Help on preventing battery failure in extreme cold

Hi everyone,

We have some solar powered multi-billion pixel camera systems installed at a few research sites along the dunes at the south end of lake Michigan (http://www.gigavision.org). They work great in the summer but in winter the battery systems have been failing due to the cold.

The systems are somewhat underpowered solar-wise for the winter months, which is by design since we only need them to be on all the time in the summer. However, I think what happens is that when the power gets low, the charge controller cuts off at 10V; then, if it is super cold for a while, the batteries drop to below 9V. Since the MorningStar controllers won't charge the batteries below 9v, the system is effectively dead. (This may not actually be the problem but it’s the best explanation I can think of given that all the batteries and new). All the systems are on Flexcharge power timers so the system is off at night. We could reduce the on time to just a few hours to save power but it seems like there is a more systemic problem with the cold affecting the batteries that we should address directly.

Anyone out there have any experience with making batteries survive the winter? Are there heater systems available for batteries that could run on an additional smaller panel? Any suggestions would be greatly appreciated.

Thanks,

Tim


System specs
Panels: 60 or 120W, 12v
Batteries: 2-3 100Ah Marine deep-cycle lead acid batteries (sears brand)
Charge controller: Morningstar 10a
Timer: Flexcharge, 12v

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Help on preventing battery failure in extreme cold

    It sounds like too much loads and too little power (solar panels/genset/etc.).

    How cold are the batteries getting? How much power do you use? How much solar panel do you have?

    Taking batteries below ~11.6 volts (resting voltage) runs the risk of permanently damaging the battery bank. Taking them to 10.5 or below probably guarantees that the batteries are toast.

    You can install a Battery Monitor (Xantrex and Victron units. and probably some others, have a programmable output that you could set to "alarm" at 50% state of charge and turn the alarm off at 80% state of charge--that will save your batteries) that turns off the loads at 50% state of charge (or 20% if you really want to deep cycle).

    Adding more batteries is probably not the answer (especially if you do not have enough solar panels/backup power sources to properly charge them).

    AGM's may be a better option... They are ~10% more efficient and will not freeze damaged if taken well below freezing with low state of charge. But they are much more expensive batteries and still do not solve the issue of going to 10.5 volts or lower (toss batteries, buy new batteries).

    And there is always the conservation angle... Make sure you have the most efficient hardware practical and that you turn off unneeded loads (night, between shots/communications cycles/etc.).

    Using PVWatts for Muskegon (trying to find lake front site for local weather conditions), 1,000 watts of solar panels (round numbers), fixed array mounted at latitude and 0.52 system derating (end to end efficiency):
    "Station Identification"
    "City:","Muskegon"
    "State:","Michigan"
    "Lat (deg N):", 43.17
    "Long (deg W):", 86.25
    "Elev (m): ", 191
    "PV System Specifications"
    "DC Rating:"," 1.0 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.5 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 43.2"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 8.3 cents/kWh"

    "Results"
    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 2.04, 32, 2.66
    2, 3.74, 56, 4.65
    3, 4.43, 71, 5.89
    4, 5.23, 78, 6.47
    5, 5.96, 88, 7.30
    6, 6.07, 85, 7.05
    7, 5.85, 83, 6.89
    8, 5.64, 80, 6.64
    9, 4.91, 70, 5.81
    10, 3.78, 56, 4.65
    11, 2.34, 34, 2.82
    12, 1.78, 27, 2.24
    "Year", 4.32, 762, 63.25
    Between summer and winter, it would look like you need to either cut your winter power use by 1/2 or 2/3'rds -- Or increase your solar array by 2-3 times... (1.78 hours of average sun per day in December vs 5+ hours of sun per day in summer).

    If you have stretches of cloudy weather, your options become:
    • A lot more solar panels+batteries
    • Small automatic or manual genset to recharge bank
    • Cut power usage when battery/solar panel performance is low
    I don't think heating the batteries would be an answer unless they are well under 32F (~20% loss in capacity). Many times an insulated box and/or burying batteries a few feet underground will address most cold weather issues (need to monitor that they don't overheat in summer).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Help on preventing battery failure in extreme cold

    Bill,

    Thanks for all the helpful info.

