Small Low-Cost Off-Grid Solar System





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    Default Small Low-Cost Off-Grid Solar System

    Greetings to all!

    I am a newbie in this forum, for the past few weeks I have been reading about solar system posts and learnt a lot.

    I am planning install a small off-grid solar system for my mom who resides in an area where Eskom is not installed yet (and no indication of when it will be installed).

    System requirements:

    • Low cost: maximum cost of equipment, house wiring and installation should not exceed R25k.
    • Daily Load: 1500 Wh (see attachment)
    • Long battery life
    • System voltage: 24V


    The system must be able to run fridge 24 hours and lights at night. It must also be able to run a washing occasionally (maybe once week). I estimated that a washing would run for 30 min (two wash cycles). The wash motor is rated 400 W and maximum power 610W. This brings the total daily load of 145 W 1500 Wh and maximum of 2087 Wh or 700 W once a week.

    Battery Specification:

    Watt-hour @ 50% DOD = 3kWh.........this brings number of 12 V 100 Ah batteries to 3, rounded to 4 to have a balanced voltage of 24 V. 2S2P battery strings brings the total to 4.8 kWh (24 V 200 Ah) which is more than enough buffer(DOD is 31%). The problem with adding more batteries is that costs increase. If I use 2x 100 Ah batteries in series (24 V 100 Ah) I get 2.4 kWh which is 62.5% DOD. Question: can I get away with 2 batteries instead of 4 in order to minimize costs?

    Solar panels specification:

    2x 330 W solar panels will yield 1122 Wh at 85% inverter efficiency.

    Inverter Specification:

    Pure Sine Wave: I read that inductive loads such as fridges and washing machines don't like modified sine wave.

    In addition, the inverter must be capable of handling surge currents up to 3-7 times the continuous current as explained here: https://sinetech.co.za/select-inverter.html. Daily continuous power is 145 W (that is excluding the washing machine). If I include the washing machine, the maximum continuous power in a week is 700 W. Following an example described in the link, I will need an inverter capable of handling up to 2100 W surge power. A 1kVA inverter capable of handling the surge power could suffice but the price difference between 3kVA and 1kVA does not justify it.

    Inverter brand: I noticed that the most recommended inverter brand is Victron however it is expensive considering that is modular (separate inverter &charge controller, and...and). The other mostly used brand is Axpert (albeit with alleged firmware issues). I have also learnt there’s a host of other inverters having similar functionality and design as Axpert, such Synpse, as discussed here: https://www.4x4community.co.za/forum...33#post4125133.
    I have obtained several quotations for the system and the total for equipment comes to around R16k. I am planning to do the project in piecemeal fashion as I don’t have enough cash. This Synpase 3kVA/2400W MPPT inverter looks appealing: https://solarequipment.co.za/product...brid-inverter/, has anyone have experience with it and the supplier?
    Recommendations about equipment suppliers, installers, or any suggestion/ comment on the above will be appreciated. Thank you.
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    Default Re: Small Low-Cost Off-Grid Solar System

    GEEEZZZZ ... I must read slower!!!

    Your Mom, no Eskom and no Eskom future.

    You need more in-depth analysis of the system ...
    Last edited by the_terrible_triplett; 2020/06/29 at 08:54 AM.
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    Default Re: Small Low-Cost Off-Grid Solar System

    The biggest problem with motors is the start up currents. Not an expert but wrt running a home 100% off grid and non constant sunlight, won't the batteries be undercharged for most parts or drained quicker than getting recharged due to usage and sunlight factors. A point I always wondered about.
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    Default Re: Small Low-Cost Off-Grid Solar System

    Hi, I installed a quite expensive 5kw system, but if I had the opportunity to do a small installation from the onset, I'd make the lights 12V and buy one of those cheapos, you know? those little 10 and sometimes 20A charge controllers that even have two USB ports to charge cellphones. you could also use the USB port on the TV to charge phones. Also the internet routers and decoders and such is also 12V, so you have two circuits, one without an inverter, a 12V with a 100ah, sommer lead acid? battery and then your more expensive circuit for your fridges, aircons and such?

    Just remember the 12V circuit must have thick wires, if you ever put an inverter on that, then you might melt the cables, a 1000W inverter on a 12V battery will pull 83A through those cables and you can easily burn the house down.

