Solar Wire Calculation with 6 24v 136 watts uni-solar panels

**SunEagle** · 10-24-2014, 02:15 PM

Originally posted by benhchang

Hi,

This is my first post and I have gone through several forum to find what I am looking for. So pls be nice. This is my first solar experiment. If everything goes well, my plan to harness most of my electrical needs through solar.

I purchase 6 uni-solar 136 watts 24v panels to put on the roof of my trailer. When the trailer is parked at home, my goal to use an inverter to generate electricity for home use.

NOCT
Pmax: 105W
Vmp: 30.8V
Imp: 3.42

Ideally, I would like to install the panels in Parallel for all 6 panels.

The problem that I have is that when I put all 6 panels into Parallel, the total Imp = 20.52 which is 3.42 * 6. According to wiring size chart, I should use 8 gauge wire. I believe the junction box wires from the panels are 10 gauge. It appears that all solar panel wires are either 10 or 12 gauge.

I know that I can have 2 pairs of panels (3.42 + 3.42) in series and 2 panels (3.42+3.42) in parallel = 13.68A where I can use 10 gauge wire.

I also have a limitation on the inverter: iMeshbean® 1000W Gird Tie Inverter MPPT Pure Sine wave for Solar Panel System DC 22V-60V TO AC 110V/120V USA.

If my math is correct, there is no way to have more than 4 solar panels in parallel due to wire gauge limitation on the solar panel junction box.

Question: What are the alternative solutions this problem with limitations on wire gauge and the inverter voltage.

Thank you,

Ben

Hello Ben. Welcome to Solar Panel Talk

I don't see where you mentioned the type of charge controller or battery you will be using. Once we know what that charge controller is we can help you find the best wiring between the solar panels and CC as well as the wire size between the CC to the battery and then to the inverter.

I just looked up that iMeshbean inverter. That is not a true grid tie inverter. It is not UL listed and can't be legally used in the US or most other places. For that matter if it is used anywhere there is a good possibility you can overload your wiring and start a fire.

**benhchang** · 10-24-2014, 03:08 PM

Thanks SunEagle for the quick response.

Right now, I have 6 panels on the roof trailer.

To connect to home, I have the following:
Disconnect switch
IMeshbean (I understand that it is not UL rated and the risk of potential fire) https://www.youtube.com/watch?v=S93wbGlzsJg

To connect to a trailer, I have the following:
MorningStar TriStar TS-MPPT-45 charge controller
Go Power! FBL-200 Class T 200 Amp Fuse with Block
Go Power! GP-SW2000-24 2000-Watt Pure Sine Wave Inverter
Go Power! TS-30 30 Amp Automatic Transfer Switch
Progressive Industries EMSHW30C Surge Protector
1 Marine Battery 100ah and will get another Marine battery 100ah.

Since winter is upon us, I am focused on connecting the solar panels to home, not trailer.

After doing some more research, it appears that I will need fused/circuit breaker combiner box for the 6 panels.

Thanks,

**Sunking** · 10-24-2014, 03:24 PM

Originally posted by benhchang

Thanks SunEagle for the quick response.

Right now, I have 6 panels on the roof trailer.

To connect to home, I have the following:
Disconnect switch
IMeshbean (I understand that it is not UL rated and the risk of potential fire) https://www.youtube.com/watch?v=S93wbGlzsJg

To connect to a trailer, I have the following:
MorningStar TriStar TS-MPPT-45 charge controller
Go Power! FBL-200 Class T 200 Amp Fuse with Block
Go Power! GP-SW2000-24 2000-Watt Pure Sine Wave Inverter
Go Power! TS-30 30 Amp Automatic Transfer Switch
Progressive Industries EMSHW30C Surge Protector
1 Marine Battery 100ah and will get another Marine battery 100ah.

Since winter is upon us, I am focused on connecting the solar panels to home, not trailer.

After doing some more research, it appears that I will need fused/circuit breaker combiner box for the 6 panels.

Thanks,

Are you joking? If you do this silly I hope you realize power from your battery will cost you some 60-cents per Kwh verse paying the electric company 10-cents. In effect what you are doing is generating electricity for 65-cents per Kwh and selling it for a dime. That is a sure fire way to go bankrupt if this was a business.

Secondly last thing you want to ever do is wire panels in parallel. You want to run as high of a voltage as possible including battery voltage on an off-grid system. If you knew that there would not be a question because you would know to wire the panels 3 in series in parallel with another 3 panels in series. So far you have done everything wrong. You are about to learn a very painful and expensive lesson. Be sure to take notes so you do not repeat your mistakes again starting with research and due diligence which it appears you did not do. If you had researched you would also know pumping 25 amps into a 100 AH battery will cook the battery.

