Off Grid System Upgrade
JYanke
Registered Users Posts: 39 ✭✭
Hello,
Considering upgrades to my offgrid system. Here are my ideas and just looking for some advice:
Current PV array is 3 panels wired in series 80 watts each (max PV Voc is 54 volts)
My battery bank now is 2 flooded deep cycle 6v batteries wired in series for 12v 230aH total
1. Upgrade to a total of 4 deep cycle flooded 6 volt batteries 230 aH each. Wired in series/parallel combo to make a 12v 460 aH bank.
Considering upgrades to my offgrid system. Here are my ideas and just looking for some advice:
Current PV array is 3 panels wired in series 80 watts each (max PV Voc is 54 volts)
My battery bank now is 2 flooded deep cycle 6v batteries wired in series for 12v 230aH total
1. Upgrade to a total of 4 deep cycle flooded 6 volt batteries 230 aH each. Wired in series/parallel combo to make a 12v 460 aH bank.
2. Add panels to my array to accommodate new battery bank size. (3 more 80 watt panels making total of 6 panels in series with 108 volts max Voc and 4.5 amp max)
3. Upgrade charge controller from Morningstar Sunsaver MPPT to a Victron Energy MPPT 150/35 controller.
3. Upgrade charge controller from Morningstar Sunsaver MPPT to a Victron Energy MPPT 150/35 controller.
Considering my present day system has had no issues keeping the 230aH bank charged and healthy for over 7 years now, Im simply thinking that the array would need doubled if I doubled the battery bank. Obviously will need to upgrade the charge controller as well and have been looking at these options from Victron Energy. Any thoughts on these controllers and am I on the right path with upgrade ideas? Thanks in advance
Comments

I wonder what you are saying when you say;JYanke said:Current PV array is 3 panels wired in series 80 watts each (max PV Voc is 54 volts)
"(max PV Voc is 54 volts) " is that for a single panel? For a string of 3 panels it would seem low as the VOC would add and thaere aren't many panels that have a VOC of 18 volts (54/3=).
Adding a parallel string is likely not a problem with the VOC but might be too high amps in some MPPT type charge controllers. 480 watts into a 12 volt system would max out a 30 amp MPPT type charge controller and some don't 'like' over paneling.JYanke said:Considering my present day system has had no issues keeping the 230aH bank charged and healthy for over 7 years now, Im simply thinking that the array would need doubled if I doubled the battery bank. Obviously will need to upgrade the charge controller as well and have been looking at these options from Victron Energy. Any thoughts on these controllers and am I on the right path with upgrade ideas? Thanks in advanceHome system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites, Midnite Epanel, 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. 
Hi. The panels I have now are 80 watts each and are 18v each. I have all three wired in series which I typically get around 54v max and 4.5 amps max from the total array. Adding three more panels in series would give me around 108 volts max. Of course this has been enough to keep the two batteries charged but I am wanting more amp hour storage for times of increased power usage

The panels sound like Vmp~18 volts (typically Voc~2122 volts)... There are Vmp~15 volts or so panelsThey were originally made to be "self regulating"Sort of charge and maintain a 12 volt lead acid bank without a charge controller.
Anyway... Start at the beginning. Sounds like your loads are fine for the existing battery bank and arrayBut lets do some math to size the "new system" configuration.
The 6 volt @ 230 AH batteries (aka "gold cart" type)I like those for making a series parallel bankVs just using 4x 12 volt batteries in parallel... Easier to take a voltmeter to each battery to check health/state of charge... If any battery is higher or lower voltage than the othersNeed to figure out why (wiring issue, bad cell, needing to EQ, etc.).
