Wash Solar Panels?

Solar panel systems are intended to be largely maintenance-free, especially here in the Northwest where regular rains provide natural cleaning.

But we haven't had much rain the last few weeks, and I noticed some bird droppings on our panels, so I was curious if a manual cleaning would make much of a difference in power output.

This morning (before 9:00 AM), I did a quick hose spray and towel wipe down. I noticed dirt collects a little more at the bottom edge of each panel.

Now we can compare the energy output of two consecutive days with the same clear, sunny weather and similar high temperatures:

Dirty: 20.98 KWH (July 24, high 78°F)

Clean: 21.70 KWH (July 25, high 80°F)

The cleaner panels appear to eke out a few more electrons (+3%), restoring production to the same level as the brand-new system last year.

First Year Statistics

Our solar panel system exceeded expectations for its first year, even with all the dreary cloudy weather we've had the past several months!

• Predicted annual production: 3450 KWH*
• Actual first year production: 3561 KWH

We surpassed the annual forecast 8 days early (on June 28).

For the year, we produced about 47% of the electricity we used. However, due to the Washington State production incentive, our utility power bills are now zero.

Here's a look at the average KWH produced per day:

Highest production day: 22.23 KWH on Friday, July 10, 2009. (Weather: sunny; high temperature: 76 degrees F)

*Annual production forecast of 3450 KWH was calculated by our solar consultant in May 2009 based on the number of solar panels, panel rated wattage output, inverter/system efficiency, site shade analysis, roof pitch, latitudinal location, orientation to south, and typical seasonal climate conditions for the region (cloud cover, temperature, etc.).