Bi-Directional Inverter for Battery systems

  • Vikram Linga
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13 Aug 2020 21:17 #8574 by Vikram Linga
Replied by Vikram Linga on topic Bi-Directional Inverter for Battery systems
Paul,

I have already set the options as you have said, and I am not seeing an impact on any metric when I switch from "No Electricity Rate" to "Enable Electricity Rate".

Regards,
Vikram

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  • Paul Gilman
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13 Aug 2020 22:28 #8577 by Paul Gilman
Replied by Paul Gilman on topic Bi-Directional Inverter for Battery systems
Hi Vikram,

Can you attach a .sam file that shows this behavior?

Best regards,
Paul.

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  • Vikram Linga
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17 Aug 2020 03:12 #8590 by Vikram Linga
Replied by Vikram Linga on topic Bi-Directional Inverter for Battery systems
Paul,

Attached is a SAM file containing two models:
  1. "Detailed PV-Battery, PPA Single owner" (150 MWac PV, 50 MWac/ 200 MWh storage)
  2. "Generic System-Battery, PPA Single Owner" used for Standalone storage (50 MWac/ 200 MWh)
The revenue and storage options for both models are set up the similarly. the PPA price is 0.09 $/kWh. The systems only charge from 4-8pm. when the PPA price has a 1.5 TOD (all other times systems are charging and have TOD=1). The PV plus battery system charges the battery 25% "from grid" and the rest "from system".

The electricity rate, when enabled, is set at its default of 0.06 $/kWh. Both systems give the same  summary metrics as far as I can see (mainly looked at NPV and checked a couple others), when the electricity rate is enabled and when it is disabled. As discussed, I believe this is an error because the NPV should be higher when the electricity rate is enabled since it is lower than the PPA price.Please let me know if I am missing something here. Thanks again I appreciate the help.

Regards,
Vikram
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  • Vikram Linga
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17 Aug 2020 03:16 #8591 by Vikram Linga
Replied by Vikram Linga on topic Bi-Directional Inverter for Battery systems
Paul,

Just making sure the previous attachment was correct. It should be the same as this attachment, but if not please use this one you will see it is the systems described int he previous post. Also I am using SAM version 2020.2.29.

Thanks,
Vikram

File Attachment:

File Name: LingaStora...8-17.sam
File Size:152 KB
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  • Paul Gilman
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17 Aug 2020 16:24 #8592 by Paul Gilman
Replied by Paul Gilman on topic Bi-Directional Inverter for Battery systems
Hi Vikram,

Thank you for sending the files with detailed descriptions.

I think this may be a bug -- it looks like SAM is using the Buy Rate on the Electricity Rates page to calculate an electricity purchase amount for grid power used to charge the battery as an annual operating expense even when you choose No Electricity Rate on the Electricity Rates page. You can verify the issue by looking at the "Electricity purchase ($)" line item on the Cash Flow tab, and also by going to the Data Tables tab, and displaying the annual "Annual energy imported from grid (kWh)" and "Electricity purchase ($)" variables. (Note that both inflation and the electricity bill escalation rate apply to the electricity purchases.)

In the meantime, a workaround for a front-of-meter storage system (PV Battery or Generic System Battery with one of the PPA financial models models) if you want to treat electricity purchases for charging the battery as negative revenue:
  1. On the Electricity Rates page, choose Enable Electricity Rate (from the blue drop-down list at the top of the page) so you can see the rate structure.
  2. Choose the Buy all / sell all metering option.
  3. Set the Buy Rate to zero.
  4. Choose No Electricity Rate.
We are investigating further and will fix this for the next release. See github.com/NREL/SAM/issues/370 to follow our progress.

Best regards,
Paul.

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  • Vikram Linga
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17 Aug 2020 18:09 #8598 by Vikram Linga
Replied by Vikram Linga on topic Bi-Directional Inverter for Battery systems
Thank you Paul.

Another question I had was with the Merchant PV-Storage option. I am not able to generate revenue using this model using the "single value" revenue mode.

I know there have been previous posts about this, such as:  https://sam.nrel.gov/forum/forum-general/3068-merchant-plant-generating-revenue.html#8442

Has this issue been fixed? And if so should the "single value" option be working?

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