LiFePO4 vs Lead Acid a cost analysis for energy storage.

[electrodacus]

Hog wash and everyone here knows it. With Lead acid you need 5 day reserve capacity which nets you 2.5 days to CYA for cloudy days. So if a person needs 1 Kwh per day on a 12 volt system using lead acid needs a 400 AH battery. If using LFP needs 300 AH to yeild the same autonomy. That is a fact jack so quit your BS make believe numbers. You keep using the same bogus data to support your view. You have to compare APPLES TO APPLES. All you got is rootie tootie fruit salad mumbo jumbo trying to baffle laymen. Pros know better and you are not getting away with it here.

Wheel is not as simple as you say.
Lead Acid in the top 20% of the charge has only 50% efficiency even in bulk part of the charge charge + discharge efficiency is around 70%
Where LiFePO4 is always over 95%
Then is better to add additional solar panels even if you need to double the array size since they are way less expensive than batteries and there is quite a bit off power generated even in cloudy days. Right now is extremely cloudy and my array still output about 20% of the rated output around 1.6A on each of the 8A panels (60 cells 240W panels).
As long as there is no snow on them they will produce from 10% (worst dark and cloudy day in winter) and usually upwards of 20% in most cloudy days.
I do have a small wind turbine 300W that helps right now wind gusts is around 40km/h again a better investment than a larger battery even if not as good as solar PV panels.
I do have the experience of almost a year now powering my house that uses 60 to 90kWh/month (2 to 3kWh/day) with a 2.5kWh LiFePO4 (24V 100Ah) and I only remained without power one night last summer since I was not aware of the capacity left in the battery.
Most of that power is used for cooking during the day directly from the solar array with very little difference from battery.
A energy meter to calculate SOC is extremely important with LiFePO4 where voltage is extremely flat so you can only really now without a counter when is full and when is empty no idea where you are in between.

[Ian S]

However (switching to oranges warning) if you are looking only at the daily cyclic use of energy and are willing and able to use a generator more often when needed instead of having multi-day autonomy in the battery bank, then you can use a 2-4X smaller LFP bank.

Even if you do include autonomy, the ability to run LFP down to nominal 0% SOC without damage while not taking the comparable FLA bank below 50% SOC to get autonomy will still count for at least a factor of two. (That assumes, of course, that you are willing to cycle your LFP all the way up to 100% SOC routinely, which is yet another fruit question.)

It certainly helps all around if each person making large and unpopular claims explicitly states all his assumptions and conditions and that later commenters on that claim either respect those assumptions or refute individually the assumptions that they think are wrong. (either unwise or contrary to physical laws, that is.)

So far I see this discussion as one where both sides (assumption: there are only two sides. That may not be correct.) are arguing a particular result while explicitly or implicitly using different assumptions.

Continue to keep it civil and we may end up with a very useful discussion.

Here are some proposed common assumptions for your evauluation:

1. For FLA, daily cycling between 80% SOC and 100% SOC is optimal and autonomy cycling as low as 50% SOC is acceptable. I inow that Chris Olson does not agree with the first part of this and he has a lot of practical experience to back this up.

2. For LFP, cycling between 40% and 60% (or some other slightly shifted range) is optimal and autonomy cycling down to 0% SOC is acceptable with a generator available.

3. Recognize that the design (engineering) goals for a commercial solar backup system with a minimum load which must always be supported may be different from the design goals of a system for an actively managed off-grid life. This can lead to a whole range of differing assumptions.

Now, on that basis, shake hands and come out fighting.

Thanks for the additional analysis. The problem with this whole discussion is there are a lot of factors to consider. IIRC, the main disagreement initially centered on system longevity and hence lifetime costs. That's complicated by what's acceptable in terms of DOD for the two systems and how that impacts longevity. Now we're fussing over initial size considerations which are also ultimately going to impact longevity and hence lifetime costs.

[Sunking]

Wheel is not as simple as you say.
Lead Acid in the top 20% of the charge has only 50% efficiency even in bulk part of the charge charge + discharge efficiency is around 70%

Where are you getting those numbers?

[electrodacus]

Where are you getting those numbers?

