☀️ Solar Roof Calculator
Estimate panels, energy production, and savings
Enter your roof area, sun exposure, and panel specs. We'll calculate how many panels fit, annual production, savings, and payback period.
Smart Roofing Calculator — Solar Roof Calculator — smartroofingcalculator.com/solar-roof-calculator/ — printed
Total roof surface area
60–80% after setbacks, vents, shade
350–450W for modern panels
3–6 hours depending on location
Check your utility bill
$2.50–$3.50/W typical installed
☀️ South-facing roof sections produce the most energy in the Northern Hemisphere.
🛠️ How This Calculator Works
This calculator determines usable roof area, divides by panel size (~17.5 sq ft) for max panels, then calculates system wattage. It uses peak sun hours to estimate daily/annual production and multiplies by your electric rate for savings.
📐 Formula
Panels = Usable Area ÷ 17.5 | System kW = Panels × Wattage ÷ 1000 | Annual kWh = System kW × Sun Hours × 365📝 Example Calculation
For a 1,500 sq ft roof with 70% usable, 400W panels, 5 sun hours: • Usable area: 1,050 sq ft • Max panels: 60 panels • System: 24 kW • Daily: 120 kWh | Annual: 43,800 kWh • At $0.13/kWh: $5,694/yr savings • System cost: ~$72,000 at $3.00/W (no federal credit for 2026 installs)
💡 Pro Tips from Roofers
- Get a professional shade analysis — even partial shading reduces output significantly.
- Microinverters perform better than string inverters on partially shaded roofs.
- Battery storage (like Tesla Powerwall) adds $10,000–$15,000 but provides backup power.
- Many utilities offer net metering — check your local policy.
- Solar panels add $15,000–$25,000 to home resale value on average.
❓ Frequently Asked Questions
How many solar panels fit on my roof?
Usable roof area is typically 60–80% of total area (after setbacks, vents, skylights, shading). Divide usable area by 17.5 sq ft per panel for a rough count. A 1,000 sq ft usable area fits about 57 panels.
How much energy does a solar panel produce?
A typical 400W panel produces about 1.4–1.8 kWh/day (depending on sun hours). In a sunny location (5 peak sun hours), one 400W panel produces ~2 kWh/day or ~730 kWh/year.
How much do solar panels cost?
Residential solar costs $2.50–$3.50 per watt installed before incentives, so a 10 kW system costs about $25,000–$35,000. The calculator shows that full cost: the 30% federal Residential Clean Energy Credit (25D) applied only to systems installed through December 31, 2025.
Is there still a federal tax credit for solar panels?
Not for new home systems. The IRS says the Residential Clean Energy Credit (25D) is not available for expenditures made after December 31, 2025 (irs.gov/credits-deductions/residential-clean-energy-credit). A system installed and paid for in 2025 can still be claimed on the 2025 return with Form 5695. For 2026 installs, check your state energy office and your utility for solar rebates, performance payments and net metering rules, which vary by location.
Does roof pitch affect solar production?
Optimal tilt equals your latitude (25–35° for most US locations). Panels on flat roofs use tilt racks. Steep roofs (>45°) see 10–15% less production. East/west facing roofs produce 15–20% less than south.
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About the Smart Calculator Team
We build free, accurate construction calculators for homeowners and contractors. This article is part of our roofing knowledge base — we also publish guides and tools for other home improvement projects:
Shopping for someone? See our gift guide for roofers & DIY homeowners.
Will the roof carry the panels? Check it with the roof load capacity calculator.
Don't know the roof size? The roof square footage calculator works it out from the footprint and pitch.
· Reviewed by the Smart Roofing Calculator editorial team