Original modeled solar data
How peak sun hours change the number of solar panels you need
Peak sun hours can nearly cut the panel count in half. Under Watt My Roof's assumptions, a home using 1,000 kWh per month needs about 35 panels at three peak sun hours, but about 18 panels at six peak sun hours.
Published August 8, 2026
Panel output by peak sun hours
This table isolates one variable: sunlight. It assumes one 400-watt panel and a 0.80 performance factor, meaning 20% is reserved for heat, wiring, inverter and other real-world losses.
| Peak sun hours/day | Annual output per 400 W panel | Panels for 1,000 kWh/month | System size |
|---|---|---|---|
| 3.0 | 350 kWh/year | 35 panels | 14.0 kW |
| 3.5 | 409 kWh/year | 30 panels | 12.0 kW |
| 4.0 | 467 kWh/year | 26 panels | 10.4 kW |
| 4.5 | 526 kWh/year | 23 panels | 9.2 kW |
| 5.0 | 584 kWh/year | 21 panels | 8.4 kW |
| 5.5 | 642 kWh/year | 19 panels | 7.6 kW |
| 6.0 | 701 kWh/year | 18 panels | 7.2 kW |
Solar panels needed by monthly kWh and peak sun hours
The dataset below uses 400-watt panels, 20% total system losses and a 100% electricity offset. These are modeled calculator outputs, not roof designs or guaranteed production estimates.
| Monthly use | 3.0 sun hrs | 3.5 sun hrs | 4.0 sun hrs | 4.5 sun hrs | 5.0 sun hrs | 5.5 sun hrs | 6.0 sun hrs |
|---|---|---|---|---|---|---|---|
| 500 kWh | 18 | 15 | 13 | 12 | 11 | 10 | 9 |
| 750 kWh | 26 | 23 | 20 | 18 | 16 | 15 | 13 |
| 1,000 kWh | 35 | 30 | 26 | 23 | 21 | 19 | 18 |
| 1,250 kWh | 43 | 37 | 33 | 29 | 26 | 24 | 22 |
| 1,500 kWh | 52 | 45 | 39 | 35 | 31 | 29 | 26 |
| 2,000 kWh | 69 | 59 | 52 | 46 | 42 | 38 | 35 |
Download the modeled data as CSV: solar-panels-by-peak-sun-hours.csv.
The formula behind the table
Watt My Roof uses the same transparent production formula throughout the calculator and guide pages. The only variable changing in this dataset is peak sun hours.
Why this matters before asking for quotes
A solar quote that ignores your local production assumptions can look cleaner than it really is. Two homes using the same 1,000 kWh per month do not necessarily need the same system. A low-sun or shaded property may need more panels, a larger system, or a different design goal.
This page is built from visible calculator assumptions instead of a hidden lead form. It is meant to help you understand sizing logic before speaking with installers, not replace a professional site survey.
FAQ
What are peak sun hours?
Peak sun hours estimate the daily solar energy available as an equivalent number of full-strength sun hours. They are not the same as daylight hours. A location with five peak sun hours may have many more hours of daylight, but only about five hours worth of full solar production.
How many solar panels do I need at five peak sun hours?
Using 400-watt panels, 20% system losses and 100% offset, a home using 1,000 kWh per month needs about 21 solar panels at five peak sun hours per day. A 500 kWh home needs about 11 panels, while a 2,000 kWh home needs about 42 panels.
Why do low-sun locations need more panels?
Each panel produces less annual electricity when peak sun hours are lower. Under this model, a 400-watt panel at three peak sun hours produces about 350 kWh per year, while the same panel at six peak sun hours produces about 701 kWh per year.
Should I use peak sun hours or my electric bill first?
Use both. Your electric bill tells you how much energy the system needs to replace, and peak sun hours estimate how much energy each panel can produce in your location.
This is original modeled data from Watt My Roof's calculator assumptions: monthly electricity use, panel wattage, peak sun hours, system losses and desired offset. See the methodology page and the 1,000 kWh solar data page for related outputs.