John Brown
Freeloading Social media influenza
But doesn't even a single lithium cell have a "topping off" period of a lower charge rate?
One family's solar story
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I can understand using high density Lithium batteries if space is a premium or it is something portable like a car or tool but in a situation where space is not tight then what is wrong with deep discharge AGM batteries, I can recall UPS instalations that used large banks of high capacity 2 volt cells but cannot remember the reason behind 2 volt cells and not 12 volt batteries.
John Brown
Freeloading Social media influenza
Maybe to facilitate changing dead cells.
Lead acid is 2v per cell. There is nothing special about 12 or even 24v. They just happen to be a good compromise for cars and trucks. So if your required voltage is say 48v as found in telecomms all over the country and your need for Amp hours is large in a serious backup battery, it is entirely sensible to assemble it from indvidual cells.
Even deep discharge agm type lead acids have nowhere near the life of lithium batteries. 500 to 1,000 cycles, not 3,500 - 8,000 cycles.
UPS are intended as backup devices, not for daily cycling. They sit on float charge and are only called on when something goes wrong.
Deep discharge recreational batteries used in RVs etc are generally only used during holidays and weekends.
Lead acid batteries used in Chinese scooters lose capacity / range quickly in daily use and would be at the 80% / replacement level inside a year.
I don't know about milk floats - assume with their huge batteries that they don't discharge them very deeply and so achieve a decent lifespan.
Even deep discharge agm type lead acids have nowhere near the life of lithium batteries. 500 to 1,000 cycles, not 3,500 - 8,000 cycles.
UPS are intended as backup devices, not for daily cycling. They sit on float charge and are only called on when something goes wrong.
Deep discharge recreational batteries used in RVs etc are generally only used during holidays and weekends.
Lead acid batteries used in Chinese scooters lose capacity / range quickly in daily use and would be at the 80% / replacement level inside a year.
I don't know about milk floats - assume with their huge batteries that they don't discharge them very deeply and so achieve a decent lifespan.
Yes.
Solar battery management systems are pretty sophisticated chargers but lithium generally is charged constant current (ie high current but capped) and then shifts to constant voltage where the current steadily reduces as the battery voltage rises.
I know my setup has the capped maximum charge rate because on a very bright day when the roof gets up towards its 9kW maximum output, we can see the battery charging top out at 6.6kW and everything above that gets hoovered up by the solar diverter. Usually worth a smile when you see it working hard like that
All L/A (regardless of type) are poor performers in comparison to the LFP/LYP lithiums (far less actual storage than lithiums for the same rated Ah) and economically don't make sense any more for any but the smallest/cheapest setups (a home setup is a substantial installation and using L/A in the long run means a substantially higher installation cost long term for the same storage capacity...)
The use of 2v cells was simply because a cell failure meant replacing that one cell, rather than 3 (throwing away 2 good cells) for a 6v battery, or 5 for a 12v battery- plus when you start getting into the larger capacity battery packs, the sheer size becoms an issue for using 6v or 12v batteries- paralleling multiple batteries gives poorer longterm results than a single series string, but a 400ah 12v single battery is literally in the 'need a forklift to move it' weight range, where a 400ah battery pack made up of individual 2v cells is 'heavy but not impossible' in weight per cell... (and a pack made up of 400Ah lithium individual cells can easily carried by a single person per cell... and will give almost 2/3 more actual stored energy available than a 400Ah L/A of the same voltage.... for years longer...
