Real world cycle life with many continous small discharge & charging

[whateversa]

Question 1: Does my example below translate to using 1 out of 6000 cycles, even though there may have been near constant discharge and recharging happening?

Scenario example:

• 5.1kwh LFP battery with 6000 cycle life and 90% DOD (Hina)
• Due to poor sunlight there are lots of discharge and slow charging going on during the day (example 1000watts solar coming in, but now and then turning on a 2000watt kettle).
• 1 cycle = 5.4kwh used (remaining 10% may not be used)
• I use 5.4kwh throughout the day in total ('consumption' power in solarman) as example
• Deye 8kw inverter

I only have 2700watt of solar panels (north facing) and I rarely see more than 2000 watts being available this time of year, if even that much.

Additionally I plan to set the Deye 8kw inverter to 24/7 grid charge to 65% as well so I have a load shedding buffer (I actually have 2x batteries btw). I assume that actually means that when the battery is down to 65% at night, it just wont use the battery while Eskom power is on - saving further cycle life.

Edited May 7, 2023 by whateversa

[frivan]

23 minutes ago, whateversa said:

(I actually have 2x batteries btw)

It looks to me if you are using half a cycle out of each battery. If all your loads are directly supplied by solar, you could argue that no cycling occurred. Theoretically you should get more cycles at lower DoD but practically your cells will lose capacity with age in any case.

[I84RiS]

3 hours ago, whateversa said:

Question 1: Does my example below translate to using 1 out of 6000 cycles, even though there may have been near constant discharge and recharging happening?

Scenario example:

• 5.1kwh LFP battery with 6000 cycle life and 90% DOD (Hina)
• Due to poor sunlight there are lots of discharge and slow charging going on during the day (example 1000watts solar coming in, but now and then turning on a 2000watt kettle).
• 1 cycle = 5.4kwh used (remaining 10% may not be used)
• I use 5.4kwh throughout the day in total ('consumption' power in solarman) as example
• Deye 8kw inverter

I only have 2700watt of solar panels (north facing) and I rarely see more than 2000 watts being available this time of year, if even that much.

Additionally I plan to set the Deye 8kw inverter to 24/7 grid charge to 65% as well so I have a load shedding buffer (I actually have 2x batteries btw). I assume that actually means that when the battery is down to 65% at night, it just wont use the battery while Eskom power is on - saving further cycle life.

It all depends on how the BMS calculates one cycle.  Unfortunately there is no standard way for reporting this and manufacturers will follow what is best for them.

Also, in your example of setting the SOC level at 65%, the inveter will still use about 75Wh from the battery (the inverter's own power consumption will be provided by the battery and not the grid).

[Chris_S]

Use your batteries as much as possible. They will deteriorate more from age than from cycling. 

[Eurard]

As far as I know there isnt a magical switch in the battery that counts down the cycles till dooms day, it is to me an indicator of expectancy.

If it says 6000 cycles up to 20%, then it means you can realistically drain the batt from 100 down to 20 back to 100 etc etc, and expect to do that 6000 times.

If you do 80% to 20% you might get more.

I drain between 90% and 60-70% mostly, some days less, between 90% and 80%.

So what this all means in reality is that you should expect your batteries not to last for 50 years, but you have a rough estimate on usage vs life of them.

I should get years more than that 6000 cycle count indicator if I take every up down as a cycle.

They clearly state your car battery as example has a 5yr or so life cycle, well my car battery is more than 7years old and still perfect, well as perfect as previous user stated concidering the age.

I wont stress too much on cycle count and rather focus on how deep the discharge, charging is.

You take care of the batteries and they will take care of you. You will clearly start to see signs when the time comes.

I am going to stagger my batteries, every year buy a new one, as long as the batteries are the same brand and chemistry, should be fine, this way there is some redundancy in them when one starts to go, and not be left with a whole bank dead in one go, but I might be semi gone by the time the first starts acting up though. lol

[Chris_S]

And after 6000 cycles they will probably still provide 80% of their day 1 capacity. 

[zsde]

46 minutes ago, Chris_S said:

And after 6000 cycles they will probably still provide 80% of their day 1 capacity. 

