General battery pack/PV planning | Second Life Storage & Solar

1)What would be an appropriate sized Battery?

• Double your daily consumption would be ideal to discharge to 50% SoC. Which allows for some headroom on low PV production days and often times helps longterm cost of ownership by not going deep on cycles during regular use. I personally oversize my batteries as much as possible.

2) What is currently an easy/cheap battery type and source? Used Cells? Used EV-Batteries?

• Cost of batteries based and remaining service life, quality, consistency will all play a roll. I prefer used EV cells by a large margin. Less labor and cost to construct packs, easier to find a large batch which is great for consistency, and depending on the vehicle mileage may have a much longer service live than used laptop packs which are probably at the end of their service life. Obtaining used of good quality (medical packs) in LARGE quantity is harder than just buying EV cells.

3) What is an approximate total cost for lets say 10kWh diy-battery usable in Europe?

• In USD, expect to pay about $100 - $225 per kWh for raw materials in EV cell cost.

4) What is the recommended Infrastructure? PV-hybrid inverter that can handle batteries? Normal Inverter and parallel battery structure?

• 100% depending on your needs and design. Something like a Victron Quattro would make for a VERY versatile setup. Allows the system to be configured in various ways including Grid or Battery priority which allows the system to act as a UPS, or use battery and use grid or gen as a supplement for higher loads too. On a side note, I would not charge though inverter, I would have a separate MPPT charge controller for PV.

Finding batteries worth using is the core challenge everyone here faces. There is no consistent inexpensive source for good used cells as supply and inventory is constantly changing. If you really want to use cells, research the cost per kWh of making cells into a battery and let that play into your decision. Using cell holders and solder vs spot welding vs PCB builds all have different costs and labor challenges involved.

For the sake of conversation I live in an area where grid power is reliable and affordable. If I look at my project and try to complete with the grid, I already lost. The ROI is poor from that standpoint, but I didnt start this project to complete with the grid. I did this project because I enjoy this stuff as a hobby and find it fun, like to learn, and thought it would be good for emergency use. Yes it makes power, saves me money, but my ROI may not be realized for years to come assuming the system even last that long. On top of that, I keep changing things around, and or buying new interesting things like a high end inverter vs a basic unit or a new MPPT controller.

On to your comments full cycles could be considered a lot for a lithium-ion chemistry. Brand new Chinese cells (Revolt) which have been well tested and documented by members here have shown significant degradation as soon as 335 cycles and continues going down as cycle count increases. Contrast that to brand name cells like Samsung, which still degrade, but hold up much better at higher cycle counts, but still show some fatigue at 500 full charge/discharge cycles with perhaps a 15% to 20% reduction in capacity.

Point is, dont cycle too deep and over-provision capacity to give your cells a fighting chance. So if you use 10 kWh per day, I would add at least 20% more to combat against capacity loss over the course of service life, and then double that to reduce the depth of discharge, and the need to fully charge which can also negatively impact cell life. So if you use 10 kWh per day, I personally would want a battery that has at least 20 to 24 kWh and I live in an area where I actually get a lot of sun. You might not need a bigger battery, but you might need even more panel to charge that capacity if you dont get a lot of sun hours otherwise you end up with a deep depth of discharge because you cant top off for the next days loads.

Alternately, you could consider using LiFePO4 chemistry lithium batteries those typically have a significantly larger cycle life (- cycles), the cells also cost more money, but they can beeasily sourced newin large prismatic cells which save a lot of time and money when building packs with cells.

Perhaps start with a small system, and build your own proof of concept before going big. You might learn some things along the way that might change how you approach your own project. I have a 7kwh PV array - producing 9,kwh per year. So far this year (thru Aug 11) the house has consumed 2,654hrs of inverter power at an average of 2,197watts per hr. In summer, the 7kwh PV array produces 40-45kwh/day of which 30kwh is used 'directly' (during PV array hrs) and 15kwh excess is strored in battery and consume thru night.

