US solar calculator
Size a home solar system from your electric bill — kW, panel count, roof area, cost after the 30% federal tax credit, and payback.
Quick answer: At $0.17/kWh and 4.2 peak sun hours, a $200/month bill needs about 12.3 kW — 30 × 410 W panels covering ~60 m². Gross cost is ~$33,825; the 30% ITC credit brings it to $23,678 net, offsetting $2,400 a year for a ~9.9 year payback.
Your details
Ballpark, not gospel. Sized at 78% real-world output with the national sun-hour average — confirm shading, roof angle and your utility's net metering rules with a local installer before buying.
Typical US system sizes by monthly bill
| Monthly bill | System size | Panels (410 W) | Net cost after 30% ITC | Payback |
|---|---|---|---|---|
| $100 | 6.15 kW | 15 | $11,839 | 9.9 years |
| $200 | 12.30 kW | 30 | $23,678 | 9.9 years |
| $300 | 18.04 kW | 44 | $34,727 | 9.6 years |
Computed at $0.17/kWh, 4.2 peak sun hours, $2.75/W installed and the 30% ITC. Run your exact bill above.
Questions people actually ask
Straight answers, no fluff. Then run your own numbers above.
How many solar panels do I need in the US?
It follows your bill. At the national average of $0.17/kWh and 4.2 peak sun hours, a $200/month bill needs about a 12.3 kW system — roughly 30 × 410 W panels covering ~60 m² of roof.
What does the 30% federal solar tax credit do to the cost?
The Investment Tax Credit (ITC) cuts 30% off the gross system cost as a credit against your federal taxes. On a $33,825 gross 12.3 kW system, that is a $10,148 credit, leaving a net cost of about $23,678.
What is the average payback period for US residential solar?
Around 9–10 years at current national averages — a $200/month bill offsets $2,400 a year against a $23,678 net cost, paying back in about 9.9 years. With 3% annual rate growth, 25-year savings reach roughly $87,500.
How much does US residential solar cost per watt in 2026?
Installed cost averages $2.50–$3.50 per watt nationally. The calculator defaults to $2.75/W — a 6 kW system lands around $16,900 gross before the credit.
Does net metering still exist in the US?
Yes in most states, but the rules are thinning. California's NEM 3.0 and several other states now credit exports well below the retail rate, which makes batteries more attractive — size them on the solar system calculator.
How much roof space does a US solar system need?
About 2 m² per residential panel including spacing. A typical 30-panel system needs roughly 60 m² (~645 sq ft) of unshaded, south-facing (or east/west) roof.
How much CO₂ does a home solar system avoid?
About 0.7 kg per kWh generated. A 12.3 kW system producing ~14,700 kWh a year offsets roughly 10.3 tons of CO₂ annually — like taking two cars off the road.
Is solar worth it if my bill is only $100 a month?
The math scales: a $100 bill needs about 6.2 kW (15 panels) with a net cost near $11,800 after the credit — the payback stays around 9.9 years. Bills under ~$75 a month are the marginal zone.
Adding batteries for backup or NEM 3.0 export rules? The solar system calculator sizes your inverter and battery bank. Comparing quotes? The solar cost calculator breaks down cost per watt, and the solar ROI calculator maps your payback year by year.