Sad Harvest Success data & economics of my first 370 cells

A

APD

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I wanted to get started in building a powerwall, thinking I could do it relatively cheaply. I love the DIY/reusing junk/getting something for super cheap with a little work aspect of this hobby, which is how I tend to live my life.

So I bought some ebay cells to get started and as an experiment to see what it would really take to make this happen. I paid more than I wanted, but I was OK with the price if I could recover 66% of the cells. They were all Lenovo/IBM packs, with cells of either 2200 or 2400 mah, based on the pack's label. I also had just about 6 packs from other brands. I had no other leads on cheaper batteries at the time other than quantities of 1 or 2 at time.

Here are my disappointing results:



image_nyttbj.jpg




So, Lets say I want to make a 7Kw powerwall, like a tesla. Here is what I would need.

150 cells @ 2 Ah = 300 Ah


300 Ah * 3.7v = 1110 Wh = 1.11 KwH

150 cells * 4 (in series) = 600 cells to make one 14.8 volt- 1.11 KwH battery

600 cells * 7 = 4200 cells to make 7.7 Kwh -14.8v Powerwall

Buying cells Vs. Harvesting:

Cheapest 2 Ah cells are $1 each, so $4200
or $0.50 per Ah

Using higher capacity cells would have fewer cells, but would still need to be less than $0.50/Ah


So lets sayI re-test my 1900 cells and they all come out over 2000.
That gives me 20% harvest success rate. I would need to process 21,000 cells to get 4200 good cells.
My local battery recycler wants $2.65 per pound.
There are 9 cells per pound.
21,000/9= 2333 pounds.


2333*2.65=$6183
A 7 KwH Tesla wall costs $3000.


To get the cost below a Tesla, I would have to get cells significantly cheaper, or have higher harvesting success rate.
To break even with the cost of a Tesla wall at my 20% success rate, I would need to get cells for $1.30/pound, or double my success rate.
These would still be used cells with unknown history/life span, and there would be months of labor involved.
I've seen others post higher success rates, which is why I bought those ebay batteries. Although 370 cells is a pretty good sample size.
I've also seen others post lower cost per pound than what I can currently get ($2.65), but $1.30/pound is pretty cheap from what I've seen posted here.

A Tesla wall has a 10 year warranty, built in cooling, and BMS.
And although I really want to continue this project and I have the ambition to do the work, Im not sure the economics are really there.

Convince me otherwise please!

EDIT:
As requested by another member...I made a math error on the number of cells required to create a pack similar to a tesla powerwall.
It turns out I only need about 1200 cells for 8.8 Kwh, not 4200.
So with a 20% success rate, I would need to process 6000 cells.
6000 cells @ 9 cells per pound = 667 pounds
667 pounds * $2.65/pound = $1766 total cost of cells
with a 50% success rate, the cost drops to $706
The cost is not as bad as I thought when I first wrote this post, but also not as good as I had hoped getting into this project (was thinking about 66-75% success rate, and lower battery pack pricing based on other people's accounts)

 
OK, so even at 75% success rate, I would need 5600 cells.
That's 622 pounds, at $2.65/pound = $1648
A little more than half the cost of a Tesla, for used/questionable cells and tons of work.
Im thinking $600-800 for cells is when it starts to become worth all the labor/tweaking/repairs/experimenting.
 
A BIG part of the DIY, is the YOURSELF part. We love the experience. It isn't always the best and most economical solution, but it is the most satisfying in knowing you're doing something that seems difficult when in reality is really easy to do. Plus all the knowledge you gleam from it all :)
 
I think you have your numbers a bit wrong though :)

Below is your quote:
150 cells @ 2 Ah = 300 Ah <<--- This is correct
300 Ah * 3.7v = 1110 Wh = 1.11 KwH <<-- This too
150 cells * 4 (in series) = 600 cells to make one 14.8 volt- 1.11 KwH battery <<-- But this isnt.

If you add 4 packs of 1.11kWh you get 4.44kWh ;)
You still have 300Ah@4s same as 300@1s but the energy stored is 4times as much.

4200 cells is more than i have in my wall and i have 25kWh ;)
 
daromer said:
I think you have your numbers a bit wrong though :)

Below is your quote:
150 cells @ 2 Ah = 300 Ah <<--- This is correct
300 Ah * 3.7v = 1110 Wh = 1.11 KwH <<-- This too
150 cells * 4 (in series) = 600 cells to make one 14.8 volt- 1.11 KwH battery <<-- But this isnt.

If you add 4 packs of 1.11kWh you get 4.44kWh ;)
You still have 300Ah@4s same as 300@1s but the energy stored is 4times as much.

4200 cells is more than i have in my wall and i have 25kWh ;)
Click to expand...

Ha! thanks for catching my error. Now the cost doesn't seem so bad!

so 1200 cells will get me 8.8 Kwh.
With a 50% success rate, I would need to buy/process 2400 cells.
2400/9 cells per pound = 267 pounds
267 pounds * $2.65/pound = $706

thats more reasonable, especially if I got a better success rate on harvesting.
 
Sweet!! With your maths there, looks like I'm already 1/2 way there with one purchase :D

That is, if I get that high of a success rate. Now starts the arduous task of disassembly. Fun, fun, fun........
 
My success rate to get >2Ah have been around 45%

But i have had hauls with as low as 20%.... But all around more like 45%

/D
 
This is the very reason why if you are building a powerwall, you HAVE to go local!

The packs you got were probably the rejects form someone eltses laptop battery haul, and he knows they were usually bad. So you were the sucker who bought them and overpayed for a bunch of dead cells.

