Your interconnection date locks a rate for ten years
Your export credit is based on TEP's Rider-14 Export Rate, a Resource Comparison Proxy export rate, and it is locked in for ten years from the interconnection date.
Rules approved by the Arizona Corporation Commission call for annual updates to the export rate to reflect market prices for solar power. The Resource Comparison Proxy is not allowed to fall more than 10 percent annually, which puts a floor under how fast it can decline but still means the direction has generally been downward.
Put those together and the timing of a project carries real weight. A system interconnecting before an annual reduction locks the higher figure for ten years, and one landing just after locks the lower one. That is not a reason to rush a decision you are not ready to make, but it is a reason to ask about dates rather than leave them to chance.
So ask TEP directly what the current Rider-14 export rate is, when the next annual update takes effect, and what rate a system interconnecting on your expected date would lock. Get it in writing, and hold every quote against it.
What happens when the ten years are up
After the ten-year lock, your credit is based on the rate current at that time, which may change annually. This is the part of the arithmetic that quotes tend to skip, because it sits beyond the horizon most sales conversations cover.
It matters because a solar system lasts considerably longer than ten years. A twenty-five year savings projection is therefore making an assumption about years eleven onward that nobody can guarantee, and you are entitled to know what that assumption is.
Ask any installer what export rate their projection assumes after year ten, and what the payback looks like if that rate is materially lower. An installer who has thought about the Arizona market will have an answer ready. One who treats the question as unusual has told you something.
The steadier part of the return is the electricity you consume as it is generated, because that avoids a retail purchase rather than depending on any export rate. Ask to see what the system is worth on self-consumption alone, before export credit is added. That is your floor.
Sizing when exports are worth less than retail
Traditional one-to-one net metering has been replaced in Arizona by net billing export rate riders, so exported solar is credited below the retail rate. Electricity consumed on site as it is generated is worth more than electricity exported.
That points toward a system matched to what your household actually uses during daylight rather than one built to cover annual consumption. Ask your installer to model the self-consumed share explicitly and to value the remainder at the actual Rider-14 rate you would lock.
Tucson's sun is exceptional, which makes production estimates generous, but a generous production estimate is only worth what the production is credited at. Do not let a large annual kilowatt hour figure substitute for the arithmetic of what those kilowatt hours are actually worth to you.
Batteries deserve a serious look for the same reason. Storing afternoon production for evening use converts a below-retail export into an avoided retail purchase. Ask for the numbers with and without storage rather than a general recommendation either way.
The state credit you claim yourself, and the federal one that ended
Arizona still has a state income tax credit of its own, claimed on Arizona Form 310, Credit for Solar Energy Devices. It is calculated by multiplying the cost of a solar energy device by 25 percent, capped at $1,000, and the form provides for tracking credit carryover across multiple years.
Ask a tax advisor how the cap and the carryover apply to your situation before you rely on a figure in a quote. A credit is only worth what you can actually use against tax owed, and an installer is not the right party to advise you on that.
Arizona also exempts solar equipment from state sales tax and excludes it from property tax, so the improvement does not raise your property tax bill the way a renovation of similar cost would. Neither arrives as a cheque, which is exactly why they get left out of people's own arithmetic.
The federal position has changed and much published material has not caught up. The 30 percent Residential Clean Energy Credit under Section 25D expired for property placed in service after December 31, 2025, so a cash or loan purchase now does not receive it. Section 48E survives at 30 percent for third-party owners under leases and power purchase agreements, so such a provider may claim it and reflect part of the value in the rate offered. Ask what they claim and what actually reaches you, and confirm with a tax advisor.