Beginners Guide to Processing 18650 Cells | Cell Database



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When talking about storage capacity what is your end cost per kwh?
#11
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 Tongue

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 Smile
Rad likes this post
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Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
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#12
(10-08-2017, 07:24 AM)daromer Wrote: 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 Tongue

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 Smile
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?
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#13
So far estimate  $300 for 4 to 5 kwh storage and 700 to 900 for charge controller and inverter. Hoping for home made bms
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#14
(10-09-2017, 08:52 AM)Geek Wrote: 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 once set 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/49V and 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 batteries that look like 14s80p. And I am a bit confused.

3. Can anyone please clarify it for me?

Thanks a million in advance,
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#15
I answered you on Facebook but i can answer here to. Note that its better in new thread Smile

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
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
Upcoming: 14S 18650~30kWh | Automatic trip breakers, and alot more
Reply
#16
(10-09-2017, 04:47 PM)Ioan Nicut Wrote:
(10-09-2017, 08:52 AM)Geek Wrote: 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 once set 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/49V and 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 batteries that look like 14s80p. 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.
Ioan Nicut and BlueSwordM like this post
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#17
For cutoff protection Geek, you should do as the guy in DIY Perks does in this video: https://www.youtube.com/watch?v=1Fs4SfVSsLk&t=505s
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.
The power of lithium ion is in our hands!
We'll show them what we're made of!
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