Please review my off grid solar diagram

[chandlox]

I am building my first system. It is for a small off-grid cabin. I spent the last two weeks learning all that I can to piece this together. I am hoping for some reviews of my plan. My primary concern is safety. It all seems to check out in my head, but You dont know what You dont know. All advice, critique and opinions are welcome.

 

[chandlox]

The plan is to isolate the pv array, the controller and the inverter from the system when i run the back up generator. The generator and converter are isolated under normal operation.

 

[chandlox]

Here is a list of the main components

Renogy 100w panels
Renogy 30a li pwm charge controller
Victron 12/1200va inverter
progressive dynamics pd9260c converter
Everstart 27DC 108 ah lead acid
3500w generator

 

[chrisski]

The 4 parallel panels each need overcurrent protection

If at all possible, hardwire the inverter

This is the wire chart I use; a 1200 watt inverter could see 140 amps at low voltage cutoff. 2 AWG may not be enough

 

[chandlox]

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[chandlox]

The 4 parallel panels each need overcurrent protection

If at all possible, hardwire the inverter

This is the wire chart I use; a 1200 watt inverter could see 140 amps at low voltage cutoff. 2 AWG may not be enoughView attachment 213595

From the specs on Victron 12/1200va inverter, looks like 2AWG is maximum size accepted. I did order inline 10amp fuses for each panel and read about why I need overcurrent protection in parallel panels. Thanks

 

[chrisski]

From the specs on Victron 12/1200va inverter, looks like 2AWG is maximum size accepted. I did order inline 10amp fuses for each panel and read about why I need overcurrent protection in parallel panels. Thanks

I missed it was a 12/1200 va inverter. That is 1000 watts constant. 2 AWG will be fine.

 

[littleharbor2]

8 strings of lead acid batteries will be impossible to maintain balanced charging/load, Read up on this link regarding battery wiring. You might also look into 2 volt batteries if you need that large of a 12 volt battery. http://www.fullriver.com/product/DC1150-2.html

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

 

[mikefitz]

Eight 108Ah batteries in parallel idealy need a higher charging current than the maximum of 20 A via the PWM controller. The generator at 60 amps is better and may be needed to bring the batteries to full absorbtion state. There could be issues with the batteries not being fully charged thus reducing service life.
Battery pack connections,

 

[jzampieron]

Handful of comments, thoughts and recommendations.

• Add DC Surge suppression on the PV lines coming into the charge controller after the 30A breaker.
• Consider using a fused combiner at the array with the DC surge suppression. Midnight solar has a few to choose from.
• Make sure all your breakers and fuses are DC rated. AC rated only is not sufficient.
• Is this a 120V or 120V/240V split phase system. I would note that on the design somewhere.
• Include some kind of surge suppression on the generator input and show a breaker/(fused) disconnect between the AC to DC rectifier/charger, which I think is mislabeled as a converter. It's code today to include it in the AC panel and most load center mfgs with plug on neutrals have a snap-in surge suppressor. Just make sure its workable at 120V single-phase if that's your design. Most are 120V/240V split phase.
• Think about grounding in your system. Since this is off grid you'll need a neutral-ground bond somewhere. Check your generator to see if the frame is bonded or not. If it is, that's your bond point and don't bond at the panel. Keep the grounds in the AC panel separate.
• Show DC Fuses between the battery array and the Bus bar. You should have a fuse as close to the batteries as possible.
• Consider carefully how you are going to wire the batteries in parallel to avoid overloading the wiring on the battery closest to the bus bars. It would be better to go from each +/- terminal directly to the heavy duty bus bars, but that might be too much wiring.
• The 100A breaker between the bus bars and the converter is a bit large for 1kw, but probably OK.
• Putting a 40A breaker on 10AWG for the charge controller is a bit too much.
• Make sure you check your specific wire amp-acities and temp ratings. Generic THHN/THWN/XHHN/XHWN will be lower than higher quality cable such as Arctic UltraFlex Blue, but also cheaper.