They are every where mostly in the datasheets of battery manufacturers even if not presented directly in this way (not a good way to advertise).
Most power is used by large devices usually that produce heat like cook-stove, microwave ... they use a lot of power for relatively short periods of time so the discharge rate of that battery is quite high even with large battery banks.
The flooded Lead Acid usually has the worse efficiency but other are quite bad also.
A lot of that loss is transformed in heat and breaking the bond between oxygen and hydrogen.
There is also another aspect that is the way Lead Acid is charged where at the top of the charge you are usually not using the available current from the PV array since you need to keep the voltage constant and reduce current usually by simple PWM. This is not the case with LiFePO4 where you only charge using CC there is no CV charge needed.
You can read this study but there are plenty of informations all over the web regarding charge/discharge efficiency. If you have better informations about charge discharge efficiency please provide a link

http://windandsunpower.com/Download/Lead%20Acid%20Battery%20Efficiency.pdf

Here is the conclusion in this article

A test procedure has been developed to allow the
examination of battery charge efficiency as a function of
battery state of charge. Preliminary results agree well
with established general understanding that the charge
efficiency of flooded lead-antimony batteries declines with
increasing state-of-charge, and that charge efficiency is a
non-linear function of battery state-of-charge. These
tests indicate that from zero SOC to 84% SOC the
average overall battery charging efficiency is 91%, and
that the incremental battery charging efficiency from 79%
to 84% is only 55%.
This is particularly significant in PV
systems where the designer expects the batteries to
normally operate at SOC above 80%, with deeper
discharge only occurring during periods of extended bad
weather. In such systems, the low charge efficiency at
high SOC may result in a substantial reduction in actual
available stored energy because nearly half the available
energy is serving losses rather than charging the battery.
Charge efficiencies at 90% SOC and greater were
measured at less than 50% for the battery tested here,
requiring a PV array that supplies more than twice the
energy that the load consumes for a full recovery charge.

[inetdog]

There is also another aspect that is the way Lead Acid is charged where at the top of the charge you are usually not using the available current from the PV array since you need to keep the voltage constant and reduce current usually by simple PWM. This is not the case with LiFePO4 where you only charge using CC there is no CV charge needed.

Just for completeness (and pedantry):

1. An MPPT CC can take partial power from the panels and still deliver relatively constant current to the battery in Absorb and Float as long as the PWM is happening at the input to the DC/DC converter. So pulsed versus steady current charging is not necessarily an issue.
2. Possibly a misleading comparison since LFP charging can still use PWM to maintain the desired current and whether you use 50% of the panel power 100% of the time or 100% of the panel power 50% of the time the result is still that you will not be able to use all of the PV power effectively for battery charging.
It is a valid point that delivering Float charging to FLA via PV can be a particularly bad waste of panel power, or an even worse waste of generator power. Sunking has some recommendations about setting Bulk, Absorb and Float voltages that recognize this difficulty and maximize the amount of PV that you can capture.

[electrodacus]

Just for completeness (and pedantry):

1. An MPPT CC can take partial power from the panels and still deliver relatively constant current to the battery in Absorb and Float as long as the PWM is happening at the input to the DC/DC converter. So pulsed versus steady current charging is not necessarily an issue.

I did not wanted to mention MPPT since that is an obsolete technology at 1$/Watt for solar PV
The idea was that it can not use the total PV power even when Battery is not full.

2. Possibly a misleading comparison since LFP charging can still use PWM to maintain the desired current and whether you use 50% of the panel power 100% of the time or 100% of the panel power 50% of the time the result is still that you will not be able to use all of the PV power effectively for battery charging.

LFP will not use PWM when is 95 or 98% charged you just stop the charging and is true that there can be during the day and still be power not used from the panels but that is a different story that lost power is just 3 cent /kWh

It is a valid point that delivering Float charging to FLA via PV can be a particularly bad waste of panel power, or an even worse waste of generator power. Sunking has some recommendations about setting Bulk, Absorb and Float voltages that recognize this difficulty and maximize the amount of PV that you can capture.

You better have wasted power from PV than generator 3cent/kWh vs at best 1.2$/kWh
I do not have a generator for my offgrid house and never considering getting one.
In stead as a backup I have a 0.5kWh LiFePO4 (A123 systems) with 2x85W PV panels (this is a separate circuit from the main one) and extremely inexpensive to have. I only used this backup one night last year my fault at estimating the main battery charge. It will not happen when I have an SOC indicator.

[Sunking]

The flooded Lead Acid usually has the worse efficiency but other are quite bad also.

Not even a remotely true statement. Lead acid charge efficiency runs from as low as 80% up to 97%. Depends on type, plate material, VRLA, and plate construction. You gotta a lot to learn. AGM efficiency is 95 to 97% with very little Peukert effect. Nickel chemistries have the lowest charge efficiency, Lead is depending on type is in the middle or near the top from 80 to 97%.

A lot of that loss is transformed in heat and breaking the bond between oxygen and hydrogen.
There is also another aspect that is the way Lead Acid is charged where at the top of the charge you are usually not using the available current from the PV array since you need to keep the voltage constant and reduce current usually by simple PWM. This is not the case with LiFePO4 where you only charge using CC there is no CV charge needed.