**benhchang** · 10-24-2014, 03:52 PM

Hey SunKing,

I appreciate your comments. However, I do not understand where you are getting 60 cents Kwh and 10 cents Kwh information.

I understand series is preferred method. However, Tri-Star inverter only allows 48v charge controller. Since the solar panels are rated at 24v, one alternative is to have 3 pairs in series. In this scenario, what would be the max voltage?

Thanks

**SunEagle** · 10-24-2014, 03:59 PM

Originally posted by benhchang

Thanks SunEagle for the quick response.

Right now, I have 6 panels on the roof trailer.

To connect to home, I have the following:
Disconnect switch
IMeshbean (I understand that it is not UL rated and the risk of potential fire) https://www.youtube.com/watch?v=S93wbGlzsJg

To connect to a trailer, I have the following:
MorningStar TriStar TS-MPPT-45 charge controller
Go Power! FBL-200 Class T 200 Amp Fuse with Block
Go Power! GP-SW2000-24 2000-Watt Pure Sine Wave Inverter
Go Power! TS-30 30 Amp Automatic Transfer Switch
Progressive Industries EMSHW30C Surge Protector
1 Marine Battery 100ah and will get another Marine battery 100ah.

Since winter is upon us, I am focused on connecting the solar panels to home, not trailer.

After doing some more research, it appears that I will need fused/circuit breaker combiner box for the 6 panels.

Thanks,

Ok the good news is that Moringstar 45amp CC can accept up to 150vdc input which (depending on the Voc of those panels) you can wire more than 2 in series. Maybe 2 sets of 3 in series. You will not be able to wire all 6 in series because that will exceed the 150VDC limit.

Not sure but I think you are getting the second battery to build a 24v system based on that Go Power inverter. That Morningstar is good for 1200 watts of panel input to charge a 24volt battery system so you are ok.

Now one possible issue I see (besides the cost of all that equipment) is that you may have too much panel wattage for that 24volt 100Ah battery system. You will have a total of 630 watts (6 x 105w). With that charger it can put about 26 amps into the battery which is a C/4 rating and a little too aggressive for most FLA batteries. Even an AGM type at 100Ah might be too small.

The second issue I see is that 2000 watt inverter is way too big for that small battery. It can drain in it a heartbeat. So the battery needs to be bigger to match up with both the charger and inverter.

I am thinking with those 630 watts you should build a battery system at 24volt around 250Ah. You can built that with 4 x 6volt 250Ah batteries. Although even then your inverter is much bigger than that battery system as well as being very inefficient. So if you are stuck on that inverter you really need to increase your battery to about 750Ah as well as adding more solar panel watt to that 1200 watt max for the Morningstar.

**Sunking** · 10-24-2014, 04:12 PM

Ben go look at the specs of the MorningStar TriStar TS-MPPT-45 charge controller. Voc input limit is 150 Voc. And check your panel specs again, you want to know the Voc, not Vmp. Those are not 24 volt battery panels, 31 volts vmp will not charge a 24 volt battery. You would be forced to use two in series at a minimum on a 24 volt battery, so all in parallel is out of the question. That only leaves you two options. 2 x 3 or 3 x 2. Check the panels VOC and add them up to stay under 130 volts. That will give you the room for cold weather. Vmp minimum for a 24 volt system is 36 volts.

Not sure where you live but electricity cost on average 11-cents per Kwh from your electric company. At best your marine battery will last 3 years as they are not designed to do what you want. 24 volts at 100 AH over the lifetime of those batteries will yield you roughly 480 watt hours a day or 5 cents worth of electricity per day. In 3 years they will give you roughly 526 Kwh usable. Now do the math and figure out what the Kwh cost of your battery expense is. Battery cost $ / 526 Kwh. See what you come up with.

Example the battery cost = $250 / 526 Kwh = $0.475 per Kwh. Now check your electric bill and see what the Power Company charges you. Should be around 11 to 12 cents. In this example you are paying 400% more for power with batteries. The laughable part is .5Kwh is nothing, about what your desktop computer uses in a day.

Few more things you have way out there:

A 24 volt 100 AH battery can only take a maximum panel wattage 300 watts on a MPPT controller, you have over 600 watts. max C/8 charge current = 12.5 amps
A 24 volt 100 AH battery can only operate a maximum inverter of 300 to 500 watts, you have a 2000 watt inverter. A 2000 watt 24 volt inverter requires a minimum 800 AH, you only have 100 AH

Nothing you have makes any sense nor your reasons for using it.

**benhchang** · 10-24-2014, 04:23 PM

After reading more about combiner box, it appears that I should get one.

