diy solar

diy solar

What’s your daily SOC range?

Skypower said:
I can see my new average daily range is now 100%(55.2 volts) to 70% (52.8volts) or 30% depth of discharge. About three out of four days it gets to 100%SOC. Opinions and what’s your range?
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I snowbird in the campervan with relatively ample panel and a relatively small bank my experience is probably not typical:
  • charge gently (3.45Vpc + plus a bit of absorption) to ~100% ( a few percentage points lower, usually). The panel:bank ratio means the bank can get charged even under poor conditions. Under normal conditions it's full by ~noon, depending on elective loads.
  • then back off a bit (float at ~3.3375Vpc) to avoid holding at ~100% SoC. In summer float might be held for 8 hours.
  • limit charging to 0.4C in those rare times the alternator is contributing
  • SoC down to ~40-60% by morning. I think the lowest I've seen was 25% although I don't remember the circumstances. Thunderstorms the day before then a late night on the laptop + electric blanket?
I have limited resources and need to make this bank last for several years, hence the gentle-as-I-can treatment. I would shoot for 90% charge but doing that on a variable charging source like solar is notoriously unreliable. So I kiss ~100% and back off.


EastTexCowboy said:
drive it like I stole it.
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I drive mine like I can't afford to replace it :)
 
fratermus said:
I snowbird in the campervan with relatively ample panel and a relatively small bank my experience is probably not typical:
  • charge gently (3.45Vpc + plus a bit of absorption) to ~100% ( a few percentage points lower, usually). The panel:bank ratio means the bank can get charged even under poor conditions. Under normal conditions it's full by ~noon, depending on elective loads.
  • then back off a bit (float at ~3.3375Vpc) to avoid holding at ~100% SoC. In summer float might be held for 8 hours.
  • limit charging to 0.4C in those rare times the alternator is contributing
  • SoC down to ~40-60% by morning. I think the lowest I've seen was 25% although I don't remember the circumstances. Thunderstorms the day before then a late night on the laptop + electric blanket?
I have limited resources and need to make this bank last for several years, hence the gentle-as-I-can treatment. I would shoot for 90% charge but doing that on a variable charging source like solar is notoriously unreliable. So I kiss ~100% and back off.




I drive mine like I can't afford to replace it :)
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You got it well managed for a camper van.
 
upnorthandpersonal said:
Having LiFePO4 sit at high states of charge isn't really the problem. Keeping them at a high voltage is
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The research paper linked by @sunshine_eggo says:

When capacity degradation occurs in LFP cells at elevated temperatures, both temperature (30–60 °C) and SOC determine the degradation rate. High storage temperature, which is the most important factor, combined with high SOC result in the greatest degradation...
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...so maybe we can't be entirely cavalier about high SoC, at least in warmer ambients.
 
Skypower said:
Sound like we’re running down the same path lol. I found dual sensor differential thermostatic control so the fan will blow any time the battery is warmer than the air. But figuring out how it works has been interesting. The instructions are in Chinese so I searched and found an English version translation. My impression is that even the Chinese version must be a mess ?. The control’s voltage was 220 AC but it actually had a drop down transformer and rectifier that landed on 12VDC and it was a cakewalk pop those two components out so I could feed it my 12VDC. But now I’m lost in translation, dead bug, winging it. I may just go with the 12V timer I have and 12V fans for K.I.S.S.
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I don’t think a switch or temp device is needed At least for where I’m at…I considered that but found the temp does about the same thing everyday , about the same time… I am home all day so thst may make it easier..about 3 o’clock is when the batts climb to ambient temp…75- 80 - 82 - what ever …during July and and probably august …June is sorta cool and not hot..
so around 3 o’clock I walk out and turn the battery fan on high and it stays on till the next morn .

about 8 or 9 am the next day I walk out and turn the batt fan off..and turn the equipment fans on
I try to make things as simple and wire free as possible…

the equipment fan is the opposite..they are turned on when I turn off the battery fan off in the morn and stay on till dark…when I lock things down for the nite…and turn them off.

I lost enough nuerons in the 70 and 80s I find I need to simplify some things in life..

so that’s where I’m at till the fall , none of this will be needed from sept thru next May or June

I believe I can just let things run freely 9 months a year…
I will know for sure once the winter sets in..
J.
 
fratermus said:
The research paper linked by @sunshine_eggo says:

...so maybe we can't be entirely cavalier about high SoC, at least in warmer ambients.
Click to expand...

