Off grid system design help

PortliPortli Registered Users Posts: 9 ✭✭
Hello, great to have found this forum. Hope you can help me a little bit here:By any chance, could you give me some further aplication / Product engineering feedback on a complete off grid system:
We build a house that sadly cannot be connected to the grid at the moment. Consumption expectation of about 300kWh/Month, almost no peaks, 110VAC , 60Hz, Splitphase. 7kW Total load installed. However they might connect it in the future, so we want as little batteries as possible to bridge the time till the utiities connect it (maybe 3 - 5 years).  The only problem seems to be a 2hp Waterpump that spikes with almost 6000VA. We think about exchaning it, but seems a 1hp pump cannot cover for it and standard solar pumps dont work for that AC applicaion.
I considered using about 900Ah at 24V batteries and if possible would like both the inverter and the batterie system to be flexible and expandable.

We got 13 x Canadian Solar 315W panels.


Can anyone recommend us how to continue from here?

 

 

Thank you again very much for the support!
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Comments

  • mike95490mike95490 Solar Expert Posts: 8,030 ✭✭✭✭
    What's the well depth and flow requirement?  the SQ flex series may work.
    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 ,

  • SandyPSandyP Solar Expert Posts: 65 ✭✭
    For your flexibility / expandability option, you may want to consider going to 48V battery bank with a lower Ah capacity, say 450Ah @ 48V?
  • jonrjonr Solar Expert Posts: 1,135 ✭✭✭✭
    The Grundfos SQ will get rid of the starting surges at reasonable cost.

    It's rare that a 1 HP pump plus a large pressure tank doesn't work for a house.
  • PortliPortli Registered Users Posts: 9 ✭✭
    Dear Sandy, why is it for flexibility better to have 48V? Thank you!
  • BB.BB. Super Moderators, Administrators Posts: 28,186 admin
    It starts with the math... The standard equations for power are:
    • Power = Voltage * Current
    • Power = Voltage^2 / Resistance
    • Power = Current^2 * Resistance
    The first equation... Note that you can have 24 volts * 100 amps = 2,400 Watts... Or you can have 48 volts * 50 Amps = 2,400 Watts... The amount of current needed for the same amount of power is 1/2 the current.

    In general, the advantages for lower current/higher voltage is that you need much smaller diameter cable (save costs on copper) and can send the same amount of power much longer distances with less voltage drop.

    For a 24 volt @ 900 AH battery bank--You can have the same storage at 48 volts and 450 Amp*Hour... Say you want to charge the battery bank at 10% rate of charge... That would be 90 Amps @ 24 volts or 45 amps @ 48 volts--Besides the smaller diameter cable needed (and fuses/breakers/etc.), higher end MPPT solar charge controllers tend to be rated around 60-80 amps or so... A 24 volt battery bank, you would need 2x MPPT charge controllers for a 24 volt bank or 1x MPPT charge controller for your 48 volt battery bank--So, right there is an ~$600 savings in MPPT hardware (plus wiring, breaker, etc.).

    Another reason is the battery bank--Many batteries that can be moved by 1-2 people (vs a crane/fork lift/etc.)--have a limited maximum AH rating... I like to recommend that you have a single string of batteries as being the easiest to install/maintain. Say you can use a 6 volt @ 450 AH battery for your bank--You can put 4x in series for a 24 volt @ 450 AH string, with two strings in parallel (24 volt @ 900 AH battery bank)--Or you can put 8x in series for a 48 volt @ 450 AH battery bank--Same storage, but all batteries in series--Tends to be cheaper to install and easier to maintain/debug. Either configuration stores the same amount of energy.

    Not that going to 48 volts is "easy"--Need higher voltage circuit breakers/fuses, need 48 VDC rated input Inverter (48 volt inverters tend to be larger than 24 volt inverters--therefore more expensive and possible higher losses at lower AC power draws), and getting into the dangerous area for getting shocks/electrocution vs 12 or 24 volt DC systems.

    My suggestion is to look at doing several paper designs and see what works best for you (costs, capability of system)--And if you think your power needs will grow in the future. And paper designs do not cost you anything (other than time). Many people start with a "small system" and keep growing it until they hit limitations (generally, for example, suggest a maximum of ~2,400 Watts to possibly ~4,000 Watts @ 24 volts maximum power):
    • 4,000 Watts * 1/0.85 inverter eff * 1/21 volts battery cutoff voltage * 1.25 NEC wiring/breaker derating = 280 Amp rated DC wiring+breakers
    • A 4kW inverter should have an 800 AH @ 24 volt battery bank minimum (your 900 AH @ 24 volt battery bank would support 4kW max).
    That is a lot of current to bus around your system.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PortliPortli Registered Users Posts: 9 ✭✭
    edited August 2016 #7
    Dear Bill, thanks for the great help!

    Noted all your comments on 48V vs 24V.
    We will also try to develop various paper designs to find the most suitable one.