My goals are
1) consume 100% of PV array input - e.g. I never go into 'float'
2) try to get my money back (grid power is only 0.12c/kwh in my situation)
3) run my home 'just fine' if things go awry like Puerto Rico and power is lost.

For #1 - I need a battery bank big enough to charge/discharge 15kwh/day in max (summer) days.
For #2 - I need the system (including the battery) to last 20yrs - e.g. 7,000 daily charge/discharge cycles.

It has cost me $307/kwh made up of ~6,500+ cells, holders, solder, wire, Batrium/longmons, failures, shelves, misc .. to build a 53kwh battery of s.
The 15kwh/day is a DOD of 29% in the range of 4.0v/cell -> 3.4v/cell.

As the battery degrades.. even when it's down to 50% of current capacity (26.5kwh) I can still get my 15kwh / day at 56% DOD. 20yrs is too long to make any meaningful predictions but charts on Battery University give me 'hope' that it might be possible.

So PV array input, battery size/expected-life, consumption, cost all work together BUT can also be like pushing both ends of a string - make a tangled mess. I had no idea when I started this almost 2yrs ago but have come to focus on GOALS. So I think if you work on your goals it will give you a framework to weight choices and costs etc.

For example - one of my goals is 20yr ROI. So I can ask myself questions like:
1) Can I get there using s?
2) Is there a DOD sweet spot that will get me there vs $$ to increase my battery size to lower the daily DOD? (in other words, does 50% reduction in DOD get me 400% longer life??)
3) Should I switch to LifePO4 or LTOs ... what do they cost?
4) Should I pay $250.00 for 100 used cells or $104 per 100 and risk a 25% failure rate/break the packs apart myself.

The answers are not immediately clear ... but at least you can fix one end of the string LiFePO4 as mentioned above would be another chemistry worth looking at.

Most EV cells are the same/similar chemistry as your typical , just in a larger form factor. At least from a voltage range standpoint, the same.

LTO cells are still in a segment that is still developing. I expect many changes here over the years. Buying now I would feel like an early adopter, but I also have limited experience with this chemistry.

I still feel some of the absolute best deals around are EV modules I got these from a salvage EV that only had less than 10k miles on it. All the cells are very healthy and consistent in terms of performance. Sure beats scraping the bottom of the barrel for s, and the savings compared to time/cost to build into packs was just night and day. I actually ended up selling 400-500 lbs of laptop packs after I got a hold of these and never looked back.

Perhaps reach out to your local automotive parts yard / salvage companies and get a hold of a EV pack and take it apart yourself.

33kWh

"I know that this ignores the potential rise of energy prices." - this is more a question of comparing 1 EUR in the bank earning a return higher than the inflation (and volatility) of energy prices.

If "For cycles: 240" is an issue you need to figure out what your going to do for the 3-phase supply and inverters before looking at cells

For your inverter, charger and any other components in the system work out a lifetime cost per kWh and factor this into your storage throughput cost as this will lower your 0.08 down a bit and then re-evaluate the cell position. Part of the value is in powered on hours and part of it is based on kWh throughput.

Solar all-in costs should be around 0.04/kWh or lower (making the margin over 0.1/kWh)

If you get an export value, over size the solar rather than buy more battery capacity... to balance more of the winter and cycle the cells


EV packs ar as mentioned, if cheap enough (base on remaining cycle life), are the best route for a build. This is probably the route I would suggest. Select carefully and research well...


