How Many Solar Panels Do I Need?
Solar panel count depends on three things: your electricity usage, your state's solar irradiance, and your roof's usable area. The calculator below gives you a precise answer in 30 seconds using NREL irradiance data and 2026 panel specs.
How Many Solar Panels Do I Need?
Calculate your system size and panel count based on your electricity usage, your state's solar irradiance, and your available roof area. Uses 410W panels (2026 residential standard).
Roof orientation, pitch, shading, and panel selection affect actual production by ±15%. EnergySage installers do free site surveys.
Get free quotes for your home →The math behind solar sizing
System size (kW) = Annual usage (kWh) ÷ State production factor (kWh/kW/year)
Production factor is how much energy each kilowatt of solar produces per year in your state. NREL PVWatts gives:
- Arizona: 1,700 kWh/kW (highest in lower 48)
- California: 1,620 kWh/kW
- Texas: 1,530 kWh/kW
- Florida: 1,485 kWh/kW
- New York: 1,290 kWh/kW
- Massachusetts: 1,245 kWh/kW
Example: Texas family using 1,200 kWh/month
- Annual usage: 14,400 kWh
- Texas production factor: 1,530 kWh/kW
- System needed for 100% offset: 14,400 / 1,530 = 9.4 kW
- Panel count at 410W each: 9,400 / 410 = 23 panels
- Roof area required: 23 × 17.6 sqft = 405 sqft
Why 410W panels in 2026?
Residential panels have grown from 250W (2018) to 410–440W (2026). 410W is the modern sweet spot:
- Premium tier (REC Alpha Pure-R, Q.Peak Duo): 405–430W
- Mid tier (Canadian Solar HiKu, Trina Vertex): 400–420W
- Budget tier (JA Solar, LONGi Hi-MO): 395–410W
Higher-wattage panels (440–460W "high-efficiency") cost ~30% more for ~7% more power. They're worth it only when roof space is the limiting factor — in which case you may need a power-density premium to fit enough capacity.
Roof area required (rule of thumb)
17.6 sqft per 410W panel × number of panels. Add 20% for inter-row spacing, walkways, fire setbacks (3 ft from ridge + 3 ft from gable end mandated by IRC code).
- 10 panels (4.1 kW): ~210 sqft of usable roof
- 20 panels (8.2 kW): ~420 sqft
- 30 panels (12.3 kW): ~630 sqft
South-facing? East-west? Tilt?
Production factors above assume optimal south-facing orientation at latitude tilt. Adjustments:
- South-facing: 100% (baseline)
- East-facing: ~85%
- West-facing: ~88% (slightly better than east — peak afternoon sun matches utility peak rates)
- North-facing: ~70% (rarely worth it)
- Flat (0° tilt): ~90% of optimal in most US locations
Sizing for net metering vs no net metering
Your sizing strategy depends on your state's net metering policy:
- Full retail net metering (FL, NJ, MA, NY, NC, OH, CO): size to 100–110% of consumption. Excess credits roll forward annually.
- Avoided-cost only (CA NEM 3.0, AZ): size to 50–70% of consumption + battery to maximize self-consumption. Oversizing is value-destructive.
- Texas (utility-dependent): check your REP. Solar-friendly REPs (Reliant, Octopus, Green Mountain) treat it as full net metering.
What if my roof is too small?
- Higher-efficiency panels: 440–460W panels squeeze more capacity into limited roof. ~$0.30/W premium.
- Premium 25%-efficient panels: SunPower Maxeon, REC Alpha Pure-RX, LG NeON 2 — up to 22.5% efficiency vs ~20% standard. Same wattage in 8% less roof area.
- Ground-mount system: if you have yard space. ~10% more expensive than rooftop but no roof-space constraints.
- Hybrid: solar + battery + grid: partial offset (60–70%) with battery for evening shifting. Lower upfront, similar monthly bill reduction.