    We got good news, we can change the 2 hp pump for a 1Hp pump. So the whole house is now mono phase.
    I think this will significantly reduce the needed inverter and battery capacity.

    We were thinking to install the following:
    Batteries: 8 x LTH 205Ah/12V for 48V
    or 16 Batteries Trojan AGM 100Ah/12V also 48V

    Outback Flexpower 1 , 3648

    And still 13 315 Watt Canadian Solar Panels.

    Thank you again for your comments.
  • BB.BB. Super Moderators, Administrators Posts: 28,186 admin
    Since this is planned to be a short term installation... Look at your power usage... A 100 kWH per month system is pretty small and can keep a smaller/very efficient home with "near normal" electrical experience (lights, fridge, laptop, TV, clothes washer, and well pump).

    A 300 kWH per month system is a lot of energy, for off grid use, and will make the system much larger.

    Other options include using  a genset for larger daytime loads (morning/evening), and using the solar / battery system for quiet times (middle of the day, nighttime).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • PortliPortli Registered Users Posts: 9 ✭✭
    I think we will need at least a 300kWh system, maybe even a bit more. But the idea is to be flexible so we can expand it later if needed.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    There are several good controllers that can handle a 4095 watt array in a 48 volt system.   But not with 13 panels.  In a 48 volt system, those will need to be three in series.  You need 12 or 15 of those panels. 

    If those are 72 cell panels, the Voc is 45 volts.  Three in series is 135 volts.  In cold weather the Voc will exceed 150 volts.  That limits your choice of controller.  (many controllers have a max Voc of 150). I believe that Midnite and Magnum make controllers that will work OK with your panels.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PortliPortli Registered Users Posts: 9 ✭✭
    Thank you all for the helpful comments. Unfortunately i could not get the info about "What's the well depth and flow requirement?" so far
  • PortliPortli Registered Users Posts: 9 ✭✭
    Seems the decision is made:
    We got rid of the 2hp pump for a 1hp pump.
    Will use a 3648Flexpower, 10 Canadian Solar 315W, 16 LTH 205 Ah 12V Batteries.

    Does this seems alright?
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Portli said:
    Seems the decision is made:
    We got rid of the 2hp pump for a 1hp pump.
    Will use a 3648Flexpower, 10 Canadian Solar 315W, 16 LTH 205 Ah 12V Batteries.

    Does this seems alright?
    No.  How will you configure 10 panels?  I presume 5 strings of 2 panels per string with an FM80.  That might work with AGM batteries (probably wouldn't be high enough string voltage with flooded batteries).

    But... your battery bank looks like trouble... four strings in parallel is trouble... especially with AGM batteries.  You should be using a single string of 2 volt batteries.  If you go flooded, you can use 12 of your panels in strings of three, but you will need a higher voltage controller than the FM80.

    --vtMaps

    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PortliPortli Registered Users Posts: 9 ✭✭
    Thank you for the feedback. Exactly, 5 strings of 2 panels was the idea with the FM80. I am not quite sure why you say the battery bank could mean trouble? Could you explain that to me?  Thank you!
  • BB.BB. Super Moderators, Administrators Posts: 28,186 admin
    Is this the exact model number of solar panels you are using?

    http://www.canadiansolar.com/downloads/datasheets/v5.4/Canadian_Solar-Datasheet-CS6XP_Maxpower-v5.4C1en.pdf

    If so, these are 72 cell panels and have Vmp~36 volts. Two panels in series is Vmp-array~72 volts and may be OK for charging your 48 volt battery bank. I do not know the voltage drop of the Outback controller--But you need around Vbatt-charging~59 volts, and Vmp-hot will be around 67 volts--Leaves ~8 volts for wiring and controller drop.

    You can use the Outback string sizing tool to confirm that your array meets Outback's operating requirements:

    http://www.outbackpower.com/outback-support/string-sizing-tool

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Portli said:
    I am not quite sure why you say the battery bank could mean trouble? Could you explain that to me?  Thank you!
    Parallel batteries are unstable and when charging them, the current does not divide equally among the parallel paths.  Here is a short discussion to read: http://forum.solar-electric.com/discussion/13179/series-rule-of-thumb

    Here is a stochastic reason to avoid parallel batteries:
    http://forum.solar-electric.com/discussion/comment/356663#Comment_356663

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • PortliPortli Registered Users Posts: 9 ✭✭
    BB. said:
    Is this the exact model number of solar panels you are using?

    http://www.canadiansolar.com/downloads/datasheets/v5.4/Canadian_Solar-Datasheet-CS6XP_Maxpower-v5.4C1en.pdf

    If so, these are 72 cell panels and have Vmp~36 volts. Two panels in series is Vmp-array~72 volts and may be OK for charging your 48 volt battery bank. I do not know the voltage drop of the Outback controller--But you need around Vbatt-charging~59 volts, and Vmp-hot will be around 67 volts--Leaves ~8 volts for wiring and controller drop.

