PV-Battery system

Hello, 

I'm an engineering student and I'm developing a battery model for my final thesis. 

I have a question related to SAM's model, specifically to the voltage model. When using the voltage-discharge curve (from the manufacturer), how do you calculate the different parameters? I mean A, B, K and Vo (the ones to fit the curve). 

Thank you very much in advance. 

Hi Irene,

Please see the description of the battery voltage model in Section 2.1 of DiOrio (2015) Technoeconomic Modeling of Battery Energy Storage in SAM listed on the Battery Publications page at sam.nrel.gov/battery-storage/battery-publications.html .

Best regards,
Paul.

Hello Paul, 

Thank you very much for answering back. 

I've studied in detail section 2.1 of the battery voltage model, but the issue I'm struggling with is that, in order to calculate B and K, I need the values of q_exp and q_nom (page 4, equations 4 and 5, image attached) and I'm not sure of how to calculate them. I think q_full is the cell capacity (Ah) at 100% SOC, but I'm not sure about the values of the current (I) and both timesteps t_exp and t_nom, in order to be able to calculate q_exp and q_nom





Thank you very much in advance. I really appreciate your help.

Kind regards, 

Irene.

Hi Irene,

Based on the paragraph before Equations 4-5 on p. 4, it looks like the current depends on the C-rate of the discharge curve. Here is a link to the source code for the voltage model:

github.com/NREL/ssc/blob/892b81b46a66a81ed6d357bc802dd82318372c4b/shared/lib_battery_voltage.cpp#L356

Best regards,
Paul.

Hi Paul, 

Thank you very much for the reply. 

I would like to ask you about another question that has arise while modeling a battery in SAM. Regarding the Electrochemical Model, when sizing the battery you have some inputs to fit the discharge curve (Cutoff voltage, Nominal zone cell voltage, Exponential cell voltage, Fully charged cell voltage, Charge removed at exponential point, Charge removed at nominal point). This inputs have some values already defined by default, and I would like to ask you if they are defined based on estimations or taken from some manufacture's datasheet.  

Thank you very much in advance. 

Kind regards, 

Irene. 

Hi Irene,

The default parameters are based on our review of the literature. They are not based on information from a particular manufacturer.

Best regards,
Paul.