Based on your recommendation, I am thinking...
Solar panels are 3 pairs of series producing ~48v and ~3.42A for each of the 3 series.
Question 1: For Home: Will this iMeshbean® 1000W Gird Tie Inverter MPPT Pure Sine wave for Solar Panel System DC 22V-60V TO AC 110V/120V handle 3 pairs of series?
Please correct my math: ~48v and ~3.42 * 3 = 10.26A.
Question 2: Based on this setup, should I get 3 fuse rated at 5 amp each for the combiner box?

Thanks

Originally posted by SunEagle

Ok the good news is that Moringstar 45amp CC can accept up to 150vdc input which (depending on the Voc of those panels) you can wire more than 2 in series. Maybe 2 sets of 3 in series. You will not be able to wire all 6 in series because that will exceed the 150VDC limit. Agreed

Not sure but I think you are getting the second battery to build a 24v system based on that Go Power inverter. That Morningstar is good for 1200 watts of panel input to charge a 24volt battery system so you are ok. Agreed

Now one possible issue I see (besides the cost of all that equipment) is that you may have too much panel wattage for that 24volt 100Ah battery system. You will have a total of 630 watts (6 x 105w). With that charger it can put about 26 amps into the battery which is a C/4 rating and a little too aggressive for most FLA batteries. Even an AGM type at 100Ah might be too small. Agreed. I am planning on installing 4 batteries in the summer when I am trailering.

The second issue I see is that 2000 watt inverter is way too big for that small battery. It can drain in it a heartbeat. So the battery needs to be bigger to match up with both the charger and inverter.Agreed

I am thinking with those 630 watts you should build a battery system at 24volt around 250Ah. You can built that with 4 x 6volt 250Ah batteries. Although even then your inverter is much bigger than that battery system as well as being very inefficient. So if you are stuck on that inverter you really need to increase your battery to 1000Ah as well as adding more solar panel watt to that 1200 watt max for the Morningstar.

Agreed

**benhchang** · 10-24-2014, 04:46 PM

Hey SunKing,

Thanks for the constructive criticism.

NOCT:
Pmax 105W
Vmp 30.8V
Imp 3.42A
Isc 4.1A
Voc 42.2V

Now I understand more about the batteries. Yes, I agree that I need much more battery storage and will increase to 4 batteries in the summer. Would you please elaborate on battery min 800ah. I was planning on getting 4 marine batteries totaling ~500ah.

Background: I have a 24 ft enclosed car trailer that I tow to race tracks. There are some tracks where shoreline is not available. Therefore, I am trying to maximize the solar power at the race track event with 4 marine batteries ~500ah for ac, heater at night, microwave, induction cooktop, lights, etc. 2000 watt inverter may be an overkill. However, I am looking for safety of running these appliances. So, while the trailer is sitting at home, my though is to disconnect the solar to the battery and connect it to the home grid tie inverter.

Originally posted by Sunking

Ben go look at the specs of the MorningStar TriStar TS-MPPT-45 charge controller. Voc input limit is 150 Voc. And check your panel specs again, you want to know the Voc, not Vmp. Those are not 24 volt battery panels, 31 volts vmp will not charge a 24 volt battery. You would be forced to use two in series at a minimum on a 24 volt battery, so all in parallel is out of the question. That only leaves you two options. 2 x 3 or 3 x 2. Check the panels VOC and add them up to stay under 130 volts. That will give you the room for cold weather. Vmp minimum for a 24 volt system is 36 volts.

Not sure where you live but electricity cost on average 11-cents per Kwh from your electric company. At best your marine battery will last 3 years as they are not designed to do what you want. 24 volts at 100 AH over the lifetime of those batteries will yield you roughly 480 watt hours a day or 5 cents worth of electricity per day. In 3 years they will give you roughly 526 Kwh usable. Now do the math and figure out what the Kwh cost of your battery expense is. Battery cost $ / 526 Kwh. See what you come up with.

Example the battery cost = $250 / 526 Kwh = $0.475 per Kwh. Now check your electric bill and see what the Power Company charges you. Should be around 11 to 12 cents. In this example you are paying 400% more for power with batteries. The laughable part is .5Kwh is nothing, about what your desktop computer uses in a day.

Few more things you have way out there:

A 24 volt 100 AH battery can only take a maximum panel wattage 300 watts on a MPPT controller, you have over 600 watts. max C/8 charge current = 12.5 amps
A 24 volt 100 AH battery can only operate a maximum inverter of 300 to 500 watts, you have a 2000 watt inverter. A 2000 watt 24 volt inverter requires a minimum 800 AH, you only have 100 AH

Nothing you have makes any sense nor your reasons for using it.