    24V system I wont recommend, unless you don't ever plan to upgrade the 3kw system, 125Amps! not abnormal, but still very high, you won't for example, get a 125A breaker, if you wish to protect your inverter further than it's own internal protections. Also what you pay in cables, capable of carrying 125A (Half welding cables? Half jumper cables?) you could add to the cost of a 48V system. If the volts double, the amps halves (I=W/V). My 2 cents good luck

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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by Thysticles View Post
    you won't for example, get a 125A breaker, if you wish to protect your inverter further than it's own internal protections.
    That's not true, you get them.
    https://lithiumbatteriessa.co.za/col...ircuit-breaker
    Last edited by faniedup; 2020/06/29 at 11:50 AM.

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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by the_terrible_triplett View Post
    GEEEZZZZ ... I must read slower!!!

    Your Mom, no Eskom and no Eskom future.

    You need more in-depth analysis of the system ...
    And no future with Eskom... I don't think the system is complicated, maybe I complicated it by adding a washing machine?

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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by VVTi View Post
    And no future with Eskom... I don't think the system is complicated, maybe I complicated it by adding a washing machine?

    Your fridge load in the table seems a bit low, unless its a camping fridge?

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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by hunter26 View Post
    The biggest problem with motors is the start up currents. Not an expert but wrt running a home 100% off grid and non constant sunlight, won't the batteries be undercharged for most parts or drained quicker than getting recharged due to usage and sunlight factors. A point I always wondered about.
    That is my concern as well hence my question above about using 2 batteries instead of 4. I was conservative with the sunlight/irradiation as I used 4 hours (I've seen some using 5.5 hours) and came up with 2 solar panels. As to whether these will be enough to charge up to 4 batteries (if I go for them) , I'll leave it to the experts.

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    Default Re: Small Low-Cost Off-Grid Solar System

    I would look at treating this like a camping setup, in other words as many as possible devices directly off 12V, that's of course if lights and such are not already in place.
    Same for the fridge, yes 12V camping style fridges are more expensive than 230V fridges, but consider it, weigh it up against the cost of a bigger inverter since one of the main reasons for a big inverter is to run the fridge.
    Eventually you could get to the point where you only need a smaller inverter for the washing machine once per week, then you might as well just keep the DC side of the system at 12V to simplify things and keep costs down.
    It's in pubs where the world's greatest ideas begin.

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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by faniedup View Post
    Your fridge load in the table seems a bit low, unless its a camping fridge?
    Strange enough not really. I have one of those KIC 340l fridge/freezer and consume around 950-1100wh for the day. Depending on how warm it is.

    Samsung front loader. 250wh per load.
    Defy Dishwasher 70C setting, 1.7kwh per load.
    Chest freezer 340lt - 1.2-1.5 kwh in the winter. Summer 2.0-2.5kwh for the day.
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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by faniedup View Post
    Your fridge load in the table seems a bit low, unless its a camping fridge?
    It's a KIC KTF 518/1 WH 170 litre refrigerator rated at 375 kWh/ year. This translates to 43 Watts per day (375*1000)/(24*365).

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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by VVTi View Post
    It's a KIC KTF 518/1 WH 170 litre refrigerator rated at 375 kWh/ year. This translates to 43 Watts per day (375*1000)/(24*365).
    375 kWh/ year works to around 1.1kWh/day. Fridge is not always on. Around 110w/h when motor running. 5w standby. 18w when you open the door with the light on.
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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by Rudi.Oost View Post
    Strange enough not really. I have one of those KIC 340l fridge/freezer and consume around 950-1100wh for the day. Depending on how warm it is.

    Samsung front loader. 250wh per load.
    Defy Dishwasher 70C setting, 1.7kwh per load.
    Chest freezer 340lt - 1.2-1.5 kwh in the winter. Summer 2.0-2.5kwh for the day.
    Your 340l KIC refrigerator consumes almost the same power as my KIC 170l (1100wh for 24hrs = 46W vs 43W for my case) which is half the size, that means yours is more efficient than mine.

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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by VVTi View Post
    And no future with Eskom... I don't think the system is complicated, maybe I complicated it by adding a washing machine?
    System is not complicated no, just not going to fit easily in a +-R16k budget.
    Ok, it can fit BUT you could be looking at spending more money sooner than you would hope for.

    12v is fine, so what the amps are higher, fuses and 50mm2 simply costs a wee bit more IF the continuous load < 1000w
    If continuous load is < 2000w, then 24.
    48 for continuous loads above 3000w

    And the loads are not continuous at even 500w 24/7/365?

    BigBoy has made THE sanest suggestion ito costs and ease of use.

    Quote Originally Posted by bigboy529 View Post
    I would look at treating this like a camping setup, in other words as many as possible devices directly off 12V, that's of course if lights and such are not already in place.
    Same for the fridge, yes 12V camping style fridges are more expensive than 230V fridges, but consider it, weigh it up against the cost of a bigger inverter since one of the main reasons for a big inverter is to run the fridge.
    Eventually you could get to the point where you only need a smaller inverter for the washing machine once per week, then you might as well just keep the DC side of the system at 12V to simplify things and keep costs down.