If I am not mistaken that is the accepted industry norm where the max cycle count claimed is based on 80% capacity left after those cycles. Whether that translates into practical experience remains open for user feedback.
A similar industry standard applies to solar panels that are supposed to still have 80% of their generating power after the claimed 20 to 30year life expectancy.

 

1 hour ago, Eurard said:

well my car battery is more than 7years old and still perfect,

you are one lucky guy. Perhaps you should get a bank of those batteries for a solar installation. I have only ever been lucky with a car battery to last that long and that was a Willard. Most of my car batteries pack up between 3 and 5years. 
 

[Eurard]

3 minutes ago, zsde said:

If I am not mistaken that is the accepted industry norm where the max cycle count claimed is based on 80% capacity left after those cycles. Whether that translates into practical experience remains open for user feedback.
A similar industry standard applies to solar panels that are supposed to still have 80% of their generating power after the claimed 20 to 30year life expectancy.

 

you are one lucky guy. Perhaps you should get a bank of those batteries for a solar installation. I have only ever been lucky with a car battery to last that long and that was a Willard. Most of my car batteries pack up between 3 and 5years. 
 

Maybe lol.

[whateversa]

2 hours ago, Chris_S said:

And after 6000 cycles they will probably still provide 80% of their day 1 capacity. 

That would be wonderful. I have been afraid of cycling my R50 000 worth of batteries so far to be honest.

 

Warranty documentation snippets:

Quote

10 years of performance warranty: will (i) retain seventy percent (70%) of its Usable Energy for ten (10)
years from the Warranty Start Date; or (ii) reach 6000 cycles, whichever comes first, on the condition that
the Product is operated under a normal use followed by the manual provided by HINAESS.

I do have the system in my garage which gets quite hot in summer, especially if i pull the car in - which I suspect may impact lifespan? I might look at getting an extractor or something to vent the garage from the roof... just opening garage doors just doesnt seem to do much for some reason.

Quote

The battery modules cannot be stored in high temperature (> 35°C) or stored directly
under the sun, or in any high humidity environment

 

Edited May 8, 2023 by whateversa

[whateversa]

Here is a helpful graph and more info on what to expect from cycle life and how depth of discharge and discharge rate affects cycles:

https://www.powertechsystems.eu/home/tech-corner/lithium-iron-phosphate-lifepo4/

Would you guys think it makes sense to set your inverter to topup with Eskom power now and then to reduce how deep your discharges go?

Edited May 8, 2023 by whateversa

[Chris_S]

1 hour ago, whateversa said:

That would be wonderful. I have been afraid of cycling my R50 000 worth of batteries so far to be honest.

 

Warranty documentation snippets:

I do have the system in my garage which gets quite hot in summer, especially if i pull the car in - which I suspect may impact lifespan? I might look at getting an extractor or something to vent the garage from the roof... just opening garage doors just doesnt seem to do much for some reason.

 

In 10 years time battery tech will be so much better and probably much cheaper. 

[Eurard]

18 hours ago, Chris_S said:

In 10 years time battery tech will be so much better and probably much cheaper. 

The batteries in 10 years will probably literally be rubbing salt in our wounds .... 

[Chris_S]

1 hour ago, Eurard said:

The batteries in 10 years will probably literally be rubbing salt in our wounds .... 

Sodium batteries. Excuse the pun

[whateversa]

Thanks guys. I guess I have some GEL battery related financial PTSD. I will use my LFP battery to the fullest now. I'm 2 days purely on solar apart from solar geyser so far!

Edited May 10, 2023 by whateversa

[Eurard]

7 minutes ago, Superfly said:

LOL.. I have 4 deep cycles lying in the garage for years now - I think I'll  just donate them to a church or something .. pretty sure at least 2 are DOA so a bit hesitant ...will have to do some testing first.

Or take them to a batt refurb place and try get some money back.

 

Same here 4 x 100ah stacked away

[Eurard]

38 minutes ago, whateversa said:

Thanks guys. I guess I have some GEL battery related financial PTSD. I will use my LFP battery to the fullest now. I'm 2 days purely on solar apart from solar geyser so far!

They are a lot more expensive but geesh, I will never use a lesser batt again.