    Looking at out weather station, it looks like it has been consistently between 0 and -20C for the last month. cold! This hasn't been a warm winter around Chicago, that's for sure.

    I know we should switch to sealed batteries and will do so in the future. at the moment it isn't an option at these sites due to budget constraints. Likewise, we'd have more solar out there but these camera systems are in wildlife areas and we are trying to limit their footprint so one panel is probably the max for now.

    Based on your suggestions and discussions with some other folks, we'll probably implement the following...
    (1) Add 1-2 more batteries so the bank is large enough to withstand long period s of cold
    (2) Reduce the system hours to only run for an hour or two during mid-day
    (3) Put the batteries in heavy duty insulated coolers that are painted black.
    (4) We may bury the batteries as well to keep the ambient temp more consistent. Might not be possible this year since the ground is frozen.
    (5) Update our software to turn of the PC and shut off the system if battery voltages are detected to be below 11 or .5V

    Any other thoughts/suggestions?


    Thanks again for the info

    Tim

    In case anyone is interested, you can explore interactive timelapse from the gigapixel cameras here: http://borevitzlab.uchicago.edu/Members/tim/gigavision-bigblowouteast
  • BB.BB. Super Moderators, Administrators Posts: 29,518 admin
    Re: Help on preventing battery failure in extreme cold
    Looking at out weather station, it looks like it has been consistently between 0 and -20C for the last month. cold! This hasn't been a warm winter around Chicago, that's for sure.
    Insulated box/buried box?
    I know we should switch to sealed batteries and will do so in the future. at the moment it isn't an option at these sites due to budget constraints. Likewise, we'd have more solar out there but these camera systems are in wildlife areas and we are trying to limit their footprint so one panel is probably the max for now.
    Problem with solar--more sq.feet is more power.
    Based on your suggestions and discussions with some other folks, we'll probably implement the following...
    (1) Add 1-2 more batteries so the bank is large enough to withstand long period s of cold
    Hate to say it--probably a bad idea. That plus using Marine batteries which are not usually very good at deep cycling.

    Looking at using inexpensive "golf cart" batteries may be better (keep costs low, cycle them till they did, replace).
    (2) Reduce the system hours to only run for an hour or two during mid-day
    Running during daylight hours hours only saves battery losses (but during cloudy weather, there is nothing much else you can do).
    (3) Put the batteries in heavy duty insulated coolers that are painted black.
    (4) We may bury the batteries as well to keep the ambient temp more consistent. Might not be possible this year since the ground is frozen.
    Take my suggestions with a grain of salt--San Francisco area is not known for much snow/frozen ground.

    You might want to drive a hole in the ground and drop a thermal couple to get an idea of how deep you would need to go to find warmer/more stable temperatures.
    (5) Update our software to turn of the PC and shut off the system if battery voltages are detected to be below 11 or .5V
    Deep Cycle Battery FAQ
    State of Charge/12 Volt battery
    100% 12.7
    90% 12.5
    80% 12.42
    70% 12.32
    60% 12.20
    50% 12.06
    40% 11.9
    30% 11.75
    20% 11.58
    10% 11.31
    0 10.5
    Cold batteries have higher resting voltage (at freezing, the resting 100% charged voltage ~1.2 volts higher:

    Charge_voltage_small.gif

    So, your 11.9 volt (cutoff the night before) may be 13.1 volts or more.

    A good, temperature corrected Battery Monitor will take much of this into account. Measuring resting voltage and temperature is a pain to determine actual capacity.

    For a nicely balanced system, you would want to match the solar panels to battery capacity around 5-13% of battery AH Rating... Take 10%:
    • 3x 100 AH * 14.5 volt charging * 0.10 rate of charge * 1/0.77 charge system derating = 565 Watts of solar panels
    More batteries means you should have more solar panels for proper charging. (big/dead batteries take a long time to recharge with a small array).

