How much solar does your home need?
Enter a year of kWh from your APS or SRP bill and see an estimated system size range. The math runs in your browser. Verix Energy is a solar sales company and does not install. A licensed, ROC-certified Arizona contractor designs and installs the final system.
Size estimate
Enter kWh to see the monthly chart.
Where does the yield range come from?
From NREL PVWatts runs for Phoenix. The estimate divides your annual kWh by a specific yield: how many kilowatt-hours one kilowatt of panels produces in a year. Roofs face different ways, so the page uses a range instead of one number.
The range
1,425 to 1,789 kWh per kW per year. The low end is a west-facing roof at a 33.45 degree tilt. The high end is a south-facing roof at the same tilt. A south-facing roof at a 20 degree tilt comes out at 1,755 kWh per kW per year.
The model inputs
NREL PVWatts version 8.5.0 for Phoenix, Arizona, at 33.45 degrees north and 112.07 degrees west. Fixed roof mount, standard module, and 14 percent system losses, with the NSRDB PSM V3 GOES tmy-2020 weather file.
What it leaves out
Shade, equipment, and the final layout can fall outside this range. Panel counts assume 410 W panels. A licensed ROC contractor sets the final size.
Source
Figures were read from the PVWatts v8 API (version 8.5.0) on October 25, 2026. NREL PVWatts.
How do I read my APS or SRP bill?
Find kilowatt-hours, written as kWh, and ignore the amount due. This estimate does not use charges.
Arizona Public Service (APS)
The current billing period is usually one month, and its kWh is printed with the usage details. APS bills also show a usage history of about the last 13 months, as a table or a bar chart, with kWh beside each month. Add the 12 most recent months. If a month lists energy delivered and energy received, use the kWh the home used.
Salt River Project (SRP)
Find kWh used for the current period. That figure is one month. SRP bills include an energy usage history, often a set of monthly bars covering about a year. Read the kWh for each month and add 12 of them.
Use a full year
Summer and winter use are different in the Phoenix Valley, so one month is not a full year. Choose your bill in step 2, or enter the 12-month total, or each month with the boxes or sliders. Check what the page reads and edit anything that looks wrong.
What else do people ask about sizing solar?
How is this size estimated?
Your annual kilowatt-hours are divided by a Phoenix specific-yield range from NREL PVWatts, 1,425 to 1,789 kWh per kW per year. The page shows an estimated system size in kW and a rough panel count using 410 W panels. It is an estimate, not a design.
Why is the result a range?
Roof direction, tilt, and shade change how many kilowatt-hours each kilowatt of panels produces. The yield range is the spread of NREL PVWatts roof-mount results for Phoenix. A licensed ROC contractor sets the final size.
Does it matter if the bill is APS or SRP?
The estimate uses kilowatt-hours, so the math is the same for both. Choose the utility named on the bill. Enter kWh, not the amount due. APS and SRP bills both list kWh for the billing period and a history of recent months.
What happens to a bill I upload here?
Uploading a bill is optional. This page reads the kWh from the file in your browser. The file and the numbers are not sent to Verix Energy or anyone else, and Verix Energy does not store them. Your browser may keep the values you typed until you close the tab. Check the numbers and edit anything that looks wrong.
Who designs and installs the system?
Verix Energy is a solar sales company in Gilbert, Arizona, and does not install solar. The final design and the installation are done by a licensed, ROC-certified Arizona contractor.
Want a design for your actual roof?
A licensed contractor confirms the final size from your roof, shade, and full usage. Call or text 480-406-3127, or request a quote.