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Thread: max Uoc allowed on residential off grid (non embedded) system

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    max Uoc allowed on residential off grid (non embedded) system

    What are the max Uoc pv array voltage allowed on residential off grid (non embedded) system?

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    Hi

    I am not aware of any restrictions on Voltage with regards to residential vs commercial.
    If you go above 1,5KV it will no longer form part of SANS 10142-1 .
    I am not sure what regulations it will then fall under . I have noticed that the PV regulations under discussion also refer to a max Uoc as 1500Vdc

    I do know that you may not exceed 25% of your incoming CB size which is a bylaw and applies to grid tie - On a domestic single phase it should not exceed 5KVA and could vary depending on the suppliers bylaws.

    As an off grid system I have not heard of a restriction in size but you would need to notify the supplier as per Nersa regulations. The supplier could have it's own set of bylaws over and above SANS 10142-1

    I am assuming that somebody has queried you on the voltage that you were going to use on the strings - Could you let us know more as to the voltage you are querying.

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    Hi

    Thanks for the reply

    This query is for one of my five bosses power backup installations/systems. To keep it simple I will only discuss the first and most urgent installation/system. Currently he have axpert 4kva inverter with a integrated 145v mppt charge controller from the sun pays( the only axpert inverter with a LOA I could find) The system is currently only used as a load shedding power backup kit, but due to cable theft he cant sit without power for more than five days multiple times per year. So I must design a system than can keep his house running for multiple days offgrid. +-70 of his energy consumption are use by his geyser and he uses +- 1000 kwh unit per month. The geyser will be converted to gas geyser if necessary. The reason for this qwerty is because the a knowledgeable guy told me that residential PV arrays pay not exceed 145 V but a 450 V system is just so much more efficient. also to get 145 v string u need to use 3 X 60cell panel PV but the with the 450 V system you can string up to 9 72 cell panels that make more sense on the available roof space on his home.

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    Hi

    I have definitely not seen or heard of a regulation that will not allow more than 450vdc on a residential property - Would be interested to hear where that regulation comes from

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    For heating of the geyser, I have designed a system which works of PV. No batteries required.
    Works far better than evacuated tubes, I have them so I compare, and I have found that by 12H30 on a winters day my water temperature is at 65 C as opposed to 45C using evacuated tubes.
    It runs during the day, and heats the water electrically, so installation is simple, simply reroute the mains wires, and install PV panels on the roof.Useda Sun Brochure.pdf
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar and LED lighting solutions - www.microsolve.co.za

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    I saw your system. Seems like a good idea but if I don't see the cost of the product on the supplier/manufacturers website I loose interest and look for a other solutions.

    Please tell me more about the system.
    1)cost?
    2)can I connect it to a solar geyser 2000w booster element to get extras 'boost' ?
    (https://shop.thesunpays.co.za/collec...year-guarantee)
    3) earthing and bonding requirements to the system ?

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    Diamond Member Justloadit's Avatar
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    Quote Originally Posted by Frans400 View Post
    I saw your system. Seems like a good idea but if I don't see the cost of the product on the supplier/manufacturers website I loose interest and look for a other solutions.

    Please tell me more about the system.
    1)cost?
    2)can I connect it to a solar geyser 2000w booster element to get extras 'boost' ?
    (https://shop.thesunpays.co.za/collec...year-guarantee)
    3) earthing and bonding requirements to the system ?
    Placing prices for product on a web page can be a problem, especially when the product is aimed for installer/distributors.
    End customers get annoyed that they are being ripped off, because they can see a cost.
    One also needs to understand the product to work out best possible price, as there are a number of options, which becomes confusing.

    The system highest cost is primarily the PV panels, and the ease of installing the panels. The Electronics part is the least expensive part of the system.

