2v cell system

[Ohms_Cousin]

Just been hit with a dilemma. Was set to go with LiFePO4 system but have found that the country I am in, has this year (2022) introduced a 10% duty rate and 16% VAT rate on Lithium batteries. Lead acid batteries are duty free and zero rated for VAT (meaning no VAT is charged on them).

I was looking at a fairly big system - somewhere around 250 KWh of capacity in LiFePO4. Not going to happen at these new import tax rates as it adds to much to the cost to import. The system was going to cost a bomb anyway, but now with the new taxes it pushes it over the edge (out of our budget).

So given Lead Acid is "free" to import I have gone back to looking at lead acid. I have been running AGM's for about 12 years now and am on my second set, so I do know about lead acid.

However I would like to have at least 50 kWh of usable lead acid so that means at least 100 kWh of battery capacity. Seems the only thing that makes sense at that size is 2v tubular cells. I dont know much about these cells, so some questions......

If I cycled a 100 kHw battery everyday down to 50% DOD how many cycles could I expect from the batteries ?

It may be better to size the battery slightly bigger and only discharge to 30% DOD - how many cycles would I expect then?

I was really looking forward to 6/7000 cycles out of LiFePO4 (hence why the size system was big - only use 60% of it ie, from 80% to 20%). I realise this is not going to happen with Lead acid but i need at least a few thousand cycles. Is this realistic?

 

[OzSolar]

Hmnn.... seems likes by the time you looked at the total life cycle cost of both that LiFePO4 might still come out on top but since that wasn't your question I can offer the below method that I would use.

You need to find the cycle life chart for the battery you're looking at. I can't quickly find a link to one but I did find this because it's the sort of analysis your trying do want to do and you will want to add LiFePO4 to your chart. http://www.hupsolar.com/buy-HUP-batteries-prices-pricing

Once you find the actual chart for the battery you want you can then compare how many cycles it gets at several different places on the chart. I randomly chose $200 per kWh for the cost of a a 2V cell flooded lead acid battery and entered the cycles from memory for a battery that I'm familiar with.

***the below is just an example that I quickly prepared. You'll need to collect your own data and build the chart***

EDIT - added my chart again. It seemed to not make my first post.

 

[Rossman]

@Ohms_Cousin if you use a quality lead acid battery such as a Rolls you will get about 4000-4500 cycles going to 50% depth of discharge regularly. The cost for Rolls batteries has gone up a fair amount as well, FWIW.

edit: from their docs:

 

[time2roll]

If the original plan was 250 kWh of LFP.... the alternate plan of 100 kWh of lead does not add up as the system would need 500 kWh to be similar to 250 LFP.

Even with the tax I recommend scaling back the LFP instead of compromising with lead. The smaller LFP will save more than the added tax.

 

[OzSolar]

@Ohms_Cousin if you use a quality lead acid battery such as a Rolls you will get about 4000-4500 cycles going to 50% depth of discharge regularly. The cost for Rolls batteries has gone up a fair amount as well, FWIW.

edit: from their docs:
View attachment 90512

Here's my numbers revised to reflect the chart that Rossman supplied and using $250/kWh for the battery which I have no idea is correct for today.
The numbers support deeper cycles being more cost effective. The cost per usable KWH over the lifetime of the battery is the lowest.

If someone wants to supply the cost per KWH and cycles for LiFePO4 I'll drop them in there and see what it looks like.

 

[OzSolar]

I used $500 per KWH for LiFePO4 batteries which seems pretty safe for your application since we can get them for less than $350 per kWH in the US at the moment.

Study it for a minute. Pretty interesting. I made no attempt to game the numbers. Taking FLA to 80% DOD works out to exactly the same cost per LEU as LiFePO4. I'd say LiFePO4 is the clear winner. That was fun!

 

[Ohms_Cousin]

Thanks for the replies.

I didnt go into too much depth of my plans for the sake of brevity. I have been in contact with EVE directly and can get reasonable pricing on 500+ 3.2v cells. Plan was to keep 250kWh for myself and sell the rest. But the new taxes caught me out.

Was wondering if I should put in a smaller lead acid bank (ie, the 100kWh) just so there is some battery on the system but realise now this is not going to work out well.

Pricing on 2v 3000 Ah cells ex China are around $650 -$700 per cell. Not even sure if those cells can be trusted to be any good compared to Rolls. I dare not even ask what Rolls cost.

But reading the comments above plus crunching numbers here, it seems even with the taxes LFP is still a better deal all round - not by a huge margin mind you, but its close. The benefits of LFP outweigh going with lead. Its a shame I will be hit with these taxes but there is nothing I can do except suck it up and pay.

However my plan to buy 500+ cells is not going to fly now. So some new planning to do to work all this out.

 

[Rossman]

I dare not even ask what Rolls cost.

They cost roughly what was said earlier in this thread ($250/kWh)

edit also what did EVE want for 500+ cells? how good was the price?

 

[OzSolar]

But reading the comments above plus crunching numbers here, it seems even with the taxes LFP is still a better deal all round - not by a huge margin mind you, but its close. The benefits of LFP outweigh going with lead. Its a shame I will be hit with these taxes but there is nothing I can do except suck it up and pay.

Keep mind if my numbers are only meant to be in the realm of reality. My main intent was to demonstrate the method one could use to analyze things once they got the battery cost and cycle life data collected.

 

[Substrate]

The one thing not mentioned is if you are recharging via solar or not. On this forum, I am assuming so.

In your country, do you have enough solar insolation hours (not just sunrise-sunset - you have to look it up), and solar power to keep the lead-acid fully charged regularly and in good shape? (P.S. - use the "winter" solar insolation hours for calculating your system)

Thats one thing great about LiFeP04 - you don't *have* to reach full charge if you plan your capacity needs correctly.

This alone could swing towards LFP as being the better value despite the taxes.