How much electricity does a solar panel produce?
Output depends on where the roof is, not only on the panel. Here's what one kW and one 400 W panel make in real cities.
One kW of panels makes 1,483–1,788 kWh a year in the cities I cover, or 4.1–4.9 kWh a day on average (NREL PVWatts). A single 400 W panel makes about 593–715 kWh a year, 1.6–2.0 kWh a day.
Output by city
| City | kWh a year per kW | kWh a day per kW | kWh a year per 400 W panel | kWh a day per panel | 7 kW system, kWh a month |
|---|---|---|---|---|---|
| Phoenix, AZ | 1,755 | 4.8 | 702 | 1.9 | 1,024 |
| Tucson, AZ | 1,788 | 4.9 | 715 | 2.0 | 1,043 |
| San Antonio, TX | 1,503 | 4.1 | 601 | 1.6 | 877 |
| Austin, TX | 1,483 | 4.1 | 593 | 1.6 | 865 |
| San Diego, CA | 1,716 | 4.7 | 686 | 1.9 | 1,001 |
| Fresno, CA | 1,654 | 4.5 | 662 | 1.8 | 965 |
NREL PVWatts v8 for the city center: fixed roof mount, south-facing, 20° tilt, 14% system losses. Daily figures are yearly averages.
Output by month
kWh per kW of panels, by month:
| City | Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Phoenix | 118 | 123 | 151 | 170 | 178 | 173 | 158 | 155 | 147 | 142 | 124 | 117 |
| Tucson | 127 | 128 | 165 | 172 | 184 | 172 | 149 | 150 | 150 | 148 | 123 | 119 |
| San Antonio | 102 | 96 | 123 | 130 | 140 | 141 | 151 | 152 | 128 | 129 | 115 | 98 |
| Austin | 101 | 94 | 119 | 135 | 139 | 141 | 151 | 154 | 131 | 123 | 98 | 99 |
| San Diego | 116 | 114 | 143 | 159 | 156 | 168 | 170 | 170 | 152 | 137 | 118 | 113 |
| Fresno | 75 | 102 | 141 | 153 | 177 | 180 | 179 | 173 | 154 | 134 | 105 | 82 |
How to estimate your own system
- Take the kWh a year per kW for your area from the table, or the calculator for any ZIP.
- Multiply by your system size in kW.
- Take off more if the roof is shaded or faces east or west.
A panel's watt rating is measured under standard test conditions; real output on a roof is lower, which is what the loss assumption above covers.
Check the production in your quote
Divide the quote's first-year production by its system size. If the result is well above the figure for your area, ask what orientation, shading and losses the installer assumed: how to check a solar quote.
Run your own numbers
Enter your ZIP and bill: I'll use NREL production for your ZIP to size a system.
Keep reading
- How much solar panels save — Yearly and monthly savings by utility, and why they change from month to month.
- How many solar panels you need — Size a system from your electric use and local sunshine, in four steps.
- Solar on cloudy days, at night and in winter — How much output drops by season in each city, and what happens after dark or in an outage.
Updated 2026-09-15.