Hi Ash,
There are two issues: First is with your inputs, and second I think is a bug in how SAM reports the credit amounts.
I think the Net Billing option is the correct one for your application. For that option, SAM calculates excess generation in each time step (in your case, excess = generation minus load in each 30-minute time step), and then at the end of the month adds up the total excess to determine the $ credit amount. That is different from net metering, where the excess generation is calculated as the total monthly generation minus total monthly load.
For the Net Billing options, you should assign both a buy rate and a sell rate for each time of use (TOU) period. The buy rate is the retail price the system owner pays for electricity to meet the load, and the sell rate is the rate the owner receives for excess generation delivered to the grid. In your file, the sell rate is zero, so the monthly credit is also zero.
As for the bug, it looks like SAM is not reporting the monthly credit amount "Excess generation $ credit earned/applied" for the Net Billing option. However, the monthly bill calculation is correct. You can verify that using the attached SAM file (based on your file) as follows:
1. In the "sell rate = 0" case, show the monthly "Electricity bill with system" and "Excess generation kWh credit earned" output variables. The latter shows the total excess generation for each month.
2. Show the same outputs for the "sell rate = 0.03" case. To simplify things, I set the sell rate for all TOU periods to $0.03/kWh, so all excess generation in a given month is credited to that month's bill at $0.03/kWh.
3. Note that the bill difference between the two cases is equal to 0.03 * excess generation, so the credit is being applied to the monthly bill. For example, in January, for sell rate = 0, the monthly bill is $6957.44, and for sell rate = $0.03/kWh the bill is $6640.10. The difference is $317.34. The excess generation for January is 10,578 kWh, and $0.03/kWh * 10,578 kWh = $317.34.
We will fix this issue for the next version of SAM. See
github.com/NREL/SAM/issues/372 to track our progress.
Best regards,
Paul.