Solar Panel Calculator

Calculate how many solar panels you need, expected production, costs, and savings. Plan your solar energy system with accurate estimates.

Check your electric bill for kWh used per month

Total system capacity in kilowatts

Power rating per panel

Average for your location

Accounts for losses (inverter, temperature, dirt)

Your cost per kWh from utility bill

Total installed cost (avg: $2.50-$3.50/watt)

Daily Production per Panel = (Panel kW * Sun Hours * Efficiency)\nPanels Needed = Daily Usage / Production per Panel\nSystem Size (kW) = Panels * Panel Wattage / 1000\nAnnual Production = Daily Production * 365\nAnnual Savings = Annual Production * Electricity Rate\nPayback = Cost (after tax credit) / Annual Savings
Example:\nMonthly Usage: 900 kWh\nPanel: 400W\nSun Hours: 5 hours/day\nEfficiency: 80%\nRate: $0.13/kWh\n\nDaily Usage: 30 kWh\nProduction/Panel: 0.4 * 5 * 0.8 = 1.6 kWh\nPanels: 30 / 1.6 = 19 panels\nSystem: 7.6 kW\nAnnual Production: 11,096 kWh\nAnnual Savings: $1,442\nCost: $21,280 -> $14,896 (after 30% credit)\nPayback: 10.3 years\n25-Year Savings: $36,050

How many solar panels do I need for my home?

Average US home uses 900 kWh/month (30 kWh/day). A 400W panel produces ~1.6 kWh/day (4 sun-hours). You'd need about 19 panels. Actual needs depend on: location (sun hours), roof space, energy usage, panel efficiency, and budget. Start with electric bills to find kWh usage.

What is the difference between kW and kWh?

kW (kilowatt) is power capacity - how much energy at one moment. kWh (kilowatt-hour) is energy over time - what you use and pay for. A 5kW system running for 4 hours produces 20 kWh. Panel rating (400W) is capacity; daily production (1.6 kWh) is energy generated.

How long does it take for solar panels to pay for themselves?

Typical payback: 6-12 years depending on: system cost ($15k-$30k), electricity rates ($0.10-$0.30/kWh), sun exposure, tax credits (30% federal ITC), local incentives. After payback, panels continue saving money for 15-30 more years. Average 25-year savings: $20k-$50k.

How do I calculate sun hours for my location?

Peak sun hours = hours of 1000 W/m² sunlight per day. US averages: Arizona 6-7 hours, California 5-6, Texas 5-6, Northeast 4-5, Pacific Northwest 3-4. Check NREL solar maps or pvwatts.nrel.gov. Winter has fewer hours than summer; use annual average for planning.

What factors reduce solar panel output?

Shading (trees, buildings): -10% to -100% if covered. Roof angle/orientation: south-facing optimal, east/west -10-20%. Temperature: panels lose 0.5%/°C above 25°C. Dirt/dust: -5%. Age: -0.5-1% per year. System losses (inverter, wiring): -10-15%. Real output is 75-85% of rated capacity.