**Sunking** · 10-24-2014, 05:14 PM

Batteries have internal resistance, when current flows through resistance develops voltage drop, or in the case of a battery Voltage SAG. With low voltage systems you wan tto limit voltage and power losses to 3% or less. So between inverter and battery 3% of 24 volts = .72 volts. Not much to work with and you also have loss on the wire to deal with to keep that 3%. That means you have to assign some value to the battery like 2 of the 3% that include the wire. To do that with a FLA battery limits the maximum amount of current they can supply without excessive voltage sag is C/8 where C = the battery Amp Hour rating to yield 2% limit. C/8 on a 100 AH battery is 12.5 amps maximum. A 2000 watt inverter of say 80% efficiency at full power draws 2500 watts from the battery and at 24 volts = 104 amps. If you were to fully load th einverter down to full power with you battery would instantly trip off line from under voltage despite the battery being fully charged up. So if max is C/8 and you need 93 amps then you know at a minimum you need 8 hours x 104 amps = 832 AH minimum requirement.

Here is the other kicker. Your 2000 watt inverter is going to draw power while sleeping doing nothing. It can be as high as 100 watts doing nothing. That means your inverter setting there doing nothing all day will completely discharge your 24 volt 100 AH batteries. Wait 5 or 6 days for them to recharge repeat process. After a few times the batteries are boat anchors.

Moral to the story after you run through a couple of designs you quickly notice Panel Wattage = Inverter Wattage, So now work that both directions.

You have a 2000 watt inverter. That requires a 800 AH 24 volt battery. A 24 volt 800 AH battery requires a 2000 watt panel system with a 80 amp MPPT controller to provide a perfect C/10 charge current of 80 amps to the batteries

You have a 600 watt panel operating a 24 volt battery that generates 25 amps of charge current which means you need a minimum 200 AH battery. A 24 volt 200 AH battery can run up to a 600 watt inverter.

None of what you have falls within acceptable operating limits of your equipment. What are you going to do?

**benhchang** · 10-24-2014, 05:47 PM

Please read above for my solar purpose

Originally posted by Sunking

Batteries have internal resistance, when current flows through resistance develops voltage drop, or in the case of a battery Voltage SAG. With low voltage systems you wan tto limit voltage and power losses to 3% or less. So between inverter and battery 3% of 24 volts = .72 volts. Not much to work with and you also have loss on the wire to deal with to keep that 3%. That means you have to assign some value to the battery like 2 of the 3% that include the wire. To do that with a FLA battery limits the maximum amount of current they can supply without excessive voltage sag is C/8 where C = the battery Amp Hour rating to yield 2% limit. C/8 on a 100 AH battery is 12.5 amps maximum. A 2000 watt inverter of say 80% efficiency at full power draws 2500 watts from the battery and at 24 volts = 104 amps. If you were to fully load th einverter down to full power with you battery would instantly trip off line from under voltage despite the battery being fully charged up. So if max is C/8 and you need 93 amps then you know at a minimum you need 8 hours x 104 amps = 832 AH minimum requirement. Got it. I will get 4 battery banks with min 832AH

Here is the other kicker. Your 2000 watt inverter is going to draw power while sleeping doing nothing. It can be as high as 100 watts doing nothing. That means your inverter setting there doing nothing all day will completely discharge your 24 volt 100 AH batteries. Wait 5 or 6 days for them to recharge repeat process. After a few times the batteries are boat anchors. Understood. My intention is to turn the inverter off when not in use

Moral to the story after you run through a couple of designs you quickly notice Panel Wattage = Inverter Wattage, So now work that both directions. The reason for the larger 2000 watt inverter is primarily for AC mounted on the trailer roof

You have a 2000 watt inverter. That requires a 800 AH 24 volt battery. A 24 volt 800 AH battery requires a 2000 watt panel system with a 80 amp MPPT controller to provide a perfect C/10 charge current of 80 amps to the batteries Please note that this is NOT an off grid system. As I mentioned that at home when trailer is parked most of the time, solar will be grid tied to 1000 watt inverter. When I am on the road at the race track, the solar panel will be connected to the 2000 watt inverter to the battery bank.

You have a 600 watt panel operating a 24 volt battery that generates 25 amps of charge current which means you need a minimum 200 AH battery. A 24 volt 200 AH battery can run up to a 600 watt inverter.

None of what you have falls within acceptable operating limits of your equipment. What are you going to do?

**Sunking** · 10-24-2014, 06:32 PM

Good luck to you Ben.

Solar Wire Calculation with 6 24v 136 watts uni-solar panels

Solar Wire Calculation with 6 24v 136 watts uni-solar panels

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