LiFePO4 - The future for off-grid battery banks?

[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)?

[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.

[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.

[Sunking]

Solarnoob you are not comparing apples to apples.

[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?

[russ]

@ steveg - Welcome to Solar Panel Talk!

We would love to hear more about your system!

Russ

[steveg]

My Off-Grid Home

Hi Russ,

We have just moved into our new off-grid home - we went off-grid because we wanted to - there is power to our street and is only 130metres away from the house.

We have solar hot water and wetback fireplace - we use the fireplsace to cook in winter when there is not enough power to use the oven and stove top (induction cooking)

We are a family of 5 my kids are 16,13,10 so plenty of internet use and TV - we have a 42" LCD tv we use in the evenings and weekend mornings for cartoons.

The house is 320m^2 including a triple garage - due to regulations we spent a large amount on insulation and double glazing.

In winter we have a power footprint of 5.5 to 6kWh using the fireplace to cook and in summer 12-15kWh per day, when we also use the dishwasher and water the garden (water pump)

I have 4kW of solar panels and have the house designed to face North (southern hemisphere - New Zealand)

I have a 7kW inverter which runs all our stuff - and the battery pack.

As soon as I figure out how I'll post pictures of the house and system.

it is early/mid spring here, so on a sunny day we get a full charge from the night before by about 11am (6-7kWh) and the extra while the sun is out my wife burns power in any way she wants to... (hence the 12-15kWh)

The charge efficiency of LiFePO4 is very high and we live in the top 30-40% of the battery so I expect my lifetime of the cells to be high.

[steveg]

also ...

Addendum : you may notice I am one panel shy on the bottom row - due to a mis calculation one of the bathroom vents is where my panel should be - we will have this fixed in due course, so I have 3500W solar hooked up right of this minute - the last 2 panels once the vent is moved.

The top row is 200W panels of Suntech the lower row is 250W 'no name' brand with Suntech wafers that I imported myself from China - the battery pack came from the same folks, to my spec (3x100Ah in parallel) x 16 in series

The BMS prevents overcharge and overdischarge - there is some weak balancing in the pack to bring the voltages over time to even values.

Been running now for 5 months.

Also - we have insurance and have passed code of compliance for our LED lighting internally (new technology that councils dont trust especially running under insulation) and the whole off-grid thing ... as the batteries are inherently safe and there is plenty of test data for LiFePO4 for impact penetration short circuit etc. as a *technology*

The wiring was done by registered electrician (I chose one that also did solar PV installs) and was signed off by same as this is required to get code of compliance which is needed before you can insure your home in NZ.

2 days after code of complaince we had a 7.1 earthquake and nothing was damaged, so light battery packs need less mounting and securing too btw... for those elsewhere this is the same size as the Haiti quake...

[leonscorpio]

SteveG, you said that your pack was $7000 U.S., are you saying the complete package including installation? I am only asking since I have family that live in NZ and they tell me it's quite expensive just to live.
I'm still learning on the whole solar thing, am looking at getting one installed in Georgia soon.
take care

[russ]

Read about your earthquake on the net! Amazingly little damage.

Strong building codes do pay off.

[Sunking]

SteveG, you said that your pack was $7000 U.S., are you saying the complete package

That would have to be the batteries alone. 4000 watt of solar panels will cost $8000 or more.

[steveg]

Hi Leon,

US$7000 for the battery pack yes - this is equivalent to >1000Ah of PbA, but lighter smaller.

I paid NZ$2000 for solar electrics install - so that is wiring the battery pack in and up to the box in the roof to take the solar panel feeds - wiring the regulator in, fusing and approval.

Lets see - right now 1NZ$=about 0.75USD - say US$1500.00

and the panels cost US$2.1/watt at the time

[steveg]

The total cost was approx 10% of the cost of the house to build (maybe a little less) - it has no payback because it is part of the house. If you purchase a car you get the utility of the car, it has no 'payback', and when you sell that car you get less for it. So for the system I have, I view it in this way also - we pay an extra for it on our house, we get the utility of it for (however long) but it doesnt devalue quite as quickly. I get to have no electricity or gas bills, and once my trees I cut are dry no costs for wood either.

You say it costs a lot to live in New Zealand? - it depends on your income - I lived in Sydney for 10 years, and it definately costs more to live there in raw $ , so it's all relative - average incomes are less in NZ is probably a more accurate statement.

[josko]

Addendum : you may notice I am one panel shy on the bottom row - due to a mis calculation one of the bathroom vents is where my panel should be - we will have this fixed in due course, so I have 3500W solar hooked up right of this minute - the last 2 panels once the vent is moved.

The top row is 200W panels of Suntech the lower row is 250W 'no name' brand with Suntech wafers that I imported myself from China - the battery pack came from the same folks, to my spec (3x100Ah in parallel) x 16 in series

The BMS prevents overcharge and overdischarge - there is some weak balancing in the pack to bring the voltages over time to even values.

Been running now for 5 months.

Also - we have insurance and have passed code of compliance for our LED lighting internally (new technology that councils dont trust especially running under insulation) and the whole off-grid thing ... as the batteries are inherently safe and there is plenty of test data for LiFePO4 for impact penetration short circuit etc. as a *technology*

The wiring was done by registered electrician (I chose one that also did solar PV installs) and was signed off by same as this is required to get code of compliance which is needed before you can insure your home in NZ.

2 days after code of complaince we had a 7.1 earthquake and nothing was damaged, so light battery packs need less mounting and securing too btw... for those elsewhere this is the same size as the Haiti quake...

It looks that you have some experiences with LFP batteries. Could you advise me if there is still a need to install solar charge regulator if you use BMS for LFP batteries?

[john p]

It looks that you have some experiences with LFP batteries. Could you advise me if there is still a need to install solar charge regulator if you use BMS for LFP batteries? Josko A BMS only regulates individual cells .. You certainly still need a charge controller to safely charge the batterypack