    I would not "waste" money on lead acid batteries, when you have to replace them after +-200 days of usage, the Royal type 100ah.

    Go for lithiums from the start, 12v/24v.https://lithiumbatteriessa.co.za/pro...31792001515610

    But IF you use 4 x 12v batteries lead acid, go 48v.
    Same battery costs as 12v with 4 batts - you just have SO much more room to move into the future.

    48v lithium costs a packet more than 12v lithium like here: A 12v Lithium bank 12v x 120ah = 1440kwh

    But comparing cycles, AGM cycles about +-800-1000 at 50% DOD ... so +-2 years more or less before replacement?
    Vs lithiums at 100% DOD about cycle +-3000 so about +-8 years.

    And 24v/48v lithiums on same ah not that much of a difference:
    24v Lithium bank
    48v lithium bank


    You biggest costs are batteries, not inverters or fuses or cables, nope batteries.
    And if you have only solar power to recharge them, no generator to assist during winter/bad weather days, weeks, it gets even more expensive ito batteries AND panels.

    I rather be brutal now than hearing you throw the towel in after spending hard earned cash when it is not producing as you expected.
    Last edited by the_terrible_triplett; 2020/06/29 at 01:19 PM.
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    Default Re: Small Low-Cost Off-Grid Solar System

    Continuing on my keeping everything at 12V trend.
    I would start out with one 12V 120 Ah lithium as per TTT's post, then add a second one before next winter.
    R5k for the battery, R5k for a 1000W inverter, between R6k and R8k for panels and solar controller, less than R5k for wiring, fuses, other consumables and maybe a battery monitor, then you have your R25k budget pretty much spent.
    Next winter you add a second lithium battery another R5k and maybe 2 more solar panels another R4k.

    It seams you already have the 230V fridge, I know this will be more effort, but the fridge can even be switched off for that 1 hour per week when the washing machine gets used, this alone can already save you from buying a huge inverter.
    Last edited by bigboy529; 2020/06/29 at 01:41 PM.
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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by Thysticles View Post
    Hi, I installed a quite expensive 5kw system, but if I had the opportunity to do a small installation from the onset, I'd make the lights 12V and buy one of those cheapos, you know? those little 10 and sometimes 20A charge controllers that even have two USB ports to charge cellphones. you could also use the USB port on the TV to charge phones. Also the internet routers and decoders and such is also 12V, so you have two circuits, one without an inverter, a 12V with a 100ah, sommer lead acid? battery and then your more expensive circuit for your fridges, aircons and such?

    Just remember the 12V circuit must have thick wires, if you ever put an inverter on that, then you might melt the cables, a 1000W inverter on a 12V battery will pull 83A through those cables and you can easily burn the house down.

    24V system I wont recommend, unless you don't ever plan to upgrade the 3kw system, 125Amps! not abnormal, but still very high, you won't for example, get a 125A breaker, if you wish to protect your inverter further than it's own internal protections. Also what you pay in cables, capable of carrying 125A (Half welding cables? Half jumper cables?) you could add to the cost of a 48V system. If the volts double, the amps halves (I=W/V). My 2 cents good luck
    Thanks for the suggestion but having two inverters seems not feasible if the same output can be achieved with one inverter.

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    Thumbs up Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by the_terrible_triplett View Post
    System is not complicated no, just not going to fit easily in a +-R16k budget.
    Ok, it can fit BUT you could be looking at spending more money sooner than you would hope for.

    12v is fine, so what the amps are higher, fuses and 50mm2 simply costs a wee bit more IF the continuous load < 1000w
    If continuous load is < 2000w, then 24.
    48 for continuous loads above 3000w
    Interesting.

    And the loads are not continuous at even 500w 24/7/365?

    yes 150W continuous and 700W maximum.

    BigBoy has made THE sanest suggestion ito costs and ease of use.





    I would not "waste" money on lead acid batteries, when you have to replace them after +-200 days of usage, the Royal type 100ah.

    Go for lithiums from the start, 12v/24v.https://lithiumbatteriessa.co.za/pro...31792001515610

    But IF you use 4 x 12v batteries lead acid, go 48v.
    Same battery costs as 12v with 4 batts - you just have SO much more room to move into the future.

    48v lithium costs a packet more than 12v lithium like here: A 12v Lithium bank 12v x 120ah = 1440kwh

    I'm also considering DIY LifeP04 bank.

