Electricity to/from battery variable is DC or AC?

Hi Paul:

I am working in a project of detailed pv + storage(DC connected) in pv smoothing configuration. I would like to ask a question regarding the variable Electricity to/from battery. I assume this variable represents the battery power so I was trying to know if it is either measured in the AC or DC side. Looking at the results from the simulation the variable seems to mix DC and AC values. When battery is charging(-) from system, it is true that:

Inverter DC input power = PV power gross + Electricity to/from battery

I have no DC power losses. However, this no longer applies when the battery is discharging(+). In that scenario, it is true that:

Electricity to/from grid = Electricity to grid from system + Electricity to/from battery

I have no AC power losses. I attach a picture of the simulation results. My question is if the variable is mixed or I am understanding something wrong.

Thanks in advance
Kind regards
Miguel

Hi Miguel,

Your observation is correct: These outputs are inconsistent. Whether they are AC or DC depends on whether the battery is AC- or DC-connected and whether the battery is charging or discharging. We plan to fix this for the Fall 2022 release:

github.com/NREL/ssc/issues/784

In the meantime, here is what those outputs represent in SAM 2021.12.02:

• To/from grid and to grid from system are both AC.
• Inverter DC input and DC power gross are both DC.
• Electricity to/from battery depends both on the configuration and what the battery is doing. In the example you show, it is AC when discharging and DC when charging.

Best regards,
Paul.