When talking about storage capacity what is your end cost per kwh?


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Ioan Nicut

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Aug 26, 2017
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Hi guys,

Hope you are well. I am a complete newbie.

I want to build my own 18650 powerwall and want to start by knowing what is the end cost per Kwh that you got for your powerwalls (not considering inverters and other hardware)

I am asking this question because I want to have an idea of what is a very goodprice of aquisitionfor an untested 18650 cell.


When talking about storage capacity whatis your end cost per kwh?


I really appreciate your input,

Ioan
 

DarkRaven

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Welcome!

If not considering inverters and other hardware then what are you considering? Just the 18650s and everything that is needed to assemble them into packs? I'm only putting together a small 2 kWh system and got the cells for next to nothing. Cell holders, solder, fuse wire are cheap, they're just a couple of bucks. Let's say 10 EUR per kWh in this case.

Are you buying your 18650s in form of laptop batteries to reclaim the cells? I consider about 1,50 EUR (or the equivalent in your currency, Google will tell you the exchange rates) per battery a decent price but the price is rising due to popularity. I've also seen around 4 EUR and more but that is insane. Especially for the smaller bulk offers of around 20 or so batteries. I guess everything is buying them now as a first step to play around with 18650s or something like that.
We are getting closer to the point where buying new cells is cheaper considering your time and effort and the failure rate.

For single cells that translates to about 0,30 to 0,50 EUR. If you can get single cells then this is the better option because you don't have to disassemble batteries first which obviously is a good thing.
 

Ioan Nicut

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Thanks very much for your imput!!!

Let me do the math for myself.

suppose that from the cells I get 50% are beyond 2000 mAh.

It means price per valid usable cell is: 1 Euro.

The Quantity of Energy per cell is 2Ah * 3.7V = 7.4 Wh

Number of pieces per KWh = 1000 Wh / 7.4Wh = 136 Euros

This does not include the price of your time and work and additional materials and hardware.

Please someone could validate my rationale?

Thanks a million Again...
 

DarkRaven

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Well, yes, sure, this is an assumption you could make. And it could turn out to be accurate, but it could be totally off as well.
Apart from the cells I got for free and will use for my system I also bought some batteries and took them apart. I can report that 74 out of about 400 cells were 1900mAh or higher, so nowhere near 50% at 2Ah.

Looking at recent offers on eBay we are more at 2 to 3 EUR per battery at least. Batteries will have three to nine cells usually. The majority will probably have three, four or six. Let's take 4,5 as an example.

2 EUR per 4,5 cells, 25% have 1900mAh or more and will be used, this will average to 2Ah. That's 1,125 cells or 8,325Wh for 2 EUR
1000 / 8,325 ~ 240 EUR per kWh at least, much worse than your assumption but sadly just as possible.

As you can see this varies wildly. And this isn't even the worst case.

If we compare this to buying new cells:
I have seen Samsung ICR18650-22P with 2200mAh for 1,82 EUR each when you buy 500 pieces. 8,14Wh per cell means just over 4kWh for 910 EUR or 227,5 EUR per kWh. You see that is entirely the same ballpark there. And these are new cells. They will give you more cycles and you don't have to put extra work into breaking them free from the laptop batteries.

Another example, Panasonic NCR18650PF with 2900mAh. 2,44 EUR each when you buy 540 pieces. This is a bit more expensive per kWh than with the Samsung cells but at 2900mAh you will get better density and can build your packs physically smaller if that is what you want. [edit] I was wrong, it is a bit cheaper even (227,4 EUR per kWh) [/edit]

And a final example, although they are not in stock at the moment: Samsung ICR18650-26J with 2600mAh, 1,86 EUR each for 500 pieces. 4,81kWh for 930 EUR, ~194 EUR per kWh.
 

BlueSwordM

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I get them for free, soooo...
So cost per KWh is the limit of a function in this case, with cost approaching infinity.

