About the Solar Panel Output Calculator
This solar panel output calculator estimates how much electricity a panel or a whole array produces. Enter the panel wattage, how many panels you have, the peak sun hours for your location and the expected system losses, and it returns production per day, per month and per year, the output of each panel and the value of that electricity at your rate.
Use it to check an installer’s production estimate, size an off-grid or RV system, compare a 350 W panel with a 450 W one, or work out how many kWh a balcony or shed panel will give you. The chart shows how strongly yearly output depends on the sunshine your site receives.
Peak sun hours are the daily solar energy at your site expressed as hours of full 1,000 W/m² sunshine — roughly 3 in cloudy northern regions, 4–5 across much of the US and 6+ in deserts. Losses cover inverter efficiency, heat, wiring, dust and shading; 14% is the default used by NREL’s PVWatts model. The result is a yearly-average estimate: winter days produce less and summer days more.
With the default inputs, the daily output is 15.48 kWh. Change any value above to recalculate instantly.
How to use the solar panel output calculator
- 1Enter the wattage of one panel and how many panels you have or plan to install.
- 2Enter the average peak sun hours for your location.
- 3Adjust system losses if you have shading or a very hot site.
- 4Enter your electricity price to value the output.
- 5Read daily, monthly and yearly kWh and compare them with your bill.
Formula and method
A panel’s wattage is its output under standard test conditions of 1,000 W/m² of sunlight at 25°C. Peak sun hours convert the actual sunshine your site receives in a day into hours of that standard intensity, so multiplying the array size in kW by peak sun hours gives the ideal energy in kWh. Multiplying by (1 − losses) accounts for inverter conversion, high cell temperatures, wiring, dirt, shading and panel mismatch.
Yearly output is the daily figure × 365 and the average month is the yearly figure ÷ 12. Specific yield is yearly kWh per installed kW, and capacity factor is yearly output divided by what the array would make running at full nameplate power for all 8,760 hours of the year. For a site-specific estimate that accounts for tilt, orientation and local weather, use NREL’s PVWatts.
- Panel W
- Nameplate rating of one panel in watts
- Peak sun hours
- Daily solar energy ÷ 1 kW/m² (yearly average)
- Losses
- Combined system losses as a fraction (14% → 0.14)
Worked examples
10 × 400 W panels with 4.5 sun hours
A 4 kW array × 4.5 peak sun hours × 0.86 gives 15.48 kWh a day. Over a year that is 5,650 kWh, or about 471 kWh in an average month, worth roughly $961 at $0.17/kWh.
Single 100 W panel for an RV
One 100 W panel with 5 sun hours and 20% losses (charge controller, battery, heat) gives 100 × 5 × 0.8 = 400 Wh, or 0.4 kWh a day — enough for lights, phone charging and a fan.
Large 7.2 kW home system in a sunny state
Sixteen 450 W panels make a 7.2 kW array. With 6 sun hours and 14% losses it produces about 37.2 kWh a day or 13,560 kWh a year, worth about $3,390 at $0.25/kWh.
Frequently asked questions
How many kWh does a 400 W solar panel produce per day?+
Multiply 0.4 kW by your peak sun hours and by about 0.86 for losses. With 4.5 sun hours a 400 W panel makes about 1.5 kWh a day, or roughly 560 kWh a year; in a sunny 6-hour location it makes about 2.1 kWh a day.
What are peak sun hours?+
Peak sun hours are the total solar energy reaching a surface in a day divided by the standard intensity of 1,000 W/m². Five peak sun hours means the site receives 5 kWh per square metre per day, even though the sun is up much longer.
Why does my system produce less than its rating?+
Panels are rated at 25°C cell temperature and 1,000 W/m² of light. Real panels run hotter, the inverter loses a few percent, and wiring, dust, shading and ageing all reduce output. Losses of 10–20% are normal.
How much does solar output vary between summer and winter?+
At mid-latitudes summer production can be two to four times higher than winter because days are longer and the sun is higher. This calculator gives a yearly average; use monthly sun-hour figures for a seasonal estimate.
How many solar panels do I need?+
Divide your yearly electricity use by the yearly output of one panel. If you use 10,000 kWh a year and one 400 W panel makes about 565 kWh, you need about 18 panels. The solar panel calculator does this sizing for you.