How many lithium batteries to equal my current lead acid system?

[Prosolar]

My current battery is comprised of 8- US Battery 440Ah in series and then two parallel strings . So, 48 V @ 880 Ah or about 42kWh

at 50% depth of discharge to prevent battery damage, that's 21 kWh of storage. If the bad guys were coming over the hill, I could discharge to 80% once in a while or 33 kWh. Let's stick with 21 kWh.

After looking at some sites, punching in numbers, to get 21kWh of lithium battery storage, the cost exceeds value let along common sense.

For example, four of the battle born 12V batteries @100 Ahrs would set me back $4k—still a long ways from the 440 Ahr of the lead acid bank (useable that I have now)

To come up with the 400Ahrs that I have currently I would have to spend $16K.

Yes, yes, and YES! I know I can discharge the lithium down to damn near zero capacity!
However to get the required 440 Ahrs of storage, needed for my three days of no sun loads, I can't see how in the world lithium will work for me.
They would also live in a rather cold environment during winter time, when temps inside the garage (where the lead acid live) could easily be 20ºF or colder for weeks. Last year the temp comp sensor for the charge controller recorded 8ºF at the batteries.

This isn't my first rodeo, i've been in solar since 1978, yet I'll admit I'm still old school with the lead acid batteries.

So is my math all wrong? I don't really want to screw around with importing Chinese cells and making my own packs. At my age, I don't have the luxury of time anymore.

I'm up for comments. So what say ye of the keepers of the lithium metal?

 

[chrisski]

If you’ve been in solar since 1978, how long has your lead acid batteries lasted?

That to me is the best data point out there. Seems lead acid will last one year if abused, but up to ten years if a decent set and well maintained. Since you’ve done this for so long, I’d like to hear some battery data.

If you went with building it out of cells, I think the total real cost would between $6k and $8k.

 

[Prosolar]

If you’ve been in solar since 1978, how long has your lead acid batteries lasted?

That to me is the best data point out there. Seems lead acid will last one year if abused, but up to ten years if a decent set and well maintained. Since you’ve done this for so long, I’d like to hear some battery data.

If you went with building it out of cells, I think the total real cost would between $6k and $8k.

I can get about 8 to 10 years with a set of golf cart batteries. The L16s (and all their variants) last me about 12-15 years. I currently don't discharge greater than 20%. They float 99% of the month. I also keep an tight eye on water levels, equalize twice a month and maintain a clean environment for them. Hell, I dust 'em!

REMEMBER!! Back in the late 70s the cost of a golf cart battery was $35 while a 100 W solar panel was $600. I did a lot of systems for ham radio operators back in the day. Now, it's flipped! A L16 is $395 and a 100 W solar panel is $75.
I got round $5k in my current lead acid battery.

$8k for Chinese batteries? Is my math correct for the Battle Born batteries? Would I in fact need $16K worth of them?

 

[John Frum]

My current battery is comprised of 8- US Battery 240 Ah in series and then two parallel strings . So, 48 V @ 880 Ah or about 42kWh

You don't explicitly say that the batteries are 6 volt.
I will assume it.
8x 6v in series = 240 amp hours@48 volts nominal.
2x strings = 480 amp hours@48 volts.
What am I misunderstanding?

 

[Prosolar]

You don't explicitly say that the batteries are 6 volt.
I will assume it.
8x 6v in series = 240 amp hours@48 volts nominal.
2x strings = 480 amp hours@48 volts.
What am I misunderstanding?

I apparently got a typo in there for the battery capacity. The US Batteries I have are rated at 440 amp hrs per cell. 8 x 6 = 48 @ 440 Ahr time two or 880 Ahr for the total bank. I fixed the goof up.

 

[John Frum]

880ah@50.4volts * .5 depth of discharge = 22176 watt hours

The popular big blue prismatic cells are 280ah.
280ah * 3.2 volts = 896 watt hours
896 watt hours * 16 cells = 14336 watt hours
14336 watt hours * .8 depth of discharge = 11468.8 watt hours
11468.8 watt hours * .9 @snoobler factor = 10321.92 watt hours
You would need 32 or 48 cells.

 

[snoobler]

880ah@50.4volts * .5 depth of discharge = 22176 watt hours

The popular big blue prismatic cells are 280ah.
280ah * 3.2 = 896 watt hours
896 watt hours * 16 cells = 14336 watt hours
14336 watt hours * .8 depth of discharge = 11468.8 watt hours
11468.8 watt hours * .9 @snoobler factor = 10321.92 watt hours
You would need 32 or 48 cells.

