Should you spring clean your solar panels?

Ever since we assembled a 1.6 MW solar panel installation at our headquarters in Mountain View in 2007, we've been wondering, "Does cleaning the solar panels make them more effective?" We thought it might, but we needed to be sure. So we analyzed the mountains of data that we collect about the energy that these panels produce — after rain, after cleaning and at different times of the year.

We have two different sets of solar panels on our campus — completely flat ones installed on carports, and rooftop ones that are tilted.

Since the carport solar panels have no tilt, rain doesn't do a good job of rinsing off the dirt they collect. (Also, our carports are situated across from a sand field, which doesn't help the situation.) We cleaned these panels for the first time after they had been in operation for 15 months, and their energy output doubled overnight. When we cleaned them again eight months later, their output instantly increased by 36 percent. In fact, we found that cleaning these panels is the #1 way to maximize the energy they produce. As a result, we've added the carport solar panels to our spring cleaning checklist.

The rooftop solar panels are a different story. Our data indicates that rain does a sufficient job of cleaning the tilted solar panels. Some dirt does accumulate in the corners, but the resulting reduction in energy output is fairly small — and cleaning tilted panels does not significantly increase their energy production. So for now, we'll let Mother Nature take care of cleaning our rooftop panels.

Accumulated dirt in the corners of a rooftop solar panel

We've also been crunching numbers on dollars-and-cents; the more energy our panels produce, the sooner we'll be paid back by our solar investment. Our analysis now predicts that Google's system will pay for itself in about six and a half years, which is even better than we initially expected.

If you want to learn more about our solar study, check out these slides showing the effects that seasonality, tilt, dirt, particulate matter, rain and cleaning have on Google's solar energy output. We hope you solar panel owners out there can tailor our analysis to the specifics of your own installation to produce some extra energy of your own!

Posted by Winnie Lam, Senior Product Manager

Search Options now on Google Images

A few months ago when we announced the Search Options panel, we promised that you would soon see similar functionality across our other search properties. Today we are rolling out Search Options for Google Images.

This new feature offers quick access to existing tools, including search by color and image type. Color search will find images that are only in color or only in black and white, or even images that contain a specific color, such as red, pink, or green. Type search is a great way to narrow down your results if you are looking for a specific kind of image, such as a photo, clip art, line drawing or face.

We've also revamped our size search. In addition to choosing from commonly searched-for sizes, now you can search for an exact image size or any image larger than a certain size. You can find images of practically any size, including 70 megapixels or more.



The new layout makes it faster and easier to combine and toggle between options. It also makes it easier for us to add additional image search options in the future, so keep your eyes peeled. Just click "Show options..." in the blue bar on the search results page to try out any of these tools.

Posted by Ken Dauber, Software Engineer, and Nate Smith, Associate Product Manager