Possible Bug In Modeling with No Net Metering

Paul,

I believe I may be missing something basic here. When I turn off net metering in SAM and zero out all the sell rates I have a zero savings/avoided cost for the PV regardless of what the buy rate is for all years. It appears that I can only fix that by having a sell rate. It looks like the savings due to PV is ignored completely in the buy rate fields. If I set the buy rate to 0 and just tweak the sell rate it is what changes the savings due to PV.

Best,

Nathan

Hi Nathan,

In SAM 2015.6.30 r2, when you run the the residential or commercial financial model with no net metering, SAM models the system as if there were two utility meters: One to measure the total electricity sold to the grid in each month, and one to measure the total electricity purchased from the grid in each month.

When the sell rate is zero for all time periods in a month, the meter that measures electricity sales records zero for that month, so that the value of the electricity generated by the renewable energy system for the month is zero.

This is different than SAM 2014.11.24 and earlier versions. In those versions, SAM models the no net metering scenario as if there were a single meter that can run backward: For hours that the system generation is greater than the load, the sell rate applies to the excess generation, and for hours that the system generation is less than the load, the buy rate applies to the net electricity from the grid.

For the next version of SAM, we are adding options for how SAM models net metering or no net metering: Net metering with kWh rollover, net metering with $ rollover, no net metering with hourly reconciliation, and no net metering with monthly reconciliation. We hope that will make it possible to model most utility rate structure scenarios.

Best regards,
Paul.

Paul,

Thanks for your quick reply. If I understand you correctly only the portion of that is exported to the grid is valued in the cashflow of the analysis. So without a sell rate all the energy offset by the PV system less than load is valued at nothing. So this would follow what the help menu says about how a feed-in-tariff should work. For our purposes where we value all energy offset by a PV system less than and up to load at the buy rate and all excess energy at the sell rate - is there a way to model this for now until the next version?

Best,

Nathan

Dear Nathan,

No, there is not a way to model that method of valuing the PV energy in the current version of SAM. In versions before SAM 2014.11.24, utility rates with no net metering do use that approach, so you could consider using an older version of SAM for now.

Best regards,
Paul.