Dead wrong, LFP or any lithium chemistry uses CV current limit algorithm. or put another way is Float Charged. LFP can be charged as high as 1C so for say a 10 AH cell can be charged as high as 10 amps, as the cell voltage reaches the charger voltage of 3.6 volts the current tapers off and voltage is constant at 3.6 volts until the charge current tapers to C/20. At that point the charge is terminated. If not terminated the battery is damaged unlike lead acid. You can leave lead acid on Float to eternity as every utility company does. Exact same algorythym as the Absorb and every Float charger made. Only difference is the set point voltage.

Only thing charge efficiency effects is the size of the panel wattage. Discharge rates with FLA by design are C/20 or less so discharge efficiency or Peukert effect is not an issue. Short burst of a microwave oven are not enough to effect Peukert Law to come into play. Now if you want to talk EV's, that is another animal where Lithium can be justified. But lithium cannot be justified for RE as of yet. Prices and cycle life are not there yet.

If you really want to know about batteries I suggest you join IEEE and buy their battery documents. I set on the 450, 946, and 1660 committee. Another good book is what I call the Battery Bible aka as the Handbook of Batteries 4th Edition written by Thomas Ready which is state of the art battery application covering all chemistries.

[electrodacus]

Not even a remotely true statement. Lead acid charge efficiency runs from as low as 80% up to 97%. Depends on type, plate material, VRLA, and plate construction. You gotta a lot to learn. AGM efficiency is 95 to 97% with very little Peukert effect. Nickel chemistries have the lowest charge efficiency, Lead is depending on type is in the middle or near the top from 80 to 97%.

If you want to advertise Lead Acid you may say that. Did you read the article above about charge efficiency vs SOC
And how may use the more expensive VRLA for energy storage instead of deep cycle flooded?

Dead wrong, LFP or any lithium chemistry uses CV current limit algorithm. or put another way is Float Charged.
LFP can be charged as high as 1C so for say a 10 AH cell can be charged as high as 10 amps, as the cell voltage reaches the charger voltage of 3.6 volts the current tapers off and voltage is constant at 3.6 volts until the charge current tapers to C/20. At that point the charge is terminated. If not terminated the battery is damaged unlike lead acid. You can leave lead acid on Float to eternity as every utility company does. Exact same algorythym as the Absorb and every Float charger made. Only difference is the set point voltage.

LFP for energy storage uses only CC charging where it gets to 95 to 98% SOC the rest of 3 to 5% will be detrimental and is not used in most applications.
Charging characteristic of LiFePO4 is quite different than LiCoO2
Also charging with more than 0.3C on most LIFePO4 is not recommended for energy storage applications and not needed for stationary solar charging.
A electric car has quite different requirements.
You will not want to float a LFP those that do so is because they use Lead Acid chargers and have no choice not the proper way.
You can float LFP without much damage under 3.4V / cell
The correct way is to charge to 3.45V or 3.5V and at that point stop the charger is charging is done at 0.3C then you have at that point more than 95% SOC not worth going higher since you only degrade the battery.

Only thing charge efficiency effects is the size of the panel wattage. Discharge rates with FLA by design are C/20 or less so discharge efficiency or Peukert effect is not an issue. Short burst of a microwave oven are not enough to effect Peukert Law to come into play. Now if you want to talk EV's, that is another animal where Lithium can be justified. But lithium cannot be justified for RE as of yet. Prices and cycle life are not there yet.

If you really want to know about batteries I suggest you join IEEE and buy their battery documents. I set on the 450, 946, and 1660 committee. Another good book is what I call the Battery Bible aka as the Handbook of Batteries 4th Edition written by Thomas Ready which is state of the art battery application covering all chemistries.

I know enough about batteries at least about the one I care about LiFePO4
And I know about Lead Acid since I investigate them for my offgrid house. I'm glad A123 System advertised their first battery at just that particular moment it was the first time I heard about LiFePO4.

My prediction for the future (I think this is my first ever prediction) is that LiFePO4 will be as wide spread for grid and offgrid energy storage as the Lead Acid is now.
That is unless another even better chemistry still based on Lithium will compete with LiFePO4
Educating people will take some time so I can not say for sure when will this happen but I think in less than 5 years before 2020
There are a few smaller companies that prepare something similar with my Solar BMS and they will be available starting next years.

[Sunking]

If you want to advertise Lead Acid you may say that. Did you read the article above about charge efficiency vs SOC

Yeah 10 years ago. Did you read it and understand. The model is completely irrelevant. They used a single 12 volt antiquated battery (Trojan 30xhs)with freakisly low charge rate of C/33 something you would never do on a solar PV system. Apparently you have selective reading skills right from your own document:

It is generally understood that battery charge
efficiency is high (above 95%) at low states of charge and
that this efficiency drops off near full charge.

In the conclusion they sum upped:

The greatest output was 96.5Ah, which resulted from
116Ah input.