Those values are for high SoC storage over MONTHS at constant temperature. Batteries in use might only be at 100% for 8hr/day with temperatures that fluctuate between fine and dangerous. I would guesstimate that batteries cycled daily would see the same degradation as the chart, but over a 3-5X timeframe, i.e., 10 months would be 30-50 months.

For daily cycling, I don't think it's worth the effort. For storage, absolutely.
 
sunshine_eggo said:
Those values are for high SoC storage over MONTHS at constant temperature. Batteries in use might only be at 100% for 8hr/day with temperatures that fluctuate between fine and dangerous. I would guesstimate that batteries cycled daily would see the same degradation as the chart, but over a 3-5X timeframe, i.e., 10 months would be 30-50 months.

For daily cycling, I don't think it's worth the effort. For storage, absolutely.
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Based on the info in the report, it seems to me that maintaining battery temperatures will have more impact on lifespan than managing SOC within some specific range. I don't want to kill my batteries since they're the most expensive part of this Rube Goldberg rig of mine, but I don't want to spend half my time managing it. I'm hitting 100% at a fairly high bulk and float on an almost daily basis, but the batteries are maintaining a nice temperature and so far very little degradation is occurring so I'm thinking I'm good.
 
sunshine_eggo said:
Holy crap... painful.

$0.0806 off peak and $0.2485 peak (2-8pm) for me - a big part of why the ROI on even a DIY system is too long.
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I'll second that holy crap part. Ours went up to $0.13 last year but back down to $0.11 this year (coop). ROI-wise it sucks but I didn't build this just to save money. However, if I were paying those prices it would be a whole different animal.
 
EastTexCowboy said:
I'll second that holy crap part. Ours went up to $0.13 last year but back down to $0.11 this year (coop). ROI-wise it sucks but I didn't build this just to save money. However, if I were paying those prices it would be a whole different animal.
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I’m not able to sell back and now California doesn’t pay much so I’m just happy to keep what I make and choose what rate I pay. You sure can see the period where I was on grid while working on my system. Dialing down what I need from the grid (over drawn) so I’m confident I can reduce it even more. The little bit of yellow is just the inverter operating draw from grid just being connected and ready to transfer. If I open the breaker that goes away and the system draws from solar/battery for it’s needs. IMG_0820.jpeg
 
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EastTexCowboy said:
I'll second that holy crap part. Ours went up to $0.13 last year but back down to $0.11 this year (coop). ROI-wise it sucks but I didn't build this just to save money. However, if I were paying those prices it would be a whole different animal.
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You guys talk about TOU a lot…and this rate and that rate… I have never heard of that here. So I just called the power co and asked them if we had TOU …The “ Energy Specialist “ told me they used to but no more … now they just charge about 30 bucks a month fee to be connected…to everyone.

I told the “ energy specialist “ I had never seen that fee listed on the bill…

The ” Energy Specialist “ told me it wasn’t listed ,but was just inserted into the power usage total…
that way if we have to raise it ,it doesnt cause as much uproar .She further assured me that we were told in advance because they post it some article they write in the little booklet we get quarterly telling us about all the things they do great as a power company for us ,and it included many recipes for local food.

I said oh, that little pamphlet that nobody reads… how thoughtful to tell us in that fashion.

I then Politely thanked the “ Energy Specialist” and ended the call…

you can’t win with these rascals .

Looking at the bill ,if I used ZERO power , it would still cost me about 45 dollars a month to be hooked up with no usage except my streetlight.( $8.50 straight fee)


but at least I would get a pamphlet every three months with some recipes.
 
Jim H said:
You guys talk about TOU a lot…and this rate and that rate… I have never heard of that here. So I just called the power co and asked them if we had TOU …The “ Energy Specialist “ told me they used to but no more … now they just charge about 30 bucks a month fee to be connected…to everyone.

I told the “ energy specialist “ I had never seen that fee listed on the bill…

The ” Energy Specialist “ told me it wasn’t listed ,but was just inserted into the power usage total…
that way if we have to raise it ,it doesnt cause as much uproar .She further assured me that we were told in advance because they post it some article they write in the little booklet we get quarterly telling us about all the things they do great as a power company for us ,and it included many recipes for local food.

