Estimate daily, monthly, and annual kWh output from solar panel wattage, panel count, peak sun hours, and system efficiency.
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Solar panel output calculator Estimate daily, monthly, and annual kWh output from panel wattage, panel count, peak sun hours, and system efficiency. The same estimate can also help with solar power output calculator searches when you are comparing nameplate panel capacity against real-world generation.
How the assumptions work
Peak sun hours are equivalent full-sun hours, not literal daylight length. System efficiency is the loss factor between nameplate output and real production, so 80% means the model assumes about 20% of theoretical output is lost to temperature, inverter, wiring, and other system effects.
Annual output
5,256 kWh
14.4 kWh/day across 4 kW of panel capacity.
Daily output
14.4 kWh
Monthly average
438 kWh
Annual savings
$630.72
Array size
4 kW
Annual yield per kW
1,314 kWh/kW/year
Approx. CO₂ offset
2,207.52 kg/year
Formula used
kWh/day = (panel W × panels × peak sun hours × efficiency) / 1,000
This estimate assumes the entered panel rating, a fixed panel count, one peak-sun-hours value, and a constant efficiency rate. It does not model shading, tilt, azimuth, temperature swings, inverter clipping, snow, soiling, or battery storage.
Solar panel output calculator guide: estimate daily, monthly
A solar panel output calculator estimates how much energy a photovoltaic array can produce from panel wattage, panel count, peak sun hours, and system efficiency.
What this solar panel output calculator solves
This calculator starts from panel nameplate wattage and multiplies by the number of panels, peak sun hours, and a system-efficiency factor to estimate daily output in kilowatt-hours. It then extends that result to monthly and annual averages so you can compare a rooftop array against household demand, battery plans, or a bill-savings estimate.
That makes it useful when you know the array size but still need to estimate energy production. It also fits the search intent behind phrases like solar panel output calculator, solar power output calculator, solar panel kWh calculator, and daily solar output calculator because the core question is the same: how much energy will this array make over time?
The core idea is simple: daily energy equals panel watts multiplied by panel count, peak sun hours, and system efficiency, then divided by 1,000 to convert watt-hours into kilowatt-hours. That is why this calculator is a planning estimate rather than a climate model. Once you choose the peak sun hour assumption, the arithmetic is straightforward.
The annual and monthly figures are derived from the daily result. Annual output uses 365 days, while the monthly figure is the annual result divided by 12. That gives a clean average for comparing a solar array to year-round household electricity use.
kWh/day = (panel W x panels x peak sun hours x efficiency) / 1,000
Use when panel wattage, panel count, sun hours, and system efficiency are known.
kW = (panel W x panels) / 1,000
Shows the array nameplate capacity before derate assumptions are applied.
Peak sun hours and system efficiency
Peak sun hours do not mean literal hours of daylight. They mean the equivalent number of full-sun hours that would deliver the same energy as the actual day. A location with 4.5 peak sun hours can have more than 4.5 hours of daylight, but only a portion of that time is at full equivalent intensity.
System efficiency is a broad loss factor that rolls together temperature loss, inverter loss, wiring loss, dirt, mismatch, and other real-world effects. A value of 80% is a reasonable rough planning assumption for many systems, but the right number depends on mounting, climate, equipment choice, and how conservative you want the estimate to be.
Worked example: 400 W panels, 10 modules, 4.5 sun hours, 80% efficiency
Suppose an array uses ten 400 W panels. That is 4.0 kW of nameplate capacity. With 4.5 peak sun hours per day and 80% system efficiency, the calculator estimates 14.4 kWh per day. That works out to about 438 kWh per month and 5,256 kWh per year.
If electricity costs $0.12 per kWh, the same output translates to about $630.72 in annual bill value before any export tariff, battery shifting, or time-of-use effects are added. That is the kind of first-pass estimate this page is designed to produce.
This tool does not simulate shade patterns, tilt angle, azimuth, roof temperature, inverter clipping, snow cover, soiling, battery storage, or location-specific irradiance databases. Those effects can move the real production number above or below the simple estimate shown here.
Use this page to size a rough solar project, compare array options, or sanity-check a quote. For site-specific engineering, compare the result against a PVWatts-style model, installer proposal, or other production forecast that uses your exact location and equipment data.
Frequently asked questions
How do you calculate solar panel output?
Multiply panel wattage by panel count, peak sun hours, and system efficiency, then divide by 1,000 to convert to kilowatt-hours. That gives a daily output estimate before annualizing it.
How many kWh does a 400 W solar panel produce per day?
It depends on peak sun hours and system efficiency. At 4.5 peak sun hours and 80% efficiency, a 400 W panel produces about 1.44 kWh per day, while a 10-panel array of the same modules produces about 14.4 kWh per day.
What are peak sun hours?
Peak sun hours are equivalent full-sun hours. They describe how much solar energy a location receives in a day after adjusting for intensity, not just how long the Sun is above the horizon.
Is system efficiency the same as panel efficiency?
Not always. Panel efficiency describes the panel itself, while the calculator’s efficiency input is a broader system derate that can include inverter, wiring, temperature, and other losses.
Why does monthly output use an average instead of an exact calendar month?
The calculator uses annual output divided by 12 to give a clean planning average. Actual monthly production will vary with season, weather, shading, and location.
Should I use this instead of PVWatts?
Use this page for a quick planning estimate. Use a PVWatts-style model when you need a more location-specific forecast with climate data and system configuration details.
