Electricity Flows are non-physical and inconsistently named

Hello!

I'm currently trying to model simple PVWatts-Battery systems in SAM and have run into a number of quirks. I tried looking through the forum to see if anyone else had run across these and I couldn't find anything. I apologize if these are obvious, but they seem very non intuitive to me. Attached is an image that summarizes them.

(a) Electricity to Battery from System is clearly positive (ie. charging) when there is not enough electricity available from the system, much less excess electricity from the system. This seems like a non-physical bug? (I also checked if it could be coming from the grid and it isn't)

(b) System power generated (light green line) is not just the system, but also the battery export. For example, after 6PM when no sun is shining the system power generated should be 0, but it starts to follow the battery -> load line at this point. In most cases here "system" refers to "solar system" as far as I can tell and it's not clear to me why this definition should change here. Furthermore, this makes it difficult to get the true solar generation.

(c) In the Detailed PV-Battery the battery dispatch includes optimizing for self-consumption but the PVWatts-Battery battery dispatch options do not include a self consumption option. Would it be possible to add this to the PVWatts-Battery as well?

Thank you!

Hi Olive,

I agree that these outputs are confusing.

For the PVWatts model with storage, AC inverter output power represents the output of the PV array. A stacked area plot of Electricity to battery from system AC, Electricity to grid from system AC, and shows where the PV array power is going:

 

And, yes, in some cases "system" means the PV array and inverter without storage and in some cases it includes storage. System power generated includes storage.

PVWatts is intended to be a simpler model than the Detailed PV model with fewer inputs, so for the PVWatts-Battery configurations, we have limited the battery input to a few basic parameters and options. We do not have plans to add more dispatch options to PVWatts with storage.

Best regards,
Paul.