Decades ago, it wasn't uncommon for those of limited means to buy 'dead cell' deep cycle 6v or 12v batteries and literally hacksaw them open to gain access to the interior busbars to 'bypass' the dead cells to make up a single good battery out of two dead ones- I know, because I did it myself lol
(it was a cheap way to get battery storage at the time lol, when battery costs were extremely expensive indeed, even for L/A- the lithiums (and even the nicads) weren't even around at the time)
The use of 2v cells was simply because a cell failure meant replacing that one cell, rather than 3 (throwing away 2 good cells) for a 6v battery, or 5 for a 12v battery- plus when you start getting into the larger capacity battery packs, the sheer size becoms an issue for using 6v or 12v batteries- paralleling multiple batteries gives poorer longterm results than a single series string, but a 400ah 12v single battery is literally in the 'need a forklift to move it' weight range, where a 400ah battery pack made up of individual 2v cells is 'heavy but not impossible' in weight per cell... (and a pack made up of 400Ah lithium individual cells can easily carried by a single person per cell... and will give almost 2/3 more actual stored energy available than a 400Ah L/A of the same voltage.... for years longer...
Decades ago, it wasn't uncommon for those of limited means to buy 'dead cell' deep cycle 6v or 12v batteries and literally hacksaw them open to gain access to the interior busbars to 'bypass' the dead cells to make up a single good battery out of two dead ones- I know, because I did it myself lol
(it was a cheap way to get battery storage at the time lol, when battery costs were extremely expensive indeed, even for L/A- the lithiums (and even the nicads) weren't even around at the time)
John Brown
Freeloading Social media influenza
Even more years ago, my father made his own high tension battery for his first home made valve radio, with a string of home made cells housed in fish paste jars. Wouldn't be much use for solar installations, though, as apart from a very low Ah rating, they weren't rechargeable.
Nope- you won't damage them by not fully charging that last bit, and indeed by not going into that last bit (where it swiitches over to CV mode, and the BMS starts 'charge shuffling' you can extend the lifespan of your battery pack even (at the expense of slightly less stored power in the batterypack)- not really an issue in my case where I have 20kwh of nominal storage available (about three days worth at normal consumption!!!) the plan for long service life is never go into that 'top off' mode when charging, and keep your cycle depth as low as possible (mine is basically going from 90% DOD to about 60% DOD overnight and recharge again the next day- they should last a quarter of a century with that regime- probably longer than me lol
John Brown
Freeloading Social media influenza
Interesting, although I wasn't suggesting there would be damage. You obviously know a lot about this subject...
The old Unigate ones were just a mass of wet lead acid batteries, I bet they were only allowed on the roads due to there slow speed otherwise they could have made a right mess with all that electrolyte flowing down the road and into drains, maybe the milk would of helped reduce the acidity.
It actually is a problem with L/A however- they do need to be fully charged on a regular basis (and even slightly overcharged occasionally for flooded cells) to agitate the electrolyte, otherwise plate damage will occur... Lithiums on the other hand can be left for months partially discharged just sitting around, or never taken to 'full charge' and it actually benefits them rather than damaging them...
John Brown
Freeloading Social media influenza
I have two 130ah efb batteries in my solar shed. So a theoretical capacity of over 3kwh. In practice I get a fraction of that, but it's hard to quantify, as it depends on the loading, which affects the voltage drop, which determines when the inverter cuts out.
EFB is basically the old 'marine grade' battery- ie a 'semi deep cycle'- kinda a cross between the standard 'starting' L/A battery and a deep cycle...
With a theory capacity of 3kwh, you effectively have only 1.5kwh of actual storage anyway and for long life expectancy, even less... (and still with a life expectancy of 3-5 years at that 50% DOD)- You 'might' get 10 years out of them, but only by keeping the DOD under 10%- but that effectively means treating it as a 0.3kwh bank...
A 3kw LFP on the other hand would cost a bit more (here its about $1.70Au for LFP, $1.90Au for LYP per Ah of cell capacity (4 cells per 12v of bank voltage) and would give you about 2.4kwh with a 13-15 year life expectancy, and 2.1kwh of storage with a 20 year life expectancy
This is what I meant before about they make better economic sense- you get more storage, and a much longer lifespan at about double the initial cost- so more upfront $, but long term.... much better value...
