Off grid system Battery Replacement

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bwoltz
bwoltz Registered Users Posts: 23
Well I don't come here too much when the system is working but my system is about due for battery replacement. In the past 15 years, the batteries only seem to last about 5 years..

The system is basically the same as the one in this discussion here except that during the posts the batteries were replaced with 16 new Trojan L16Ps and I added a MPPT 60 controller to one of my panels.

http://forum.solar-electric.com/showthread.php?1636-Needed-upgrades-repairs-off-grid-system&highlight=bwoltz

The system has been running fine up until about a month ago. Slowly the system has been loosing cells on the L16s.. The system is running 4 banks of 4 L16Ps. 2 of the banks are starting to give problems. One battery shorted a cell so I dropped to 3 banks. Since then 4 other batteries have shorted cells and I'm now down to 2 banks..

Is about 5 years all I can get out of these batteries? Is part of the problem that the system doesn't charge the batteries hard enough.. Seems to me if that were the case I'd have a battery sulfation problem and not a shorting problem.. I'd think that shorting would be from hitting the batteries too hard and knocking lead of the plates..

Anyway it's time again.. I noticed that Trojan has come out with L16REs. Hopefully they will do better..

Since I've just recently retired, I'm thinking about adding another set of panels. The Genset has about 6600 hours on it and may need replacement / rebuild (Onan NHD).

Thanks for any suggestions..

Bruce

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Off grid system Battery Replacement

    Welcome back Bruce--I cringe at my 5 year old posts (I was new(er) at the time:blush:).

    Anyway--What is your daily Watt*Hour or Amp*Hour (at 24 volt) load? I am a big believer in sizing your bank to your loads (nominal 1-3 days of storage with maximum 50% discharge--Nominal would be 2 days * 1/50% discharge = ~4x your daily power needs).

    5 years seems to be a bit short life for otherwise good batteries. Are you using distilled water for refills?

    Any occasional deep cycling/long time to recharge/exposed plates/etc. that may damage a bank?

    I am not a big fan of parallel battery strings... I would suggest looking at a larger AH cells and try to get to one string (or even forklift batteries if you can move those big guys in your installation).

    Also, I suggest using a DC Current Clamp Meter (like this $60 unit) to monitor current sharing between strings... May help you to identify poor current sharing (dirty connections, failing cells) earlier--Although, over 15 years you have probably gotten pretty good at debugging your bank.

    Battery Monitor in your system?
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: Off grid system Battery Replacement
    bwoltz wrote: »
    The system has been running fine up until about a month ago. Slowly the system has been loosing cells on the L16s.. The system is running 4 banks of 4 L16Ps. 2 of the banks are starting to give problems. One battery shorted a cell so I dropped to 3 banks. Since then 4 other batteries have shorted cells and I'm now down to 2 banks..

    Is about 5 years all I can get out of these batteries? Is part of the problem that the system doesn't charge the batteries hard enough.. Seems to me if that were the case I'd have a battery sulfation problem and not a shorting problem.. I'd think that shorting would be from hitting the batteries too hard and knocking lead of the plates..

    Thanks for any suggestions..

    Bruce

    I do not have personal experience with this, but I can pass along what I have read:

    This sort of shorting is not likely from fallen active material, since there is lots of space below the plates in an FLA battery just to allow for this. But the more common cause is "moss" or tiny tendrils of lead which grow to eventually bridge the gap between plates. This is supposedly caused by long term mild overcharging without ever having really high discharge currents to melt them back. Batteries for long term float use often have separators between the plates to minimize this, but eventually the tendrils win. (Think of grass and cracks in concrete!)
    Supposedly there are techniques which are occasionally successful to burn out the moss and restore the cell to at least partial use. But they require connecting directly to the shorted cell(s), without going through the other cells in the battery. It might be worth investigating since the batteries are a loss anyway.

    For the health of your new batteries, look into the recommendations for minimizing moss growth and controlling it when it happens.