I'm biased, however, for me LTO deciding factors were :
1. No issue with low temperature (no heating / cooling of cells) so they can sit outside or wherever (point 9)
2. Long cycle life and low maintenance (once built no messing with the cells for a long while, hopefully)
3. Worst case discharge to 0V does not do any real damage
4. Self discharge is near zero - tested a cell left in the shed a year...
5. Portable packs (ok not really chemistry dependent, unless you take point 1 into account)
6. I have fixed my energy cost (with solar) for the next 10+ years, hopefully 20, electric price is only going one way.... tax.
7. Just as good as a pension, appart from you have the asset and can look at it, even put your feet up on it while you have a cup of tea (boiled in a kettle powered by the pack !)...
8. Mature technology, although lacking actual cycle life testing to 30,000 cycles (I think they only had about 15,000 cycles in the test data). It is still developing though
9. No bursting into flames if the cells are damaged, very difficult to set on fire

I like options.... I agree with all said here. For me - the biggest / key issue that I've tripped on is *trustworthy* battery purchase. Its complicated because you don't (typically) have the $10,000-$15,000 (or whatever - big number) to buy 40kwh (or whatever) worth of batteries all at once. I bought mine in 20 separate purchases over last 2 years - a few hundred here, a $ there, etc. So it became important that:
1) I had trustworthy source. I tried several ebay (china) and got burned badly. I'm afraid of Alibaba.
2) Stead source. I have come to believe its better to have same cells for my batteries as much as I can manage... so I need to re-purchase additional cells over time.
3) I rejected the 'troll laptop stores for dead laptop batteries' as its too much of a crap shoot - I feel better buying used batteries that have had some known history.

I wound up with Alarm Hookup and Power2Spare as the only 2 sources that I feel comfortable with thru much experience. They both give me 1) reliable delivery as adverstised AND 2) I can repeat purchases so that when I build a battery (1,680cells) I can purchase like 400 at a time and be fairly sure I can get all the same over 9 months.

These 2 sources are pretty much format.

The price of LTO as far as a few quick queries is *way out there* and LifePO4 CALB keep coming up double/triple compared to . I've longed for Nissan Leaf(s) as they are 3.7 volt chemistry, but again - its a lot of money to find out I was delivered 45ah batteries instead of 66ah. Unfortunately I do not have any contacts for battery sources... that would be invaluable! so I'm limited to retail purchase.

One advantage of is I can repair / adjust a 'battery' by adding/replacing a few cells. If I did 200ah prismatics, I'd have to replace the entire 200ah cell. The downside is is A LOT OF WORK! I now have 6,700 cells and I'm pretty much committed at this point.

Bottom line - figuring out some good sources of batteries is (in my opinion) a key issue and depending on their stock and price points - it can well direct one into certain paths.

CrimpDaddy said: You mentioned your yearly usage is about 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 kwh / year. My average consumption is watts/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 asmaller battery and you'll likely find that1) you're doing ahigh 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 but just leave room for future growth.

DeepB said: 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 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 its not worth the risk. Plus, you dont 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 dont fall off like that and have better long term characteristics. You get what you pay for.

Its 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 s which you will most likely end up wanting to test each and every one.

Rant over =) Generally speaking, I would say your thoughts would be on point regarding EV packs vs high quality . 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.

CrimpDaddy said:

DeepB said: 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 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 its not worth the risk. Plus, you dont 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 dont fall off like that and have better long term characteristics. You get what you pay for.

Its 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 s 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 tobe 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-Cells-in-a-Generic-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-Cells-Are-they-any-good Considering I paid less than 10% of what a new genuine Japanese/Koreancell 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.

Group Battery Purchase

We are getting to a point where LiFePO4 prices are coming down and our collective desire is going up. By using the power of collective bargaining we should be able to find some way to create a "Group Battery Purchase" where we can get the price down because of volume.

Let me first apologize in advance for the people here that make battery building and selling a business. The people who would likely go in on a group purchase are those that post here regularly and are very knowledgable about all aspects of this technology. The "public" will need to buy pre-configured battery packs, but many of us here are nearly manufacturers ourselves in our depth of research and knowledge. So what we are doing is not for the "common man".



Patrick has presented an ability to deliver these LiFePO4 Cylindrical Cells () under the condition that a bulk purchase of 100 can be done at a price of $30 each.

