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General battery pack/PV planning
#11
I am happy with buying everything I need for a start (~10kWh?) in bulk.

Are chinese suppliers really that bad? Are there known ok ones?

Unfortunately I do not really have a local reliable source, so it would be ebay or other online platforms (yes, I am looking at Alibaba)
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#12
You mentioned your yearly usage is about 6000 kWh, assuming you use the same amount everyday, that is about 16 kWh per of consumption on a daily basis.  Then take into account your cycle depth and cell degradation, double that.  Your purchase IMO should be somewhere in the tune of 32 kWh.

Because you are most likely going to have to import cells if you cant find them locally, you could consider shopping on density.  Healthy Tesla model S pack is about 5 kWh each, and it's dense and small which would in turn reduce cost of shipping.

Depending on your system voltage and design, you could start with a couple of those, and get a fast and easy 10 kWh as a starting point.  Note: These modules are in a 6s configuration.
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#13
(08-15-2019, 03:57 PM)Crimp Daddy Wrote: You mentioned your yearly usage is about 6000 kWh, assuming you use the same amount everyday, that is about 16 kWh per of consumption on a daily basis.  Then take into account your cycle depth and cell degradation, double that.  Your purchase IMO should be somewhere in the tune of 32 kWh.

Because you are most likely going to have to import cells if you cant find them locally, you could consider shopping on density.  Healthy Tesla model S pack is about 5 kWh each, and it's dense and small which would in turn reduce cost of shipping.

Depending on your system voltage and design, you could start with a couple of those, and get a fast and easy 10 kWh as a starting point.  Note: These modules are in a 6s configuration.

Agree with this.  My system produces 9500kwh / year.  My average consumption is 2200watts/hour for 13hrs/day.   At this rate i average 13.5kwh of battery use daily with high of 20kwh.  The extrapolation matches very close to 32kwh suggested by @Crimp Daddy.    

You can start with a smaller battery and you'll likely find that 1) you're doing a high DOD and shortening its life or 2) going into float a lot and leaving PV array input power on the table.  If you do find these situations, you can expand your battery ...  so just leave room in your planning for that. What I'm trying to say is - its OK to start with smaller battery Smile but just leave room for future growth.
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#14
(08-15-2019, 10:23 AM)DeepB Wrote: Are chinese suppliers really that bad? Are there known ok ones?

Unfortunately I do not really have a local reliable source, so it would be ebay or other online platforms (yes, I am looking at Alibaba)

Yes. No.  

Just to elaborate… knowing what I know about the industry, there is no way ever that I would place a large order, especially for 18650 format cells, from China, eBay, or any other import supplier.  Be wary of Japanese brands coming out of China.
 
There are so many reports of counterfeiting, re-wraps, poor quality, fraud that it’s not worth the risk.  Plus, you don’t really have a mechanism for recourse working with an international export seller.  Many have tried, and failed.
 
Even the good Chinese cells, like the ReVolt I mentioned previously, worked great up to a certain point, which was 335 full cycles and then degrade at an expedited rate.  Most all name brands, LG, Panasonic, Samsung don’t fall off like that and have better long term characteristics.  You get what you pay for.
 
It’s not uncommon to see a bait and switch either… where they sell you a small batch of good cells for review, and ship something else when you place a large order.  Buyer beware is all I can say.
 
You are probably tired of me constantly bringing up EV cells as the preferred option, but I trust them.  I trust them because they were purchased by a large automotive manufacture for use in a production EV car.  I trust the manufacture of the cells, in my case that is Samsung, and the company who assembled those cells into a module, Bosch.  The likelihood of getting screwed is pretty slim.  Same can be said for a brand name laptop pack, but those are generally end of life which is why I stay away.
 
If you want big capacity from China, I would buy large prismatic LiFePO4 before ever considering a bulk order of 18650s which you will most likely end up wanting to test each and every one.
 
Rant over =)
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#15
Ok, I understand that.

However:
I would NOT buy 18650 from China. I would buy LTO (or LiFePO4 if LTO is too expensive).

With EV Battery Packs I have the problem that with expected cycle life they seem far to expensive. Same actually is the case for 18650 (at least in my opinion).

To get reasonable cycles I would have to dramatically overplan capacity, which adds additional costs.

So at the moment it seems (at least for me) LTO is the preferred chemistry.
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#16
Generally speaking, I would say your thoughts would be on point regarding EV packs vs high quality 18650.  The expected cycle life should be similar.  One thing to keep in mind is that in EV applications these batteries are probably stressed far greater than in a stationary powerwall application.  They have such a low resistance / high discharge potential that any generation of heat is almost non-existent.

If you really wanted to maximize capacity utilization, you could charge no more than 4.0 to 4.1 per cell, and discharge no more than 3.3 to 3.5v.  You would use up most all the available capacity while being kind to your batteries.  That alone should still increase your service life vs trying to fully charge it each time.

LiFePO4 is great, it has a much higher advertised cycle life, but it comes with it own challenges.  Monitoring SoC is far more difficult/critical, you will most likely need to use one of those battery monitors from Victron, along with a quality BMS as it's significantly harder to determine SoC by voltage alone.  The voltage stays relatively flat across the discharge chart, and steeply falls as it approaches empty (like fall off a cliff without warning).  Just something to keep in mind when designing a system.  That said, I would still over-provision LiFePO4 as well to keep the cells healthy.  Regardless of the type of cell, keeping it in balance to prevent under/over voltage conditions at the cell level is what is really important.  Chinese LiFePO4 cells have also been known to NOT have the best consistency, which is why over-provisioning helps, as it reduces the chance of a cell in the pack hitting a critical SoC at the top or bottom end.

