"The Rain Will Clean Them." Here's Why That Doesn't Work in Bakersfield.

By Miguel, Elite Pressure Wash Services · Bakersfield, CA

It's the first thing almost every solar owner says: "Don't the panels just get cleaned when it rains?"

It makes sense. Rain washes your car off. It should wash your panels off too.

In a lot of places, that's close enough to true. In Bakersfield, it's the reason a lot of panels sit dirty for most of the year.

Bakersfield barely gets rain when it matters

Bakersfield averages around 6 inches of rain a year. Most of it falls between November and April.

That means from late spring through fall, which is exactly when the sun is strongest and your panels should be producing the most, there's usually no rain at all. Months of dust pile up with nothing to rinse them off.

So even if rain did clean panels perfectly, it shows up at the wrong time of year.

And when it does rain, it doesn't do what you think

Here's what actually happens on a Bakersfield roof:

• Dew glues the dust down. On cool nights, a thin layer of moisture forms on the glass. It mixes with the dust and dries into a film that sticks. By the time rain shows up, it's not loose dust anymore.
• Light rain makes mud. A short sprinkle wets that film and then evaporates. A lot of the time it just leaves streaks of dried mud behind.
• Rain only gets part of it. Research on dirty panels has found rain usually brings back only part of the lost output, not all of it. The stuck-on layer stays.
• Bird droppings don't rinse off. Rain does almost nothing to droppings that have baked on in the sun.

That's why panels around here can go from black to tan by the end of summer, even after a few rainy days in between.

How to tell if rain is doing the job on yours

You don't have to take our word for it. After the next good rain, check two things:

1. Look at the panels a few days later. From an upstairs window or across the street. If you still see a haze, streaks, or spots, the rain didn't get it.
2. Check your app. Compare a sunny day before the rain to a sunny day after. If production barely moved, the rain didn't fix the problem.

If both look the same after the rain, your panels need more than weather.

What actually gets them clean

A real cleaning uses a soft brush and clean water to break that film loose and rinse it away, without scratching the glass. It gets the baked-on droppings and the dust in the corners where the frame meets the glass, which is right where rain leaves the most behind.

The bottom line

Rain helps a little. But in Bakersfield it shows up at the wrong time of year, and it leaves the stuck-on layer behind. If your panels look hazy a week after a storm, the rain isn't cleaning them. It's just moving the dirt around.