Gilbert · Phoenix
Gilbert — The Two-Story
The 8.4 kW system behind the numbers on our home page — sized to cover 108% of a growing family's use, with a payback in the sixth year.
The home
A two-story production home in one of Gilbert's newer neighborhoods — four bedrooms, a pool going in, two EVs on the horizon, and a summer APS bill that had crept past three hundred dollars a month. The roof was a clean, unshaded south-and-west composition surface, close to ideal. The only real question was how big to go, and the honest answer was: not as big as the roof would allow.
What we built
An 8.4 kW array — 21 panels — sized against the family's last twelve months of usage plus a realistic bump for the pool pump. That lands the system at about 108% of annual use: enough to zero out the bill in most months and bank a small credit, without spilling a lot of cheap exported power under Arizona's net billing. A string inverter with per-panel optimizers keeps the west-facing panels productive into the expensive late-afternoon hours. We left room on the roof and in the plan to add a battery when the EVs arrive.
This is the system modeled on our home page: about 14,800 kWh a year, roughly $2,190 off the annual bill, and a payback in the sixth year after the federal tax credit. A year in, the family's numbers are tracking the estimate.
Specifications
| System size | 8.4 kW |
|---|---|
| Panels | 21 × 400 W monocrystalline |
| Inverter | String inverter with per-panel optimizers |
| Est. production | ≈ 14,800 kWh / year — ~108% of use |
| Bill offset | ≈ $2,190 / year |
| Payback | 6.4 years (after 30% federal tax credit) |
| Timeline | 6 weeks |
| Cost band | $24,000–$28,000 (before tax credit) |
Our first full APS bill after activation was eight dollars. Firstlight modeled it almost to the dollar a year earlier.
— The Reyes family, Gilbert
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