With a theory capacity of 3kwh, you effectively have only 1.5kwh of actual storage anyway and for long life expectancy, even less... (and still with a life expectancy of 3-5 years at that 50% DOD)- You 'might' get 10 years out of them, but only by keeping the DOD under 10%- but that effectively means treating it as a 0.3kwh bank...
A 3kw LFP on the other hand would cost a bit more (here its about $1.70Au for LFP, $1.90Au for LYP per Ah of cell capacity (4 cells per 12v of bank voltage) and would give you about 2.4kwh with a 13-15 year life expectancy, and 2.1kwh of storage with a 20 year life expectancy
This is what I meant before about they make better economic sense- you get more storage, and a much longer lifespan at about double the initial cost- so more upfront $, but long term.... much better value...
Another issue with Lead acid is that as the state of charge falls the freezing point decreases, so if your battery is fully charged you will be somewhere very cold if it freezes but if it is almost flat then just minus ten can freeze it and internal condition also has an effect so at least Lithium can be self warming !
That's one of the biggest advantages of the LYP lithiums- they can handle heat better- charging up to 85C- if my batteries are at 85C- then they are the least of my worries lol) and can be charged down to -40C...
The LFP have a smaller temp range, between about -20 and need to start reducing their charge rate above 40C (which in Ozzie summers, the air temps here can be over 40C, hence my going the LYP route)
L/A are similar to LFP in range, about -10C (although as you said, they can have issues with freezing at certain charge capacities lol) and need to reduce charge above 40C as well...
(One thing about your little joke- it is Li-PO cells aka cellphones etc that have the 'burny flamy' issues- LFP and LYP are a different chemistry, and are actually less flammable than L/A even!!!)
My batteries were installed on 4th January in winter and the first thing I did was box them in 25mm of Celotex rigid foam insulation. As a protection against sub zero temps and against being dented by stuff moving through the workshop.
Even in mid summer they have never become even modestly warm so the celotex is there to stay.
Max discharge rate on my LFP's is the same as the max charge rate. 6.5kW in or out for 16.6kWh capacity. That's essentially 0.4C where C is the capacity of the battery.
In fact the reason we have a largeish battery is so that it can power both the oven and a kettle or microwave at the same time and that adds up to 6.5kW. A bit random but sometimes design decisions are like that...
Even in mid summer they have never become even modestly warm so the celotex is there to stay.
Max discharge rate on my LFP's is the same as the max charge rate. 6.5kW in or out for 16.6kWh capacity. That's essentially 0.4C where C is the capacity of the battery.
In fact the reason we have a largeish battery is so that it can power both the oven and a kettle or microwave at the same time and that adds up to 6.5kW. A bit random but sometimes design decisions are like that...
That's another reason I went the LYP- they can handle a charge rate of up to 3C, and a max peak discharge of up to 10C (as eventually they will be powering not only the house but the workshop as well, with a lathe, mill etc to fire up...)
With my 400Ah cells, thats a max charge of 1200A, and a discharge of 1200A continuous, with a 5 second peak at 4000A!!!
ETA Big Clive just released a 'teardown' of a LiPO cell, and mentions that the LFP chemistry is much safer than LiPO (in fact I have never heard of a LFP or LYP actually catching fire at all...)
Opening a lithium cell
Youtube, 5 min long
With my 400Ah cells, thats a max charge of 1200A, and a discharge of 1200A continuous, with a 5 second peak at 4000A!!!
ETA Big Clive just released a 'teardown' of a LiPO cell, and mentions that the LFP chemistry is much safer than LiPO (in fact I have never heard of a LFP or LYP actually catching fire at all...)
Opening a lithium cell
Youtube, 5 min long
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John Brown
Freeloading Social media influenza
All very illuminating. So, if I'm reading this correctly, I'd probably be better off even with a couple(my 4kw inverter is 24v in)of 50ah LFPs, than I am with my 2 130ah EFBs? Worth considering, especially as I could parallel up another pair, if finances allowed.EFB is basically the old 'marine grade' battery- ie a 'semi deep cycle'- kinda a cross between the standard 'starting' L/A battery and a deep cycle...
