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How to deal with prime number of modules for 1 orientation


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Good morning everyone,

I have drafted on Autocad a preliminary layout of a rooftop PV syst.

According to the available surface on each roof pitch, on some orientations it is possible to put a number of PV modules which is not divisible by any number (aka prime number).

As you can see in the table down below, you can actually install 173 PV modules,South West oriented.

Nevertheless, 173 is a prime number, so when it comes to put that value in the "system definition section" on PV syst , I am not able to create a sub array called "South West" with 173 modules, as this cannot be calculated as "nr of modules in series X nr of strings".

May you kindly suggest how to proceed in this case?

Thank you a lot!!



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Reference letter for each building, does this mean that B, H, N, and P are different buildings, and hence, would be separate arrays? 

In any case, this is a pretty broad question without details, so I will give a range of answers. You can change the module wattage to fit your DC capacity better, round to the nearest string quantity that fits your DC target (as closely as possible), or use microinverters/optimizers. You may not be able to hit 79.58kW exactly, and will have to install something less that fits. 

Edited by dtarin
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Hi, I second @dtarin's answer. 

As an additional note: in such a case it may also help to consider how you would effectively string the 173 modules. If some strings turn out to have a different number of modules (e.g. 17 strings of 9 modules and 2 strings of 10 modules), then you can prepare 2 sub-arrays. It will help if you have a multi-MPPT inverter, which you can then balance, or string inverters in mind. You can also modify a central inverter to accept two inputs, so that you can put all your strings on the same inverter.

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