Does flow direction of current matter for efficency?

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    Greg Smith Community Moderator
    Early Adopter

    I understand the application and explained how they work. I am merely trying to manage your expectations of system performance. 

    The optimizers will try to keep the strings at a constant current. If one side has 2A and the other side has 8A then they will do whatever they can to keep the current as high as they can across the entire string. They don't know that half of them are flopped over the other side of the roof. They just know there is less current on one half. So, 8A versus 2A is this scenario. If the sunlight changes, a cloud moves over the array, the temperature changes, a bird poops on the array, soiling starts to build up, etc., then the specific current values in your scenario mentioned will change, and so will the current in that string. While overlapping a string is not optimal, it is not the end of the world. Optimizers paired with modern string inverters do a great job at harvesting as much energy as they can. 

    This behavior answers your question about how they "work," but often, this leads to the next question about actual production values- How many kilowatt hours will my system produce a day, month, year, etc?  Since your array is not optimal, the estimations are even more difficult without software.

    The good news is that Tigo offers a visual representation of the extra harvested energy using our patented software algorithms. This is called Reclaimed Energy. We have seen as much as a 30% gain of recovered energy that would have been lost to module mismatch, but on average, we see about 7%. Not too shabby.

    Even better news is that our sales engineers have these software tools and can help calculate a yearly estimate of production if that is what you want.

     

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    Greg Smith Community Moderator
    Early Adopter

    Hi Elio, you are very perceptive and understand our process better than most, including the 25% number. That is in this Help Center article- Optimization with Predictive IV and Impedance Matching.

    This limitation is true for all MLPE, including competing optimizers and microinverters. We can only do so much to correct for module mismatch and recover as much lost energy as possible. Tigo uses sophisticated patented algorithms to provide value for this recovered energy and display it in our EI App and Portal. It is called reclaimed energy.

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    Greg Smith Community Moderator
    Early Adopter

    Hi Simon, there are a lot of assumptions and a lot of theory crafting in your scenarios that would require some design software to truly analyze. However, I will say that no optimizer in the world can compensate for a poor design. I don't know where you live, but there are only a few places in the world where a north-facing array makes sense. You certainly may install modules on a north-facing roof, but production will be weak.

    Disregarding that design element, another glaring design no-no is stringing modules over a roof to different planes is not recommended. The string will have varying current and voltages. The optimizers will do their job as best they can but the inverter is still responsible for finding the maximum power point of that string.

    This design will produce something for the SunGrow inverter to work with, but it is difficult to say how much.

     

     

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    Simon H

    Hey Greg,

    thanks for the quick reply.

    I am aware that this design should be avoided. But i disagree with the usefulnuess of north-facing modules. Given the interplay of panel price and energy price, and space availability it might make sense to face panels north in in many parts of the world (probably not the US though).

    However, truth be told, all the questions I asked (in regards to how the optimizers would work in those scenarios) are still unanswered.

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    Greg Smith Community Moderator
    Early Adopter

    I agree, the modules are so cheap now and the rules have changed. If a north-facing roof gives something, then that is better than nothing.


    I was purposefully vague in production and system behavior because there is no easy way to predict your scenarios. That is the honest answer. It requires some heavy software analysis. It doesn't matter where the string "starts" since they are all connected in series. Our optimizes will try to keep the current of each module at the same level but they can only do so much.

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    Alan Davidson

    You would do much better to have all North Facing panels in one string and all South Facing panels in a second string.  Then the optimizers can have a chance at giving maximum output for each string. As noted above, mixing panels with different orientations in the same string is not a wise move.  Alan

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    Simon H

    Hey, thanks for the reply.

    Once again: I am aware that the setup is not optimal. But in this case there is no other way. And let's just stick with this please.

     

    However, someone selling it's own product should be able to explain the workings of it's own product right? My questions are definitely not rocket science and i don't see why they would require heavy software analysis.

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    Simon H

    Thank you Greg, this helps.

    Now, considering what you described:

    It makes sense that the optimizers do not know that half of them are on the north side. However, I am wondering how do the optimizers on the north side know that they should increase current from 2A to 8A? Maybe this question is totally retarded, but my electrical knowledge is basic at best.

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    Elio B

    Hello everyone! 
    Simon, I understand your problem very well and in particular the last question you asked, because I also have a similar problem, namely :  How do those optimisers (Tigo TS4-A-O), which manage photovoltaic panels (6 panels) in the shade all connected in series with each other and with an optimiser, adjust the current value (to the detriment of the voltage) to the one that produces the maximum intensity because it is fully exposed to the sun?
    Theoretically, the most penalised Tigo should 'read' the impedance of the system arriving from the inverter and adjust accordingly, but I have the doubt that the Tigo cannot cope when the unbalance is more than 25%, is this possible, Greg?
    In my case, it is a chimney shadow moving over the PV panels during the day, but I have not seen this current adaptation, except when the shadow almost completely disappears from the PV panel involved.
    Thanks

     

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