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This article will cover the main practices when doing electrical design with PVcase fixed tilt system and operating principles behind electrical connections.

In general, there are two actions that can be used to connect strings to electrical devices - Auto generate or Semi-auto generate.

Auto generate algorithm.

Auto generate connects strings to electrical devices based on user defined configuration and PVcase's automatic algorithm. An example below shows the operating principle of automatic generation when 8 strings are being connected to one string inverter. Color coding indicates the final connections.

The software starts connecting strings from the opposite side to the fame alignment and tries to fill up one full device without having to connect frames from different rows ( 1 ). At the end of the row the algorithm sees that there's a lack of strings for a fully connected device ( 2 ) and keeps them unconnected until it encounters a similar situation on another row ( 3 ). This algorithm results in for the most part evenly connected strings and practically connected left-over strings that are close to the alignment side.

In situations when the amount of strings per device does not divide per frames evenly, electrical connections are made with the same logic - trying to fit a fully connected device per row and leaving out strings. In the example below, a frame holds 4 strings but the combiner box connects 10 strings. In this case, for the most part of the area we have 1 combiner box per row and 1 combiner that connects leftover strings from each row.

Semi-auto generate algorithm.

Semi-auto generate lets the user assign strings to devices based on their own assessment by requiring to select particular strings for each electrical device. This gives a lot of flexibility in situations when the layout is too complicated or simply not suitable for auto generation (example below).

Semi-auto generate works well with the AutoCAD layiso command. Try isolating the transformer and string objects and continue with generation.

Automatic generation algorithm notes

The automatic generation algorithm works well for the most part but can introduce these unpractical situations in which a combination of the auto and semi-auto generation must be used:

1. Frames are connected far from each other.

In some cases the auto generation algorithm finds missing strings for another connection quite far apart:

In this case, you can use the semi-auto generation to fix this issue:

2. Using auto-generate in parts. 

When you prefer to leave uneven connections at the opposite side of an area or only connect a part of an area using auto generate you can do this in two parts.

The first step is to use auto generate on evenly connected frames on one side( 1 ). Then the second step is to select the rest of the strings in a separate generation ( 2 ).

Then the final output looks like this ( 3 ).

3. Mixing auto and semi-auto generations.

We would usually recommend using a combination of both these features. Usually the automatic generation algorithm works fine for a larger part of your fixed-tilt area. When some changes need to be made for trickier areas - that's where semi-auto generation comes in.

For instance, in the example situation below there are two areas that connect inverters to one transformer.

This larger highlighted part of both areas can be generated using the auto algorithm. 

A step by step process of that can be seen in the GIF below.

Afterwards, semi-auto generate can be used on the rest of the upper PV area.

For the rest of this first area the auto-generate can be used again.

Important: Notice the stop when connecting two areas with each other. This is because the only way to do so is by using semi-auto generate. 

Having placed devices for both areas there's just one thing left to do - fix the numbering.
Doing the generation in parts results in placing devices which in turn impacts the numbering. Which means situations like this occured:

To fix this we have the Renumber button which allows us to set a starting number for a device and then select devices either one by one to define the order or use a multi select for default numbering.

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