Being serious though, you're right. We are recycling cells. You can't compare the raw cost of new cells vs recycled cells. While you get the best bang for buck with recycled cells, the work you put into it is... off putting for most people.
The best bet to get good used cells is mostly lowering the current draw per cell, meaning more cells per parallel pack and higher capacity due to lower current, causing lower resistance, or, trying to get them immediately after they're thrown in the garbage.
 

egam

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For good packs that have a minimum of 10 watt hours per cell, you will pay $1.25.
By focusing my buying at the better packs, I pay more, but also get higher capacity cells.

10 watt hours/3.7 = 2700 mah.

60 watt hour 6 cell packs or 90+ watt hour 9 cell packs are a good goal to shoot for.

If you are forced to buy used packs, look for these capacities.
Then at best plan on 40% cells above 2000 mAh.
Another 40% will be less than 2000mah
The last 20% will be unusable.

If you only use the ones above 2000 mah in your powerwall, then your cost per pack should be less than $4.50 pack for net 3-4 good cells in a 9 cell pack.
$3.00 per pack for 6 cell packs for 2-3 good cells.

Your cost per kW hour is $125. Just for cells. Not including time involved.

And it's a LOT of work to sort these out.

New cells with 2200 mah capacity can be found for 1.25 per cell.
And they are all good cells so you gain your time back.

5kw Tesla battery modules go for $1400 for 444 cells. ($3.15 per cell for 3.5 amp hour cells)
Cost per kwhr is $280/ kwhr.

https://m.ebay.com/itm/Tesla-Model-...kWh-444-Panasonic-18650-3400mAh-/262333679871
 

Ioan Nicut

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Aug 26, 2017
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Egam, thank you very much for your help.


DarkRaven said:
Well, yes, sure, this is an assumption you could make. And it could turn out to be accurate, but it could be totally off as well.
Apart from the cells I got for free and will use for my system I also bought some batteries and took them apart. I can report that 74 out of about 400 cells were 1900mAh or higher, so nowhere near 50% at 2Ah.

Looking at recent offers on eBay we are more at 2 to 3 EUR per battery at least. Batteries will have three to nine cells usually. The majority will probably have three, four or six. Let's take 4,5 as an example.

2 EUR per 4,5 cells, 25% have 1900mAh or more and will be used, this will average to 2Ah. That's 1,125 cells or 8,325Wh for 2 EUR
1000 / 8,325 ~ 240 EUR per kWh at least, much worse than your assumption but sadly just as possible.

As you can see this varies wildly. And this isn't even the worst case.

If we compare this to buying new cells:
I have seen Samsung ICR18650-22P with 2200mAh for 1,82 EUR each when you buy 500 pieces. 8,14Wh per cell means just over 4kWh for 910 EUR or 227,5 EUR per kWh. You see that is entirely the same ballpark there. And these are new cells. They will give you more cycles and you don't have to put extra work into breaking them free from the laptop batteries.

Another example, Panasonic NCR18650PF with 2900mAh. 2,44 EUR each when you buy 540 pieces. This is a bit more expensive per kWh than with the Samsung cells but at 2900mAh you will get better density and can build your packs physically smaller if that is what you want. [edit] I was wrong, it is a bit cheaper even (227,4 EUR per kWh) [/edit]

And a final example, although they are not in stock at the moment: Samsung ICR18650-26J with 2600mAh, 1,86 EUR each for 500 pieces. 4,81kWh for 930 EUR, ~194 EUR per kWh.

Thank you very much for your help. This is indeed a thorough financial breakdown. Can you please point me to where I can buy the NEW cells? I really appreciate your imput!
 

DarkRaven

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Geek

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On an extreme budget. $300 per kwh. Including BMS. I have 6 months to code my Arduino and more than 500 cells left to test.

Second hand batteries and about 4kwh
 

daromer

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I think one very very important parameter is missing here.

The price per Wh stored energy initially can be rather high but also irrellevant. If calculate only by that factor we wuld never get our money back unless we get the cells for free.

What actually most important if you ask me is the total number of Wh you get out of them before they are considered to be waste and goes to the bin :p

Calculating this can be done rather simple but also rather complex. I will do one very simple here just to show.


