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urgent: Down-regulation on the account of the MPP Voltage Range


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Dear developer team,

 

I hope my message finds you very well, I have an question which is so urgent please. This simulation I have been doing is critical to the point that many decisions will be taken on for this already running PV system. I'm acting as a consultant for this system hence results and its explanation is important. My question is why for this project (project file and PDF simulation report are attached) the losses due to down regulation on the account of mpp voltage is so high? it represents almost 9% of the annual losses? I can see that the operating voltage is operating normally and within the range of the MPP voltage of the inverter, however there are lots of self-shading as you can see in the 3D design and the energy balance. Could this be the reason? and what's the physical explanation to these down regulation losses? does it mean for example that there are many times during the year that the operating voltage will fall behind or beyond the MPP tracking range? I don't get it. Will a minutely simulation will be useful in this case? could the inverter be the reason?

 

Please advise as the situation is critical and thank you for your usual great support!

Sharm Bride Hotel - Actual - 9 Sept R02.pvprj

Sharm Bride Hotel design & simulation - as built - 13 Sept R02.pdf

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Hello Ragy,

I checked your system's configuration and I see there are 17 modules in a string and the modules have NOCT voltage of 39,8V which under NOCT gives 676,6V string voltage.

The inverter's MPP voltage range is 570-850V. So as you expected it is possible that the string voltage is only slightly above DC start voltage of inverter (620V)

To my knowledge, this impacts the efficiency and hence is high power loss due to MPP voltage range.

This is only my opinion and the PV Sol team can give a better explaination

Regards

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Hi Ragy,

the reason for the downregulation losses due to the MPP voltage range is that in winter time the modules are causing a shade on each other:

image.png

You can see the module-specfic shading losses in the carpet plots very well:

image.png

The modules are connected 11 in parallel by 17 in series, so the resulting module array characteristics look like this:

image.png

As you can see there is a pronounced drop of current in the upper voltage range above 400V. In the power-voltage plot it looks like this:

image.png

So the maximum power point at this specific point in time (01.01. at 11 to 12 am, with these specific shading and irradiance values) would be around 410 - 430 V. But the lower end of the MPP voltage range is at 570 V. Of the available 35 to 40 kW, the inverter can only take 10 to 20 kW. The difference between these points (maximum available power and best point that the inverter can reach) is the loss due to MPP voltage range.

Hope that helps,

Martin

 

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2 hours ago, developer_mh said:

Hi Ragy,

the reason for the downregulation losses due to the MPP voltage range is that in winter time the modules are causing a shade on each other:

image.png

You can see the module-specfic shading losses in the carpet plots very well:

image.png

The modules are connected 11 in parallel by 17 in series, so the resulting module array characteristics look like this:

image.png

As you can see there is a pronounced drop of current in the upper voltage range above 400V. In the power-voltage plot it looks like this:

image.png

So the maximum power point at this specific point in time (01.01. at 11 to 12 am, with these specific shading and irradiance values) would be around 410 - 430 V. But the lower end of the MPP voltage range is at 570 V. Of the available 35 to 40 kW, the inverter can only take 10 to 20 kW. The difference between these points (maximum available power and best point that the inverter can reach) is the loss due to MPP voltage range.

Hope that helps,

Martin

 

Dear Martin,

I can't thank you enough for the prompt and professional reply and support. It's really helpful. besides the shading problem, which is the main one, because of your reply I noticed also that the inverter's MPPT range is relatively narrow, which is something I may need to take care of in our next projects. One more thing: It's impressive how the PVSOL evaluates the system losses, particularly considering the MPP down-regulation which I haven't seen in similar design and simulation software so far! that made me love PVSOL even more. Finally, I would be glad to hear your opinion about solving this problem should you don't mind.

Thanks again and all the best

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3 hours ago, Vishnu said:

Hello Ragy,

I checked your system's configuration and I see there are 17 modules in a string and the modules have NOCT voltage of 39,8V which under NOCT gives 676,6V string voltage.

The inverter's MPP voltage range is 570-850V. So as you expected it is possible that the string voltage is only slightly above DC start voltage of inverter (620V)

To my knowledge, this impacts the efficiency and hence is high power loss due to MPP voltage range.

This is only my opinion and the PV Sol team can give a better explaination

Regards

Hello Vishnu,

Thank you also for your reply and time. I think your reply was similar to what the developers replied; it's related to the much self-shading on the modules which in turn made the string voltage during sometimes of the year drop below the min. MPP voltage range.

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