Capacity: 10Ah
Volt: 3.3v
Dimension(mm): 40*138mm
Weight(g): 400
Standard Discharging: 1.0C
Quick Discharging: 3.0C
Max Discharging: 10.0C
Cycle Life: >Times
Temperature(Discharge): -20~75
Storage Temperature: 0~45
Self-Discharge (Month): <5%
Energy Density wh/L: 170
Energy Density wh/Kg: 80
Initial Internal Impedance<6m

http://www.made-in-china.com/showroom/yesa001/product-detaildqSmjwhOPfco/China-LiFePO4-Cylindrical-Cell--.html

I notice on this link that they say the minimum to order direct from China is 10 pieces, but they don't say the price.

A Two Stage Process

As I see it there is a two stage process that needs to take place:

First... it's necessary that collectively we identify the absolutely best deal that can be found. If the best deal is through Patrick then that's great and we can go forward. If another deal is found that might have counter balancing conditions (like a very high volume restriction) then we collectively need to cross that bridge when we get there.

Second..., once the best deal is found, if a number of people are required to make up a high volume order we need to get first a pledge of interest and later that needs to be followed with some more concrete $$$ to prove that this is going to happen. We might want to require an advance of 10% of the purchase price so if someone backs out the remaining cells can be turned around without anyone feeling hurt. (other than the person that backed out, but that's their problem) The other option is to somehow make the money transfer done collectively all at once... I'm not sure how that might be done, but if Patrick was involved he could probably use his business to do the accounting side of it.

Feel free to comment on any aspect of this process or present a deal that you might have found... Wow, That is one sweet deal at a very desireable time

:? However, Yesa sells these at $35 each (month ago) without buying 100 at a time. Also, we were told by a US seller that some of these from China are seconds that didn't make the grade and are almost a year old, this is why there is no MFG date markings on the ouside cover. I don't know how much of this is true, or these particular cells either. BUT... Shipping from China alone is $180 for 32 cells.
I'm all for saving money and definately buying 32 of these wonderfully designed cells in a month. But still leaning towards buying from our local North American brothers (who post here)... for a few reasons.
a) We save $$$ on shipping charges
b) We support our countrymen and have closer ties if we have any problems.
c) And lastly, I worked in manufacturing for many years, don't get fooled by appearance, It costs more to make a quality item, and get them independently tested like our local boys did. It's late, hope this makes sense tomorrow morning.

P.S. I think these cells should'nt cost more than $30 though, heck, street drugs are cheaper than that, so i'm told PingBattery,

I represent a group of people who are very dedicated to electric vehicles and are searching for a dependable and affordable supplier of LiFePO4 battery packs. Our group has an online website where products are discussed. We would like you to register with us and "sell" your product through us. We can give you additional credibility with the electric vehicle crowd because we have some really smarts guys in our group.

http://endless-sphere.com/forums/viewtopic.php?f=14&t=

My name is "safe" online

There seems to be no response, so that makes me suspect that they are either too busy (or already on their chinese vacation) or they are not interested in selling themselves to an educated audience. I'm sure there's no shortage of people who will buy anything they post on ebay so they might not need to bother even trying to sell. We will see.

It would be nice to get a relationship set up with people who do live in China and can get the raw batteries at "chinese" prices. However, the shipping is rather expensive so when you do the final calculation the "original price" and the "final delivered price" are quite different. My guess is that in China the cells go for maybe about $15 - $20 each and all the rest is shipping and markup. It would be nice to know more... Hey everybody,

I thought I'd chime in here, and let you know how things stand as I see them.

First, the cells are 10C rated, 12C max as I understand it it. 3C charge is correct.

Second, I talked to the powers that be, and we can do $30/cell with a minimum 30 cell order. $35/cell is to cut down on onesy-twosy orders, which are a pain, almost more trouble than they're worth. Hopefully this will also eliminate the logistic trouble of coordinating the buy, the money, etc.