With a theory capacity of 3kwh, you effectively have only 1.5kwh of actual storage anyway and for long life expectancy, even less... (and still with a life expectancy of 3-5 years at that 50% DOD)- You 'might' get 10 years out of them, but only by keeping the DOD under 10%- but that effectively means treating it as a 0.3kwh bank...
A 3kw LFP on the other hand would cost a bit more (here its about $1.70Au for LFP, $1.90Au for LYP per Ah of cell capacity (4 cells per 12v of bank voltage) and would give you about 2.4kwh with a 13-15 year life expectancy, and 2.1kwh of storage with a 20 year life expectancy
This is what I meant before about they make better economic sense- you get more storage, and a much longer lifespan at about double the initial cost- so more upfront $, but long term.... much better value...
Well, the LYPs I run come as a single cell, rather than a '12v battery' (although LFP is available as '12v' or '24v' batteries as well as single cells afaik there are no manufacturers making LYP 'batteries' at all, there's only a handful making LYP at all), with an inbuilt BMS in the battery as well but not all are capable of being run in series though, some are, some aren't, depends on the manufacturer and their BMS
So you need 8 cells in series to make a 24v nominal battery bank...
A 24v 50Ah LFP has a theory/label storage of 1.2kwh with a practical storage of 0.96kwh at 80% DOD (15 years lifespan), your 130Ah EFB's have a theory storage of 3.12kwh with a practical limit of 1.56kwh (3-5 years lifespan) so not quite equivalent storage
A 24v 78Ah LFP bank would give you the same actual storage as your 130Ah EFB for 15 years, or a 24v 84Ah LFP again is the same actual storage as the 130Ah EFB for 20 years... (but remember your EFB will last much less at that 50% DOD...)
remember, the 'theory' storage is V x AH
So for both its 24v x 130Ah (3.12kwh)
But for L/A its practical storage is 50% DOD (0.5x label storage) is 3-5 years (at 1.56kwh usable), at 25% DOD (0.25x of label storage) 5-7 years (0.78kwh usable). and 10% DOD (0.1x label storage) its 8-10 years (0.312kwh usable)
LFP has the same 'label' storage so still the same there...
But you get that 80% DOD (0.8x label storage) for 13-15 years (2.496kwh usable), or 70% DOD (0.7x label) for 18-20 years(2.184kwh usable)
But yes you can use a smaller LFP Ah capacity so you get the same actual storage as the L/A EFB (but it will still last far longer in service life than the EFB will)
A LFP 78Ah will give you that 1.56kwh of actual storage for 13-15 years, and a 84.5Ah one will give you the same 1.56kwh for 18-20 years as the EFB for 3-5 years at 50% DOD
The theory 3.12kwh 130Ah EFB at 10% DOD will last 8-10 years but only has an effective 0.312kwh of actual storage, where a LFP of the same actual storage capacity of 0.312kwh is only 15.6Ah with a service life of 15 years or a 16.8Ah LFP for 20 years
It all depends on how hard you drive them- L/A need BIG banks to get long life... and although they are cheaper initially to buy them, buying ten times as much of L/A to get half the service life of a lithium that only costs twice as much per AH- see why I said it makes economic sense to go the lithium route????
That's why you don't find professional installs of L/A any more...
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Any update on how your system is fitting your needs?
I ask, as I'm looking at a new build home to my own (with professional help) specifications.
I'm planning on minimal external input, so solar, pus 0.5-1kva wind, air source heat pump, rainwater storage for toilet flushing, clothes washing, garden watering.
Right now, a small diesel generator is cheaper than connection to the grid & I'd also save £180 a year on standing charge, which buys a lot of heating oil, sorry, diesel...
