What happens on each side of 10 kW AC
For systems of 10 kW AC or less, excess generation accumulates as kilowatt hour credits applied to future bills, and those credits do not expire while the account remains open.
That is unusually good. Many states forfeit or donate unused credit at an annual true-up date; here, under this threshold, there is no such reset to design around.
For systems larger than 10 kW AC, the treatment changes. Rather than banking kilowatt hour credits, the customer is paid monthly for excess generation at the utility approved purchase rate, which sits below the retail rate.
So the change at the threshold is not gradual. It moves your exports from retail-equivalent banked credit onto a lower monetary purchase rate, for everything you export rather than only for the increment above 10 kW.
Why a design just above the line deserves scrutiny
A system at 10.5 kW AC does not earn a little less per exported kilowatt hour than one at 9.5 kW AC. It is on a different arrangement, and the additional capacity has to justify moving the whole system onto it.
That is a high bar, and it means the sensible default in PNM territory is to design at or below 10 kW AC unless there is a specific reason not to.
Ask what AC rating the proposed system carries, not just the DC nameplate. Those are different numbers and the threshold is expressed in AC.
If a design sits just above the line, ask what it would look like at or below it and what the two projections say. That comparison should be on the page rather than something you have to request.
Sizing within the threshold
Because credits under the threshold do not expire while the account is open, New Mexico does not punish a modest annual surplus the way states with an annual forfeit do. That is a genuine advantage.
It does not make oversizing free, though. Capacity you never use is capital spent on electricity that sits as credit indefinitely rather than reducing a bill, and the state credit is capped at $6,000 regardless of system size.
So build from your last twelve months of bills, ask what percentage of your annual usage the design covers, and ask what justifies capacity beyond it.
A planned increase in load is a good reason: an electric vehicle, a heat pump, an addition. Rio Rancho households adding cooling capacity or an EV have a legitimate case for sizing ahead, provided the design stays under the AC threshold.
What a projection here needs to contain
The 30 percent federal Residential Clean Energy Credit under Section 25D expired for property placed in service after December 31, 2025, so a cash or loan purchase receives no federal tax credit.
The state Solar Market Development Tax Credit remains at 10 percent up to $6,000, subject to a $30 million annual cap and a one-year application window. Senate Bill 55, which would have raised it to 30 percent, did not pass.
Add the gross receipts tax deduction, the property tax exemption, and net metering at the retail rate under the arrangement that matches your system size.
Ask for the AC rating stated explicitly and, if the design is near 10 kW AC, for both sides of the threshold modelled. That single number is worth more attention than most of the equipment discussion.