    The system handles elements from 1kW to 3kW directly. 4kW elements require a specially manufactured unit.
    The unit is available on a pre-wired base plate for installation in the ceiling, or in an IP65 enclosure for installation on a concrete roof or under the roof eves.
    The unit comes standard with a mains back up relay in which one can use the grid as aback up for over use of hot water, or when there are days of poor sun radiance.
    The unit also has an attachment, KWHMO-PR323, for monitoring the amount of energy used from the sun, along with a geyser water temperature sensor and a programmable timer with 3 settings and a manual mains over ride selection.

    The system can use 5 off 60V 265W panels in series, or 3 or 4 or 5 or 6 off 270/275/300/330/350 watt panels, but requires a DC2DC converter to bring the DC up to 300V DC

    As you can see it starts becoming a little complicated.

    We do not sell PV panels, as this has become a major problem with certain suppliers off loading PV panels at ridiculous prices into the market as and when they need quick cash.
    We do not provide the rails and installation accessories, as this becomes site dependent.

    What we do provide as at the 23/9/2020
    Distributor price ex our offices and exclude VAT

    Chassis mount plate pre-wired R 5,577.00
    includes
    SOLAR GEYSER CONVERTOR UNIT
    MAINS BACKUP UNIT
    DC D/P 1200V 10A Circuit Breaker
    2P Mains Isolator 32A
    Din Rail Terminals
    Din Rail Earth Terminal
    Wire Harness
    Base mount PV Electrostatic Surge arrester with LEDs
    MC4 Chassis sockets
    Base Plate

    Wall Mount SOLAR GEYSER System R 7,003.00
    SOLAR GEYSER CONVERTOR UNIT
    MAINS BACKUP UNIT
    DC D/P 1200V 10A Circuit Breaker
    2P Mains Isolator 32A
    Din Rail Terminals
    Din Rail Earth Terminal
    Wire Harness
    Chassis mount PV Electrostatic Surge arrester with LEDs
    MC4 Chassis sockets
    IP65 enclosure

    We recommend one of these for best use of the geyser system
    If you wish to have the KWH Meter, geyser temperature and Mains over ride unit and remote display KWHMO-PR323 add R 2,350.00.
    If you wish to have a remote geyser temperature (bar 5 LED) and mains override unit add R 950.00

    If you require Dc2DC converters
    2PV panel in series - 10A 60V or 72V R 1 422.00
    3PV panel in series - 10A 90 or 108V R 1 760.00
    4PV panel in series - 10A 120V or 138V R 1 842.00
    5PV panel in series - 10A 150V or 180V R 1 935.00
    6PV panel in series - 10A 180V or 216V R 2 100.00

    Picture of the base plateClick image for larger version. 

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    I would use this as a stand alone system and not parallel this with the evacuated tubes.
    One has to be careful about what is offered in the evacuated tubes, in my opinion, they over sell the amount of energy that is collected, and causing you to under size the system to get the cheaper price.
    Another point not mentioned is that the amount of energy the tubes absorb diminishes with time, and then is noted by the lack of sufficient hot water temperature at the end of the day, especially in winter which is the time that you use more hot water, and have less sun radiance.
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar and LED lighting solutions - www.microsolve.co.za

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    Now that I have an idea of the cost of the system its something I can consider.
    I assume I need to install an earth electrode for the PV system as this will be seen as an off grid installation?
    What are the maximum length of cable allowed between your system and the geyser element?
    Can we have an image of the KWHMO-PR323 remote unit?

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    With any PV system, you require to earth the frame, so yes shortest path to earth and to an electrode.
    The system electrical earth may not be at the same point as the PV earth electrode, as the frame earth is for lightning protection, and electrical earth is for circuit fault protection.

    There is no maximum length for the wires, follow typical electrical current/wire rules both from the PV panels or the geyser side. We have optimized the installation to be close to the geyser more for simplicity of installation. The DC2DC convertor pushes the PV voltage to 300V DC, so the current changes accordingly, so that the volt drop across the cable becomes negligible.

    Below brochure on KWHM-PR323
    Attached Files Attached Files
    Victor - Knowledge is a blessing or a curse, your current circumstances make you decide!
    Solar and LED lighting solutions - www.microsolve.co.za

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