I'm willing to adjust to 0.95 if you are.

 

[chrisski]

32 Cells alone would cost A little more the $4800. 2 BMS would take this to $5000. THose are shipped to your door prices. From there, its if you add active balancers, and whatever other hardware needed.

Part of the higher cost for me going to lithium from a 12 volt system to a 24 volt system. I’m getting 16 Cells.

Really sounds from what you said, that you could stick to Lead Acid and be fine.

 

[Prosolar]

Poked around this forum looking at the prismatic batteries. Seems to be kinda crap shoot. Need more information about the cells

 

[time2roll]

As long as the lead is working for you, save your money.

 

[rhino]

Poked around this forum looking at the prismatic batteries. Seems to be kinda crap shoot. Need more information about the cells

See https://diysolarforum.com/threads/introducing-the-new-improved-shenzhen-luyuan-technology-co.15880/
Amy is a member of this forum as well and is well respected/reliable seller of cells.

 

[John Frum]

I'm willing to adjust to 0.95 if you are.

Sold!

 

[snoobler]

Poked around this forum looking at the prismatic batteries. Seems to be kinda crap shoot. Need more information about the cells

If you purchase from trusted suppliers, it's not a crap shoot. There is some uncertainty in the total capacity, but the 0.95 factor seems to be holding, i.e., even the cheapest commodity cells purchased from reliable suppliers will have 95% of rated capacity for a small fraction of the cost of matched cells from U.S. distributors. The trade-off is wait time. You may need to wait a few months to get your stuff.

A good rule of thumb for 280Ah commodity cells is $1000/8 cells yielding 5.7kWh USABLE capacity

As long as the lead is working for you, save your money.

This... So. Hard.

Sure, when it's time to upgrade, yeah. Consider LFP.

 

[Hedges]

Yes, commercial lithium batteries cost a lot of money. With about 5x the cycle life or more, they cost the same number of $$/kWh of cycles; you pay 5x up front and they (hopefully) last 5x as long.
That's only if you cycle them deep enough and often enough. At 80% DoD every night, lead-acid can last a couple or a few years, quality FLA longer than quality AGM. Lithium can (theoretically) last 10 years, possibly more.

As you note, sizing a battery bank for 3 days without sun is expensive - and means only cycling it 15% on a typical night. Under those conditions lead-acid forklift batteries can last 15 years, negating the longer life benefit of lithium.

Another advantage of lithium is it doesn't care what charge rate, up to about 0.5C (except when cold or very hot), vs. lead-acid which has a preferred charge rate. Also, lithium can be left at any SoC except full or empty, while lead-acid wants to be topped off. Also, capacity isn't reduced much in freezing weather, the way lead-acid is.

Disadvantages include can't charge below freezing, and allowed charge rate tapers off at lower temperature. Simplest way to deal with that is determine maximum "C" rate your PV could charge at, and set BMS to cut off charging if battery temperature ever drops below corresponding temperature. If PV gives 0.05C, OK down to zero degrees C, but if charge would be 0.20C then maybe down to 10 degrees C. That is for protection; to actually use lithium in your freezing environment, you will have to insulate and heat them so they can be recharged.

However, cost of DIY lithium battery can be fewer dollars than lead-acid. Which could make the switch a no-brainer. Compared to my SunXtender AGM, I think DIY with 280 Ah LiFePO4 cells and BMS would be about 40% the cost. Some small-name battery companies (think of it as them doing DIY for you) about equal price per kWh capacity.

Don't believe the cycle life quoted by lithium battery vendors. Perhaps 95% of brands tested failed long before reaching that life. A couple brands actually delivered. To me, all the more reason to DIY so you already know how to repair, replace BMS or whatever.

Are LFP prices artificially high?

Cost is irrelevant to sale price. market value is king. profit drawn from building, marketing, future sale reduction pricing, etc. I would be EXTREMELY surprised if sales were anywhere close to material and labor and manufacturing costs... It's like the cannabis market. It costs MAYBE $50 to...

diysolarforum.com

 

[Steve_S]

Poked around this forum looking at the prismatic batteries. Seems to be kinda crap shoot. Need more information about the cells

A Known Good Vendor who has supplied Thousands of cells to our membership is Luyuan Tech who sells Genuine Grade-A Matched cells WITH Matching Test Reports as they are Properly Matched & Batched at the factory.
Fully Matched 280AH cells = $125USD, Bulk Commodity cells = $91.50 ea.