    And depending on your use and the battery design, 5 years may be pretty good. <sigh>
    SMA SB 3000, old BP panels.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,479 admin
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    Re: Off grid system Battery Replacement

    It seems, spend 2x as much for a better battery, and the bank MAY last 2x longer...

    Install a 2x larger bank, and it MAY last 2.x times longer...

    And all it take is one "oops" to kill the 2x as expensive bank (or the "cheap" 1x bank).

    -Bill :cry:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Off grid system Battery Replacement

    Are we talking about four parallel strings of L16P's? They are 420 Amp hours each; four in parallel would be a whopping 1680 Amp hours. There is no way that either a 60 Amp charge controller or inverter-charger could put out enough current to properly recharge these batteries. On a 24 Volt system you're looking at a need for two 80 Amp charge controllers and two 2500 Watt arrays. Even if you could come up with the charge current trying to keep it even through all the batteries is very difficult with four parallel strings: bus bars are a must.

    Time to go back and re-evaluate the loads, then re-design the whole thing before any more money is spent.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: Off grid system Battery Replacement
    inetdog wrote: »
    For the health of your new batteries, look into the recommendations for minimizing moss growth and controlling it when it happens.

    There is a fair sized group of fanatics who dedicate their lives to reclaiming old LA batteries and extending the lives of the ones they have. Going all out in this direction does not seem like the best use of time and money for on off-gridder, and also requires being able to run special charge conditions 24 hours a day.

    But you will find some gems in their postings that may help you too. (In particular the need for high amp drain for short periods (but not deep discharge) as part of the battery's life cycle, and the dangers of trickle rather than float charging.) One starting point which discusses dendrite growth is this link: http://leadacidbatterydesulfation.yuku.com/topic/701/The-critical-need-for-discharging-while-pulse-conditioning#.T-NkhuJYv8o
    SMA SB 3000, old BP panels.
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: Off grid system Battery Replacement
    . Even if you could come up with the charge current trying to keep it even through all the batteries is very difficult with four parallel strings: bus bars are a must.

    There is an alternative to bus bars which may be easier for some people to implement, and uses only standard connectors. Take a look at the description here: http://www.smartgauge.co.uk/batt_con.html
    It works best for battery banks with 2 or 4 strings.
    SMA SB 3000, old BP panels.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Off grid system Battery Replacement

    4 parallel banks - I'd look into upgrading to a 48V system, or at least plan on it when the inverter needs replacement, rewire to just 2 banks at 48V.

    As to cells dieing, bummer.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • bwoltz
    bwoltz Registered Users Posts: 23
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    Re: Off grid system Battery Replacement

    Well thanks for the good information...

    It sounds like system may not be hitting the batteries hard enough. Some of this is due to the system design and some due to possibly my own misunderstanding..

    First off getting an accurate load might be a little hard. Originally the system in Sept 97 was sized for about 12KWH a day with on solar panel that was only capable of about 5KWH (25/30 amps @24) (12 BP590s on a track) and 3 banks of L16s (no P) The system would slowly loose energy and the Trace 4024 would start once every 2 or 3 days and replenish the bank.. The Genset is a 6500 watt Onan NHD commercial converted to propane (6300 watts). The system is totally automatic. The Genset is configured to charge the batteries at about 100 amps. This originally lasted about 4 years in which the generator accrued about 2800 hours.. Concerned about generator time I had added by the original installer new batteries but 4 banks of 4 and and additional solar panel that was sized slightly larger (12 100 watt PW100 (only good for 95 watts)). This system did what I hoped and dropped the Genset hours to about 1600 for the next 6 years.. I think under these conditions the battery eventually lost storage and started to boil water out (got almost 6 years).. This 3rd set of batteries the storage has been good until loosing a cell then it sucked.

    I know that the the usage has varied from the above spec.. I've had 2 teenage / adult kids using computers nightly up util about 10 months ago when one moved out..I sure that the load on the system increased since for the last 5 years I've seen about 1800 hours on the gen set. Currently laundry has also decreased but the remaining sibling likes to use the microwave and may be up until 3 in the morning playing electronic games. Fortunately for my power requirements, he'll be moving out in August to go to school up in Irvine..