I said oh, that little pamphlet that nobody reads… how thoughtful to tell us in that fashion.

I then Politely thanked the “ Energy Specialist” and ended the call…

you can’t win with these rascals .

Looking at the bill ,if I used ZERO power , it would still cost me about 45 dollars a month to be hooked up with no usage except my streetlight.( $8.50 straight fee)


but at least I would get a pamphlet every three months with some recipes.
Click to expand...
I'm off grid except for grid assist on the rare times I need it, but nothing fed back to them, so TOU would have no impact on me. But the local POCO just has a flat rate per kwh plus their connection fee or whatever else they call the charges. No TOU. Oh, and yeah, we get the recipe pamphlets they mail out which they're paying for out of those fees we're paying in as coop members so I'm really glad for that. :cautious:
 
EastTexCowboy said:
I'm off grid except for grid assist on the rare times I need it, but nothing fed back to them, so TOU would have no impact on me. But the local POCO just has a flat rate per kwh plus their connection fee or whatever else they call the charges. No TOU. Oh, and yeah, we get the recipe pamphlets they mail out which they're paying for out of those fees we're paying in as coop members so I'm really glad for that. :cautious:
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No wonder there is always a group of people in suits on the cover grinning so big…
they have locks on the poker game…the fix is in…
they take my money at will….
and in turn share with me how to fry a chicken…
 
Jim H said:
You guys talk about TOU a lot…and this rate and that rate… I have never heard of that here. So I just called the power co and asked them if we had TOU …The “ Energy Specialist “ told me they used to but no more … now they just charge about 30 bucks a month fee to be connected…to everyone.

I told the “ energy specialist “ I had never seen that fee listed on the bill…

The ” Energy Specialist “ told me it wasn’t listed ,but was just inserted into the power usage total…
that way if we have to raise it ,it doesnt cause as much uproar .She further assured me that we were told in advance because they post it some article they write in the little booklet we get quarterly telling us about all the things they do great as a power company for us ,and it included many recipes for local food.

I said oh, that little pamphlet that nobody reads… how thoughtful to tell us in that fashion.

I then Politely thanked the “ Energy Specialist” and ended the call…

you can’t win with these rascals .

Looking at the bill ,if I used ZERO power , it would still cost me about 45 dollars a month to be hooked up with no usage except my streetlight.( $8.50 straight fee)


but at least I would get a pamphlet every three months with some recipes.
Click to expand...
I get the same $~30/mo charge from my Utility (So Cal Edison). If I bank enough credits that month though, it can, and is usually, negative.
 
fratermus said:
...so maybe we can't be entirely cavalier about high SoC, at least in warmer ambients.
Click to expand...

Temperature is the real issue, and kills LiFePO4 faster than anything else. You can be at 100% SoC and 0C and you will have far, far less impact than being at 50% SoC at 30C for the same amount of time. That's why I mention that SoC isn't a huge deal compared to temperature. Some datapoints from the paper:

Operating conditionTemperature (°C)Capacity loss (%)Resistance increase (%)
100% SOC, Calendar for 8 months3019
100% SOC, Calendar for 8 months45741
100% SOC, Calendar for 5 months602658
30% SOC, Calendar for 5 months601526

So at 30% SoC and 60C you see a 15% loss after just 5 months, compared to only 1% at 100%SoC and 30C after 8 months.

Similarly, another datapoint:

Operating conditionTemperature (°C)Capacity loss (%)Resistance increase (%)
100% SOC, Calendar for 12 months2552
50% SOC, Calendar for 12 months2535
100% SOC, Calendar for 12 months451520

Just two percent difference for 100% vs 50% at 25C over 12 months. And that's assumed to have the battery sit at that temperature and state of charge for an entire year, not cycling at all.

This is very clear in this data point; the capacity loss between 100% and 50% over an entire year is practically negligible:

Operating conditionTemperature (°C)Capacity loss (%)Resistance increase (%)
100% SOC, Calendar for 12 months2552
50% SOC, Calendar for 12 months2535
100% SOC, Calendar for 12 months451520
50% SOC, Calendar for 12 months451221

So I still stand by my assessment that state of charge doesn't really matter if you allow the cell to settle and not keep it at a high voltage when the cell is in regular use. Temperature is the biggest thing to keep an eye on.
 
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