Products list direct from CN

Main products Lifepo4 battery, LTO battery and 142 more Products from Shenzhen Luyuan Technology Co., Ltd. on Alibaba.com

szluyuan.en.alibaba.com

Bulk Cells typically test between 260AH-280. You get a guaranteed 260AH.
Matched cells typically test between 282Ah-295AH. You will get the 280AH.

48V/280AH/14,3kWh. (figure $2000 USD with BMS, Fuse & Box,)
$4000 USD = 28kWh @ 48V.
NOTE: S&H GUESSTIMATOR says $2100 BUT you must open a Chat/Messenger session to get a REAL Quote, the guesstimator is woefully off,

BTW: I went from Rolls Surette Heavy Lead 22kWh to 30.4kWh of LFP, the lead just did not make sense anymore... LFP was cheaper than buying set of Rolls-Surrette S6 L16-HC (was S-550). plus no fusting with watering and acid or equalization runs etc...

Please have a look at the links in my signature, there is a lot there that will help you along your adventure.
Hope it helps, Good Luck.
Steve

 

[Prosolar]

32 Cells alone would cost A little more the $4800. 2 BMS would take this to $5000. THose are shipped to your door prices. From there, its if you add active balancers, and whatever other hardware needed.

Part of the higher cost for me going to lithium from a 12 volt system to a 24 volt system. I’m getting 16 Cells.

Really sounds from what you said, that you could stick to Lead Acid and be fine.

A Known Good Vendor who has supplied Thousands of cells to our membership is Luyuan Tech who sells Genuine Grade-A Matched cells WITH Matching Test Reports as they are Properly Matched & Batched at the factory.
Fully Matched 280AH cells = $125USD, Bulk Commodity cells = $91.50 ea.

Products list direct from CN

Main products Lifepo4 battery, LTO battery and 142 more Products from Shenzhen Luyuan Technology Co., Ltd. on Alibaba.com

szluyuan.en.alibaba.com

Bulk Cells typically test between 260AH-280. You get a guaranteed 260AH.
Matched cells typically test between 282Ah-295AH. You will get the 280AH.

48V/280AH/14,3kWh. (figure $2000 USD with BMS, Fuse & Box,)
$4000 USD = 28kWh @ 48V.
NOTE: S&H GUESSTIMATOR says $2100 BUT you must open a Chat/Messenger session to get a REAL Quote, the guesstimator is woefully off,

BTW: I went from Rolls Surette Heavy Lead 22kWh to 30.4kWh of LFP, the lead just did not make sense anymore... LFP was cheaper than buying set of Rolls-Surrette S6 L16-HC (was S-550). plus no fusting with watering and acid or equalization runs etc...

Please have a look at the links in my signature, there is a lot there that will help you along your adventure.
Hope it helps, Good Luck.
Steve

Hi, steve,

you and I chatted on the midnite solar forum about lithium batteries. I'm still concerned about cold weather operation. I have been kicking around the idea of adding a back up to my 20 year old trace inverter using one of the new DYI inverters from Midnite solar and a lithium battery pack. It's a project in planning right now

mike

 

[Supervstech]

If you are needing to replace your bank, the positives of LFP are nice. Lower cost over the life is one, but not the biggest. Size and weight are bigger if that is a reason. Charging and maintenance ease, environment needs, LFP doesn’t need water, equalizing, or peak voltage float. LFP doesn’t offgas unless SERIOUS problems are present.
another LFP bonus is the charge efficiency… lead wastes around 25% of solar power to efficiency and charge rate differences to available sun… lithium is far more efficient with energy transfer.

BUT… if you have lead, and are comfortable with the maintenance, and it is performing well… why change it?
low temp is certainly a hazard for LFP, but building an insulated box around them often is PLENTY to keep them warm. Adding heat to an insulated box isnt difficult.

 

[Steve_S]

Hi, steve,

you and I chatted on the midnite solar forum about lithium batteries. I'm still concerned about cold weather operation. I have been kicking around the idea of adding a back up to my 20 year old trace inverter using one of the new DYI inverters from Midnite solar and a lithium battery pack. It's a project in planning right now

mike

One common solution folks use is a silicone heating pad with the thermostats that heeps the cells at 50F or so, powered directly from the battery pack itself. Now there are a few Nasty Energy Hogs but there are many which are quite efficient. Several people here use them with great success and Will have reviewed several. I myself have a heated powerhouse so it does not play into my setup , therefore I've not used those myself.