    A 565 Watt Array in December will produce, roughly:
    • 1.78 hours of sun per day * 565 watts of panel * 0.52 derating = 523 WH per day December
    • 523 WH / 12 volts = 44 AH per day
    The above is assuming a 85% efficient inverter... Multiply the above numbers by 1/0.80 (x1.25) if your equipment is DC powered.

    Also, if you cannot justify a Battery Monitor, for $60 there are some nice DC Amp*Hour / Watt*Hour meters that you can use to monitor your typical daily load (AH/WH usage). Flip the meter around and connect it to your solar charge controller, and you can log power generated.

    You need to know your power needs and panel output... Without that--we are guessing.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • SlimDieselSlimDiesel Registered Users Posts: 17
    Re: Help on preventing battery failure in extreme cold

    Sounds like one of the most hard-core off-grid applications out there: unattended.

    With a single panel, you definitely have too much battery. You're never going to get close to even the low end of the recommended charge rate for a big FLA deep-cycle. If you can't upsize the panel, you might think of downsizing the battery. I'm sure others will (and already have as I was typing) give real reasons why.

    Another thing you might do is optimize the angle for winter harvest... nearly vertical. Not only will that give maximum snow-shedding but it will give maximum watts when you need it most. During the summer you can afford to be sub-optimal because there is so much more available and the battery will be much better behaved.
  • System2System2 Posts: 6,290 admin
    Re: Help on preventing battery failure in extreme cold

    Just to clarify on the batteries, we are using Sears Deep-cycle Marine:
    http://www.sears.com/shc/s/p_10153_12605_02827582000P?prdNo=3&blockNo=3&blockType=L3

    I've previously used a lot of the Costco/Kensington deep-cycle marine 100Ah batteries with good success but there's no Costco around our site in Chicago so we went with Sears.

    Bill, can you clarify if deep-cycle Marine are still not good at deep cycling for this application or am I just confused? Got a link to recommended batteries? (SLA or otherwise)

    System pulls about 12w total. Everything is 12v so there's no inverter in the system It is currently on 3 hours a day at 8,12 and 4.
    System pictures here (if you're interested): http://www.flickr.com/photos/timescience/sets/72157624629095427/

    Thanks for all the suggestions!

    Tim
  • icarusicarus Solar Expert Posts: 5,248 ✭✭✭✭
    Re: Help on preventing battery failure in extreme cold

    Here is the best battery info out there:

    http://www.batteryfaq.org/

    http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

    Tony.

    PS I concur, too much load, not enough charging. adding batteries will only prolong the agony.

    t
  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Help on preventing battery failure in extreme cold

    "REAL" deep cycle batteries will definitely be better, but don't waste any more money on batteries until either you add enough solar to properly change them, OR reduce the load so the batteries aren't killed. No matter how expensive the batteries, if they're not properly charged and / or they're allowed to discharge too far, it's money down the drain, good money after bad.
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: Help on preventing battery failure in extreme cold

    System pictures here (if you're interested): http://www.flickr.com/photos/timescience/sets/72157624629095427/

    Tim
    Interesting research topic

    went to the above link and note that there is no metadata time of day stamp for the video, so I am guessing here that this was in the late afternoon, from the shadow angle.

    In the video I noticed that the shadow from the pole is near perpendicular to the PV panel.

    If so the PV may be misaligned for max collection.. the panels should be pointed to Solar Noon position, ie not necessarily due south.

    In the other link you posted, I could see that the 2 panels are at different angles and azimuths. there may be some minor gains to be had by realigning.

    Shadows are your enemy. Especially when you are under solar paneled... so much as a single shadow from a blade of that grass can cause up to 50% losses from your panels, they need to be elevated to be shadow free all year. Also consider 2 angles in a year , summer and winter, to max your gains.

    cheers

    e
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • westbranchwestbranch Solar Expert Posts: 5,142 ✭✭✭✭
    Re: Help on preventing battery failure in extreme cold

    Timescience, is this the low power CPU mentioned in the text of pic#5?

    http://www.compulab.co.il/fitpc2/html/fitpc2-datasheet.htm

    thanks
    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
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