Enter panel count, rated DC watts, an assumed daily equivalent of full irradiance on the array, and an aggregate loss allowance. This short energy model is not PVWatts: its single loss input must include any inverter and temperature effects you intend to represent. PVWatts models those separately from its 14% system-loss input.
Solar Panel Output: worked example
| Number of panels | 20 |
|---|---|
| Watts per panel | 400 |
| Peak sun hours per day | 4.5 |
| System losses | 14.0% |
| Energy per day (kWh) | 31 |
| Energy per year (kWh) | 11,300.4 |
Solar Panel Output: changing Number of panels
| Number of panels | Energy per day (kWh) | Energy per year (kWh) |
|---|---|---|
| 16 | 24.8 | 9,040.3 |
| 18 | 27.9 | 10,170.4 |
| 20 (example) | 31 | 11,300.4 |
| 22 | 34.1 | 12,430.4 |
| 24 | 37.2 | 13,560.5 |
Solar Panel Output: compare input ranges
| Input | Tested from | To | Energy per day (kWh): low input | Energy per day (kWh): high input | Swing |
|---|---|---|---|---|---|
| Peak sun hours per day | 4 | 5 | 27.5 | 34.4 | 6.9 (22%) |
| Number of panels | 18 | 22 | 27.9 | 34.1 | 6.2 (20%) |
| Watts per panel | 360 | 440 | 27.9 | 34.1 | 6.2 (20%) |
| System losses | 12.0% | 16.0% | 31.7 | 30.2 | 1.4 (4.7%) |
Solar Panel Output: individual input comparisons
| Input | Value | Energy per day (kWh) | Energy per year (kWh) |
|---|---|---|---|
| Number of panels | 16 | 24.8 | 9,040.3 |
| 18 | 27.9 | 10,170.4 | |
| 20 | 31 | 11,300.4 | |
| 22 | 34.1 | 12,430.4 | |
| 24 | 37.2 | 13,560.5 | |
| Watts per panel | 320 | 24.8 | 9,040.3 |
| 360 | 27.9 | 10,170.4 | |
| 400 | 31 | 11,300.4 | |
| 440 | 34.1 | 12,430.4 | |
| 480 | 37.2 | 13,560.5 | |
| Peak sun hours per day | 3.6 | 24.8 | 9,040.3 |
| 4 | 27.5 | 10,044.8 | |
| 4.5 | 31 | 11,300.4 | |
| 5 | 34.4 | 12,556 | |
| 5.4 | 37.2 | 13,560.5 | |
| System losses | 10.0% | 32.4 | 11,826 |
| 12.0% | 31.7 | 11,563.2 | |
| 14.0% | 31 | 11,300.4 | |
| 16.0% | 30.2 | 11,037.6 | |
| 18.0% | 29.5 | 10,774.8 |
Solar Panel Output: combined input changes
| Number of panels / Watts per panel | 320 | 400 | 480 |
|---|---|---|---|
| 16 | 19.8 | 24.8 | 29.7 |
| 18 | 22.3 | 27.9 | 33.4 |
| 20 | 24.8 | 31 | 37.2 |
| 22 | 27.2 | 34.1 | 40.9 |
| 24 | 29.7 | 37.2 | 44.6 |
Solar Panel Output: which assumptions move the result?
Solar Panel Output: values and definitions
| Quantity and definition | Value used |
|---|---|
| Number of panels | 20 |
| Watts per panel | 400 |
| Peak sun hours per day — Average daily hours of full-strength sun for your location and season. | 4.5 |
| System losses — Aggregate loss assumed for this simple model; this is not the separately defined PVWatts system-loss input. | 14.0% |
| Energy per day (kWh) | 31 |
| Energy per year (kWh) | 11,300.4 |
Solar Panel Output: half and double Peak sun hours per day
| Peak sun hours per day | Energy per day (kWh) |
|---|---|
| 2.3 | 15.5 |
| 4.5 | 31 |
| 9 | 61.9 |
A full production model uses weather, array orientation, shading, temperature and inverter behavior. Do not import PVWatts’ 14% system-loss figure as though it includes all those effects. The yearly result assumes the entered daily average applies to the whole year; actual seasons vary.
Solar Panel Output: formula
U.S. Department of Energy: Homeowner's Guide to Going Solar · PVWatts: System loss input
Common error: Using the panel's rated watts as if it delivered them all day. Ratings are for ideal test conditions, and real output sits well below them for most of the day.
Energy & Utilities calculators: Solar Payback Calculator, LED Bulb Savings Calculator, Generator Size Calculator, Electricity Cost Calculator, EV Charging Cost Calculator, MPG Calculator.
A solar array's yield is its rated power times the hours of full-strength sun times what survives wiring, heat and dirt. Twenty 400 watt panels are 8 kilowatts on paper. With 4.5 peak sun hours and 14 percent losses, they make about 31 kilowatt-hours a day.
Peak sun hours are not daylight hours. They are the hours of full-strength sun that would deliver the same energy, and they swing with the season.
Use sun hours for your own location and for the roof's tilt and direction. A shaded or north-facing roof can produce far less than the default.
Work out the return on the solar payback calculator, your usage on the electricity cost calculator and backup on the battery runtime and generator size calculators. The EV charging and LED savings pages show where the energy goes, and the roof pitch page relates to panel tilt.
Is this the PVWatts model?
No. It is rated DC power times assumed sun hours times one aggregate retained-energy fraction. PVWatts models weather, temperature and inverter conversion separately.
What does the 14% example mean?
It is an aggregate assumption in this simplified equation, not a universal measured loss or a complete PVWatts default configuration.
How much electricity does a solar panel produce per day?
An assumed 400-watt panel multiplied by 4.5 peak-sun hours gives 1.8 kWh before losses. Reaching 1.5 kWh would imply a combined reduction of about 16.7%. State that assumption explicitly; the site’s actual resource, orientation and loss model determine whether either daily value is representative.
What are peak sun hours?
The number of hours per day when sunlight is at its full standard strength, which determines the energy a panel collects.
What causes solar system losses?
Separate the model’s loss categories. PVWatts shows a 14% default system-loss input, but it models temperature and inverter conversion separately. Shading, soiling, wiring and mismatch can also vary by installation; combining every loss into 14% or applying the same loss twice misstates the output.