eight Rolls S-550 (2 strings, total ~800Ah @ 24V)
One FM80
One VFXR3524A
Hub 10
Mate3s
FNDC and Trimetric
Location: Sierra foothills

Re: Solar Panel Advice

Post by provo » Mon Jul 27, 2020 7:29 pm

daverad1 wrote:
Mon Jul 27, 2020 12:46 am

I have a FlexMax 80 that will be charging a bank of 4 Vmaxtanks AGM Deep Cycle Batteries 12V 155Ah running in series for a total of 48 volts. Any recommendations of the best solar panel feed to the OutBack device? I was thinking of using solar panels in the 300 watt range. I assume I need to run the solar panels in series to the Outback to achieve the same 48 volts as well?
According to the spec sheet on that battery, the maximum charging current is 45A. 45A x 48V = 2160W, which is maybe the upper limit for your array to not overcharge the battery. I don't know AGM's, so others may correct me here. Six panels near 360W, or eight near 270W, would give three or four pairs of a reasonable voltage.

pss
Forum Czar
Posts: 607
Joined: Mon Jul 24, 2017 8:40 am
My RE system: 8330 watts in three strings, Flexmax 60 x 3, Radian 8048A, GSLC load center, Mate 3S, Hub 10.3, FN-DC and 900 Amp, 48V Trojan T105-RE battery bank.

Re: Solar Panel Advice

Post by pss » Mon Jul 27, 2020 9:11 pm

I have three arrays and 3 FM60's. One of the arrays has 12 panels, 240 watts each and the other 2 are made up of 8 panels, 340 watts each panel. The 240 watt panels are connected as 3 in series, then 4 parallel strings. Open circuit voltage runs 80 to 105. The 340 watt panels are connected as 2 in series, 4 strings. The open circuit voltage of this configuration is 80-90 volts. Note my climate never dips below 45-50 with sun in winter. The goal of having an array of panels charge a 48 volt battery bank using an MPPT charge controller is to provide a voltage that can reach the absorb values of the battery bank, usually around 58-59 volts and possibly even equalize the battery bank if needed, usually around 64 volts. The MPPT controller contains firmware which takes the input voltage of the array and amperage of the array and then applies the self contained algorithm to reduce the voltage and increase the amperage flowing into the batteries. The net result in more power into the batteries during the phases of their charge cycle while using the programmed input characteristics of the battery bank to meet the goals of absorb voltages, float voltages and amps needs to reach a full charge of 100%. So the net result is you can locate the best deal on panels in your area, 60 or 72 cells doesn't matter, its your math and how you wire them that count.

Generally speaking, in order for the charge controller to have any overhead to apply the firmware algorithm and increase charging efficiency, the input voltage needs to be about 18-24 volts above the voltage for a 48 volt battery bank. So if the bank is 48 volts, you would like the PV voltage coming in to be at least 66 volts to give the charge controller some room to apply the MPPT software. In fact, the higher the PV voltage, the better for the charge controller, keeping mind the limits of the input voltage to 150 volts and the amperage, in your case 80 amps. The maximum input wattage or power used in the absorb cycle of the battery bank is usually provided by the manufacturer of the batteries and is generally about 10-15% of the battery's 20 hour discharge capacity. So if a battery has a 20 hour power rating of 100 amps, then the maximum charging current would be 10-15 amps for that battery in the absorb phase.

Lastly and important is the wiring and fuses/breakers/switches used to connect all together. In my case, I chose to use the maximal gauge wire that fits the charge controller's terminals. I then used the maximal gauge wire into the Outback GSLC. Circuit breakers there between batteries and charge controller. From my batteries, all interconnections used were with 4/0 gauge wire and 4/0 into the inverter. Each string of batteries has a DC terminal fuse on the positive pole of the last battery in the string. Then each string has a large DC amperage capacity single pole marine style switch on the positive before attaching to a heavy copper bus plate (this allows individual strings to be turned off for servicing without a full shutdown). This buss plate combines the strings of batteries into the inverter, again with the proper sized breakers.

The arrays each have a grounding rod at their base. From the combiner box (each box has a DC lightening arrestor wired into the box), the wiring travels to a DC disconnect switch (I have a three pole with a single switch handle that turns off and on all three arrays) that also contains solar fuses for each array within the switch. The wiring then travels to the charge controllers as described above.

Lastly comes conduits. There are easily googled tables that will tell you what size conduit will be required for the gauge of wire you are using and how many strands of that gauge can be put into the conduit. The conduit will not necessarily keep the wire from being exposed to water. Instead it is there to prevent accidental severing, electrocution, rats, etc from ruining the continuity. The insulation on the wire provides the waterproofing. Too small a conduit with too large a gauge wire and/or too many strands with too high an amperage flow has the potential to melt the insulation and short or cause a fire.

So do your research, ask questions, understand your problems and be certain of the solutions, build it right, build it smart and you will be rewarded with expectations met, peace and quiet and sleep. Do it wrong, sloppy, haphazardly and you will experience grief, anger and unmet expectations leading to disappointment.

fcwlp
Forum Guru
Posts: 475
Joined: Wed Jan 22, 2020 9:40 am
My RE system: GS8048A, FM80 w/3,600 W PV Fixed, FM80 w/2,700W on Zomeworks tracker, Mate3, 24 Trojan 2V L16 1100AH @ C20, Grid-Tied with Kohler 14RESA LPG Generator and MEP-803 Diesel if needed
I also install and maintain grid-tied and off-grid systems, details will be given for these system if required
Location: 80 miles NE of Phoenix at 5500'

Re: Solar Panel Advice

Post by fcwlp » Tue Jul 28, 2020 11:15 am

pss wrote:
Mon Jul 27, 2020 9:11 pm
Generally speaking, in order for the charge controller to have any overhead to apply the firmware algorithm and increase charging efficiency, the input voltage needs to be about 18-24 volts above the voltage for a 48 volt battery bank. So if the bank is 48 volts, you would like the PV voltage coming in to be at least 66 volts to give the charge controller some room to apply the MPPT software.
The minimum design input voltage will be for the highest temps experienced and remember your panels will be a higher temperature than your ambient. For a 48V system with FLA batteries I design for ~70V to give enough headroom for the equalization. For AGMs or Li you could target the mid 65V range. Use the OB string sizing tool to understand how both the high and low temps for your region affect the PV voltage.

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