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Horizontalstring Direction


szucsnorbi
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Hi,

 

I started to planed an open field power-plant. There is some shadowing effect because of the low distance between the rows. I wanted to compare two possible solution with direction of stings layout (3 separate horizontal sting and 3 string in vertical direction).

I attached the vertical project’s file. I deployed a wall (it is the cause of shadow) and 3x23 mounted pv panels. I thought horizontal direction should have produced more energy then vertical because the shadow effect only one-third (1 string) of total area, not 3 string.

But the result was unbelievable because vertical project yearly yield was a little bit higher.

 

I don’t understand this situation, are you sure that the software working well?

 

thanks in advanced to help,

Norbert

vertical.pvprj.zip

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Dear Norbert,

 

thanks a lot for your question and for attaching the project file. Your question brings up several topics which I will try to answer.

 

First of all it is important to connect the shaded and the unshaded strings to different MPP trackers. You chose the SMA Tripower 15000 TL which provides three MPP trackers. To get the highest yield out of your PV system, it is recommended to connect the modules horizontally (one of your test cases) and connect the shaded string to one MPP tracker and the unshaded strings to the others.

 

Then, if you want to really investigate the influence of nearby objects on the shading and the energy output for different connection patterns, you should move the wall closer to the PV array. Your location is in Hungary and the wall is some 2 meters away from the PV array. So from March to October, there is no shadow at all on the modules and then it is hard to see a difference in the yearly energy yield of the system.

 

But if you would compare e.g. the hourly output of the system on Jan 01, 10h00, you would in fact see a difference, even if you connect all three strings to one MPP tracker. You can compare the hourly results of the csv file that you can export after the simulation.

 

I investigated your project in our simulation core which allows me to record the I-V characteristics of the strings and the whole system at any given time. The situation I investigated was Jan 01, 10h00, here is a screenshot of the shadow that’s on the modules:

 

post-2-0-89642900-1418662504.jpg

 

So, the bottom row has a shadow, middle and top row not. Note also that the first module in the bottom row does not have a shadow.

 

When the strings are connected vertically (how it should not be done in real life), the electrical output is as follows:

 

post-2-0-65761400-1418662526.jpg

 

One can see that all strings behave approximately the same, since in all strings there is one third of the modules that have a shadow. The shadow causes the modules to go down on the I-V curve of the diffuse radiation, you can see that drop for each string in the voltage area from 550 – 830 V. So, in sum, the I-V curve of the whole field also has this current drop above 550 V, which leads to a power curve with a maximum of 1400 W @ 550 V.

 

When the strings are connected horizontally, that is parallel to the shadow, the curves look like this:

 

post-2-0-15314300-1418662543.jpg

 

You see two strings (2 and 3) without any shadow, whereas string 1 has to go down on the I-V curve of diffuse irradiance for nearly the whole voltage range (here you can see that there is one module without shadow in the bottom row J ) In this case, the field curve has only a little current drop at 150 V and the maximum power is at 1700 W @ 750 V.

 

This effect can lead to varying simulation results as well, but as I mentioned above, if there is only shadow in the winter (and only in the morning and evening), you won’t notice any significant difference in the yearly energy yield.

 

We hope that helps to answer your question, kind regards,

Martin

shadow.jpg

vertically.jpg

horizontally.jpg

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Dear Martin,

 

Thanks for your quick reply.

I would like to test a lot of configuration to know which version generate the most energy. For me the yearly yeald is the most important and the first question is two MPP tracker how much more energy can generate than only one tracker?

What is your advice? I should make simulation only in wintertime (when there is shadow effect ) to see the difference?

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Dear Norbert,

 

I prepared two projects for you, where the wall is placed closer to the PV array, and the connection of the strings is done as described above. Here you can see a difference in the yearly energy yield of about 50 kWh/kwp (connected horizontally you'll have 17.861 kWh/year, connected vertically it is 16.933 kWh/year.

 

You can play around with the connection patterns in those projects to see their influence on the yearly energy yield.

 

Hope this helps,

Martin

Two MPP horizontally.pvprj

Two MPP vertically.pvprj

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