One half hour can set a whole month's charge
SRP's Customer Generation price plan has a per-kilowatt demand charge based upon your usage of energy supplied by SRP. The demand charge is based on 30-minute intervals during on-peak hours when your home uses the most electricity.
Read that carefully, because it behaves unlike an energy charge. You are not billed on total consumption for the month, you are billed on the highest half-hour of on-peak draw. One evening where the air conditioning, the oven and a vehicle charger overlap can set a charge that applies for the whole billing period.
A solar array reduces the energy you buy across the day, which is genuinely valuable. What it does not automatically do is flatten that peak half hour, particularly if the peak happens after production has fallen away.
So ask any installer directly: what does this system do to my demand charge, and how do you know. If the answer is a general statement about reducing bills rather than a specific one about the demand component, the quote has not engaged with how you are actually billed.
The on-peak windows, and why the season matters
On-peak hours are weekdays from 5 to 9 a.m. and 5 to 9 p.m. from November through April, and weekdays from 2 to 8 p.m. from May through October.
The summer window is the one that interacts with solar most awkwardly. From 2 to 8 p.m. between May and October, production is strong at the start and gone by the end, while household cooling demand runs right through and typically peaks late. The last hours of the on-peak window are when a demand charge is most likely to be set and when the array is contributing least.
The winter windows are different again, with a morning peak from 5 to 9 a.m. before meaningful production has begun. A rooftop array does essentially nothing for a peak set at 6 a.m. in January.
Map your own household against those windows before you buy. When does the air conditioning run hardest, when do you cook, when does a vehicle charge, and could any of that move outside the window at no real cost to you. Shifting a vehicle charger to overnight is free and can matter more than a larger array.
Where storage earns its place
A demand charge is the clearest case for battery storage in residential solar, because a battery can discharge into that peak half hour in a way panels cannot. That is a specific, measurable job rather than a vague resilience benefit.
SRP offers demand and export based price plans for customers with on-site generation and battery energy storage systems, so storage is contemplated within the plan structure rather than being an awkward add-on.
Ask for the arithmetic rather than the recommendation. What is my expected demand charge without storage, what is it with, what does the storage cost, and over what period does the difference repay it. An installer who works SRP territory regularly will have done this calculation many times.
Also ask what the battery does during an outage, and be clear that these are two different benefits that happen to come from one piece of equipment. Buying storage for demand savings and being disappointed by its outage behaviour, or the reverse, is a common and avoidable outcome.
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.