Battery system charging instantly (bug?)

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sarvtex
Topic Author

16 Mar 2023 17:26 - 16 Mar 2023 22:53 #11999 by sarvtex

Battery system charging instantly (bug?) was created by sarvtex

While simulating a PV + Battery system where the battery is only allowed to charge from the system (meet load priority), it appears that the battery sometimes charges instantly. Looking at the time series, it doesn't seem like this increase in SoC is not accounted for in the "Electricity to/from battery AC (kW)", the energy just seems to appear.

I'm a fairly novice user so I don't know what could be causing this. Is this a known issue?
I'm using the 2022.11.21 release.

Thanks in advance.

Last edit: 16 Mar 2023 22:53 by pgilman.

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pgilman

16 Mar 2023 22:56 #12000 by pgilman

Replied by pgilman on topic Battery system charging instantly (bug?)

Hello,

Please attach a .sam file that demonstrates this behavior if you would like me to help troubleshoot.

Also, when including images in posts on this forum, please attach each image as a file and then insert it into the message. Copying and pasting images directly into the message does not work.

Best regards,
Paul.

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sarvtex
Topic Author

17 Mar 2023 16:37 #12002 by sarvtex

Replied by sarvtex on topic Battery system charging instantly (bug?)

I've attached the .sam file.
There are two case files, one with real PV simulation and another with power plant with manually set power output, in both cases the battery charging problem happens fairly early in the year, around the 8th or 9th of January.

Thanks in advance,
Lucas.

pvBattery_cad.sam

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pgilman

17 Mar 2023 17:45 #12003 by pgilman

Replied by pgilman on topic Battery system charging instantly (bug?)

Hi Lucas,

The Maximum C-rate of charge and discharge on the Battery Cell and System page is set to 1, which allows the battery to fully charge or discharge over a single hour. To limit the charge or discharge rate, reduce the maximum C-rate.

For the PV - Battery case, the negative values of "Electricity to/from battery AC" in your plot show power going to the battery as it is charged. You can add "Electricity to battery from system AC" to see that the power is coming from the PV system.

When you display the time series graph in "stepped lines" mode, the vertical lines make it appear that power is changing instantaneously.

Best regards,
Paul.

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sarvtex
Topic Author

17 Mar 2023 18:49 #12004 by sarvtex

Replied by sarvtex on topic Battery system charging instantly (bug?)

It doesn't seem like the electricity is coming from the system or grid. I've attached a short csv file I obtained from the time series, it includes SoC, Electricity to/from battery, System to Battery and Grid to Battery. At t=202.5, SoC increases from ~47 to 95%, this doesn't match the to/from kW numbers.

graphdata.csv

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pgilman

20 Mar 2023 23:36 #12011 by pgilman

Replied by pgilman on topic Battery system charging instantly (bug?)

Hi Lucas,

Thank you for following up.

The problem is caused by the voltage table having two rows with the same cell voltage, which causes SAM to calculate an incorrect current value. A workaround is to make the voltage at 40% depth-of-discharge something slightly greater than 48, such as 48.01.

We will fix this issue in the next update to SAM 2022.11.21: github.com/NREL/ssc/issues/1007

Best regards,
Paul.

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