Third, we don't have a huge number of cells yet; we've got a few test packs and some loose. If any are going to be ordered, it should be this week, as we're going to be out of pocket for the next two weeks. It was said earlier that Chinese New Year is almost upon us, and this may delay things, I don't know. At least you know we're not sitting on some old inventory.

Fourth, I am expecting about 3 weeks shipping time to San Francisco (leaving any complication of the New Year aside). Frankly, I expect it faster, but would rather give an outside quote than disappoint people.

Fifth, there is the issue of testing. We can certainly put some on a CBA and give discharge curves. I can also send one to somebody on the board for independent analysis. My thought was DoctorBass if he is amenable, but I am open to suggestion. Fechter works in the neighborhood, and I could just drop one off to him - much faster if he has the time.

Lastly, what I am expecting in response. What I am looking for is a sense of commitment. If you want delivery in the next 30-45 days, you need to speak up and state your interest (you can certainly PM me, that might be more comfortable for everyone), so that we can get an idea of what to do. Let's say Tuesday (midnight PST) cutoff. No deposit required - it's the honor system. Remember the honor system works both ways - if you are unrealistic that might affect any future dealings. You can state this in any way you want:
I definitely want xx cells!
Think I want yy cells, but want to see the test results.
I'm sort of interested in zz cells, but not really sure . .

Obviously, the more commitment, the higher priority for your order. I can't say fairer than that.

Have a great weekend!

Patrick

Patrick said: ...we can do $30/cell with a minimum 30 cell order.

I could use the full 30 and make two bikes with them, but would rather start small if possible. 15 is all I would need (in series) to produce a 48 volt pack that should be able to pull (4C) 40 amps pretty easily. That's $450 for a 48v 10ah (480 Wh) pack.

Anyone out there interested in 15 so that you could split it with me?

This is half of the price of LifeBatt.com for the same cells. ($440 for 8 compared to $450 for 15)

However, I still have to ask if there is a big hurry. It's only the beginning of February and most of us won't be actually using our bikes until about May or June. The weather in the midwest really sucks, my garage is still in the 40 degree range, so I won't be working on anything for a while.

I just have this feeling that if I buy something now that a few months later the price will drop. It's like buying a flat panel tv a few years ago... everything was $. Now you can get the same product for about $700, so I'd rather buy the minimum amount that I need for now and not any more. Yes, the cells are threaded (have bolts) on each end. Red on one end, black on the other. I will post a few pictures later (in the middle of cooking, another joy in life, the BBQ timer is beeping). Also have some codes (and presumably serial numbers) on each.

They are not made in Shenzen (China), but in Taiwan.

Also, I agree with Safe. LiFePO4 is exploding, and (although not literally) I mean that in both a good and bad way. Yes, always something better "just around the corner". Myself, I still use lead - I've got so much (maybe 10 kWh) who cares? But how far away that corner is is a personal question. If you are happy with what you've got - stay with it!

However, his example was years compared with months. It may take a month or two just to get these. I'm not pushing it, just trying to offer an alternative to earlier adopters. http://visforvoltage.org/forum/-hands-test-48-volt-20-ah-lifepo4-pack-ping-battery

Re: Hands on Test : 48 Volt 20 AH LiFePO4 pack from Ping Battery

Submitted by andys on Thu, 01/17/ - 02:23.
In answer to the question above, I also own a YESA 48v 12AH pack that cost more than the 48/20 does from Ping. Pings pack has way more power and capacity in my experience with them both on the same scooter, and of course it should being a 48/20. So far, its a way better deal. I didn't ask too much detailed info on what individual cells he used. He mentioned something about them being a "soft as opposed to a hard style" that YESA uses. The cells he uses are also more compact. YESA's 48/20 wouldn't fit in my battery box.

The "soft" cells are what is called "prismatic cells". They are like a foil pouch so you can pack more of them in a tighter space.

Don Harmon

So PingBattery is using some odd LiFePO4 cells, not the cells.