    I've always used distilled water. Probably didn't check battery current balance enough on the banks..Work and play got in the way but retired now.. :blush: Last time was probably around Christmas then I got back into it after losing one bank more closely 2 months ago.. At that point the system was distressed a little. Some of it from shorted cell drawing down the bank.. I disconnected the bad bank and was gone for about 10 days and when I got back home I found the system having problem with another bank 2 cells shorted and the other 2 banks slightly low on electrolyte, could see the plates.

    The system utilizes method 2 here for interconnect

    http://www.smartgauge.co.uk/batt_con.html

    The gauge on the banks are at least 00 and the feed wires 000.

    I guess maybe with the current system it might be better to add another 2500 watts and a charge controller.. One of the issues I have is that the charge controllers run independent of each other. At 2500 watts and say 900 for the other 2 I could get potentially say 140 amps out of them.. If the Genset should start up I could get 240 amps (it runs interdependent of the charge controllers).. I would expect that mean I need 2400 amp hours of batteries? Or can you hit them at 20% (I'm thinking 10%) of the rated AH for charging.

    On the discharge side, the SW4020 and the house typically only pulls 5 to 15 amps at 120 or say 25 to 75 out of the batteries.. Most of the time the house is may be drawing 1 to 8 amps.. Not a lot on the discharge side as far as peak current go other than short bursts of the toaster and microwave..

    One of the thing we do is generally wait until the generator is running to do laundry.. This minimizes load on the batteries and inverter since the power to the house goes directly from the generator. We also do laundry on sunny days which lowers the charging of the batteries but minimizes energy loss of pushing energy in and out of the batteries. Could this be wrong??

    I don't have any problem going to one string to 2 volt batteries on the 24V system.. The inverter is still good but is aging.. Still the simplest way to go is to stay 24V. I don't have to rewire the panels. I'm not sure the C40 or the Outback can be setup for 48V (need to check)

    I don't have a battery monitor should I get one?? I figure the Trace would do OK.. This last time I set the system to start up at a higher low voltage, maybe that was bad?

    Bruce
  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
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    Re: Off grid system Battery Replacement
    If the Genset should start up I could get 240 amps (it runs interdependent of the charge controllers).. I would expect that mean I need 2400 amp hours of batteries? Or can you hit them at 20% (I'm thinking 10%) of the rated AH for charging

    In the 2007 post you linked to, you said that the genset is "set to auto-start on low voltage." If that's still true, it seems pretty unlikely it would turn on if the pv was delivering its maximum power to the batteries. Even if the gen did turn on, a full 240 amp charge would be brief, and I doubt a c/5 charge rate would hurt them if it wasn't long or frequent.

    I've given my L-16s that much charge from my pv alone, although it's not a regular occurrence. Hasn't cause any immediate problems.

    Anyway I'll echo the other posts: sounds like you would benefit from still more pv charging amps and a 48 volt system. I know it's work but it would be worth it to save your batteries, and pv is a lot cheaper than it was in 2007.....
  • bwoltz
    bwoltz Registered Users Posts: 23
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    Re: Off grid system Battery Replacement

    The more common scenario for over charging would be for the Genset to start first. It can take 6 to 8 hours to bring the batteries up.. The sun comes up next.. and the arrays start doing their thing.. Not uncommon. Batteries are lowest in the morning..

    Bruce
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    Re: Off grid system Battery Replacement

    Well first the good news, You should qualify for a 30% tax credit off your tax liability for money spent on batteries and panels (as well as inverter or CC if you choose to replace them) Your loads are moving away! Might be the time to see how well you'll manage with out the extra loads, before increasing things too much. A microwave isn't a huge load, unless you cooking rice or something (rice takes as long as in a pan of water and uses much more electric.)

