Why Your Solar Panels Make Less Power in July, and How Much of That You Can Fix

By Miguel, Elite Pressure Wash Services · Bakersfield, CA

You'd think July would be your best month. Longest days. Strongest sun. Not a cloud in the sky.

So why aren't your panels producing as much as you'd expect?

Two reasons. One you can't do anything about. The other you can.

Reason #1: Heat makes panels less efficient

This surprises people. Solar panels don't love heat. They love light.

Panels are tested at 77°F. For every degree hotter they get, they lose a little bit of output. On a Bakersfield roof in July, panel surfaces can get well over 140°F. At that temperature, even a perfectly clean panel is producing noticeably less than it would on a cool, sunny day.

That's physics. Nobody can clean it away, and anyone who tells you otherwise is overselling.

Reason #2: Summer is also the dirtiest time of year

Here's the part people miss. The hottest months in Bakersfield are also the driest. By July, your panels have usually gone months without real rain, collecting dust off the fields, construction, and the wind.

So in summer you're getting hit twice: once by the heat, and once by the dirt. And it's all happening right when your AC is running the hardest.

The heat you can't fix. The dirt you can.

How to tell which one is costing you

1. Compare July to last July. Heat hits every summer about the same. If this July is noticeably lower than last July on similar sunny days, the heat isn't the reason. Something else is.
2. Look at the panels. From an upstairs window or across the street. Dark and glossy means the heat is most of what you're seeing. Tan, hazy, or spotted means dirt is adding to it.
3. Watch a cool, clear day. On a cooler sunny day in spring or fall, a clean system should bounce back strong. If it doesn't, the panels need attention.

One thing not to do

Don't try to cool your panels down with the hose on a hot afternoon. Cold water on hot glass can crack it. If you clean them yourself, do it first thing in the morning while they're cool.

The bottom line

Some summer loss is just the Bakersfield heat, and nobody can change that. But a lot of owners blame the heat for a loss that's really dirt. Compare your numbers year over year, and if they're down, the fix is on your roof.