How to tell if your solar panels are working
A system can underperform for months before anyone notices. Here's what yours should make, and how to check.
Compare what the system actually made with what it should make for your city and month. The monitoring app or inverter display shows kWh per day and month; the table below shows typical output for a 7 kW system. A drop well below the same month last year, zero output on a sunny day, or an error light on the inverter means it's time to call the installer.
What a 7 kW system should make, by month
| City | Jan, kWh | Apr, kWh | Jul, kWh | Oct, kWh | Year, kWh |
|---|---|---|---|---|---|
| Tucson, AZ | 889 | 1,204 | 1,043 | 1,036 | 12,516 |
| Surprise, AZ | 819 | 1,197 | 1,134 | 1,008 | 12,495 |
| Peoria, AZ | 847 | 1,197 | 1,127 | 994 | 12,397 |
| Phoenix, AZ | 826 | 1,190 | 1,106 | 994 | 12,285 |
| Glendale, AZ | 805 | 1,197 | 1,120 | 1,001 | 12,278 |
| Chandler, AZ | 819 | 1,183 | 1,099 | 1,008 | 12,271 |
| Tempe, AZ | 826 | 1,197 | 1,099 | 994 | 12,264 |
| Gilbert, AZ | 819 | 1,190 | 1,120 | 1,008 | 12,250 |
| Scottsdale, AZ | 798 | 1,176 | 1,092 | 1,001 | 12,215 |
| Chula Vista, CA | 833 | 1,120 | 1,190 | 1,015 | 12,096 |
| San Diego, CA | 812 | 1,113 | 1,190 | 959 | 12,012 |
| Oceanside, CA | 784 | 1,113 | 1,183 | 987 | 11,886 |
| Bakersfield, CA | 546 | 1,099 | 1,232 | 980 | 11,788 |
| Carlsbad, CA | 805 | 1,099 | 1,162 | 903 | 11,683 |
| Clovis, CA | 581 | 1,085 | 1,253 | 938 | 11,613 |
| Fresno, CA | 525 | 1,071 | 1,253 | 938 | 11,578 |
| San Jose, CA | 560 | 1,036 | 1,295 | 945 | 11,368 |
| San Antonio, TX | 714 | 910 | 1,057 | 903 | 10,521 |
| Austin, TX | 707 | 945 | 1,057 | 861 | 10,381 |
| Toms River, NJ | 546 | 952 | 1,015 | 714 | 9,632 |
| New York, NY | 574 | 812 | 1,043 | 749 | 9,471 |
| Elizabeth, NJ | 532 | 910 | 952 | 714 | 9,317 |
| Yonkers, NY | 539 | 777 | 1,001 | 707 | 9,226 |
NREL PVWatts for each city: fixed roof mount, 20° tilt, facing south, 14% losses. East- or west-facing roofs make less: which direction panels should face.
Five checks
- Monitoring app. Look at daily kWh on a clear day. Zero at noon means something is off.
- Inverter light or display. Green or "producing" is normal; red, orange or an error code is not. Write the code down for the installer.
- Same month last year. Weather varies, but output shouldn't fall much more than panels age, about 0.5% a year (how long panels last).
- Your utility bill. Exported kWh and credits should appear; if they stop, the system or meter may be off.
- Look at the array from the ground. New shade, heavy dirt or damage after a storm.
Common causes of low output
- A tripped breaker or inverter fault.
- New shade from trees or buildings.
- Dirt, pollen or snow: whether cleaning pays.
- A failed panel, optimizer or microinverter.
- Hail damage you can't see: hail and solar panels.
Run your own numbers
Enter your ZIP and bill to see what a system should make and save where you live.
Keep reading
- How much electricity a solar panel produces — Daily, monthly and yearly output per kW and per 400 W panel, city by city.
- How long solar panels last — Lifespan, how much output drops each year, and what a 7 kW system still makes in year 25 in each city.
- How to clean solar panels — Whether cleaning pays, what a dry season costs in lost power, and how to clean or clear snow safely.
Installer records by city: solar companies in Phoenix, solar companies in Tucson, solar companies in San Antonio, solar companies in Austin, solar companies in San Diego, solar companies in Fresno, solar companies in Chandler, solar companies in Scottsdale, solar companies in Gilbert, solar companies in Glendale, solar companies in Tempe, solar companies in Peoria, solar companies in Surprise, solar companies in San Jose, solar companies in Bakersfield, solar companies in Clovis, solar companies in Chula Vista, solar companies in Oceanside, solar companies in Carlsbad, solar companies in Toms River, solar companies in New York, solar companies in Elizabeth, solar companies in Yonkers.
Updated 2026-09-22.