Solar Roof Panel Calculator
Find out how many current residential solar panels can fit on your usable roof area, what the system size would be, and roughly how much electricity it could generate in your Texas location.
Step 1
Enter your usable roof area
Use the approximate rectangle where panels can actually be installed. The usable-area slider accounts for common vents, setbacks and access space.
Step 2
Choose a panel model
These are preloaded residential models with published manufacturer dimensions and power ratings. Product availability can change, so each model includes a manufacturer source.
Step 3
Add Texas production assumptions
Compare panel models
How different panel sizes change the fit
Same roof. Different module dimensions and wattage. This table shows why panel count should be calculated from the actual model, not from a generic “400-watt panel” assumption.
| Panel | W | Dimensions | Panels fit | System | Est. annual kWh |
|---|---|---|---|---|---|
| Qcells Q.TRON BLK M-G2+ 440W | 440 | 67.8 × 44.6 in | 36 | 15.84 kW | 23,121 |
| REC REC Alpha Pure-RX 470W | 470 | 68 × 47.4 in | 30 | 14.10 kW | 20,581 |
| Canadian Solar TOPHiKu6 460W | 460 | 69.4 × 44.6 in | 36 | 16.56 kW | 24,172 |
| Maxeon Maxeon 7 445W | 445 | 70 × 40.75 in | 36 | 16.02 kW | 23,383 |
How this solar roof panel calculator works
The calculator first converts your roof length and width into a usable rectangle. It then applies your usable-area percentage and tests the selected panel in both portrait and landscape orientation. The larger valid arrangement becomes the estimated fit.
Why panel dimensions matter
Two panels can have similar wattage but different physical dimensions. A longer or wider module can change the number of rows and columns that fit on the same roof. The result can change system size even when the roof area stays exactly the same.
How production is estimated
Production is a planning estimate based on a city-level solar-resource assumption, the selected roof orientation, shading, and a 14% planning loss factor. NREL's PVWatts V8 uses newer NSRDB weather data and more detailed module, thermal and inverter models, so a site-specific PVWatts or installer design can produce a different result. Learn more about PVWatts.
Use this before comparing solar quotes
Once you know roughly how many panels fit and the resulting system capacity, move to the Texas Solar Calculator to estimate installed cost, payback and long-term savings for your home.
Important limitations
- This tool is an early planning estimate, not a structural or electrical design.
- Roof vents, skylights, chimneys, setbacks, fire access and local code can reduce panel count.
- Exact production requires site-specific irradiance, roof tilt, azimuth, shading and equipment assumptions.
- Manufacturer products and specifications can change; verify the linked datasheet before purchasing.