Solar Panel Output Calculator

Solar panel output depends on panel wattage, sunlight hours, system efficiency, and your local climate. Calculating expected energy production and financial savings helps you evaluate whether solar is right for your home.

Key formulas: Daily Energy Output (kWh) = Panel Wattage (kW) × Peak Sun Hours × System Efficiency Annual Output = Daily Output × 365 Annual Savings = Annual Output × Electricity Rate ($/kWh)

What each variable means:

• Panel Wattage: rated output under Standard Test Conditions (STC): 1,000 W/m² irradiance, 25°C cell temperature. Common residential panels: 300W–450W each.
• Peak Sun Hours (PSH): the equivalent hours of full-intensity sunshine per day at your location. Not the same as daylight hours. Varies from ~2.5 PSH (Seattle) to ~6.5 PSH (Phoenix).
• System Efficiency: accounts for inverter losses (~4%), temperature derating (~5–10%), shading, soiling, wiring losses. Typically 75–85% total.
• Electricity Rate: what your utility charges per kWh. U.S. average was about $0.16/kWh in 2024, but the spread is enormous: roughly $0.09 in Louisiana against $0.33 and up in Hawaii and California. Leave it blank if you only want the kWh figures. This calculator will not guess a rate for you, because the guess would drive the entire savings number.

U.S. peak sun hours by city:

• Phoenix, AZ: 6.5 PSH
• Dallas, TX: 5.5 PSH
• Atlanta, GA: 5.0 PSH
• Denver, CO: 5.5 PSH
• New York, NY: 4.5 PSH
• Seattle, WA: 2.5 PSH

Worked example: 10 panels × 400W = 4,000W = 4 kW system. Location: Atlanta (5.0 PSH). System efficiency: 80%. Daily output = 4 kW × 5.0 × 0.80 = 16 kWh/day Annual output = 16 × 365 = 5,840 kWh At $0.16/kWh, annual savings = 5,840 × $0.16 = $934/year

That last line is where most solar estimates quietly go wrong, so it is worth being blunt about it. The kWh figure is physics and holds up well. The dollar figure is entirely at the mercy of one number you supply, and rates vary almost fourfold across US states, so the same 4 kW array on the same roof is worth $525 a year in Louisiana and $1,900 in Hawaii. Anyone quoting you a national-average payback has already thrown away the only input that mattered.

A note on what this does not include. Output here is gross generation, not what you save. If your utility offers full retail net metering, the two are close. If it credits exports at a wholesale rate, or you are on a time-of-use tariff that pays little for midday power, the money can be a third lower than the kWh suggest even though the panels perform exactly as calculated. Check the export rate before the panel spec sheet.

Federal solar tax credit (ITC): 30% of system cost deducted from federal income taxes (available through 2032 at 30%, then steps down). For payback including system cost, incentives, and rising rates, use the Solar Panel Payback Calculator.