You need to start looking locally. Scrap yards, computer repair stores, recycling centers, construction businesses, large corporate businesses with laptop batteries ect.

Ebay is not a viable place to get cells from for a large-scale project like a powerwall. Sure if you just want some dirt cheap cells for your flashlight, they would be great. But for our usage, we need more good cells than we can source from ebay.

Also to add, depending on who you talk to, each place valuyes laptop batteries differently. For example, my computer repair shop sells them to me for 50 cents a battery. My scrap yard sells them to me for $1 a pound. My computer recycling center wants $2 a pound. If your recycler wahts $2.65 a pound for cells, that is just too much . I reccomend going directly to the places your recycler is getting his cells from in the first place (businesses, schools, computer repair shops) and go to them directly. If he is going to charge you out of ass for laptop batteries, find his suppliers and buy from them.
 
CUDAcores89 said:
. My scrap yard sells them to me for $1 a pound.....
Click to expand...

So I wonder what his buying price is ?

It seems a good strategy to enquire at scrap yards what their buy and sell price is, before they know which you are doing ...

The few I've got have come from computer shops for free ...(I live in Thailand) ... but scrap price is generally around a dollar US/lb ... that's 11 cells ....

Prices vary greatly...https://forums.iscrapapp.com/forums/topic/lithium-ion-batteries/ ... A wholesaler in Nigeria on that link seems desperate to sell .... transport cost is a big factor , if you're a scrap buyer who lives in a country that doesn't have an end processor (or live far away from one), what you gona do ?put tonnes in a container and ship them .... the added cost will push their value down , perhaps that's why many scrap places don't buy them.

And what exactly does the end processor do to get the lithium (I guess that's what they're after) ? ...does he have lots of people taking out the cells from the plastic ??? If so we need to find this place and work out a deal ...lol.... then what happens to the cells ?
 
CUDAcores89 said:
This is the very reason why if you are building a powerwall, you HAVE to go local!

The packs you got were probably the rejects form someone eltses laptop battery haul, and he knows they were usually bad. So you were the sucker who bought them and overpayed for a bunch of dead cells.

You need to start looking locally. Scrap yards, computer repair stores, recycling centers, construction businesses, large corporate businesses with laptop batteries ect.

Ebay is not a viable place to get cells from for a large-scale project like a powerwall. Sure if you just want some dirt cheap cells for your flashlight, they would be great. But for our usage, we need more good cells than we can source from ebay.

Also to add, depending on who you talk to, each place valuyes laptop batteries differently. For example, my computer repair shop sells them to me for 50 cents a battery. My scrap yard sells them to me for $1 a pound. My computer recycling center wants $2 a pound. If your recycler wahts $2.65 a pound for cells, that is just too much . I reccomend going directly to the places your recycler is getting his cells from in the first place (businesses, schools, computer repair shops) and go to them directly. If he is going to charge you out of ass for laptop batteries, find his suppliers and buy from them.
Click to expand...

Local shops had NONE or only thin prismatic/pouch cells.
Electronic waste is managed by the state here in upstate NY.
The local state facility wouldn't even let me look at what they had.
I even went to a large Interstate battery shop....they don't accept lithium, only lead acid, etc.
Schools and large businesses often need receipts to dispose of their batteries to comply with environmental regs.
I ended up getting them for $2.25, and was able to pick through them so I only took packs with higher capacity cells (2500+) and he will buy back my unwanted cells at half price, which will bring the price to $2/lb if 25% of them are junk. Plus I can recover some of the wasted $$ from my ebay purchase. The guy told me that just about 6 months ago, he was selling them for $0.60-0.70 per pound.

I was able to get 237 pounds in one trip, which should be enough to build a decent wall, and I wont have to wait a year by only getting a few packs at a time. So far they are testing at 75% above 2000mah, so Im feeling a lot better than when I started this thread.
Yes I agree that first batch from ebay was likely somebody else' reject pile.
 
ozz93666 said:
The few I've got have come from computer shops for free ...(I live in Thailand) ... but scrap price is generally around a dollar US/lb ... that's 11 cells ....
Click to expand...

A 18650 cell is 45 grams. So that's 10 per pound MAX. Plastic and circuit board weighs 40-60grams. Because of the additional plastic and circuit boards, I use 9 cells per pound to estimate my needs.

I would rather have a some extra cells than come up short. When your dealing with hundreds of pounds, the difference between 9 and 11 cells per pound is significant.
 
APD said:
A 18650 cell is 45 grams. So that's 10 per pound MAX. Plastic and circuit board weighs 40-60grams. Because of the additional plastic and circuit boards, I use 9 cells per pound to estimate my needs.

I would rather have a some extra cells than come up short. When your dealing with hundreds of pounds, the difference between 9 and 11 cells per pound is significant.
Click to expand...

Nine cells per pound probably yields five or so usable cells. At $1.50 a pound that's 30 cents a cell if you don't count your labor.

Thirty cents a cell that probably will yield four watt hours of long term charge discharge if you go for a life prolonging regime of conservative limits.

Two hundred and fifty cells to the kWh, so 250*3/10=$75 a kWh of usable storage, again discounting labor and things like investment in testing apparatus.
 
ozz93666 said:
A wholesaler in Nigeria on that link seems desperate to sell ....
Click to expand...

Funny. These cells should be MORE in demand in Nigeria than in developed countries. Does this mean lots of these cells are ending up in Third World dumps? I would like to be able to intercept this river of 'dead' batteries!

Where were you able to get 237 lbs?
 
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