For a solar power system5% rate of charge can work for weekend/sunny weather system. 10% to 13%+ rate of charge better for full time off grid use (aka "keeping the batteries happy"). 460 AH (battery bank) * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 433 Watt array minimum
 460 AH (battery bank) * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 866 Watt array nominal
 460 AH (battery bank) * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1,126 Watt array typical "cost effective" maximum
And there is also sizing the array based on your daily loads... Assuming fixed array near Akron OH:
http://www.solarelectricityhandbook.com/solarirradiance.htmlAkron
Measured in kWh/m2/day onto a solar panel set at a 49° angle from vertical:
Average Solar Insolation figures
(For best yearround performance)
If you were using (230 AH * 0.25 discharge= ) 57.5 AH per day... A 480 Watt array would need hours of sun per day of:Jan Feb Mar Apr May Jun 2.54
3.13
3.80
4.60
4.87
5.23
Jul Aug Sep Oct Nov Dec 5.38
5.12
4.86
3.85
2.48
2.17
 57.5 AH * 12 volts = 690 WH per day average
 690 WH per day * 1/0.52 off grid AC system eff * 1/480 Watt array = 2.76 Hours of sun per day "break even"
Depending on the size of your arrayA quick calculation for an MPPT solar charge controller: 480 Watt array * 0.77 panel+controller deratings * 1/14.5 volts charging = 25.5 Amp minimum MPPT controller rating (suggested)
BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset 
Thanks Bill. Awesome information as always. You are correct, I meant each panel has 18v vmp max.According to your calculations my current system (3 panels at 80 watts each) is capable of roughly a 5% rate of charge for the 230 AH bank.230 AH * 14.5v * 1.298 * 0.05 = 216 Watts min
I think the 5% rate of charge will be okay for my use of the cabin. (As it has been so far for the 230aH bank) Would love to make it more efficient but can’t justify the extra cost at the moment.I also want to try to utilize the three panels I already have, and sourced the same ones from a place called Sunelectronics where I bought the original 3. The panels would be about $74 a piece plus shipping.The Victron Energy 150/35 MPPT has the following ratings which I think would work?
Rated Charge: 35 A
Nominal PV Power: 12v:500W
Max PV Short Circuit Current: 40A
Max PV Open Circuit Voltage: 150V coldest
Absorption: 14.4V adjustable
Float: 13.8 adjustable
Max Efficiency: 98% 
I don't see any reason why the Victron 150/35 would not work... Unless you want to add capacity in the future (would need a new/second charge controller for larger array).
You have the choice of 2s/3p, or 3s/2p, or 6s/1p (series/parallel) connections for your array... I did not see an efficiency curve for the VictronBut typically the most efficient is about 2x Vbatt (2x 15 volts = 30 Volts Vmparray)... However, going higher is not going to cost much (perhaps a lost of 1% or so in efficiency).
There is an issue with 6 panels in seriesIf you happen to be a region that gets terribly cold6 panes in series may exceed 150 VAC.
You can use this Midnite calculator for min/max array voltages vs temperature:
http://www.midnitesolar.com/sizingTool/index.php
Probably the simplest would be 3 series x 2 parallel strings... Still reasonably high voltage for the array  And can use smaller AWG wiring. Depending on how far your array is from the battery charger/shed... Looking typically fro 1% to 3% maximum voltage drop from array to charge controller.
https://www.calculator.net/voltagedropcalculator.html
If you don't want to run a another array wiring string (or rewire with heavier cables)6s x 1p is probably OK (I don't think Ohio gets that cold...).
BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset 
Thanks Bill. Would you mind describing what you mean by 3 series x 2 parallel strings “3s/2p”. Trying to wrap my head around how the 6 panels would be wired in that configuration. At the moment my panels are not far from the controller and battery bank and have the following:
panels to midnite solar 150vdc 15 amp breaker: MC4 4mm^2 wires
breaker to charge controller: #12 AWG
charge controller to battery bank: #12 AWG
*would also have to upgrade the breaker for the new array 
This does an OK job:
https://www.explorist.life/solarpanelsseriesvsparallel/
Basically, solar panelsyou connect + of panel A to  of Panel B; then + of panel B to  of Panel C... The  of A and + of C are now your three panels in series (3x Vmp).
You connect both 3 panel series strings together ( to , and + to +) and that adds the current (Imp) from each string to 2xImp.
The first is 3s x 1p... The second is 1s x 3p... Solar panels are (more or less) a bunch of 0.5 volt cells in series... A Vmp~18 volt panel has 36 cells in series. You would just take two strings of the left drawing and combine the outputs together (+ to + and  to ) for a 3 series * 2 parallel strings.
Note that batteries are just a bunch of 4 volt cells in series (a 12 volt Lead Acid battery has 6 cells in series). Your 2 volt AGM cells are 24 in series for a 48 volt battery bank.
Please make sure you understand the wiring... In some cases, miswiring can toast your solar panels or worst.
How long is the cable run from your panels to the charge controller?
You presently have a Midnite controller (what model)?
BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset 
Thanks Bill. Im following you now.The panels are wired in series using short lengths of the MC4 4mm^2 wire. From the panels I have roughly 10 feet of MC4 4mm^2 wire to the Midnight Solar “Solar Array Combiner” model MNPV3 with a 150vdc 15a breaker.Maybe a foot or so of #12 AWG running from breaker to the Morningstar 15A Sunsaver MPPT
Few more feet of #12AWG from the Sunsaver to the batteries 
So looking at the 3s/2p configuration I would have 480 watts and still have the 54 volts Vmp but would double my imp from 4.5 to 9.I think I would still have to change the controller. The Sunsaver specs says it handles up to 60v but shows max pv wattage is only 200 w on 12v

You usually do not need a combiner box for 1 or 2 parallel connected strings. For 3 or more parallel strings, then the combiner is used. One (or two) breakers/fuses per string.
The series protection fuse/breaker is there to prevent the other paralleled panels feeding current to a shorted panel/string. The fuse/breaker for the shorted panel/wiring trips and stop current flow (and reduce the chance of starting a fire).
If you are using a combinerIt sounds like you have a 1 series x 3 parallel panels? And are (probably) for the MorningStar MPPT (sunsaver) controller?
Placing 3s x 1 parallel string would b maxing out the Vpanel input for the Morningstar (Vocarray 60 volts maximum).
Have to be clear Voc (voltage open circuitno load on array), and Vmp (voltage maximum powerPulling the "optimum" Imp current maximum power from the solar panels). For your panels, Vmp~18 volts, and Voc~21.5 volts or so... These specifications are based on the cells at ~75F... When panels get cold (overnight, cold environment), Vmp and Voc rise... When panels get hot (typical under full sun warm weather, not much wind), both voltages fall.
SoI am a little bit confused at the moment.
Regarding wiring... 4mm^2 wire is roughly 11 AWG. If you want to send 9 amps for 10 feet @ ~54 VDC, then the voltage drop calculator would be:
https://www.calculator.net/voltagedropcalculator.html?material=copper&wiresize=4.132&voltage=54&phase=dc&noofconductor=1&distance=10&distanceunit=feet&eres=9&x=9&y=2Voltage Drop Calculator
Result
Voltage drop: 0.23
So voltage drop is not a big issue (you can calculate each length of cable+current. Note this calculator assumes 10 foot one way run = 20 feet of actual wire run).
Voltage drop percentage: 0.42%
Voltage at the end: 53.77
And you can use the NEC table for look up max current for 12 AWG wire (US "odd AWG" wiring is not commonly used):
https://lugsdirect.com/WireCurrentAmpacitiesNECTable30116.htm
And 12 AWG is good for 20 amps typical. So you can double your array and use the same 11 AWG cable to bring power from the array to the charge controller Vpanel input.
BillNear San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset 
Thanks Bill. To be honest I installed the combiner box mainly as a means to mount the breaker and have an easy way to disconnect the PV array. Also considered potential of expanding the system one day. However, all thats in the combiner box is the one 15a breaker. My panels are just three 80 watt panels wired in series and route to that breaker (3sx1p)
I will digest all this great info and let u know if I have any questions. Appreciate all the help
joe 
Good Morning Bill,
when you reference “rates of charge” such as 5%, 10%, 13% etc. could you elaborate a little more about this? What exactly does a 5% rate of charge entail? Thanks 
For our needs, we use the battery AH capacity at the 20 hour discharge rate;... There are other rates uses from 6 hour to 100 hour discharge rateBut 20 hour is pretty standard with many battery manufactures.
That means: 100 AH / 20 hours = 5 amps (for 20 hours from 100% to 0% state of charge)
 100 AH * 0.05 (5%) rate of charge = 5 amp rate of charge
 100 AH * 0.10 (10%) rate of charge = 10 amp rate of charge
 100 AH * 0.13 (13%) rate of charge = 13 amp rate of charge
If you have 4x "golf cart" batteries that are 6 volt @ 200 AH and want a 12 volt bank, you put 2 batteries in series for 12 volt (2 * 6 volt) string of batteries, and put 2x strings in parallel for 400 AH (2 * 200 AH). That gives you a 12 volt @ 400 AH battery bank. A 10% rate of charge would then be: 400 AH * 0.10 (10%) = 40 Amps charging
 40 Amps charging * 14.5 volts nominal charging voltage * 1/0.77 Hot panels and charge controller deratings = 753 Watt array nominal (for 10% rate of charge)
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset 
If you had a battery rated at 100 amperehours a 10% charging rate would be 10 amps. 5% rate would be 5 amps etc.Island cottage solar system with appriximately 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing due south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter which has performed flawlessly since 1994. Outback Flexmax 80 MPPT charge controller four 467Ah AGM batteries. Insignia 11.5 cubic foot electric fridge 1/4hp GSW piston pump. My 31st year.
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