Solar Panel Output Calculator
How much electricity a solar array generates in a day, a month and a year — from its size, your sunshine hours and a realistic performance ratio.
A panel's rating is its output under standard test conditions: bright, cool and perpendicular.
How the solar panel output calculator works
A panel's rating is its output under standard test conditions: bright, cool and perpendicular. Real output is lower, so the industry uses a performance ratio — typically 0.75 to 0.85 — covering heat losses, wiring, inverter efficiency, dust and imperfect angle. A 6.6 kW array in a place averaging 4.5 peak sun hours generates about 6.6 × 4.5 × 0.8, or 23.8 kWh a day.
"Peak sun hours" is not hours of daylight. It is the day's total solar energy expressed as equivalent hours at full strength, which is why a location with twelve hours of daylight might have only four peak sun hours.
Formula: daily kWh = system kW × peak sun hours × performance ratio
Worked examples
| Inputs | Daily generation | Note |
|---|---|---|
| A 6.6 kW array at 4.5 sun hours | 23.76 kWh | 23.8 kWh a day |
| A 4 kW UK system at 3.5 hours | 11.2 kWh | 11.2 kWh a day |
| A large 13 kW array | 52 kWh | 52 kWh a day — well above typical use |
FAQFrequently asked questions
How much does a 6.6 kW solar system generate?
About 23.8 kWh a day at 4.5 peak sun hours with a 0.8 performance ratio — roughly 8,700 kWh a year.
What are peak sun hours?
The day's total solar energy expressed as equivalent hours at full strength. It is much less than hours of daylight.
What is a performance ratio?
The share of the panel's rated output actually delivered, after heat, wiring, inverter and dust losses. 0.75 to 0.85 is typical.
Why is winter output so much lower?
Shorter days and a lower sun angle. Winter generation can be a third of summer at higher latitudes.
Does shading matter much?
A great deal — shading part of a string can cut output disproportionately unless the system uses optimisers or microinverters.
Where these figures come from
- UK DESNZ / DEFRA — Greenhouse gas reporting: conversion factors — the flight, fuel and waste emission factors used here
- Scarborough et al. (2014), Climatic Change — Dietary greenhouse gas emissions — the per-diet daily emission figures
- US EPA — Technical Assistance Document for the Reporting of Daily Air Quality (AQI) — the PM2.5 breakpoints the air quality calculator uses
- Australian Government — National Greenhouse Accounts Factors — the official Australian emission factors
Last checked: September 2026. Factors are taken from published government and peer-reviewed sources, each named on the page with its year.