Solar Panel Calculator
Enter your average monthly electricity use and your region to get the system size, number of panels, yearly production, and roof area you need, plus an honest cost and payback estimate for 2026.
- System size
- 8.4 kW
- Panels
- 21
- Yearly production
- 11,038 kWh
- Roof area
- 441 sq ft
Cost and payback
Edit these to your own numbers. Incentives default to $0 because the 30% federal residential tax credit ended for systems placed in service after December 31, 2025; enter any state, local, or utility incentive you qualify for.
- Net cost
- $25,200
- Yearly savings
- $1,766
- Payback
- 14.3 yrs
- 25-yr net savings
- $18,952
Estimates a grid-tied residential system. Production is system size times your region's peak sun hours times 365, with a 20% loss factor for inverter, heat, wiring, and shading losses. Actual output depends on your roof pitch, orientation, and shading; run your address through NREL PVWatts for a precise figure. The 25-year net savings is simple (no rate inflation or panel degradation) and is not financial advice.
Start with your real usage, not your roof
The single most important number is your average monthly kWh, which is printed on your power bill. Sizing solar to your actual usage is what keeps you from overpaying for panels you do not need or underbuilding and still paying the utility. Sun matters too: the same house needs a smaller system in Arizona than in Ohio because each panel produces more. Picking gear? See best portable solar panels and best solar generators, and weigh the big decision in solar lease vs buy.
Frequently asked questions
How many solar panels do I need to power my house?
Most US homes need about 15 to 25 panels. The exact number depends on how much electricity you use and how much sun your area gets. Take your annual kWh (monthly use times 12), divide by your region's yearly production per kW (peak sun hours times 365 times about 0.8 for losses) to get system size, then divide the watts by your panel wattage. A typical home using 900 kWh a month in an average-sun region needs roughly a 8 to 9 kW system, or about 21 panels at 400 watts each.
What size solar system do I need?
Size it to cover your yearly electricity use. A home using 10,800 kWh a year (900 a month) in a 4.5 peak-sun-hour region needs about an 8.4 kW system. Sunnier regions need a smaller system for the same usage, because each kW produces more. Enter your real monthly kWh, which is on your power bill, to size yours.
How much does a solar system cost in 2026?
Installed residential solar runs roughly $2.50 to $3.50 per watt before any incentives, so a typical 8 kW system is about $20,000 to $28,000. Note that the 30% federal residential tax credit (Section 25D) expired for systems placed in service after December 31, 2025, so most homeowners who buy a system in 2026 no longer get that credit. State, local, and utility incentives may still apply.
Is solar worth it in 2026 without the tax credit?
It can still pay off, but payback periods are longer now that the 30% federal credit has expired for owned systems. Without it, a typical system pays back in roughly 12 to 16 years depending on your electricity rate, sun, and install cost, versus 8 to 12 years with the old credit. Solar makes the most sense where electricity is expensive and sun is strong. Leases and power purchase agreements can still access a federal credit through the system's owner.
How many kWh does a solar panel produce per day?
A single 400-watt panel produces roughly 1.3 to 2.4 kWh per day, depending on sun. In a 4.5 peak-sun-hour region with normal losses, that is about 1.4 kWh per panel per day; in a sunny 6-hour region, closer to 1.9 kWh. Multiply by your panel count for a daily total.
Sizing uses the standard production model (system size times peak sun hours times 365, with a 20% loss factor) and NREL regional sun-hour averages. Estimates only; actual output varies with roof orientation, pitch, and shading. Cost and payback are estimates, not financial advice. See our disclaimer.