Solar Panel Output Calculator — Daily, Monthly & Annual kWh
Calculate how much electricity your solar panels will produce per day, month and year. Enter system size and peak sun hours to get accurate kWh production estimates.
Estimate scope & data quality
- SEO Quick Estimate Uses the inputs available in this calculator.
- Personalized Estimate Use your own bill and location information where this calculator supports it.
- Detailed Solar Economics NOT_COMPUTABLE here without a verified tariff, system design, quote, and eligibility record.
- Data quality
- NOT_AVAILABLE
- Result limitation
- Calculator output is not a source-complete customer result.
A tariff credit is distinct from annual savings. If a result is NOT_COMPUTABLE or CONFLICT, it must not be replaced with an estimate or treated as canonical.
How to use this calculator
- Enter your solar system size in kilowatts (kW). A typical US home system is 6–10 kW.
- Set your daily peak sun hours using the state selector on the right, or enter a custom value. US average is 4.0–5.5 hrs/day.
- Adjust the system efficiency factor (default 80%) — this accounts for inverter losses, wiring losses, shading and temperature.
- Set annual degradation rate (default 0.5%/yr) — this is how much output drops each year due to cell aging.
- Daily, monthly, annual and year-25 production estimates appear instantly.
Understanding your results
How solar output is calculated: Daily output (kWh) = system size (kW) × peak sun hours × efficiency factor. A 7kW system with 5 peak sun hours and 80% efficiency produces 7 × 5 × 0.80 = 28 kWh per day.
Peak sun hours vs hours of daylight: Peak sun hours are not the same as hours of daylight. Peak sun hours measure the total solar energy received in a day, expressed as equivalent hours of full-intensity sunshine (1,000 W/m²). Los Angeles has about 5.8 peak sun hours per day; Seattle about 3.8; Phoenix about 6.5. Use the state selector to load your local value.
System efficiency factor (derate): Real-world solar systems never achieve 100% of their theoretical output due to: inverter conversion losses (~2%), wiring losses (~2%), soiling/shading (~3–5%), temperature effects (~3–5%) and clipping losses (~1–3%). The standard NREL derate factor is 0.86 (86%), but for conservative estimates 0.80 (80%) accounts for real-world conditions including partial shading.
Annual degradation: Solar panels degrade about 0.3–0.7% per year. At 0.5%/yr, a system producing 10,000 kWh in year 1 produces 9,500 kWh in year 10 and 8,750 kWh in year 25. Most manufacturers guarantee 80% of rated output at 25 years (implying maximum 0.8%/yr degradation).
Seasonal variation: Solar output varies significantly by season. A system producing 30 kWh/day in June may only produce 12 kWh/day in December in northern states. Annual totals are more meaningful than single-day estimates for financial planning.
Frequently asked questions
Direct answers for US homeowners.
Related guides
In-depth articles on sizing, costs, and energy decisions.