title: "Solar + Battery in Arizona: Beating the Peak Demand Charges" summary: "A Phoenix homeowner uses solar panels and a battery to slash $250/month APS bills by shifting energy away from expensive peak hours." storyType: battery state: AZ savingsMonthly: 190 systemSize: "10.4 kW + 13.5 kWh" date: "2026-02-10" tags:
- solar
- battery
- arizona
- demand-charges
- time-of-use
Background
Phoenix, Arizona — summer capital of air conditioning. Our 2,400 sq ft home runs the AC from April through October. On APS's Saver Choice rate plan, electricity during peak hours (3–8 PM) costs roughly $0.24/kWh while off-peak is around $0.06/kWh. Our summer bills regularly hit $350+, sometimes $400.
The math was clear: we needed to avoid buying electricity during peak hours.
System Design
After getting five quotes through EnergySage, we chose a local installer (Harmon Solar) and designed the system around time-of-use optimization:
- Panels: 26 × REC Alpha Pure-R 400W (10.4 kW)
- Inverter: SolarEdge SE10000H with power optimizers
- Battery: Tesla Powerwall 3 (13.5 kWh usable)
- Orientation: Southwest-facing roof (slightly off south, good for afternoon generation)
Why the Battery?
Without a battery, our solar system would export heavily during the day (when electricity is cheap) and we'd still buy expensive peak power from 3–8 PM as production dips. The battery stores midday solar production and discharges from 3–8 PM, covering the peak window.
Costs and Incentives
| Item | Amount | |------|-----:| | System cost (panels + inverter + battery) | $38,200 | | Federal 30% tax credit | -$11,460 | | AZ state tax credit ($1,000 cap) | -$1,000 | | APS battery incentive | -$750 | | Net cost | $24,990 |
We financed with a 10-year home equity loan at 6.5% APR. Monthly payment: ~$280.
Results After 12 Months
Production
Annual solar production: ~17,800 kWh (averaging 5.7 kWh/kW/day — excellent for Arizona's solar resource).
Bill Impact
| Period | Before Solar | After Solar+Battery | |--------|:-:|:-:| | Summer (Jun-Aug) | $280–$400/mo | $30–$65/mo | | Winter (Dec-Feb) | $90–$130/mo | $10–$25/mo | | Annual average | $210/mo | $20/mo |
Monthly savings: approximately $190/month ($2,280/year).
Battery Performance
The Powerwall cycles once daily in summer (full charge by 2 PM, supports the house through 8 PM peak). In winter, it often only partially cycles. After 12 months, no degradation visible in the app.
Lessons Learned
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Battery sizing matters. With a larger home or multiple AC zones, a single Powerwall can be tight during the hottest summer days. We occasionally draw a small amount of peak power when it's 115°F+ outside and the AC runs nonstop. A second battery would eliminate this but didn't pencil out economically.
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Installer knowledge of utility rate plans is crucial. Our installer programmed the Powerwall to optimize for APS's specific TOU schedule. The savings difference between correct and default programming is significant.
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Shade analysis was accurate. EnergySage's satellite-based shade analysis matched actual production within 5%. No surprises.
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The app is addictive. Watching real-time energy flow — solar charging the battery while powering the house while exporting excess — never gets old.
Would We Do It Again?
Absolutely. Our break-even point is approximately 11 years (accounting for financing costs) or about 7 years if we'd paid cash. Given Arizona's rising electricity rates (6-8% annual increases recently), the actual payback will likely be faster. And the Powerwall provides backup power during outages — something our neighborhood experiences a few times per summer during monsoon storms.