    I'd look into a forklift battery if you can manage it, I purchased a 24V 800 Amp Hour(20 hour rate) for @ $2500, or about 8 of your L16 and I have hopes of it lasting 15+ years, NAWS(Northern Arizona Wind and Sun) as well as others have pushed 20+ years out of them. They are a bit different, but currently looks like the best bang for the buck. Of course if you can't drop the 1100lbs battery where you can use it it might create problems.

    Solar has never been cheaper, all though tarriffs on China made panels have increased the base a bit, panels at $1.20-140 a watt are a reality and with the tax credit might well be worth the investment. Loosing some loads you might look to a slightly smaller battery bank, and with a slightly larger array hope to fully charge w/o the use of the genny other than long cloudy spells. Your looking to reach float on a regular basis. actually with a reduced bank you may find you are able to get close to float daily, but running out as the capacity has been reduced.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
  • bwoltz
    bwoltz Registered Users Posts: 23
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    Re: Off grid system Battery Replacement

    On the tax credit, I though it only applies to grid tie systems.. Or is this a new federal energy thing..

    While the system is limping along on the 2 banks right now I've been looking into up dating the system.. Weather has been good and if we conserve a little the batteries are almost fully charged by the end of the day and down to about 24.4 volts in the morning.

    Right now the simple solution is to replace the current set of batteries with new and add a set of panels. Will probably go with 12 L16RE-2V to try a single chain.. The system will stay 24 volts.. It drops the capacity a little but with fewer kids my energy use will be less and the wife and I can conserve on cloudy days.. Since there is a possibility of overcharging if the genset starts in the morning and the sun comes up, I've been thinking that I could use the output of the generator to control a relay that disconnects enough panels to keep charging under control.. This is not optimum from energy point of view but it saves the batteries from over charging. I'd expect that with the newer inverters might be smart enough to monitor charging from other sources.

    This process has brought up some questions..

    Many have recommended going to a 48 volt system.. I'm not sure I understand why.. Sure IR losses are less. but I've already spend the money on the copper for the system. I guess it gives one the ability to run less parallel strings of batteries to achieve capacity. I'm not sure I understand why parallel strings are bad.. Sure, one is taught to not do this on banks where the batteries may sit for some time as the any imbalance in charge / capacity of the batteries will bleed don't the system and it will eventually go dead. My argument is that this system is never idle.. It's pretty much always either storing energy or providing energy.. The system runs 7/24. If you guys can point me to some references or case studies, that would be great.

    I do think now that part of the problem is that during the summer months the system was not charging the batteries to full and there was not enough load bring the batteries down enough for the Genset to fire off.. Hopefully adding panels and newer RE batteries will increase battery life and lower genset usage.. Also we can be a little more aggressive in the energy usage.

    I paid almost 6 bucks a watt for the original 2 sets of panels, I see package deals for less than a buck a watt.. No brainer.. MPPT seems like the way to go when updating.. Can boost the array output and minimize copper acquirement there.. It also makes change to 48V at a later date easier on this panel set.. I'll probably go ground mound fixed. I've got a south facing slope that is below the view line.. The mounting kits seem expensive. Would if be better to just make the racks out of steel, weld then together and have them powder coated?

    Thanks for the help..

    Bruce
  • SCharles
    SCharles Solar Expert Posts: 123 ✭✭
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    Re: Off grid system Battery Replacement
    bwoltz wrote: »
    On the tax credit, I though it only applies to grid tie systems.. Or is this a new federal energy thing..


    Bruce



    Never has been for grid-tie only nor is it currently.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
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    Re: Off grid system Battery Replacement
    bwoltz wrote: »
    On the tax credit, I though it only applies to grid tie systems.. Or is this a new federal energy thing..
    Its not that new, been around for at least a few years. There are many state incentive programs that are funded in part by the power companies, and those are for grid tie only
    bwoltz wrote: »
    Will probably go with 12 L16RE-2V to try a single chain.