No matter how you slice it comes out to 96.5/116 = 83% efficiency from 0% SOC to 100% SOC. Take a lithium to 0% SOC and you have a boat anchor. I do not sell batteries or chargers like you do so I don't have a bias.

[Sunking]

My prediction for the future (I think this is my first ever prediction) is that LiFePO4 will be as wide spread for grid and offgrid energy storage as the Lead Acid is now.
That is unless another even better chemistry still based on Lithium will compete with LiFePO4
Educating people will take some time so I can not say for sure when will this happen but I think in less than 5 years before 2020
There are a few smaller companies that prepare something similar with my Solar BMS and they will be available starting next years.

Maybe, but I doubt it. Lithium will win the EV market only because of Specific Energy Density which is critical for motive power but meaningless for RE and energy storage. Smart money is on Lead Carbon Acid batteries. Same low price as lead acid, 20,000 cycles to 100% DOD. Lithium cannot touch that.

[Sunking]

You will not want to float a LFP those that do so is because they use Lead Acid chargers and have no choice not the proper way.
You can float LFP without much damage under 3.4V / cell
The correct way is to charge to 3.45V or 3.5V and at that point stop the charger is charging is done at 0.3C then you have at that point more than 95% SOC not worth going higher since you only degrade the battery.

You got a lot to learn about lithium batteries and charging algorithms.

I know enough about batteries at least about the one I care about LiFePO4

We call that a One Trick biased Pony in engineering.

[electrodacus]

Yeah 10 years ago. Did you read it and understand. The model is completely irrelevant. They used a single 12 volt antiquated battery (Trojan 30xhs)with freakisly low charge rate of C/33 something you would never do on a solar PV system. Apparently you have selective reading skills right from your own document:

It is generally understood that battery charge
efficiency is high (above 95%) at low states of charge and
that this efficiency drops off near full charge.

In the conclusion they sum upped:

The greatest output was 96.5Ah, which resulted from
116Ah input.

No matter how you slice it comes out to 96.5/116 = 83% efficiency from 0% SOC to 100% SOC. Take a lithium to 0% SOC and you have a boat anchor. I do not sell batteries or chargers like you do so I don't have a bias.

There is no much difference in Lead Acid batteries. That was just one article there are plenty of them and all state that charge/discharge efficiency is around 50 to 60% in typical storage applications since you use only the top 20 or 30% and that is where any Lead Acid battery is the most inefficient.

About selective reading skill "95% at low SOC" but did you watched the graph low SOC is well under 50% where you are almost never use the battery not relevant.

Simple experiment since most of you have Lead Acid in offgrid installation. Measure the discharge power after battery is full 100% SOC and then charge the battery back to full and see what is the difference between what you took from the battery and how much you needed to put back to make that 100% SOC again.
I bet it will be around 50 to 60% efficient at best.
And this will be real word data no lab test.
Some of you must have the equipment and necessary knowledge do do this data log.

[electrodacus]

You got a lot to learn about lithium batteries and charging algorithms.



We call that a One Trick biased Pony in engineering.

Read this article

http://batteryuniversity.com/learn/article/charging_lithium_ion_batteries

CC can be dose even for LiCoO2 with a bit more loss in capacity than LiFePO4 but with the same positive effect in prolonging the battery life and that is what you want for stationary energy storage.
Using CC only up to 4.2V with LiCoO2 will get you 85% SOC but improved cycle life by much more than 15% witch will make for a better price/kWh stored even much better if you stop at 3.9V 8x increase in cycle life wile still having 70% SOC that will get you 5 to 6x better price/kWh during lifetime.
For LiFePO4 is way better if you do CC up to 3.6V and stop there you have over 95% SOC depending on battery manufacturer there is a small variation. And with only CC you prolong the battery life so is no brainier in stationary application where energy density is not important.

[Sunking]

Some of you must have the equipment and necessary knowledge do do this data log.

I do and it is around 75 to 80%. Like I said charge efficiency onlyu effects panel wattage, not battery capacity. You are barking up the wrong tree.

[Sunking]

Read this article
http://batteryuniversity.com/learn/a..._ion_batteries

Read that a dozen times over the years and says exactly what I have stated. A lithium uses a Constant Voltage Current Limit algorithm. I love using your own articles against you. It makes it easy.

"The Li‑ion charger is a voltage-limiting device that is similar to the lead acid system. The difference lies in a higher voltage per cell, tighter voltage tolerance and the absence of trickle or float charge at full charge. "

Which means when the Charge current tapers off to C/20 it must be terminated or you will damage the cell. It is the exact same CV algorithm as lead acid. The difference is you must terminate a lithium charge and not allow it to float like you can a Lead Acid to keep topped off.