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  • Inverters DC inputs and PV Panels brands

    Hi there!

    I'm new in the forum. This time I bring a question about inverters.

    I was hired to oversee the Electrical Installation of a public building in East-Timor (South East Asia). As you can imagine, this location is wonderful for a PV installation, with 340 sunny days a year. I have a University degree in Electronics Engineering and I have 14+ years' experience in low voltage Electrical Installations. I have also taken two courses of PV Engineering and I'm on may way of getting an Masters' degree in PV Engineering.

    In the project I'm working for, the PV system has already been designed. It was designed to use three inverters of 50 kWp in parallel, each one with eight strings of 23 PV panels, making it a total of 552 PV panels. The Designer has requested the panels to be of the brand Canadian Solar and the inverters AE Solar Energy. The inverters proposed by the Designer consist on four DC inputs and one MPPT, so to allocate the 8 strings, they are paralleled in the inverter's DC box.

    Now the Contractor has presented me with a complete solution from the brand CHINT, which I appreciate, since the PV panels and the inverter would be of the same brand.

    The problem with the proposed solution is that these CHINT inverters have only three DC inputs, with three MPPTs. These inverters allow for the installation of 9 DC strings, by paralleling three strings on each DC input. Actually, the inverters come with 9 DC terminals for connections of the strings. and I would imagine that inside the inverter's DC box there is some sort of parallel connection of the strings. The Contractor insists they can allocate the 8 strings of PV panels in the 9 DC terminals, by "lust leaving one of them unused". This would be three strings for two of the MPPTs and two strings for the third one.

    As far as I understand, one of the MPPTs would be operating at 2/3 the current at DC side with respect of the others.

    My question is, is this a viable solution? Can I just leave one of the DC terminals unused? Would this imbalance between the three MPPTs make the whole system work at a lower power point than desired? I really don't know what happens inside the inverters beyond each MPPT to figure out what happens if the one of the three MPPTs operates at 2/3 the power.

    Another question is, what kind of a downgrade is to change from Canadian Solar for CHINT for the PV panels? I know Canadian Solar is a Tier 1 brand of PV panels, and I don't know CHINT yet.

    Any help will be much appreciated.

    Have a nice day guys!

  • #2
    Not being familiar with the CHINT brand at all, I can only offer that if you read the manual, you may discover that not all MPPT channels need be used, and it may work as you describe.

    PV panels. These can be very long lived, if made correctly in a robust manner. Canadian Solar is a reliable, well known brand, but getting warranty support in your location is the prime consideration. How is support for Canadian Solar ? What about Chint ? Which company do you think will be around in your area in 5 years ?
    Powerfab top of pole PV mount (2) | 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

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    • #3
      Originally posted by Mike90250 View Post
      Not being familiar with the CHINT brand at all, I can only offer that if you read the manual, you may discover that not all MPPT channels need be used, and it may work as you describe.

      PV panels. These can be very long lived, if made correctly in a robust manner. Canadian Solar is a reliable, well known brand, but getting warranty support in your location is the prime consideration. How is support for Canadian Solar ? What about Chint ? Which company do you think will be around in your area in 5 years ?
      Mike90250 thank you very much for your answer.

      In fact that's true, it seems like not all of the MPPT channels need to be used. What I don't know is what would happen with the overall efficiency if kept unbalanced. The manual does say the following

      Connecting all of the inputs at zone "PVIn1" will result in only utilizing 33% of the inverter power.
      I'd say there should be no problems if the CHINT provider could provide some sort of calculation (which I already requested) to demonstrate that the overall system would yield as much as peak energy as predicted in the design.

      Our contractor also got a quotation from an Indonesian company including Canadian Solar PV panels, so I would imagine that the warranty support would come from Indonesia, which is relatively close to here. CHINT is a company from China, I would imagine that they would be able to provide warranty support and even send some engineers over for that matter given this is no small installation.

      Which company I think will be around in the are in 5 years? That's a tough one. I wouldn't know, but if I were to bet, I'd say CHINT.

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