I wish I knew more about LTO, perhaps it's time I get some cells for myself and make a small test system.
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#17
Quick search

For bought 18650 vs ali LiFePO4 vs a Dutch supplier LiFePO4 for the same capacity 200Ah 48v
18650 ~3500 euro
ali LiFePO4 ~3300 euro
Dutch supplier LiFePO4 ~12.000 euro
LTO i dont even dare to look at it.

Second handed 18650 cells bought ~1100

Its all down to what you want to spent in the next couple of years to come.
Second handed 18650, i think i must change them every 5 to 7 years.
According to what i have read so far, and i think there is no reason to doubt that.

The prices increases everywhere but also your paycheck.
Simple example: what was costing a bread 10 or 20 years ago, and what is it costing right now.
what where you earning 10 or 20 years ago, and what are you earning now?

In the long run the LiFePO4 would be cheaper?
Still learning English. Learning Li ion and solar technology.

4200 cells in packs Exclamation above 2500mah and 90%soh.
1500 waiting for testing.

Saving for 3 times phoenix inverter 48/3000 230v to gain also 380v
3 chargers?

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
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#18
(08-15-2019, 10:49 PM)Crimp Daddy Wrote:
(08-15-2019, 10:23 AM)DeepB Wrote: Are chinese suppliers really that bad? Are there known ok ones?

Unfortunately I do not really have a local reliable source, so it would be ebay or other online platforms (yes, I am looking at Alibaba)

Yes. No.  

Just to elaborate… knowing what I know about the industry, there is no way ever that I would place a large order, especially for 18650 format cells, from China, eBay, or any other import supplier.  Be wary of Japanese brands coming out of China.
 
There are so many reports of counterfeiting, re-wraps, poor quality, fraud that it’s not worth the risk.  Plus, you don’t really have a mechanism for recourse working with an international export seller.  Many have tried, and failed.
 
Even the good Chinese cells, like the ReVolt I mentioned previously, worked great up to a certain point, which was 335 full cycles and then degrade at an expedited rate.  Most all name brands, LG, Panasonic, Samsung don’t fall off like that and have better long term characteristics.  You get what you pay for.
 
It’s not uncommon to see a bait and switch either… where they sell you a small batch of good cells for review, and ship something else when you place a large order.  Buyer beware is all I can say.
 
You are probably tired of me constantly bringing up EV cells as the preferred option, but I trust them.  I trust them because they were purchased by a large automotive manufacture for use in a production EV car.  I trust the manufacture of the cells, in my case that is Samsung, and the company who assembled those cells into a module, Bosch.  The likelihood of getting screwed is pretty slim.  Same can be said for a brand name laptop pack, but those are generally end of life which is why I stay away.
 
If you want big capacity from China, I would buy large prismatic LiFePO4 before ever considering a bulk order of 18650s which you will most likely end up wanting to test each and every one.
 
Rant over =)

Do you have a link to the ReVolt cycle testing? I searched the forum and couldn't find anything. 

I agree that Korean/Japanese brands coming out of China are to be assumed to be fakes, rewraps, etc. I have several fakes that I found in generic laptop packs. I even have a thread about it: https://secondlifestorage.com/t-Genuine-...neric-Pack Luckily I did not deal directly with China for my laptop packs, and I would honestly not buy from a Chinese supplier because they don't really have any accountability, they are hard to deal with, etc. Also, the newer production generic cells are probably from startups that just want to put out product as fast as possible.  

As for the generic cells, I am finding in my cycle testing that 2/3 of my generics are falling off a cliff after 500 cycles, while the LG and 1 generic are still degrading slowly. https://secondlifestorage.com/t-Generic-...y-any-good Considering I paid less than 10% of what a new genuine Japanese/Korean cell of the same capacity cost, I'm not really complaining about only getting 500 stress-test 100% DOD cycles. 

To sum up: (1) Don't buy Japanese/Korean brands from China for full price; (2) If you buy from China, expect to receive inferior cells; (3) generic cells and fake cells can still be very good and safe cells, just make sure you don't overpay for them and make sure they have some sort of "brand" attached to them.
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Formerly known as Dallski
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#19
WOW - this thread is dynamite !

I feel this thread gets to the heart of it all - in 2 pages by diehard hardcore users with real world experience.

I have pretty much reached all the conclusions given here but only after reading hard over many forums for the last 2 years......yet its all here in 2 pages. Just fantastic. Well done to all who contributed !
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#20
About LTO, one word: expensive! Look at this example from BLS on Aliexpress. 60 Yinlongs 40Ah for around USD 3,200 which is 53 each! Looking at the specs I don't know with what inverter these things can be used optimal. Charge cutoff at 2.9 V so lets say your inverter goes up to 62V. 62/2.9 = 21 pieces. Now to get everything out of these Yinlongs (remember you want to go to DoD 100 percent) your inverter should be discharging all the way down to 21 x 1.5 = 31,5 V. What inverter is doing that?? So they're even more expensive cause you can't use them from begin to the end hence you need more batteries for the same capacity. Price around USD 3,200 for 5,5 kWh that is not fully usable.

Maybe you should consider these LiFePo4's the same shop is offering. They are priced way better. 6,600 USD for 206 x 3,2 x 48  = 31,6 kWh! That is roughly double the price for 10 times the capacity. Now they are talking! Usable for 100 percent the next 10 years or so. God knows what capacity we can buy then for this money.

Regards, Rik
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