Divide your average monthly electricity usage (in kWh) by average peak sun hours in your location, then multiply by 1.25 for efficiency losses. Most US homes use 700–1,200 kWh/month and need a 6–10 kW system. Never size by square footage — size by actual kWh consumption.
Monthly kWh usage ÷ (peak sun hours × 30 days) × 1.25 = system size in kW
Example: A home using 900 kWh/month in Philadelphia (4.5 peak sun hours): 900 ÷ (4.5 × 30) × 1.25 = 8.3 kW system.
| Monthly Usage | Recommended System | Typical Home Profile | Estimated Cost (2026) |
|---|---|---|---|
| 400–600 kWh | 3–4 kW | Small home or condo; mild climate | $7,500–$15,200 |
| 600–800 kWh | 4–6 kW | 1,000–1,500 sq ft; average usage | $12,500–$22,800 |
| 800–1,000 kWh | 6–7 kW | 1,500–2,000 sq ft; average usage | $19,000–$26,600 |
| 1,000–1,200 kWh | 7–8 kW | 2,000–2,500 sq ft; moderate AC use | $21,000–$30,400 |
| 1,200–1,500 kWh | 8–10 kW | 2,500–3,000 sq ft; heavy AC or EV charging | $25,000–$38,000 |
| 1,500+ kWh | 10–14 kW | Large home, pool, or EV fleet | $32,000–$53,200 |
| Region | Peak Sun Hours/Day | Key States | Sizing Impact |
|---|---|---|---|
| Southwest | 5.5–7.0 | AZ, NV, NM, Southern CA | Smaller system needed for same output |
| Southeast | 4.5–5.5 | FL, GA, TX, NC, SC | Average sizing |
| Mid-Atlantic | 4.0–4.8 | VA, MD, NJ, PA, NY | Standard sizing |
| New England | 3.8–4.4 | MA, CT, RI, VT, NH, ME | Size up 10%–15% |
| Pacific Northwest | 3.0–4.0 | WA, OR, Northern CA | Size up 15%–25% |
| Mountain West | 5.0–6.5 | CO, UT, ID, MT, WY | Average to smaller sizing |
Sources: EIA average US residential electricity use; NREL peak sun hours by state; Modernize.com system cost data 2026
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