Solar Panel Output Calculator
Daily and monthly kWh plus bill savings from system size and sun hours.
What it does
Solar production follows one multiplication: panel kilowatts times peak sun hours, minus system losses. Peak sun hours compress the whole day into equivalent full noon hours, which lets one number describe deserts and cloudy coasts alike.
The tool above takes system size, local sun hours, loss share, and electricity rate. It returns daily and monthly kilowatt hours with the bill savings.
Roof direction and tilt move real output around the estimate. South facing roofs near latitude tilt perform best in the northern hemisphere, while east west splits trade noon peaks for longer mornings and evenings.
Net metering rules decide the money as much as the sun. Full retail credit for exported power pays far better than wholesale rates, so the same system earns differently across utilities.
How to use
- Enter the system size in kW DC from the quote.
- Enter local peak sun hours as a yearly average.
- Keep 15% losses unless the quote states measured ones.
- Compare monthly kWh against twelve months of bills, not one.
Formula
- kW
- DC nameplate size of the array.
- sun hours
- Peak equivalent hours, not daylight hours.
- losses
- Heat, soiling, shade, wiring, and inverter share.
Installers quote DC size while inverters cap AC output, so clipping shaves a little off oversized arrays at noon. Yearly sun hour maps smooth seasons into one average.
Worked example
Example: 5 kW system, 5 sun hours, 15% losses, $0.17 rate
Midsize home array in good sun at average US rates.
- Daily: 5 x 5 x 0.85 = 21.25 kWh, shown as 21.3.
- Monthly: 21.25 x 30 = 637.5, shown as 638 kWh.
- Share of a 900 kWh home: 637.5 / 900 = about 71%.
- Savings: 637.5 x $0.17 = $108.38 a month.
Reference table
| System | 4 sun hours | 5 sun hours | 6 sun hours |
|---|---|---|---|
| 4 kW | 408 | 510 | 612 |
| 6 kW | 612 | 765 | 918 |
| 8 kW | 816 | 1020 | 1224 |
| 10 kW | 1020 | 1275 | 1530 |
Limits
- Yearly average math. Winter months run well below it.
- Roof angle, direction, and shade need site detail.
- Rate plans and export credits decide money, not physics.
- Panel wear near half a percent a year excluded.
Common mistakes
- Sizing off one summer bill instead of the yearly total.
- Ignoring shade that moves across seasons.
- Comparing DC quotes to AC consumption directly.
- Forgetting export rates differ from import rates.
- Skipping roof age. Old roofs want replacement first.
Try it yourself
Quick checks. Answers sit tucked under each question.
6 kW at 5 sun hours, 10% losses. Daily?
6 x 5 x 0.90 = 27 kWh a day.
Monthly savings at $0.20?
27 x 30 = 810 kWh. Then 810 x $0.20 = $162.
Questions
What is a peak sun hour?
One hour of 1000 W per m2 sun. Five peak hours can span ten daylight hours of weaker sun.
How big a system covers my bill?
Divide yearly kWh by local sun hours times 365 times 0.85. A 10,800 kWh home at 5 hours needs about 7 kW.
Do panels work on cloudy days?
Yes at reduced output, roughly a quarter to half. Snow cover blocks until cleared.
What do system losses include?
Heat, dirt, shade, wiring, inverter, and mismatch. Fifteen percent is typical.
How long do panels last?
Twenty five to thirty years of warrantied output, fading about half a percent yearly.
Is net metering required?
No, but it decides payback. Full credit states pay back years faster.