2014.11.24 Net Metering Definition

Was there an update to how net metering is modeled in this release. It seems SAM is still defining net metering different than the net metering available to us in Nebraska. When we sign up for net metering, it means excess produced in a month is credited at that month's retail rates for that month only (netting), and sale of un-utilized excess is done at a lower rate at the end of each billing period (month). We cannot bank at retail for future months, we can only bank/net for the month we are in.

The help indicates that if net metering is checked, excess kWh credits carry over to the next month. Credits are settled at the end of the year. Monthly carryover of credit at retail makes this option not valid for us, so I assume this should not be checked.

The help indicates that if net metering is not checked, excess generation is sold at a sell rate for that hour. This would somewhat work if sell rate was set to buy rate (retail), but would not account for month-end settling of net excess at below retail rate. Further, unchecking "net metering" on the rate page blacks out the hourly sell rate in the energy rate section.

Is there some other way to model how net metering is done in all of the state of Nebraska that I am missing?

Thanks.

Dear Jay,

Thanks for posting the first question about the new version of SAM!

Your observations are correct. There are a lot of net metering variations in the U.S., and SAM only models one general approach that we hope works for most scenarios.

Your description is very helpful, and we'd like to hear from anyone else trying to model different kinds net metering.

Best regards,
Paul.

I would think that no net metering would mean no compensation for excess generation anywhere in the US - this is really the larger benefit of net metering over monthly credit carryover. Yet the model is indicated to compensate at "sell rate for that hour" under "without net metering"? And "sell rate for that hour" doesn't really have meaning in a tiered rate structure...all while the "flat sell rate" cell is active?

Hopefully future versions of the model can accommodate more than one approach to net metering like it does with other aspects of rate schedule.

Hi Jay,
I just re-read your first message, and see that you say "...unchecking 'net metering' on the rate page blacks out the hourly sell rate in the energy rate section." Could you double-check that? When Enable net metering is checked, the all of the sell rate inputs are disabled. But when the checkbox is not checked, the sell rate inputs should be enabled. Note that all of the Energy Charge inputs (buy rates and sell rates) are disabled when Enable time-of-use and/or tiered energy rates is not checked.
I think the only limitation in SAM that prevents it from not modeling the Nebraska net metering law is that SAM does not provide an input for a rate to apply to the monthly net excess generation, which the law stipulates be "compensated at the local distribution utility's avoided cost of electric supply over the billing period."
With net metering disabled, SAM does not compensate for net monthly excess generation. Instead, for time steps when the load is greater than the system's output, it applies the buy rate to purchase electricity, and for time steps when the load is less than the system's output it applies the sell rate to excess electricity in that time step.
Best regards,

Paul.

Paul, in California net metering accumulates excess production $ value credits to the end of the year (True Up Period). If the customer consumes more electricity $ value than produced in the early months of the year, the charges can be completely offset by producing more electricity $ value in later months.
To use the SAM model for a PG&E customer I use the Cash Flow Send to Excel with Equations and edit the Value of electricity savings.
Thanks for your explanation. I was wondering how the SAM developers came up with its net metering definition.

Hi Tom,

Thank you for that explanation. Given the different definitions of net metering rules in different states, it's tricky to create a model that works for all of them without being too complicated to use.

That's especially true for rate structures like the PG&E E-1 rate that has net metering with time-of-use and tiered rates, where the distinction between monthly rollover of dollars or kilowatt-hours is important. In California, the monthly rollover of credits is in dollars, but the annual true-up is based on a comparison of kilowatt-hours produced and consumed.

We're discussing this now, and hope to modify the implementation to make a little more flexible so it can model some of the subtleties of California net metering. Stay tuned for these changes in the next version of SAM, scheduled for release around the end of this month (June 2015).

Best regards,
Paul.