Net metering question

Paul,

Good morning. We're looking at a couple of projects in a market where you can only use 49% of the monthly net metering credits (kWh's) in the subsequent months up to a full calendar year. Can you tell me or give me guidance on how to model this restriction in SAM?

Thanks in advance, Brian S.

Hi Brian,

I can't think of a way to model that scenario in SAM. Would you mind telling me in what market that rule applies, and if possible, sending me a link to a description?

Best regards,
Paul.

Hi Paul, the market is Central America and the link would be to a Spanish website. Do you still want it?

Also, it sounds like they're going to have a two prices for electricity if you interconnect a solar PV system. One price for what you consume and another discounted price for the avoided cost of the solar or what you produce. Is there a way to model the latter in SAM? I'm assuming I would handle that through the Flat Energy Rates, i.e., Flat buy rate and Flat sell rate. Correct?

And for simplicity purposes, I guess the easiest way to model the 49% issue is to never model a system that net meters. That I would size a size cancel 100% of the lowest monthly consumption amount and go from there? Your thoughts?

Thanks, Brian S.

Hi Brian,

Yes, please do let me know where to find a description of the net metering rule, even if it is in Spanish.

When you model a rate structure with net metering, you cannot specify a different buy and sell rate because, by definition, net metering means that the system offsets purchases (i.e., the meter "runs backwards"), so there is no need for separate rates.

In SAM 2015.6.30 r4 (the current version), if you model the rate structure without net metering, you can specify both a buy and sell rate. SAM calculates the total monthly consumption and total monthly net generation (power delivered to the grid) in kWh, and applies the buy and sell rates ($/kWh) to those totals. Without net metering, SAM assumes that all of the power generated by the system is compensated at the sell rate, and all of the power consumed by the building or facility is purchased at the buy rate.

The "Monthly Data" variables on the Data tab of the Results page will show you how SAM calculates the monthly utility bill. You can examine those variables to see what the model is doing.

It is impossible for us to design SAM to exactly replicate all of the retail electricity rate structures, net metering rules and feed in tariffs that exist or are under consideration in the United States, let alone around the world, but we are doing our best to make it flexible enough to model the key features of as many possibilities as we can. Stay tuned for the next version of SAM for more improvements...

Best regards,
Paul.

Hi Paul, your explanation makes sense. Thanks for clarifying the net-metering question for me. I understand completely, and just so you know, I'm a big fan of SAM and NREL, so I'm not disappointed at all with SAM's capabilities. Anyway, I'll post the net-metering (or non net-metering) rule shortly...Brian