Both Will Prowse and David Poz have some YouTube videos on battery wiring. Worth watching.


Disclaimer: I am an engineer, but I am not your engineer and this is not professional advice.

 

[chandlox]

8 strings of lead acid batteries will be impossible to maintain balanced charging/load, Read up on this link regarding battery wiring. You might also look into 2 volt batteries if you need that large of a 12 volt battery. http://www.fullriver.com/product/DC1150-2.html

SmartGauge Electronics - Interconnecting multiple batteries to form one larger bank

Thanks, I digested the material. I will wire the batteries via one of the approved methods, im favoring using the opposite negative than the positive, or wiring them all directly to a bus bar with equal length wire. Truthfully i dont think I need the 864ah battery bank, it just sounded nice, lol. Ive reduced the design to 6 batteries.

I think in your recomendation for 2 volt batteries you are implying i could use them in series to build 12v strings, and maybe have two strings parallel for easier balancing.

Are 2 volt batteries stacked to 12v superior to a single 12v battery? What causes this, is it inherent to their design?

 

[Hedges]

Individual 2V batteries you could charge separately, rather than "equalizing" by over-charging others in series to bring up the lowest.

A single string of batteries or cells minimizes issues with parallel batteries. But it also means if one string fails you have zero.

You can select larger capacity battery or cell to make it 1 string. At some point the battery would be too heavy to move (like a forklift battery). 1x 12V, 2x 6V, 3x 4V, 6x 2V. Any of those can be made out of 100 lb. to 150 lb. batteries, something you can move with a dolly.

Higher voltage is another way to get more capacity, e.g. 4x 12V in series for 48V.
But your 1200W inverter is a reasonable size for 12V system.

If you connect 2 or 4 batteries in parallel (or 8), there are ways to connect diagonally, then diagonally again, maintaining perfect match. So I would suggest 4 not the 6 batteries you're considering. Better though to have 4x 6V.

You can use wet cell FLA, like Trojan golf cart, or Rolls Surette for premium.
But it is said you will kill your first battery bank. So best to start cheap.

You can use AGM. My bank is 8s 6V 405 Ah SunXtender, for 48V 20 kWh.
AGM is zero maintenance, but must be charged correctly. And sufficiently as mentioned by others; need enough PV. More freeze resistant, essentially freeze-proof fully charged. Quality batteries have about 10 year float life, and 700 cycles.

LiFePO4 is another option. Many advantages, including OK left partially charged. But can't be charged below freezing.


You can get a small all-in-one, 24V or 48V, with MPPT charger.
I'm not sure I see the reason for using components, in a low wattage system with large battery.

 

[chandlox]

Eight 108Ah batteries in parallel idealy need a higher charging current than the maximum of 20 A via the PWM controller. The generator at 60 amps is better and may be needed to bring the batteries to full absorbtion state. There could be issues with the batteries not being fully charged thus reducing service life.
Battery pack connections,
View attachment 213608

Thanks for the input. I am changing the wiring method on the battery bank.

Also, I read that ideally the charger amp rating should be approx %10 percent of the battery bank Ah. So I now understand why you made your comment. To somewhat remedy the situation, im reducing the bank to 108ah x 6 batteries. Im not ready to buy a quality mppt or add more panels to improve my PV input. I figured this way I could run the generator at least once a week (maybe more with cloudy days) and have the proper amps to bring the batteries to full absorption.

I choose the pwm because I read that they are more reliable (although less effficient) than mppt. I plan upgrading down the road, but id like to grasp the basics before doing the research for the ideal mppt controller and committing.

 

[Gold Country Russ]

I just looked up the panel and see the operating @ 20.4V & 4.91A. If I were doing it, I would wire the panels in series-parallel for 40.8V & 9.82A and use 14Ga to the charge controller. If you use 24V (16.6A max out) after the charge controller 12GA would be fine to the buss. I would find a used 24V pallet jack, floor scrubber, or similar battery on Craigslist or something. Using 24V components with 1/2 the amperage makes everything generally smaller and cheaper especially cable. Going to 48V is a good option too.