    But comparing cycles, AGM cycles about +-800-1000 at 50% DOD ... so +-2 years more or less before replacement?
    Vs lithiums at 100% DOD about cycle +-3000 so about +-8 years.

    And 24v/48v lithiums on same ah not that much of a difference:
    24v Lithium bank
    48v lithium bank


    You biggest costs are batteries, not inverters or fuses or cables, nope batteries.
    And if you have only solar power to recharge them, no generator to assist during winter/bad weather days, weeks, it gets even more expensive ito batteries AND panels.

    I rather be brutal now than hearing you throw the towel in after spending hard earned cash when it is not producing as you expected.

  20. #18
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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by VVTi View Post
    yes 150W continuous and 700W maximum.
    No brainer then ... it is 12v.

    And IF ever you feel you are in a "corner", to sell a 12v system on Gumtree is easy!
    Even faster on 4x4 forum's classifieds.
    Only IF you upgrade to say 48v much later.

    This is by no means a final suggestion, but a quick calc on 150w for 24 hours and 700w peaks for +-2 hours with one days backup and using 200ah LEAD ACID batts to 50% DOD, this is the wh you are looking at:
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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by bigboy529 View Post
    Continuing on my keeping everything at 12V trend.
    I would start out with one 12V 120 Ah lithium as per TTT's post, then add a second one before next winter.
    R5k for the battery, R5k for a 1000W inverter, between R6k and R8k for panels and solar controller, less than R5k for wiring, fuses, other consumables and maybe a battery monitor, then you have your R25k budget pretty much spent.
    Next winter you add a second lithium battery another R5k and maybe 2 more solar panels another R4k.

    Thanks bigboy. I can a 3kVA inverter with integrated controller for the price of 1kVA inverter.

    https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwinrNn4iKfqAhUb7e0KHfszDv4YABAJ GgJkZw&ohost=www.google.com&cid=CAESQOD2Ob3_81_CXD K019MkAa1pJOXzynZfp0IwgJZQM7yFyabHyRKIy7R0aPfyLPKQ uDeFKokUQwVEdZB2atOyq9w&sig=AOD64_0uB6qmRSLPmyy7FJ EGEp_aoG2FNw&ctype=5&q=&ved=2ahUKEwiPtdD4iKfqAhXbQ UEAHUImBJoQ9aACegQIDhA-&adurl=


    https://solarequipment.co.za/product/synapse-3-0-24v-hybrid-inverter/

    https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwigtcrtiafqAhUHtO0KHRETDOYYABAF GgJkZw&ohost=www.google.com&cid=CAESQOD205wr8Lv2A0 r4mJo6Exl80N-2fqFn_LL5jlGDWiduRpFIQaxIVJ--WRd8Rl5CjJDjbGXiywj5FrkdQsmnoa4&sig=AOD64_1lxKMKhS 4QnTA9q9FvR9Sgxk6jIg&ctype=5&q=&ved=2ahUKEwiq3MHti afqAhUOTsAKHYhSApoQ9aACegQIDRA-&adurl=

    https://www.googleadservices.com/pagead/aclk?sa=L&ai=DChcSEwigtcrtiafqAhUHtO0KHRETDOYYABAK GgJkZw&ohost=www.google.com&cid=CAESQOD205wr8Lv2A0 r4mJo6Exl80N-2fqFn_LL5jlGDWiduRpFIQaxIVJ--WRd8Rl5CjJDjbGXiywj5FrkdQsmnoa4&sig=AOD64_3JJnpq73-PvlMfHx3YH4NzzYd-_g&ctype=5&q=&ved=2ahUKEwiq3MHtiafqAhUOTsAKHYhSApo Q9aACegQIDRBE&adurl=

    Where can I get 12V 100Ah lithium batteries for R5k?


    It seams you already have the 230V fridge, I know this will be more effort, but the fridge can even be switched off for that 1 hour per week when the washing machine gets used, this alone can already save you from buying a huge inverter.
    Yes this can definitely work.

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    Default Re: Small Low-Cost Off-Grid Solar System

    Quote Originally Posted by the_terrible_triplett View Post
    No brainer then ... it is 12v.

    And IF ever you feel you are in a "corner", to sell a 12v system on Gumtree is easy!
    Even faster on 4x4 forum's classifieds.
    Only IF you upgrade to say 48v much later.

    This is by no means a final suggestion, but a quick calc on 150w for 24 hours and 700w peaks for +-2 hours with one days backup and using 200ah LEAD ACID batts to 50% DOD, this is the wh you are looking at:
    Thanks TTT, this is a nice tool, I had to do my calculations on Excel

    12V 200Ah batteries average cost is R4500x 6 = R22k...way beyond my budget

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