 

[Prosolar]

If you are needing to replace your bank, the positives of LFP are nice. Lower cost over the life is one, but not the biggest. Size and weight are bigger if that is a reason. Charging and maintenance ease, environment needs, LFP doesn’t need water, equalizing, or peak voltage float. LFP doesn’t offgas unless SERIOUS problems are present.
another LFP bonus is the charge efficiency… lead wastes around 25% of solar power to efficiency and charge rate differences to available sun… lithium is far more efficient with energy transfer.

BUT… if you have lead, and are comfortable with the maintenance, and it is performing well… why change it?
low temp is certainly a hazard for LFP, but building an insulated box around them often is PLENTY to keep them warm. Adding heat to an insulated box isnt difficult.

Thanks for the input. I won't be replacing the lead acid batteries for a while, I hope they out last me. What I'm thinking about is adding onto my system. The Trace 5548 inverter I'm currently using is about 20 years old. I know it only a matter of time before it up and quits. I'm thinking of adding a second 48 V system with another inverter. While I could run it off of the lead acid battery, it thought it was time I get into the 21st century and try out some lithium batteries.

but tell me.... if I were to replace what I have, 440 Ahr with an equal amount of lithium such as the battle born, would I in fact have $16K worth of batteries?

 

[snoobler]

440Ah * 48V = 21120kWh

You would need 21120/.8 = 26400Wh LFP assuming 80% usable.

Each BB has 1280Wh, so you would need 20.6 of those batteries (round down to 20), so 5 strings of 4S at closer to $20K

If you are okay running them down to 0%, then yes, 16 batteries is correct at about $16K.

Alternatively, DIY for even more capacity (28kWh) will run you $4000.

 

[Supervstech]

Thanks for the input. I won't be replacing the lead acid batteries for a while, I hope they out last me. What I'm thinking about is adding onto my system. The Trace 5548 inverter I'm currently using is about 20 years old. I know it only a matter of time before it up and quits. I'm thinking of adding a second 48 V system with another inverter. While I could run it off of the lead acid battery, it thought it was time I get into the 21st century and try out some lithium batteries.

but tell me.... if I were to replace what I have, 440 Ahr with an equal amount of lithium such as the battle born, would I in fact have $16K worth of batteries?

Well… you would need 18 12V-100Ah Battleborn batteries, or 18 24V-50Ah … and they sell for around $900 each. There are lower priced options from them. And sales happen. But, yeah, sounds like $16K. However, running 100% loads on lithium doesn’t yield the cycle life improvements over lead… keeping in the 80% DOD and not filling beyond 95% gives the 2000-5000 cycles most expect. So, ya might even want an extra 4… pushing up to the 20K range…

Will has reviewed several batteries that are far lower cost, amperetime, and chins I think we’re reviewed with mixed results. Some of the battery builders out there are selling enclosed packs, with cold weather protection and heating for 1/2 the price of Battleborn. So shop around for sure. Check the threads on the different options.

 

[Prosolar]

440Ah * 48V = 21120kWh

You would need 21120/.8 = 26400Wh LFP assuming 80% usable.

Each BB has 1280Wh, so you would need 20.6 of those batteries (round down to 20), so 5 strings of 4S at closer to $20K

If you are okay running them down to 0%, then yes, 16 batteries is correct at about $16K.

Alternatively, DIY for even more capacity (28kWh) will run you $4000.

Thanks for verifying what I thought. I've watched a lot of video with a couple living off grid and having battle born (or other brand) batteries and wondered how they could afford it.

 

[Hedges]

A PV panel costs $0.025/kWh (amortized over 10 years)
AGM costs $0.50, FLA costs $0.25/kWh over its cycle life.
Name brand lithium batteries cost $0.50/kWh (if they deliver the promised 3500+ cycles)
DIY lithium costs $0.05/kWh (again if they last)

My system is grid-backup, with AGM just big enough to get through one night and enough PV to recharge it 5 times over during the day.
If you have a backup generator and you added extra PV (cheap now), undersize battery might work for you. But DIY lithium is affordable.

 

[NwCali]

My box 10kwh 48vdc battery cost $2800 to my door, so two of those $5600.

Build it yourself for far less.

You could still dust them (if you wanted). But you'd not have to add water/baby them to just sit there.

 

[NwCali]

the battle born

Why are you stuck on battle born? Do they look that sexy? IMO there are better/cheaper options out there.