 

[littleharbor2]

Thanks, I digested the material. I will wire the batteries via one of the approved methods, im favoring using the opposite negative than the positive, or wiring them all directly to a bus bar with equal length wire. Truthfully i dont think I need the 864ah battery bank, it just sounded nice, lol. Ive reduced the design to 6 batteries.

I think in your recomendation for 2 volt batteries you are implying i could use them in series to build 12v strings, and maybe have two strings parallel for easier balancing.

Are 2 volt batteries stacked to 12v superior to a single 12v battery? What causes this, is it inherent to their design?

2 volt batteries are generally high amp hour rated for building larger banks with minimal parallel strings.
Yes, series wire 6 at a time for 12 volts nominal. You have gotten plenty of good info from others here so no need to cloud the waters with more of the same.

 

[chandlox]

Individual 2V batteries you could charge separately, rather than "equalizing" by over-charging others in series to bring up the lowest.

A single string of batteries or cells minimizes issues with parallel batteries. But it also means if one string fails you have zero.

You can select larger capacity battery or cell to make it 1 string. At some point the battery would be too heavy to move (like a forklift battery). 1x 12V, 2x 6V, 3x 4V, 6x 2V. Any of those can be made out of 100 lb. to 150 lb. batteries, something you can move with a dolly.

Higher voltage is another way to get more capacity, e.g. 4x 12V in series for 48V.
But your 1200W inverter is a reasonable size for 12V system.

If you connect 2 or 4 batteries in parallel (or 8), there are ways to connect diagonally, then diagonally again, maintaining perfect match. So I would suggest 4 not the 6 batteries you're considering. Better though to have 4x 6V.

You can use wet cell FLA, like Trojan golf cart, or Rolls Surette for premium.
But it is said you will kill your first battery bank. So best to start cheap.

You can use AGM. My bank is 8s 6V 405 Ah SunXtender, for 48V 20 kWh.
AGM is zero maintenance, but must be charged correctly. And sufficiently as mentioned by others; need enough PV. More freeze resistant, essentially freeze-proof fully charged. Quality batteries have about 10 year float life, and 700 cycles.

LiFePO4 is another option. Many advantages, including OK left partially charged. But can't be charged below freezing.


You can get a small all-in-one, 24V or 48V, with MPPT charger.
I'm not sure I see the reason for using components, in a low wattage system with large battery.

Great overview of batteries, thanks.

I considered a 24v system but I have the progressive dynamics pd9260 in a box brand new, ordered it three years ago as a backup for rv, but never used it. Its the 12v output model. So i figured its a nice way to use my back-up generator to juice the system when the sun doesnt shine.

Yeah, 6v batteries do look like a better option, just the cost is high for quality ones. Yeah, cheap batteries first time, most likely they will be abused or misused. Im able to get the 12v deep cycle 108ah for $110 out the door, so its hard to beat. Even if they only give me half the cycles its a wash.

2, 4 or 8 but not 6 in parallel? Theoretically, could I just make all the battery leads the same length and be balanced? I could not find any diagrams of wiring 6 parallel, but it seems a few forum membs said they do it in other threads.

I attached my idea of what 6 parallel would be. Tell me if im crazy, and ill just do 4 diagonal. Being cheap batteries im trying to keep DOD as high as possible.

 

[Hedges]

That's probably close for the battery matching.
Don't know how much difference it makes, but you could use busbars and 3 cables of equal length for each 3 batteries.

Usually we think of a copper plate with bonds. The idea of using Polaris came to me, and another forum member is already doing that. Some Polaris let the cable connect from either end.

By selecting one large enough that the insulation slips through, you can put Polaris on the middle of a cable, connect both sides. In that case 4x Polaris with 2 setscrews could join them. With enough setscrews, you could eliminate the other busbars.