AGM vs LiFePO4 cost per kWh

[ssean]

Hi everyone,

I live in Puerto Rico. We have very expensive grid power here, in addition to a very unreliable power grid.

I'd like to design a battery backup system.

Initially, this will be charged from the grid, and in the event of a power failure, a backup generator. Once I find a home to purchase, I will be installing solar panels.

I've been looking at various battery options.

1) Rolls S6-460AGM-RE - 415AH AGM batteries @ 6 volts. @ $500 each
2) AliExpress 280AH @ 3.2V @ $100 each
3) SIMPLIPHI POWER PHI 3.8KWH LITHIUM (LFP) BATTERY, 48V @ $2695 each

Do these numbers look correct?

Brand	ah	volts	qty required for 48v system	price each	total cost @ 48 v	kwh @ 48v	$/kwh
Rolls AGM	415​	6​	8​	550​	4400​	19.12​	$230.126​
Ali Lifepo4	280​	3.2​	15​	100​	1500​	13.34​	$112.444​
Simplifi	75​	48​	1​	2695​	2695​	3.6​	$748.611​

 

[gnubie]

As paper figures go, that's all correct but you should add in an expected number of cycles column. Once you add that you'll see your lifetime cost change a lot. The Rolls AGM would only be 19.12kW if you take them down to dead flat. That'll work but they won't last you all that long (check the spec sheet) while the lifepo4 will still be trundling along nicely.

Don't forget the BMS for the LiFePO4 cells too.

 

[Forbisher]

16 of the 3.2V 280Ah cells for a nominal 48V battery.
You have 15 cells by mistake.

 

[snoobler]

I vigorously recommend you learn to properly maintain a flooded cell battery. I own 4X S-605 6V, and they are indestructible. The FLA line have better cycle life than the AGMs. The 4000 series have a 2000 cycle life at 50% DoD. The 5000 series have a 4250 cycle life at 50% DoD. AGMs are only about 1000.

You want to pick something from their Renewable Energy line:

https://www.rollsbattery.com/wp-content/uploads/2019/11/RE-sheet.pdf

For a fair comparison, you need to select high quality LFP from a reliable supplier, not the cheap Ali ones.

When designing a battery backup, you should size it for the loads you anticipate having to run and their run times, so this stage may be a little premature.

 

[Forbisher]

For a fair comparison, you need to select high quality LFP from a reliable supplier, not the cheap Ali ones.

When designing a battery backup, you should size it for the loads you anticipate having to run and their run times, so this stage may be a little premature.

To be fair to his wallet to get the most Kwh per $ and more cycles than lead acid there is nothing wrong with buying DIY LFP but add on the cost of a BMS.
Those cheap Ali cells would be my choice.