ScrotusGobbleBottom
Solar Enthusiast
Yes. That is my school of thought. You should have longer than a 5 hour discharge from 100 to zero.
Yes, a happy battery is a friendly battery.
Realistic Cycle life?
- Thread starter Jonathan86
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timselectric
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Just my opinion.
But I think that the C rate is more important than the DOD, for longevity.
Because of this I have no concerns charging to 100% daily. And discharging down to around 7% on occasion. I wouldn't worry about going to 0%, but I like to keep a little reserve for emergencies.
After about 5 years I will do a capacity comparison. And see what the degradation actually is.
I believe that everyone agrees that 1% per year is normal.
So after 5 years, 95% (or more) would be an acceptable result.
But I think that the C rate is more important than the DOD, for longevity.
Because of this I have no concerns charging to 100% daily. And discharging down to around 7% on occasion. I wouldn't worry about going to 0%, but I like to keep a little reserve for emergencies.
After about 5 years I will do a capacity comparison. And see what the degradation actually is.
I believe that everyone agrees that 1% per year is normal.
So after 5 years, 95% (or more) would be an acceptable result.
OffGridInTheCity
Solar Wizard
As @sunshine_eggo commented - cycles are meaningless without qualifications. I don't think 2,000cycles @ 35% DOD can be extrapolated to 700 cycles at 100% DOD. They're different experiences and is why I try to provide context of what a 'cycle' is for my operation when I share my info.
I guess what's most important - how many years will my solar system function as I want using my existing DIY powerwall. For me, I'm hoping the rest of my life
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RCinFLA
Solar Wizard
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Capacity degradation is not the whole story. As capacity degrades, the battery impedance degrades, causing greater battery voltage slump under load current.
'Second life' used batteries are batteries that have degraded capacity and cannot support high EV discharge current without excessive voltage slump. Besides lower capacity and greater voltage slump under load, the cells generate more internal heating when subjected to larger discharge/charging current. Too much internal heating accelerates their demise.
'Second life' used batteries are batteries that have degraded capacity and cannot support high EV discharge current without excessive voltage slump. Besides lower capacity and greater voltage slump under load, the cells generate more internal heating when subjected to larger discharge/charging current. Too much internal heating accelerates their demise.
timselectric
If I can do it, you can do it.
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But for solar storage applications. You shouldn't have high current discharging. If you do, you don't have enough capacity to begin with.
Brucey
Solar Wizard
Yes I would agree that 700 would be a worst case scenario and the actual cycle impact of just a 35% dod on life may be far less at 300 cycles or lessAs @sunshine_eggo commented - cycles are meaningless without qualifications. I don't think 2,000cycles @ 35% DOD can be extrapolated to 700 cycles at 100% DOD. They're different experiences and is why I try to provide context of what a 'cycle' is for my operation when I share my info.
I guess what's most important - how many years will my solar system function as I want using my existing DIY powerwall. For me, I'm hoping the rest of my life
Jonathan86
New Member
Thank you. I am pretty certain at this point that I will be going with Victron, I like the UI and understand that I need a transformer based inverter system, plus the longevity seems top notch. However, the choices in batteries has me overwhelmed, and I'm pretty indecisive to begin with, as I want to make the best possible choice.
Haaaa… with the life I have led/ lead….I assure you I won’t be here for 7000 cycles .. and probably not 3500 ..doubtfully 1750…..BUTTTTT …I will leave a request in my will for someone to notify all concerned how my batts fared…..I just completed cycle 1,936 on my oldest 18650 14s battery and no sign of degradation - which is nearly 6 years of operation. Lifetime average of 35.1% DOD. LifePo4 chemistries are reported to have more cycles at 80% DOD than 18650 INR chemistries.
What's important in my mind is a *low stress* operation (not communications necessarily). A properly sized battery bank for mild charge/discharge C levels, mild DOD, and mild ambient temps/humidity should lead to the best life span. Based on my experience so far, I'm inclined to believe 7,000 cycles for LifePo4 is possible.
But of course it takes a long time (on the order of 21yrs) for actual proof of 7,000 cycles at 335 cycles/year. May enough of us be on this forum long enough to prove or disprove the lifespan numbers
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sunshine_eggo
Happy Breffast!
SOK, Trophy or EG4 server rack.
Jonathan86
New Member
Do manufacturers specify fully charging batteries cause degradation? I haven't seen that, though I think I heard it said for electric vehicle batteries. Is it best for longevity, to not charge up to 100%?
Jonathan86
New Member
It sounds like you're saying C rate has the greatest effect? And so it's best to size the system correctly in order to keep the C rate very low at all times?
SupraSPL
Solar Enthusiast
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From what I understand 35% DOD 2000 times would be described as 700 cycles. 700 cycles is pretty good for an 18650 (Lithium NMC)
For a good sized LiFePO4 solar battery, cycle count per year tends to be very low along with C rates. So we will really be looking at calendar aging and how much capacity remains at 10, 15 and maybe 20 years. It would interesting to find out what approach (if any) extends calendar life the most (low cycle count, staying out of the knees, low rate of charge/discharge, mild temps, compression or lack of, etc)
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Jonathan86
New Member
I was thinking of purchasing everything from current connected. From what they sell, I was thinking SOK or EG4. Unfortunately they are now sold out of the $1100 SOK batteries until June. I don't want to wait that long, as my current batteries are basically worthless, and I'm running off a generator every day. Is there any significant reason to go with one over the other, of the three you mentioned? Do you suggest staying away from the EG4 power pro?
Jonathan86
New Member
What do you mean by "staying out of the knees" and compression?
sunshine_eggo
Happy Breffast!
Trophy is a small outfit, but they provide amazing service and I think they probably cost the most $/kWh.
SOK is a bigger brand, and CurrentConnected is like their main U.S. distributor or some such, and we all know that CurrentConnected doesn't suck.
EG4 is EG4. I believe they are generally a good product, but when things go wrong, tales of support challenges seem too common - purely my opinion.
I know nothing about the power pro.
SupraSPL
Solar Enthusiast
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Staying out of the knees meaning avoiding that part of the voltage/SOC curve where voltage drops or rises rapidly. I generally avoid letting the cells discharge below 3V which also leaves you some emergency capacity as mentioned earlier.
In the rare case I am topping them off I stop charging at about 3.55V (99% SOC) instead of 3.65V but you could stop at 3.45V. I use 3.55V because I like to give the BMS a chance to do a little top balancing.
In the rare case I am topping them off I stop charging at about 3.55V (99% SOC) instead of 3.65V but you could stop at 3.45V. I use 3.55V because I like to give the BMS a chance to do a little top balancing.
sunshine_eggo
Happy Breffast!
The knees are the extremes where the voltage changes comparatively rapidly:
Compression is related to DIY battery builds. Cell manufacturer's often recommend that the cells are compressed together with a given range of forces to maximize their cycle life.
marionw
Solar Enthusiast
One thing to note: The current software provided to monitor SOK batteries with the "Pbms Tool" software does not provide the ability to upgrade firmware and SOK is shipping their newer inventory with newer firmware (please confirm). The SOK software does however allow you to modify BMS protection parameters and monitor other aspects of the battery. EG4 LifePower4 batteries and the software do allow you to monitor the battery, change BMS protection parameters AND upgrade firmware.
timselectric
If I can do it, you can do it.
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