General battery pack/PV planning

DeepB

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Hello,

I am currently building a house (in Austria, Europe). It will have PV (I want to produce more energy than I use).

The yearly usage will be approximately 6000 kWh. Base load (Servers, infrastructure, ventilation...) will be around 200W. I need 3 Phases.

1) What would be an appropriate sized Battery?
2) What is currently an easy/cheap battery type and source? Used 18650 Cells? Used EV-Batteries?
3) What is an approximate total cost for lets say 10kWh diy-battery usable in Europe?
4) What is the recommended Infrastructure? PV-hybrid inverter that can handle batteries? Normal Inverter and parallel battery structure?

thanks
Daniel
 
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 18650 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 18650 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.
 
I would need to get to about 100/kWh usable (for whole powerwall, not only battery) with a life of 1000 cycles to make it competable to the grid.
As this is not the only reason I will go (a bit) over that, but it must definately be <<150

Are there any alternatives to recycled 18650 cells in that price range?
 
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 18650 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 1000 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 (3000-4000 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 18650 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.
 
Cell cost for me was 260/kWh (all in, imported, delivered to door) however they are LTO chemistry and have 1000's of cycles life remaining (and can do 90% DoD /charge each day) so the cost per kWh over the next 15/20 years works out low enough to compete with the grid for solar storage and off peak charging in winter. It's not always the cheapest cells that make sense :
https://secondlifestorage.com/t-How-much-should-you-pay-for-batteries

Also for 3 phase you may need to consider what your doing a bit more carefully :
https://secondlifestorage.com/t-Controllable-grid-tie-inverter?pid=53140#pid53140

"Servers, infrastructure, ventilation" with 200W ? I can't leave mine powered up as they use nearly 1kW.

Summary I would say, if you want a large capacity, either go for large format cells or spend a LOT of time testing, soldering, building with 18650's.

3-phase - do your homework carefully.
 
I have a 7kwh PV array - producing 9,5000kwh 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 18650s.
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 18650s?
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 :)
 
1000 Cycles was just used for my calculation.

Current price for electricity is 0,153/kWh when I buy it, and ~0,05-0,06/kwh when I sell it.

So every kWh that I sell to the provider and have to buy again (for instance at night) costs me ~0,1
If I store it I calculate with 80 % efficiency, so I save 0,08/kWh.
A battery that lasts 500mcycles can cost 40/kWh usable
For 1000 cycles 80/kWh usable
For 3000 cycles: 240.
I am hesitant to calculate with more than 3000 cycles.

I know that this ignores the potential rise of energy prices.

Are there better suited batteries for me other than LiIon/18650?
LTO-Cells seem inhteresting, especially if new, what are the sources to buy in bulk?
 
LiFePO4 as mentioned above would be another chemistry worth looking at.

Most EV cells are the same/similar chemistry as your typical 18650, 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 18650s, and the savings compared to 18650 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

image_uchsrt.jpg
 
"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 3000 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 $1000 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 1600 all the same over 9 months.

These 2 sources are pretty much 18650 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 18650. 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 18650 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 18650 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.
 
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)
 
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.
 
CrimpDaddy said:
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 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 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 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 18650s which you will most likely end up wanting to test each and every one.

Rant over =)
 
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.
 
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.
 
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?
 
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 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 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 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 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.
 
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 !
 
About LTO, one word: expensive! Look at this example fromBLS 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 sameshop 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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