Lets say we have 10kWh of battery storage. This would be 900 cells if we went with 3Ah cells. Total cost if we buy them new around: 3EUR piece and that would be 3700EUR.
So thats 370Eur per kwh. Rather high price right? BUT...

Lets start to calculate on how much we gonna get out of the cells. And im just going to show 2 numbers taken out of my head and you could stretch this alot and with some proper math you can find the best point too.

Lets say we use around 80% of the capacity. At that range we know that we will get some where around 400 cycles of them and its stated that you in the end have somewhere around 60-70% capacity left. so basically the total Wh you get out of them would be:

400*0.8*0.85*10000 = 2710kWh. So now our price per stored kWh is around: 0,13EUR/kWh stored energy. And we still have some where around 60% capacity left...

Lets say we dont fully charge and we dont go to bottom? Ie lets say we use 60% DOD instead. And potentially get 1200 cycles with above cycles....

1200 * 0.6*0,85*10000 = 6120 kWh. And suddenly our price per kWh is down to : 0.06EUR per kWh.

But the problem with above is that on the first case you have max 8kWh useable and on the second only 6kWh.
So if you need to use the 10kWh you need to extend it a bit further. But at the same time it will hold a bit more cycles.


Above is just a very very very generic example and it can be done very very complex. There is very good docs on internet made on how to calculate this where the optimal is and what tht end cost would be but the forumals ar rather extensive. Above is just simplified based on them. I am trying to get some kind of webpage/excell done that can kind of do such graphs for ya but have not come that far yet. Because this is essential when you go into calculating how the cost will be and the durability on the setup built.

Sorry if it wasnt the original questions answer but i though this was needed here :)
 
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Ioan Nicut

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daromer said:
I think one very very important parameter is missing here.

The price per Wh stored energy initially can be rather high but also irrellevant. If calculate only by that factor we wuld never get our money back unless we get the cells for free.

What actually most important if you ask me is the total number of Wh you get out of them before they are considered to be waste and goes to the bin :p

Calculating this can be done rather simple but also rather complex. I will do one very simple here just to show.


Lets say we have 10kWh of battery storage. This would be 900 cells if we went with 3Ah cells. Total cost if we buy them new around: 3EUR piece and that would be 3700EUR.
So thats 370Eur per kwh. Rather high price right? BUT...

Lets start to calculate on how much we gonna get out of the cells. And im just going to show 2 numbers taken out of my head and you could stretch this alot and with some proper math you can find the best point too.

Lets say we use around 80% of the capacity. At that range we know that we will get some where around 400 cycles of them and its stated that you in the end have somewhere around 60-70% capacity left. so basically the total Wh you get out of them would be:

400*0.8*0.85*10000 = 2710kWh. So now our price per stored kWh is around: 0,13EUR/kWh stored energy. And we still have some where around 60% capacity left...

Lets say we dont fully charge and we dont go to bottom? Ie lets say we use 60% DOD instead. And potentially get 1200 cycles with above cycles....

1200 * 0.6*0,85*10000 = 6120 kWh. And suddenly our price per kWh is down to : 0.06EUR per kWh.

But the problem with above is that on the first case you have max 8kWh useable and on the second only 6kWh.
So if you need to use the 10kWh you need to extend it a bit further. But at the same time it will hold a bit more cycles.


Above is just a very very very generic example and it can be done very very complex. There is very good docs on internet made on how to calculate this where the optimal is and what tht end cost would be but the forumals ar rather extensive. Above is just simplified based on them. I am trying to get some kind of webpage/excell done that can kind of do such graphs for ya but have not come that far yet. Because this is essential when you go into calculating how the cost will be and the durability on the setup built.

Sorry if it wasnt the original questions answer but i though this was needed here :)
Thanks man, I really appreciate your wisdom and sharing this with me.

What is the DOD you are using on your 18650 pack? How do you set up the system to stop discharging the batteries and start charging them with solar?
 