    Two volt cells is a good idea (avoid parallel batteries). I don't particularly like the Trojan brand of 2 volt cells because each 2 volt battery is really 3 cells in parallel. I don't think that matters as far as performance or longevity, but it means three times as many cells to maintain. One (of many) of the advantages of a single string of batteries is less cells to maintain. That advantage does not apply to the trojans.

    You asked about why parallel strings of batteries are bad. Its because they are unstable. When charging it is hard to get the current to divide equally among the strings. Even if the strings have impossibly perfect connections and impossibly equal electrical characteristics they are still unstable. If one string is slightly warmer than the others (inevitable) it will draw more current which will make it warmer which will make it draw more current which will make it warmer, etc. Other than that, as the strings age they will diverge in their electrical characteristics and some will be overcharged (positive grid corrosion, mossing) and others will be undercharged (sulfation).

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • solarvic
    solarvic Solar Expert Posts: 1,071 ✭✭✭✭
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    Re: Off grid system Battery Replacement
    SCharles wrote: »
    Never has been for grid-tie only nor is it currently.
    I got an email from a reputable Alternitive energy company last year that installing an off-grid backup system qualifys for the 30% tax break. My tax preparer figured that it qualifys also. I didn,t even need it anyway as my SS was low enough I didn,t need it. My tax man said if I got a big gaswell check before 2016 I can use the deduction on that then. :Dsolarvic:D
  • bwoltz
    bwoltz Registered Users Posts: 23
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    Re: Off grid system Battery Replacement
    Are we talking about four parallel strings of L16P's? They are 420 Amp hours each; four in parallel would be a whopping 1680 Amp hours. There is no way that either a 60 Amp charge controller or inverter-charger could put out enough current to properly recharge these batteries. On a 24 Volt system you're looking at a need for two 80 Amp charge controllers and two 2500 Watt arrays. Even if you could come up with the charge current trying to keep it even through all the batteries is very difficult with four parallel strings: bus bars are a must.

    Time to go back and re-evaluate the loads, then re-design the whole thing before any more money is spent.

    Well, the current arrays and the inverter working together would have worked well if they provided power at the same time.. While in some cases this is true.. Most of the time especially during the summer, the panels were able to supply enough power to sustain the system for weeks on end.. This was not good for the batteries and they never saw a full charge.. This is motor than likely what stressed the batteries and led to their demise..

    My short term solution is has been to replace the batteries and adjust up the 24 hour low battery voltage generator start.. I dropped the capacity to 12 L16RE-2Vs (1110 20 AH rate). I sent email to the Trojan Tech support and they say that the batteries can be hit from 10% to 13% of the 20 amphour rating..

    Next plans are to add 2300 watts Solar panels. 80 amp MPPT controller(Midnight solar classic 150 actually 94 amp), battery monitor (Outback Power FN-DC Multichannel DC System Monitor), possibly a Ethernet hub that supports Wifi to the house..

    Has anyone had any experience with these panels?

    http://www.perlightusa.com/wp-content/uploads/product/pdf/plm-m-60-usa-series-spec-sheet.pdf

    The new solar panels look to be a snap (literally) on the connections now days with the MC4 cabling and Midnight solar outdoor breaker panels..

    The shed has one more buried 2 inch conduit that I can use for the input from the shed..Panels will be ground mount and about 30 feet from the shed. With 10 panels I'd wire 2 in series to drop the gauge wire requirements.. Issues are finding ground mounts to fit the panels and permitting.. Also I need to disable one of the input sources if the generator should start and the sun come up later.. The midnight solor looks to have an input that could be used but the function is sort of unclear..

    Messing with the numbers.. I'm thinking that the average daily consumption will cycle the batteries less than 20% capacity.. Most of the high energy stuff like washer and dryer will be done during the day..


    Bruce
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
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    Re: Off grid system Battery Replacement
    bwoltz wrote: »
    Also I need to disable one of the input sources if the generator should start and the sun come up later..

