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Off grid fridge project in west africa
#1
As there are frequent power outages where I live in west africa, I would like to try setting my fridge off grid.
(I am also very keen to learn about solar and batteries)

The first guidance I am looking for is about the type of cells to use in the battery pack: ambiance temperature is fairly high there, around 30 degrees C (from 26 to 35), so are LiFePO4 cells much better than regular 18650 Li-ion (eg Panasonic NCR18650PF) in this case?

I am not too price sensitive, I am looking for the safest, best long term solution.

One other issue is that I cannot ship anything there (no service and customs issues), so I plan to ship everything to the uk where I regularly go, and bring it back by plane, where there is usually a 160wh limit per battery size. So I can only go for the smaller LiFePO4 (40Ah).

Thanks for the help!
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#2
If you dont have a price limit and safety in mind then its LiFepo 10x before you go LiIon.
LiFePoe4 have alot higher cycle count and you cant kind of not get them to start a fire Smile

LiFePo4 bricks would be nice for your task and those also are better suited for 12V system if thats your plan. LiIon is either 24V or 48V+. Not 12v...
Korishan likes this post
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#3
Thanks.

So I am now looking at buying Winston 3.2V/40Ah cells.

I was initially thinking of going with a 24v battery, as I understand it is more efficient and will be easier to scale up if I later need more power. Are there any advantages of 12v apart from the fact that you can tune more easily the number of cells and solar panels?

Given that locally I have only found 24v/250W panels, I am now hesitating between 3 panels at 24V and a 12V battery, or 4 panels at 48V and a 24V battery.
My fridges uses about 1.4kwh/day, and from the solar map I am supposed to get between 3.16 and 4.26 kwh/day per kw depending on the season, so 3 panels sounds enough, which would plead in favor of a 12v battery, with 4s6p for a total of 3kwh.

Any advice for a MPPT charge controller? The outback flexmax sounds quite popular, does the efficiency and features justify the relative high price?

And finally any suggestion for a bms?

proabably too many questions!
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#4
It depends on price again. In some places 12V systems are cheaper but if you need the output go 24 or even 48V.

Outback is nice stuff. If its worth the extra money im not sure. The efficiency is not that much better but the guarantee is in many times
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#5
I finally found time to make some progress on my system.
It would be much appreciated if someone can take a quick look in case I have missed anything, in particular safety wise.
I will use:
- 3 275W pv panels (rated 31V and 8.9A)
- MPPT PCM60X charge controller
- 16A && 32A DC breaker (https://www.ebay.co.uk/itm/382128784099)
- 16s 40ah LiFePO4 battery, with batrium watchmon4 bms
- 80A fuse on the battery (https://goo.gl/RqfCrx)
- 2kw inverter (https://goo.gl/g2fxP1)
- 4mm2 cable from pv to charge controller
- 16mm2 cable between battery/charge controller/inverter
- 10mm2 cable for grounding pv panels and charge controler

see attached schema



Is a shunt trip advised for my system? (I have not ordered the batrium expansionBoard...) 
I am not sure I fully understand in what situations it would help vs the fuses and breakers.

Thanks!
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#6
I have used the breakers from here as they combine postage so a few breakers turn out quite cheap, they do work well :
https://www.aliexpress.com/item/2P-32A-D...39138.html

The polarity and current direction of the DC breakers is important so the feed / surege source is wired into the top, i.e. battery pack in the top, inverter in the bottom.

Suggestion / Option
With the 275W panels, buy an extra panel and use a PWM controller, change to 15s and charge to 4V max.

Overall you should get more energy at a lower cost with the extra panel and a cheap PWM controller and the PWM controller should be more reliable over time. Less costly to replace as well..

The Vmp from 2 panels in series is 62V (drop 1V for inline diodes) so 61V. Drop another V for cable losses and you end up at 60V. 15s at 4V per cell tops out at 60V...

Sometimes MPPT route can be more costly with smalleer systems than a good panel voltage and a cheap PWM controller.
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#7
some pictures of the project:
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#8
Your wiring diagram looks good except near PV1, PV2, PV3 you only need 1x fuse there.
In the blue battery box, take care that the body of cellmons do not touch anything else - the black paint is not full insulation & they could short out, eg to another cellmon, post or copper cell link, etc.

Try to have some tilt with your solar panels so dust gets washed off - otherwise dust will build up. 5 degrees is enough.

I hope the round table is strong enough - batteries are very heavy!
Running off solar, DIY & electronics fan :-)
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