How many solar panels do you need to power your home? Use this free solar panel calculator to find the number of panels, system size in kW, roof space, installed cost and payback period from your electric bill. It uses peak sun hours for your region and real 2026 installation prices, so you can check a solar quote before you sign.
Solar Panel Calculator
How many panels you need, what it costs and when it pays back.
Assumes 14% system losses, 0.5%/yr panel degradation and 3%/yr electricity price rise. Real quotes depend on roof angle, shading and local net-metering rules.
How to Use the Solar Panel Calculator
- Enter your monthly electricity use in kWh (it is printed on your bill). If you only know your bill, switch to the bill tab and enter the dollar amount.
- Check the electricity rate. The default is $0.18 per kWh; your bill shows your actual rate.
- Choose your region so the tool uses the right peak sun hours.
- Pick a panel wattage. Most new residential panels are 400 to 450 watts.
- Set the bill offset. 100% means the panels produce as much as you use in a year.
- Adjust the installed cost and rebates if you have a quote or local incentive.
The Solar Panel Formula
The calculator uses the same basic math installers use:
System size (kW) = yearly kWh ÷ (365 × peak sun hours × 0.86)
Number of panels = system size in watts ÷ panel wattage
The 0.86 factor covers real-world losses from the inverter, wiring, heat and dust (about 14%).
Example: a home using 900 kWh a month uses 10,800 kWh a year. With 4.5 peak sun hours: 10,800 ÷ (365 × 4.5 × 0.86) = 7.65 kW. With 400 W panels that is 7,650 ÷ 400 = 20 panels.
Peak Sun Hours by Region
| Region | Typical peak sun hours | Panels for 900 kWh/month (400 W) |
|---|---|---|
| Pacific Northwest, New England | 3 – 4 | 22 – 29 |
| Midwest, Mid-Atlantic | 4 – 5 | 18 – 22 |
| Southeast, Texas, Florida | 5 – 5.5 | 16 – 18 |
| Arizona, Nevada, Southern California | 6 – 7 | 13 – 15 |
How Much Do Solar Panels Cost in 2026?
The national average installed price for home solar is roughly $2.50 to $3.50 per watt before incentives, so a typical 7 to 8 kW system costs about $18,000 to $27,000. Price per watt drops on larger systems and rises with premium panels, complex roofs or battery storage.
Important for 2026: the 30% federal Residential Clean Energy Credit (Section 25D) ended for systems installed after December 31, 2025. That makes state rebates, utility programs, and comparing several quotes more important than ever. Enter any local rebate in the “Rebates / credits” box.
Ways to Need Fewer Panels
- Swap old bulbs for LEDs (see our LED savings calculator).
- Install a smart thermostat to cut heating and cooling use.
- Find energy hogs with the appliance energy cost calculator.
- Shift laundry, dishwashing and EV charging to sunny midday hours with smart plugs and schedules.
Frequently Asked Questions
How many solar panels do I need for 1,000 kWh per month?
With 400 W panels and 4.5 peak sun hours, you need about 22 panels (an 8.5 kW system) to cover 1,000 kWh per month. In sunny states like Arizona, about 15 panels can be enough.
How many solar panels does it take to run a house?
The average US home uses around 850 to 900 kWh per month and needs 17 to 25 solar panels of 400 W, depending on how much sun the area gets.
How much roof space do solar panels need?
A 400 W residential panel is about 21 sq ft. Twenty panels need roughly 420 sq ft of usable, unshaded roof, plus space for fire setbacks.
Is the 30% solar tax credit still available in 2026?
No. The federal Section 25D credit for homeowner-owned solar ended for systems installed after December 31, 2025. Check your state and utility for remaining rebates.
How long do solar panels take to pay for themselves?
Most US homes see a payback of 7 to 14 years. It is faster with high electricity rates, lots of sun and good net-metering, and slower in cloudy areas with cheap power.
More Free Smart Home Tools
- Appliance Energy Cost Calculator – what each appliance costs to run
- Thermostat Savings Calculator – estimate yearly savings from a smart thermostat
- Generator Size Calculator – running and starting watts for backup power
- LED vs Incandescent Savings Calculator – savings from switching to LED
- AC BTU Calculator – find the right air conditioner size for any room
