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System Advisor Model (SAM)

Lower output on one simulation yet lower losses in loss diagram for it

Kellock LSbp
Topic Author

22 Oct 2021 14:20 #10167 by Kellock LSbp

Lower output on one simulation yet lower losses in loss diagram for it was created by Kellock LSbp

I am running a comparison on a site. Two simulations both with 1 minute data. For one of them I have the NOCT thermal loss model for the other I have the CEC heat transfer model. For the CEC model one the module temperatures are lower. The resulting 'Module deviation from STC' is -6.68% for the CEC model simulation and -15.06% the NOCT. However the Net DC energy is higher for the simulation with higher losses. In addition the CDC model simulations has lower PR and production even though it has less % losses in the diagram.
I would attach the meteo file but it is too large.

PSU1min.sam

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pgilman

23 Oct 2021 00:23 #10172 by pgilman

Replied by pgilman on topic Lower output on one simulation yet lower losses in loss diagram for it

Hi Leo,

This system has a relatively high DC/AC ratio so it is possible that the system with less efficient modules (due to the choice in thermal model) experiences less inverter voltage clipping. You should be able to see those losses in the loss diagram as "Inverter MPPT clipping."

Best regards,
Paul.

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Kellock LSbp
Topic Author

25 Oct 2021 11:20 - 26 Oct 2021 17:11 #10176 by Kellock LSbp

Replied by Kellock LSbp on topic Lower output on one simulation yet lower losses in loss diagram for it

Hi Paul

If you can see the two loss diagrams below the MPPT clipping is higher, but only 0.008%. The first power loss flow diagram is for the model running the NOCT thermal model
[img]

Last edit: 26 Oct 2021 17:11 by pgilman.

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Kellock LSbp
Topic Author

25 Oct 2021 11:43 - 26 Oct 2021 17:12 #10177 by Kellock LSbp

Replied by Kellock LSbp on topic Lower output on one simulation yet lower losses in loss diagram for it

I have tried to reply and it doesn't look like it worked so I have replied here again. Hopefully it doesn't double it up.

The energy flow diagrams show a minimal difference in MPPT clipping. You can see below the difference. The NOCT simulation is first. The Nominal DC energy is the same as the Heat transfer one, but the & losses are greater afterwards. However the Net DC is higher (leading to higher Inverter power clipping but that just shows the simulation is having that higher Net DC when it shouldnt).
[img]

Last edit: 26 Oct 2021 17:12 by pgilman.

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pgilman

26 Oct 2021 17:33 - 26 Oct 2021 17:33 #10192 by pgilman

Replied by pgilman on topic Lower output on one simulation yet lower losses in loss diagram for it

Hi Leo,

The best way to include images in your posts is to attach them as image files (.png, .jpg, etc.) and then insert them into your message. Copying and pasting images into the text body usually does not work well.

In my tests on the PSU-2015 hour case in your file, I'm seeing the following results:

Cell Temp Model	Deviation from STC (%)	Annual Energy (kWh)
NOCT Model	-18.387	4,747,149
Heat Transfer Model	-18.934	4,734,120

In this case, the differences between the two thermal models are very small.

You might look at the time series results for variables like ambient temperature from the weather file, cell temperature, and DC power to see if they offer an explanation of the results you are seeing.

Best regards,
Paul.

Last edit: 26 Oct 2021 17:33 by pgilman.

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Kellock LSbp
Topic Author

23 Nov 2021 15:26 #10306 by Kellock LSbp

Replied by Kellock LSbp on topic Lower output on one simulation yet lower losses in loss diagram for it

Hi Paul

Thank you for the help you have given. I can't seem to recreate the problem I had before, so it was probably something I was doing wrong. Out of interest what weather file are you using for your two simulations above? Would I require atmospheric pressure data and wet-bulb temperature data in order to make the Heat transfer model work. Or have you used the same weather file but made the Heat transfer model to work.

I attach two screenshots of what I am doing. I am using the heat transfer model but you can see that the temperature experienced by the modules is the same as that of the ambient temperature. What am I doing wrong?

Kind regards, Leo Kellock