    Please elaborate... Your new 1110 AH batteries will happily take 125 amps and a bit more won't really hurt. How many DC amps does your generator-charger supply?

    Once you get to the absorb stage of charging there is no problem with over amping your batteries. When you are in bulk stage the charging sources are additive and you can push more amps in than is desirable for your batteries. This is something that I have ranted about in the past on several occasions. Even if you have an all Outback system with a FNDC there is no way to regulate Bulk charging.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • bwoltz
    bwoltz Registered Users Posts: 23
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    Re: Off grid system Battery Replacement

    It looks like I may need to cut power from the new panel set if the Genset is running since they will capable of approximately the same current. (both can be configured) It will probably be through a relay between the panels and MidNite Solar MPPT controller if the controller cannot be told to shut down.. Not sure if there are any issues with cutting input to the Midnite.. and switching it on later.. through a relay.. Also not sure if it hurts the solar panels for them to run unloaded (expect not)

    The Inverter charger is configurable.. Right now it's set to about 90 amps.. The peak from the other 2 sources are are 25 amps a piece.. So right now I can hit it the bank with 140 amps Probably a little high but expect that charging may be done before peak solar current is reached.. I understand about bulk charging being the problem.. Absorb is nothing more than constant volatge after bulk has been completed..

    I too am concerned about pushing too much into the batteries.. In the past I had too little.. The task is to get it right in the 10-13% 20 hour AH range. With this system I could potentially see the batteries getting 230 amps if all systems, panels and Genset, are providing power.. I need to control this.. While burning propane probably irks some over using solar there isn't an easy automated way to shut down the Genset without declaring an error.. I can try a relay to the Genset stop circuit but expect that when the motor quits the inverter will try to restart... I can try this manually just to see.. It would be the better way to go but I expect that the MidNite cannot set a relay based on output current only battery voltage / charge state.. Not sure the Aux relay programming is kind of vague to me.. Need to read the manual more..

    Bruce
  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: Off grid system Battery Replacement
    bwoltz wrote: »
    Also not sure if it hurts the solar panels for them to run unloaded (expect not)

    The Inverter charger is configurable.. Right now it's set to about 90 amps.. The peak from the other 2 sources are are 25 amps a piece.. So right now I can hit it the bank with 140 amps Probably a little high but expect that charging may be done before peak solar current is reached.. I understand about bulk charging being the problem.. Absorb is nothing more than constant volatge after bulk has been completed..

    I too am concerned about pushing too much into the batteries.. In the past I had too little.. The task is to get it right in the 10-13% 20 hour AH range. With this system I could potentially see the batteries getting 230 amps if all systems, panels and Genset, are providing power.. I need to control this.. While burning propane probably irks some over using solar there isn't an easy automated way to shut down the Genset without declaring an error.. I can try a relay to the Genset stop circuit but expect that when the motor quits the inverter will try to restart... I can try this manually just to see.. It would be the better way to go but I expect that the MidNite cannot set a relay based on output current only battery voltage / charge state.. Not sure the Aux relay programming is kind of vague to me.. Need to read the manual more..

    Bruce

    If you do not pull all of the available current from the panels, the voltage will rise as the current goes down until it hits the Voc (temperature corrected) for the panels with no current flowing and no harm will be done to them.

    Some people who want to maximize the contribution of the solar panels to charging the batteries recommend that you simply skip the Absorb phase of the Charge Controller by setting the Absorb voltage equal to the Float voltage. The reason is that the slow tapered charge usually used in absorb will not take full advantage of the power output of the panels if the batteries are lightly discharged to start with. As long as you monitor the battery temperature, an FLA battery will tolerate staying in bulk mode for a greater portion of the cycle.

    Since you will also have the generator available once the sun goes down, it is not as critical for you to maximize the panel contribution except to save on fuel costs.
    SMA SB 3000, old BP panels.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: Off grid system Battery Replacement
    inetdog wrote: »
    Some people who want to maximize the contribution of the solar panels to charging the batteries recommend that you simply skip the Absorb phase of the Charge Controller by setting the Absorb voltage equal to the Float voltage. The reason is that the slow tapered charge usually used in absorb will not take full advantage of the power output of the panels if the batteries are lightly discharged to start with. As long as you monitor the battery temperature, an FLA battery will tolerate staying in bulk mode for a greater portion of the cycle.

