Off grid solar system design

[Sunking]

The battery bank voltage is going to be 48V. To get the right size of a charge controller, I do this math: (6240*0.7) / 48 = 91*1.25 = 113.75 So my charge controller should have an output amperage of at least 120A.

I told you already your math for the controller is wrong.

Controller Current = Panel Wattage / Battery Voltage.

6240 ] 48 = 130 amps. You are going to need two expensive controllers you don't need and more battery to handle it. . So the reason you are not getting a lot of help is because your numbers are way off and will not work. I cannot help you any more than I can tell you how to get to the USA on a motorcycle from Africa. Not going to happen

But here is what I will say based solely on what size battery I think you have based on 300 pounds @ 48 volts. Your battery has to be on the order of 250 to 300 AH. At 48 volts in your area only requires 1200 to 1500 watts of power and a 30 amp controller. At 6000 watts requires a much larger 1200 AH battery.

Go from there.

[Diallodjeri]

Please folks I need your suggestion. I made some changes to my system after receiving much input and hopefully my math got much closer to reality.

Astronergy panels (260W, 8A, and 30V) in series of 4 => 260w*4 => 1040W, 8A and 120V
6 parallel of those 4 panels put in series: 1040W*6 = 6240W, 120V and 32A
The battery bank voltage is going to be 48V. To get the right size of a charge controller, I do this math: (6240*0.7) / 48 = 91*1.25 = 113.75 So my charge controller should have an output amperage of at least 120A.

FYI: There is 250V charge controller on the market:

https://www.victronenergy.com/solar-...250-85-250-100

[MichaelK!]

Let's start with the panels. Astronergy panels (260W, 8A, and 37V) in series of 6 => 260w*6 => 1560W, 8A and 222V. Where does the 37V number come from? Is it on a nameplate that says Voc=37.0V? That is NOT the voltage the panels will operate at. They operate at the Vmp, which I would guess is about 30.5V. That's mistake #1. Second, which controller are they going to feed? Most mainstream controllers have a max voltage of 150V. Mine is 200V. So, six panels in series producing a Voc of >222V is going to destroy most controllers out there. The numbers are important. Mistake #2. Unless you have a special high voltage controller, you are going to make very expensive mistakes. And, I'm guessing that replacement service in most parts of Africa are not going to be very speedy? Some people here get impatient because of stary-eyed newbies that think solar is the solution to everything. They learn reality the hard way. Just about every day, someone still has to explain why a 100W solar panel can't power a 100W load.

[Diallodjeri]

Thanks a lot for your help. I need to provide more information about my system. The system is not going to be installed here in the States, but in the part of Africa where the temperature never gets below 64F, so there is no concern there other than it can get above 100F in the summertime.
The system in a sense is an off-grid because we don't have such an option of a grid-connected system, but I still can use the grid whenever I need to. I just need to unplug from solar power and plugin to the grid manually whenever necessary. In that part of the world it is almost useless to be connected to grid because you only have power 10 to 16 hrs a day.

The battery size I'm planning on getting is 8KW or 16KW Lion @ 48V

The loads that are going to be on the system are couple AC, one freezer, one refrigerator, a water pump with a total consumption of 7kW/h all of them being used simultaneously which is never going to be the case. Some of them are going to be used during the day while others only at night.

I just want to make sure I do understand the technical details of the system I'm planning to build.

Thank you!

[Mike90250]

Without knowing details of your Loads, your proper battery size cannot be arrived at. Once you know the battery size, you calculate how much solar and charge controller you need to recharge it and what size backup generator. ( unless you never get snow or clouds )

Beware, some states now have limits for Li battery bank sizes, San Francisco has a 20kwh limit before needing to meet stringent fire code rules.

https://pv-magazine-usa.com/2018/08/07/challenges-for-batteries-in-the-california-fire-code/

https://www.claimsjournal.com/news/national/2018/05/18/284771.htm

So, once your Li system goes much over 400ah @ 48V, you get to use the new code. Conveniently, this is about the size of many Wall of Power installs. Sadly, it's only going to run the average grid house 12 hours, or less. Regardless about some members enthusiastic support of Li batteries, their dangers in the hands of neophytes is no longer being ignored and new codes are being developed to restrict the sizes of many new installs. The insurance companies are getting tired of the expensive claims, and the hazmat cleanup of Lithium battery fires.

The other unspoken con of off grid Li batteries, is they don't work well when cool, and when cold, can't be recharged.
Charging amps must be reduced below 40F, cease all charge at 33F (actually goes to 32, but if you get it wrong, you have killed your batteries)
When packs are taken out of cars, everyone assumes we are not charging/discharging fast, so the thermal management system is discarded. Come winter, you can realize your mistake.

[Diallodjeri]

Thank you for your reply.
Your response would have been much more helpful if you could tell me why my measurement was wrong. FYI: I don't have a 4000 pound battery, I have 300 pounds lithium ion battery so that part is not really a concern that's why I did not mention it.

[Sunking]

Everything is wrong. Your units of measure are wrong.

Example MPPT Controller Current = Panel Wattage / Battery Voltage. You are way off and a lot more nasty surprises waiting for you.

Second you will need a permit from the Employment Prevention Agency and you local Fire Department along with a building with spill containment in the event your 4000 pound $16,000 battery leaks. Even more fun in store for you in 3 to 5 years when you get to dispose and replace the batteries. You will have to have a licensed battery contractor install and remove them to meet EPA an dlocal FD requirements. Never going to happen.

[Diallodjeri]

Hello folks,
I hope you guys can help me rectify anything that is not going to work as intended in this diagram. Here's the set up I want to adopt with my off-grid system:
Astronergy panels (260W, 8A, and 30V) in series of 4 => 260w*4 => 1040W, 8A and 120V
6 parallel of those 4 panels put in series: 1040W*6 = 6240W, 120V and 32A
The battery bank voltage is going to be 48V. To get the right size of a charge controller, I do this math: (6240*0.7) / 48 = 91*1.25 = 113.75 So my charge controller should have an output amperage of at least 120A. This is my basic understanding of how solar system work.
Please tell me if something is wrong with this picture.
Thank you.

Please folks I need your suggestion. I made some changes to my system after receiving much input and hopefully my math got much closer to reality.