Battery Capacity

Hi SAM Team,

I am modeling a PV+BESS project and have a question regarding how SAM handles battery capacity and losses.My input for the LFP battery nameplate capacity is 200.6 MWh.

 

However, the simulation results show that the system requires approximately 230 MWh to reach 100% SoC.

 

If this difference is due to Round Trip Efficiency (RTE), I would expect the 'excess' energy to be accounted for during the discharge rather than the charge. As it stands, it appears as though the system is behaving as if it has a 230 MWh capacity instead of the 200.6 MWh I defined in the system input.

Could you please advise on:

1. Why the charging energy exceeds the nameplate capacity in the results?
2. Where can I explicitly input or view the RTE/Efficiency settings for the battery system?
3. What is the SAM default value for LFP battery efficiency?

Thank you for your time and help.

Best regards,

Hi Tanatip,

SAM's battery model determines the battery charge and discharge power based on the battery parameters including the voltage curve, thermal properties, and for battery life. The battery's roundtrip efficiency and amount of energy required to charge and discharge the battery depends on the load and operating conditions rather than on a fixed input value.

SAM reports the battery roundtrip efficiency in the results, for example in the Metrics table on the Summary tab of the Results page:

 

Best regards,
Paul.



 

Hi Tanatip,

Following up on my previous reply: A possible explanation of the difference between the energy being delivered to the battery and the nameplate capacity is a discrepancy between the cell nominal voltage (under "Current and Capacity" on the Battery Cell and System page) and the voltage range defined by the voltage properties under "Battery Voltage" on the Battery Cell and System page.

The battery voltage (Vdc) and battery total charge (Ah) are useful output variables for seeing how the battery is operating.

Best regards,
Paul.