Battery average hours of autnomy

jlsilva
Topic Author

19 Aug 2023 23:38 #12443 by jlsilva

Battery average hours of autnomy was created by jlsilva

Hello,

In Battery Bank Sizing, when sizing by "Spefy Cells", cells in this context means a battery? Or a unit cell inside the battery?

I am considering cells = battery pack (LiFePO4, 48V and 100Ah)

Take that consideration above, another doubt is about "Battery average hours of Autonomy". I didn't get what exactly it means. For example, if I did size a battery bank to suppy XkWh for 1 (one) autonomous day, it means that, when the grid is off, my battey bank is able to supply the loads during an entire day until reach the min SOC. Then, i don't undertand the value of Battery average hours of Autonomy in Sumary, if I designed my battery bank to supply XkWh for an entire day.

For exemple, my loads require 102 kWh//day. (considering a DOD of 65%). Having a Lithium Iron Phosphate with 4,32 kWh (48V and 100Ah).. should be necessary 102/4.32 ~ 24 batteries to supply the loads for a day. Is that correct? Instead of 12h, the Battery average hours of Autonomy is 3.03h.

I do not understand this result. Could you help me up?

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pgilman

21 Aug 2023 21:16 #12444 by pgilman

Replied by pgilman on topic Battery average hours of autnomy

Hi Juliao,

For SAM's battery model, a battery "bank" is made up of "cells" connected in series and parallel to achieve the desired maximum discharge power and energy storage capacity of the battery bank. SAM uses the inputs for cell nominal voltage in Vdc and cell capacity in Ah to calculate the bank capacity. You can either specify the number of cells in series and strings in parallel yourself (Specify cells option on the Battery Cell and System page), or have SAM calculate those inputs based on a desired bank size (Set desired bank size option). The equations for these calculations are described in the Help topic for the Battery Cell and System page -- press the F1 key or click Help from that page to see the topic.

SAM reports the "Battery average hours of autonomy" metric when you include grid outage inputs in your model and choose the Calculate hours of autonomy for a hypothetical outage option on the Grid Outage page. This metric is an indication of how many hours the battery would be able to meet the critical load given the system design and operating conditions. (See the Grid Outage Help topic for more details.) This is different from the nominal Time at maximum power on the Battery Cell and System page, which expresses the battery bank nominal capacity in h instead of kWh.

Best regards,
Paul.

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jlsilva
Topic Author

22 Aug 2023 05:04 #12446 by jlsilva

Replied by jlsilva on topic Battery average hours of autnomy

Mr. Paul,

Thanks for the answer.

Julião

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jlsilva
Topic Author

22 Aug 2023 16:26 #12448 by jlsilva

Replied by jlsilva on topic Battery average hours of autnomy

Mr. Paul,
Would please provide the equations? How SAM evaluate if the system designed is albe to met the critical loads and/or the hours of autonomy in each step? I didn't get how each one is calculated.

I appreaciate any help you can provide.

Best regards.

Julião

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pgilman

22 Aug 2023 23:45 #12450 by pgilman

Replied by pgilman on topic Battery average hours of autnomy

Hi Julião,

Please see this post for some additional information about this: sam.nrel.gov/forum/forum-general/3903

Best regards,
Paul.

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jlsilva
Topic Author

26 Aug 2023 23:25 #12461 by jlsilva

Replied by jlsilva on topic Battery average hours of autnomy

Paul,

Thanks.

But I really didnt undertand how the values of "Hours of autonomy during grid outage in each timestep" are calculated!!!!

Help with the equation please. I couldn't reproduce the values calculated by SAM.

Could give me a quick example? How to calculate that number of hous by myself?

I apprectiate any help you can provide.

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