About Solar System Sizing Calculator

Estimates a residential solar panel system based on your monthly electric bill and electricity rate. Derives daily kWh consumption, then factors in peak sun hours (auto-populated for 18 U.S. states or manually entered), system efficiency (70–95%), and panel wattage (300–500W) to determine the number of panels, total system wattage, inverter size (120% of panel capacity), required roof area (20 sq ft per panel), and estimated total cost. Optional battery backup sizing calculates storage capacity for 1–7 days of autonomy. Reports annual CO₂ savings in tons.

• Energy derivation: monthly bill ÷ rate = monthly kWh; ÷ 30 = daily kWh
• Panel count: (daily kWh × 1000) ÷ (sun hours × efficiency) ÷ panel wattage, rounded up
• Cost estimate: panels at $0.80/W + inverter at $0.30/W + battery at $500/kWh + 30% installation markup
• 18 U.S. states with pre-loaded peak sun hours (3.4–6.5 hrs/day)
• CO₂ savings: daily kWh × 365 × 0.92 lbs/kWh, converted to tons

Frequently Asked Questions

How accurate are the cost estimates?

They are rough ballpark figures using average 2024 pricing ($0.80/W for panels, $500/kWh for batteries). Actual installed costs vary widely by region, roof complexity, permitting, and available incentives. The federal Investment Tax Credit (ITC) is not factored in—subtract 30% from the total for a post-credit estimate.

What are peak sun hours and why do they matter?

Peak sun hours represent the number of hours per day when solar irradiance averages 1,000 W/m². A location with 5 peak sun hours means a panel produces its rated wattage for an effective 5 hours. Arizona’s 6.5 hours means you need fewer panels than Washington’s 3.4 hours for the same energy output.