How Many Solar Panels Do I Need?
You'd need about
21panels
A 8.4 kW system to cover 102% of your use in Texas.
System size
8.4 kW
Annual production
13,000 kWh
Energy offset
rounded up to whole panels
102%
Panel wattage
400 W
iSized for Texas (~5.3 peak sun-hours/day). Your real count depends on usable roof area, shading, and orientation — a planning ballpark, not a roof design.
How the sizing math works
Sizing solar is independent of price — it's pure physics. We work in three steps:
- Find annual usage. If you give a monthly bill, we divide it by your state's residential electricity rate and multiply by 12 to estimate annual kWh. (Entering kWh directly is more accurate.)
- Solve for system size. A 1 kW array produces roughly peak sun-hours × 365 × performance ratio kWh per year. We use an 80% performance ratio to account for inverter, wiring, heat, and soiling losses, then size the array so its yearly production covers your target offset.
- Convert to panels. We divide the system wattage by your panel wattage and round up to whole panels — so the panel count is always a real, installable number.
That's why two homes with identical bills can need different systems: sunnier states (more peak sun-hours) need fewer panels for the same offset, and higher-wattage panels cut the count further.
Next steps
Sizing is step one. Once you know how big your system is, see what it costs and when it pays for itself:
Frequently asked questions
- How many solar panels do I need to power a house?
- A typical US home uses about 10,000–12,000 kWh per year, which usually needs roughly 15 to 25 modern 400 W panels — a 6 to 10 kW system. The exact number depends on how much electricity you use and how many peak sun-hours your state gets, so enter your own figures above for a tailored count.
- How is solar system size calculated?
- We convert your usage to annual kWh, then divide by your state's peak sun-hours × 365 days × an 80% performance ratio to get the system size in kW. Dividing that wattage by your panel wattage (and rounding up to whole panels) gives the panel count.
- Does panel wattage change how many I need?
- Yes. Higher-wattage panels produce more each, so you need fewer of them for the same system size — for example, switching from 350 W to 450 W panels cuts the count by roughly a fifth. The calculator lets you change panel wattage to compare.
- Should I size solar for 100% of my usage?
- Many homeowners target 100% offset, but the right number depends on your net-metering rules and whether you plan to add an EV or heat pump. Where exported power is credited below the retail rate, sizing closer to your daytime use can pay back faster. Use the target-offset control to test scenarios.