Off grid solar system design

[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.

[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]

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.

[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]

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!

[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]

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

[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]

Thank you,
As a solar fanatic, you should know that array never produce the maximum wattage they are rated for, that's why I degraded their performance to 70% instead of leaving it at 100% when calculating the charge controller amperage. I think my math is right and I'm not sure about yours.

Here I tried to sum up my daily consumption from my array. The ACs are mini-split with an inverter.
AC#1: 220V, 11.8A => #hrs of use 8 a day => 220*11.8 = 2596W

AC#2 :220V, 5.9A => #hrs of use 8 at night => 220*5.9 = 1298W

Refrigerator: 110V, 5A => #hrs of use 8 a day => 110V*5 = 550W

Freezer 115V, 2A =>#hrs of use 6 => 115V*2 = 230W

4 fans with total consumption of 250W => #hrs of use 6 a day

I have don't know yet the consumption of the water pump but, I can safely assume it's going to around 1-2KWh and it will run for maybe 6 hrs. These are the heavy equipment I will have on the system and some of them are being used just during a day.

I can adjust my direct consumption from my array during a day to anywhere between 5 and 7KWh. My goal is to harvest at least 5 to 7KWh from my array.
I'm also planning to use only Victron products because I do have a local Victron dealer.

[Mike90250]

A half HP water pump will pretty much consume about 1kw when running. That's what my XW logs my pump at. It is not 400w as simple math / hp cac would assume, because simple math leaves out motor losses and power factor, which the XW actually measures.

[Sunking]

As a solar fanatic, you should know that array never produce the maximum wattage they are rated for, that's why I degraded their performance to 70% instead of leaving it at 100% when calculating the charge controller amperage. I think my math is right and I'm not sure about yours.

My math is spot on perfect right out of engineering design best practices textbook. Your math is make believe. Every bit of it is wrong. Example

AC#1: 220V, 11.8A => #hrs of use 8 at night => 220*11.8 = 2596W

Is pure make believe math. WATT HOURS = Watts x Hours. 2596 watts x 8 hours = 20,768 Watt hours. More than most homes in the USA use in a day.

Now here is the reality. Just to run that AC unit on solar will require a 5000 Watt Panel System, 100 amp controller and a monster sized 48 volt 2000 AH battery.
I can't help you as your goals are not even realistic. You will fail if you proceed and loose a lot of money doing it. I am no Solar Fanatic, I am a professional engineer with 40 years experience.

[Diallodjeri]

AC#1: 220V, 11.8A => #hrs of use 8 at night => 220*11.8 = 2596W. Actually, in this math, I just wanted to show that I will be using 2596W for 8hrs meaning it will be 8 x 2596W. Another thing is that I mixed up which AC would be used at night versus a day. AC#1 220*11.8 *8 = 20,768 would be used only during a day. AC#2, 220*5.9*8 = 10,384 would be used at night.

On the other hand, I'm assuming you agree with me on the deration rate of the panels output to 70% because of the high temperature and dust.

[SunEagle]

Thank you,
As a solar fanatic, you should know that array never produce the maximum wattage they are rated for, that's why I degraded their performance to 70% instead of leaving it at 100% when calculating the charge controller amperage. I think my math is right and I'm not sure about yours.

Here I tried to sum up my daily consumption from my array. The ACs are mini-split with an inverter.
AC#1: 220V, 11.8A => #hrs of use 8 a day => 220*11.8 = 2596W

AC#2 :220V, 5.9A => #hrs of use 8 at night => 220*5.9 = 1298W

Refrigerator: 110V, 5A => #hrs of use 8 a day => 110V*5 = 550W

Freezer 115V, 2A =>#hrs of use 6 => 115V*2 = 230W

4 fans with total consumption of 250W => #hrs of use 6 a day


I have don't know yet the consumption of the water pump but, I can safely assume it's going to around 1-2KWh and it will run for maybe 6 hrs. These are the heavy equipment I will have on the system and some of them are being used just during a day.

I can adjust my direct consumption from my array during a day to anywhere between 5 and 7KWh. My goal is to harvest at least 5 to 7KWh from my array.
I'm also planning to use only Victron products because I do have a local Victron dealer.

You actually forgot to multiply the load wattage by the # of hours it will run.

That AC#1 calculates to 2596w x 8 hrs = 20768 watt hours = 20.8kWh
AC#2 comes to 1298w x 8 hr = 10384wh = 10.4kWh
Frig comes to 550w x 8 hr = 4400wh = 4.4kWh
Freezer comes to 230w x 6 hr = 1380wh = 1.4kWh
Fans comes to 250w x 6 hr = 1500wh = 1.5kWh
water pump estimated at 1-2kWh

Add all that up and you will come close to 40kWh so please run a calculation based on that number or higher since you didn't include any losses or small wattage loads.

[Diallodjeri]

You actually forgot to multiply the load wattage by the # of hours it will run.

That AC#1 calculates to 2596w x 8 hrs = 20768 watt hours = 20.8kWh
AC#2 comes to 1298w x 8 hr = 10384wh = 10.4kWh
Frig comes to 550w x 8 hr = 4400wh = 4.4kWh
Freezer comes to 230w x 6 hr = 1380wh = 1.4kWh
Fans comes to 250w x 6 hr = 1500wh = 1.5kWh
water pump estimated at 1-2kWh

Add all that up and you will come close to 40kWh so please run a calculation based on that number or higher since you didn't include any losses or small wattage loads.

I didn't actually forget to multiply the load wattage by the # of hours it will run, but I just assumed people will know these numbers are meant to be an hourly usage. I guess I did not make very clear my explanation. The big AC 2596*8 = 20,768W will only run whenever possible only during a day and the small one 1298*8 = 10,384W will run on the battery at night.

[SunEagle]

I didn't actually forget to multiply the load wattage by the # of hours it will run, but I just assumed people will know these numbers are meant to be an hourly usage. I guess I did not make very clear my explanation. The big AC 2596*8 = 20,768W will only run whenever possible only during a day and the small one 1298*8 = 10,384W will run on the battery at night.

So all that data does not determine how many watt hours you will consume each day.

Try to remember that going off grid means you are relying totally on your batteries because the sun will not be shining every day. So your battery system will have to provide the entire amount of watt hours you plan on using.

So my question is what loads will you use each day and for how many watt hours. Once you total that amount you will come close to sizing your battery system. Once you have that determined you size your panel wattage.