    You can use the Outback string sizing tool to confirm that your array meets Outback's operating requirements:

    http://www.outbackpower.com/outback-support/string-sizing-tool

    -Bill
    Yes, those are the exact panels we are using.
    Thank you!
  • PortliPortli Registered Users Posts: 9 ✭✭
    After all the helfull comments, using the stringsizing tool of outback etc. we now came up with following solution:

    9 Panels Canadian Solar 315W
    4 Batteries Trojan 205 AGM at 48V to not have several strings, expandable later on if needed
    Outback 3648 Flexpower with FM 80

    I think this will be a safe bet to start and we can always expand later on.

    Would you agree with this?

    Thank you again!


  • Marc KurthMarc Kurth Solar Expert Posts: 448 ✭✭✭✭
    Unless you have a reason not to, I would suggest looking at Trojan's flooded batteries instead of their AGM's. They are well known to work with a long and illustrious history.  (and this comment is coming from an AGM guy)

    Do some Google research on longevity reports for Trojan AGM's - and take note of the fact that they don't do a lot of promotion of their AGM product line..........

    But then, if you only need a short life, almost any battery will do.

    Marc



    I always have more questions than answers. That's the nature of life.
  • Marc KurthMarc Kurth Solar Expert Posts: 448 ✭✭✭✭
    edited August 2016 #20
    vtmaps said:
    Portli said:
    I am not quite sure why you say the battery bank could mean trouble? Could you explain that to me?  Thank you!
    Parallel batteries are unstable and when charging them, the current does not divide equally among the parallel paths.  Here is a short discussion to read: http://forum.solar-electric.com/discussion/13179/series-rule-of-thumb

    Here is a stochastic reason to avoid parallel batteries:
    http://forum.solar-electric.com/discussion/comment/356663#Comment_356663

    --vtMaps

    I will add a comment to this:
    Multiple parallel strings can serve a long and useful life, if the owner understands the dynamics of their battery bank.
    - Yes, there is obviously a continuous tendency to develop imbalances between strings. Well known, documented and proven.
    - Yes, those imbalances will become detrimental over time, if ignored. Also well known and long proven!

    No matter how perfectly you design the wiring/busbar layout for equal resistance, it won't solve the issue over the long haul of 3-10+ years - because of variations in individual battery resistance.

    In reality, you should be watching your single string bank for the same reasons. Go ahead and read charging or heavy load voltages across all 2v batteries in a 48v string. You will likely not find more than two close to identical.

    What I almost never see discussed is the real world full of applications with deep discharge multi-parallel banks - every day.

    Flooded battery bank owners are already accustomed to long term adjusting of water levels, cleaning connections and checking SG on a schedule. If you are forced to go multi-parallel for economic reasons- don't panic. Just understand that rotating battery location in the banks and strings every year or two or three is a required "maintenance" item on multi-parallel battery banks.

    At the risk of being repetitive: I like single strings.But I am also a realist when considering customer needs.

    Respectfully,
    Marc

    Edit to add: I did not mean this to come off as a know-it-all. When I re-read it, I didn't like how it sounded, There are many people here who are way smarter than I am. I am here because I learn something almost every time from the experienced people who are willing to share. I can only offer MY experience in return - and I am willing to keep learning!


    I always have more questions than answers. That's the nature of life.
  • jonrjonr Solar Expert Posts: 1,135 ✭✭✭✭
    Marc Kurth said:  Just understand that rotating battery location in the banks and strings every year or two or three is a required "maintenance" item on multi-parallel battery banks. 

    As BB once said:  "use a DC Current Clamp meter to ensure that parallel strings are properly sharing current between strings."

    And I'll add "based on the measurements, you can adjust cable paths/lengths to eliminate most of the parallel balance issue." 
  • Marc KurthMarc Kurth Solar Expert Posts: 448 ✭✭✭✭
    Yes, Sir that is important at startup and forevermore. We should all keep an eye on the amperage draw/load - and the voltage differential between batteries in single and multiple string battery banks.

    Again, I always suggest 2v cells when feasible because you can watch each cell. Sometimes the economics or logistics don't allow it....but that is less common than people assume.

    As you highlighted, I feel that battery position rotation should be a regular maintenance thing as opposed to an "uh oh, what is wrong" reaction!

    Marc
    I always have more questions than answers. That's the nature of life.
  • vtmapsvtmaps Solar Expert Posts: 3,738 ✭✭✭✭
    Portli said:
    After all the helfull comments, using the stringsizing tool of outback etc. we now came up with following solution:

    9 Panels Canadian Solar 315W
    That will be trouble.   Three of those panels in series will damage the Outback controller.  (see post #10)

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • SandyPSandyP Solar Expert Posts: 65 ✭✭
    Portli : The Victron Web page below has an overview of the impact of temperatures and voltages (and cable length) on battery charging : 

    https://www.victronenergy.com/blog/2014/03/28/matching-victron-energy-solar-modules-to-the-new-mppt-charge-regulators/
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