    I've never heard tat one before. Nor would I recommend it since it assures the batteries don't get fully recharged ever. Nor will it maximize panel contribution as Float Voltage is lower than Absorb Voltage therefor you would be drawing less power from the panels.

    The way to do it is to use the panels as the primary charge source and use the generator only as needed. Then you need to be able to take advantage of opportunity loads once the batteries are charged (or nearly charged) to maximize power output from the panels.

    In any event, all charge sources should be regulated with identical settings (or as near as possible) so that they will work together. Yes, there may be an occasional short-lived rise in current. That will not damage the batteries. Long-term over-current needs to be addressed. You should not design a system that needs high current from panels and from the generator at the same time in order to charge.
  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
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    Re: Off grid system Battery Replacement

    Bruce,

    In answer to your question RE the SW Poly PV modules. These are relatively new, at least in the USA market. Would expect that few if any here have very much experience at all with them.

    Have been running Shell Mono PVs for seven years now. SolarWorld bought Shell's PV business. A recent installation here uses SW 245 Monos, and those have been good so far -- have been on line for only about 8 months, tho. I've had no issues with any of these PVs.

    SW says that their PVs are made in USA. Believe that the current production SW PV have their 2.0 or 2.5 frames. The 2.0 is a top-clamp only style PV mounting, the 2.5 style SW frame is top or rear mount per the Data Sheet. The 2.0 frame can be a less flexible mounting method in come cases (vs the traditional bolt/nut on a real flange, which is missing on the 2.0 frame).

    Wind-Sun sells the Polys, so you might ask them about overall experience/opinion on these PVs.
    You probably have seen the DS on the 230 Poly:
    http://lib.store.yahoo.net/lib/wind-sun/SW-230-specs.pdf

    My bottom line: I prefer Mono PVs. But, if I were in the market for Poly PVs, SW would be at the top of my list. Kyocera makes very good Poly/Multi PVs as well.
    Just Opinions, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • bwoltz
    bwoltz Registered Users Posts: 23
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    Re: Off grid system Battery Replacement

    Thanks for the additional replies...
    Nor will it maximize panel contribution as Float Voltage is lower than Absorb Voltage therefor you would be drawing less power from the panels.

    Maybe he has it backwards?
    Long-term over-current needs to be addressed.

    Well in my case is currently under charging..
    You should not design a system that needs high current from panels and from the generator at the same time in order to charge.

    That's been my problem with the last set of batteries.. I could come up with a lame excuse that panels and installation back in 97 and 02 was so high that justifying lower battery life. was economically OK.. :D.. My last replacement (07) was more of a slimeball get er done as I was still working for a living and didn't want to deal with it... Unfortunately batteries jumped 50% in price.. Now that I'm retired I can give this some thought and priority..

    I sent email to Midnite and they say using a relay on the input is OK.. Finding a relay looks to be an issue.. The only thing I've found is a solid state relay that will work at 100VDC / 100 A. There are lower current rated ones but with Solid State voltage drop in the relay is of concern and the relay will need a heat sink.. plus it is only normally open.. I need to invert the logic and burn a few milliamps to use it.. Mechanical relays may be an issue as breaking DC current flow can create arcing at the contacts.. It takes a special relay and they are pricey.. At least the ones I have found.. Anyone know of a possible source for 100VDC high current relays?? Normally closed?

    Vic,

    Thanks for the info on the panel configurations..

    I notice that you say you prefer monocrystalline over poly.. As far as I can tell the main reason for mono over poly is efficiency.. The polies will be bigger.. Is there any other reason? Life? Fortunately for me I've an area where I can ground mount them and they are not even visible from the house..

    Bruce