LiFePO4 - The future for off-grid battery banks?

[steveg]

So I'm comparing the cost of AGM deep cycle batteries with LiFePO4 batteries, and it seems that LiFePO4 will win out.

Hear me out...

Goal - Provide 1 kW of power.

Assuming 80% DoD for LiFePO4 and 20%DoD for AGM (Which will give us approximately 5 years for each type of battery), we will need:

x24 3.2V, 16AH of Headway LiFePO4 batteries for a 12.8V, 96AH pack (1.28kW) and

x2 12V, 255AH, Concorde AGM Groupe 8D batteries for 12V, 510AH pack (6.12 kW).

since 80% DoD of 1.28 kW = 1.0 kW and
20% DoD of 6.12 kW = 1.2 kW

Price for x2 Groupe 8D Concorde batteries ~ $1,200
Price for x24 Headway LiFePO4 batteries ~ $600

.. not to mention x24 LiFePO4 batteries only weighs about 30lbs.

I guess the price of the Battery Management System for the LiFePO4 cells and the complexity of the system far exceeds that of the AGM batteries for now. Perhaps the technology is still immature.

Are there any technical barriers from preventing the use of LiFePO4 batteries as solar battery banks? Maybe the discharge rate (100A)?

Hi!

I have an off-grid home with LiFePO4 cells and did this for the *exact* reasoning above - I use it for cooking and all power for my home. I designed the system around the cells, and used a Morningstar MPPT regulator in 'custom' mode.

My pack was US$7000 and came with BMS it is 300Ah 51.2V (nominal 48V)

Any questions?

[Sunking]

Solarnoob you are not comparing apples to apples.

[Mike90250]

....

I guess the price of the Battery Management System for the LiFePO4 cells and the complexity of the system far exceeds that of the AGM batteries for now. Perhaps the technology is still immature.

Are there any technical barriers from preventing the use of LiFePO4 batteries as solar battery banks? Maybe the discharge rate (100A)?

That's the problem, the Battery Management System (BMS). You need:
Main battery charger controller
BMS at each cell
They all have to talk to each other, and then have to be UL listed, if you want to retain insurance coverage in your home. None are, yet.

If I wanted to convert to LiFePO4, it'd only take a few set points in my charger, but the BMS can't easily be accounted for.

In a 48V/6KW system like I have, full power is only 125 ADC. 2 parallel sets of batteries should handle that fine. Adding Air Conditioning, would likely need 2 more banks, creating a 400A 48V system. Any of the 96 BMS modules going bad is going to lead to a bad experience.

[solarnoobie]

or i just found these on EBay -

Thundersky - 2.5 - 4.25V, 100ah LiFePO4 batteries - $140 each.

So x4 of them will give us about 1 kW, at a cost of $560.

[solarnoobie]

So I'm comparing the cost of AGM deep cycle batteries with LiFePO4 batteries, and it seems that LiFePO4 will win out.

Hear me out...

Goal - Provide 1 kW of power.

Assuming 80% DoD for LiFePO4 and 20%DoD for AGM (Which will give us approximately 5 years for each type of battery), we will need:

x24 3.2V, 16AH of Headway LiFePO4 batteries for a 12.8V, 96AH pack (1.28kW) and

x2 12V, 255AH, Concorde AGM Groupe 8D batteries for 12V, 510AH pack (6.12 kW).

since 80% DoD of 1.28 kW = 1.0 kW and
20% DoD of 6.12 kW = 1.2 kW

Price for x2 Groupe 8D Concorde batteries ~ $1,200
Price for x24 Headway LiFePO4 batteries ~ $600

.. not to mention x24 LiFePO4 batteries only weighs about 30lbs.

I guess the price of the Battery Management System for the LiFePO4 cells and the complexity of the system far exceeds that of the AGM batteries for now. Perhaps the technology is still immature.

Are there any technical barriers from preventing the use of LiFePO4 batteries as solar battery banks? Maybe the discharge rate (100A)?