Geek

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So far estimate $300 for 4 to 5 kwh storage and 700 to 900 for charge controller and inverter. Hoping for home made bms
 

Ioan Nicut

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Geek said:
So far estimate $300 for 4 to 5 kwh storage and 700 to 900 for charge controller and inverter. Hoping for home made bms

Wish you very much luck man. Home made BMS?

Speaking of BMS, understood that BMS is to manage and protect the battery. It also insures top and bottom levelling of the batteries.

1.Can someone validate my understanding about BMS's?

Watched one of Peter Matheus's videos where he explains that he onceset up his system to discharge and charge the cell/battery between 2.73V/49V and 4.1V/57.4V

2. If the BMS does the above what BOX insures controlling the discharging and charging between 2.73V/49Vand 4.1V/57.4V???

I was told by some vendor that I MUST buy some batteries that provide exactly a multiple of 12V. I kind of smiled because I know you guys are using working batteriesthat look like14s80p. And I am a bit confused.

3.Can anyone please clarify it for me?

Thanks a million in advance,
 

daromer

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I answered you on Facebook but i can answer here to. Note that its better in new thread :)

1. The charger only sees the full voltage
2. The bms does in some cases controll the charger. Atleast this is how it should work.
3. Some chargers made for lead acid only works on loops of 12V yes. But many of them can set voltages kind of in between. So yes.

Regarding DOD. I dont set any bottom value. I only set top value as base and thats 3.5V on LiFe and 4V on LiIon.

The bottom only has an emergency switch. Since i got that huge battery bank i will only get to the bottom couple of times each year. Most times i dont go below 80% DOD
 

Geek

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IoanNicut said:
Geek said:
So far estimate $300 for 4 to 5 kwh storage and 700 to 900 for charge controller and inverter. Hoping for home made bms

Wish you very much luck man. Home made BMS?

Speaking of BMS, understood that BMS is to manage and protect the battery. It also insures top and bottom levelling of the batteries.

1.Can someone validate my understanding about BMS's?

Watched one of Peter Matheus's videos where he explains that he onceset up his system to discharge and charge the cell/battery between 2.73V/49V and 4.1V/57.4V

2. If the BMS does the above what BOX insures controlling the discharging and charging between 2.73V/49Vand 4.1V/57.4V???

I was told by some vendor that I MUST buy some batteries that provide exactly a multiple of 12V. I kind of smiled because I know you guys are using working batteriesthat look like14s80p. And I am a bit confused.

3.Can anyone please clarify it for me?

Thanks a million in advance,

So 14s is 14 batteries in series full charge is 58.8v. 80p means 80 cells in parallel. Lithium chemistry batteries are difficult to marry with 12/24/48v equipment. If you gander around you will see the many ways some of us get around this conundrum.

For example 3s will give you 12.8v full charge, but is only 9v fully discharged. So you would loose a lot of capacity just to the fact most 12v inverters don't like to go too far below about 11v. However if you go 4s, you get a full charge voltage of 16.8v, which once again most 12v inverters won't like either.

However Victron are one manufacture who does make inverters and charge controllers suitable (not made for) but can be programmed to suit Lithium battery setups. However they don't do balancing. Balancing is very important with Lithium batteries. Especially second hand like the cells many of us use.

That is my current thinking. I am going to cheap out as much as possible to get a system up and running. That means built in safety mechanisms. Instead of trying to do everything at once, I will set up a simple emergency charge shutoff at 4.2v, and only run my cells to 4.1. My balance circuits will be primitive, probably cheap eBay BMS. As I start to save money on the power bill I shall gradually improve my setup.

My first pilot project will be to simply test my cells off grid. I have 600+ to test now.
 

BlueSwordM

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For cutoff protection Geek, you should do as the guy in DIY Perks does in this video:
It's simple, cheap(even for a configurable non-IC based BMS), and very smart. I'm currently waiting for the parts so I can build a 24V setup, and I'm so excited.

Ditto for the charging shutoff to 4.1V. You should also incorporate basic cooling with a 200mm fan running on PWM based on temperature for basic cooling, just in case of cooling down higher resistance cells.
 
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