On the DC charged/discharged energy

Hello SAM staff.

I have two questions on the way SAM calculates the energy imported/exported at the battery DC bus.

I modelled a battery whose DC nominal capacity is 4,073.472 kWh

1) When I charge such a battery, from SOC=0% to SOC=100%, I get that the total energy imported at the DC bus is -4383.1 kWh (time step is 5minutes)



Energy calculated as follows:



How is it possible to charge the battery 7.6% more than its DC nameplate capacity?

2) When I discharge the same battery the total energy exported at the DC bus is 4278.6kWh :


 
Energy calculated as follows:



How is it possible to discharge the battery 5% more than its DC nameplate capacity?

Attached you find the case of such an example.

Many thanks in advance

Best regards
Francesco
 

Hi Francesco,

Hi Francesco,

This has to do with the nominal battery voltage and the battery voltage curve, which you can see on the Battery Cell and System page, under "Voltage."

The DC nameplate capacity is based on the nominal cell voltage. For the battery in your system, the nominal cell voltage is 3.2 VDC, which is equivalent to battery depth-of-discharge (DOD) of about 94%, indicated by the green dotted line that I added to the voltage discharge graph from your file:

 

This makes the battery slightly undersized.

See this article for some insight into nominal voltage: batteryguy.com/kb/knowledge-base/battery-glossary-nominal-voltage/

Best regards,
Paul.