☀️ Solar Panel Output Calculator
Enter your panel wattage, how many panels, your peak sun hours and a system-efficiency factor to estimate daily, monthly and yearly production.
Per day
8.64 kWh
Per month
263 kWh
Per year
3,156 kWh
Daily kWh = total watts × peak sun hours × system efficiency ÷ 1000. Peak sun hours are the equivalent hours of full (1 kW/m²) sun for your location — roughly 3–4 in cloudy northern regions and 5–6+ in sunny climates, and lower in winter; look yours up from a solar-irradiance map (e.g. NREL). System efficiency of ~75–85% accounts for inverter, wiring, heat, dust and mismatch losses. An estimate — real output varies with weather, shading and panel age. 🔒 In your browser.
How the solar panel output calculator works
A solar array's energy output is its power rating multiplied by how much usable sun it gets and how efficiently the system delivers it. The tool works it out as total watts × peak sun hours × system efficiency ÷ 1000 for the daily kilowatt-hours, then scales that to a month and a year. "Peak sun hours" is your location's daily solar energy expressed as equivalent hours of full 1 kW/m² sun.
This is an estimate. Real output swings with the weather, the seasons, shading, panel temperature and ageing (~0.5%/year). For off-grid sizing use your worst-month peak sun hours, not the annual average — a temperate site can get 3–4× less sun in December than June. Look up your location's figures on a solar-irradiance map such as NREL's.
Frequently asked questions
How much energy does a solar panel produce per day?
Panel watts × peak sun hours × system efficiency ÷ 1000 kWh. A 400 W panel at 4.5 peak sun hours and 80% efficiency makes about 1.44 kWh a day. Multiply by the number of panels for the array total.
What are peak sun hours?
The number of hours per day that sunlight averages 1,000 W/m² — the standard test intensity. It bundles a whole day's sunlight into an equivalent number of full-strength hours, typically 3–4 in cloudy regions and 5–6+ in sunny ones, and much lower in winter.
How many solar panels do I need?
Divide your daily energy use (kWh) by what one panel produces per day (panel watts × sun hours × efficiency ÷ 1000). If you use 10 kWh/day and each panel makes 1.44 kWh, you'd need about seven — then round up for cloudy days and losses.
Why is my real output lower than the panel rating?
Panels are rated at ideal lab conditions. In the field you lose energy to inverter and wiring losses, heat (panels get less efficient hot), dust, shading, and mismatch — together roughly 15–25%, which is the system-efficiency factor.
What system efficiency should I use?
Around 75–85%. NREL's PVWatts uses about 14% DC losses (a 0.86 factor) plus inverter losses, giving a whole-system figure near 0.77–0.80 for many installs. Use ~0.80 as a reasonable default and adjust for a hot, dusty or shaded site.