The cold weather seems to adversely effect the overnight SOC (state of charge).

softdownsoftdown Solar Expert Posts: 2,405 ✭✭✭✭
The overnight SOC was dropping to 88% ~ a month ago. Now it drops down to about 50 F in the room with the batteries. The overnight SOC reading has consequently been dropping down to about 82%.

Sound about right? Or reason for concern?
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,514 admin
    Not really... Dropping to ~75% SOC over one night is about what we aim for with an "optimum" system design (2 days of useful storage to 50% maximum discharge).

    As we get into winter (northern hemisphere)--Will your power usage increase? And your solar harvest will probably decrease--needing more generator use as bad weather/poor insolation sets in.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • softdownsoftdown Solar Expert Posts: 2,405 ✭✭✭✭
    edited November 2015 #3
    It seems that the charge controllers estimate of SOC is a fairly rough estimate. It surely just goes by battery bank voltage.

    Since my batteries are a hybrid between a starter battery and a deep cycle battery, (I have studied them to some extent) it seems prudent to try to keep the SOC over 80%.

    When their reading falls below 75% SOC, I doubt they have near as much energy as true deep cycle batteries would offer.

    With this line of reasoning, my batteries have failed to supply two days of power in very rough weather.

    I figure that adding four panels facing to the west will help in poor weather.

    Four panels facing to the east will augment the two panels charging the forklift battery. So I can use the forklift battery for ~ 3 days on an intermittent basis.

    Then the diesel Kubota come into play. It surely is not fond of starting in very cold weather. I just put in some cold weather additive and cross my fingers.

    Is power usage increasing lately? Possible. I just got Netflix HD and watch 1-2 movies/day on a 65" "LED". I highly recommend the value of Netflix ($10/mt for HD, snap to set up) so far. Though they do not offer a large number of movies via streaming....they do offer thousands along with more television shows than I have heard of.

    I was a Boy Scout extraordinaire. Motto: Be Prepared

    BB. said:
    Not really... Dropping to ~75% SOC over one night is about what we aim for with an "optimum" system design (2 days of useful storage to 50% maximum discharge).

    As we get into winter (northern hemisphere)--Will your power usage increase? And your solar harvest will probably decrease--needing more generator use as bad weather/poor insolation sets in.

    -Bill


    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • zonebluezoneblue Solar Expert Posts: 1,218 ✭✭✭✭
    edited November 2015 #4
    Mate you are trying to measure the length of a rubber band here.

    As bill said the season brings less charge production, but if your system is completing a full absorb every day, then the only real difference in overnite DOD is in your loads, and to a much lessor extent a slight drop in capacity with temperature (which comes principally from increased internal resistance). See http://batteryuniversity.com/learn/article/discharging_at_high_and_low_temperatures

    For loads, the nite is longer, thus the  lights are on longer, tv on longer, etc etc.

    I caution you and everyone else to not brandish SOC figures around without SG readings to back it up. Everything else is someones idea of an estimate/ necessary incomplete math model.


    1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
    http://zoneblue.org/cms/page.php?view=off-grid-solar


  • BB.BB. Super Moderators, Administrators Posts: 29,514 admin
    For "non" deep cycle batteries--They do have the capacity below 80% state of charge--They just may not have the cycle life (cycling below about 85% SOC for starting batteries, i believe the thinner lead plates fail/much fewer charge cycles).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,665 ✭✭✭✭✭
    BB. said:
    For "non" deep cycle batteries--They do have the capacity below 80% state of charge--They just may not have the cycle life (cycling below about 85% SOC for starting batteries, i believe the thinner lead plates fail/much fewer charge cycles).

    -Bill
    Definitely! The saying the cat with nine lives is similar to a non deep cycle battery being cycled.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • PNjunctionPNjunction Solar Expert Posts: 762 ✭✭✭
    The problem may be that your charger or solar charge controller is not temperature-compensated.  Thus in colder temps during the day, where the voltage needs to be compensated upwards, your battery may not be getting the charge it used to do when it was warmer.  Thus, it drops to a lower value overnight.

  • softdownsoftdown Solar Expert Posts: 2,405 ✭✭✭✭
    It is temperature compensated. Pretty sure its just lights and television causing this. Just got Netflix and am watching some movies. Plus....the short days. Was dropping to 78% SOC with old, upright freezer. Jumped back up to 88% SOC with new, high efficiency chest freezer. Then started back down....83% isn't bad.

    Not sure why people always think batteries are either starters or deep cycle. Some batteries are somewhere in between. If 8Ds were purely starter batteries, they would offer ~ 1900 CCA instead of 1400 CCA. This board has not missed a single opportunity to pounce upon my batteries.
    The problem may be that your charger or solar charge controller is not temperature-compensated.  Thus in colder temps during the day, where the voltage needs to be compensated upwards, your battery may not be getting the charge it used to do when it was warmer.  Thus, it drops to a lower value overnight.


    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,665 ✭✭✭✭✭
    The reason you don't get big smiles is that people would read that it is a good thing to do and there would be dozens of failures here.
    You may have time to deal with this but many folks just want a solid system that lasts 5 to 10 years or more. Many have wives or significant others that would put an end to the lights going out  also. 

     By getting a battery that is designed for both starting and cycling, one ends up with a battery that is really not great at either.
    It is not anything new that you are doing, that is for sure!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

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