"Generic System-Battery, PPA Single Owner" used for Standalone storage (50 MWac/ 200 MWh)
The revenue and storage options for both models are set up the similarly. the PPA price is 0.09 $/kWh. The systems only charge from 4-8pm. when the PPA price has a 1.5 TOD (all other times systems are charging and have TOD=1). The PV plus battery system charges the battery 25% "from grid" and the rest "from system".
The electricity rate, when enabled, is set at its default of 0.06 $/kWh. Both systems give the same summary metrics as far as I can see (mainly looked at NPV and checked a couple others), when the electricity rate is enabled and when it is disabled. As discussed, I believe this is an error because the NPV should be higher when the electricity rate is enabled since it is lower than the PPA price.Please let me know if I am missing something here. Thanks again I appreciate the help.
Just making sure the previous attachment was correct. It should be the same as this attachment, but if not please use this one you will see it is the systems described int he previous post. Also I am using SAM version 2020.2.29.
Thank you for sending the files with detailed descriptions.
I think this may be a bug -- it looks like SAM is using the Buy Rate on the Electricity Rates page to calculate an electricity purchase amount for grid power used to charge the battery as an annual operating expense even when you choose No Electricity Rate on the Electricity Rates page. You can verify the issue by looking at the "Electricity purchase ($)" line item on the Cash Flow tab, and also by going to the Data Tables tab, and displaying the annual "Annual energy imported from grid (kWh)" and "Electricity purchase ($)" variables. (Note that both inflation and the electricity bill escalation rate apply to the electricity purchases.)
In the meantime, a workaround for a front-of-meter storage system (PV Battery or Generic System Battery with one of the PPA financial models models) if you want to treat electricity purchases for charging the battery as negative revenue:
On the Electricity Rates page, choose Enable Electricity Rate (from the blue drop-down list at the top of the page) so you can see the rate structure.