« Back to Home Page

Sign up for the 3p daily dispatch:

Un-Analytics: Google’s Solar Panel Performance Problem

3p Contributor | Friday September 9th, 2011 | 5 Comments

Dirty solar panels dramatically reduce energy capture

By: Dan Auld

Google loves talking about world before analytics — when most website owners knew almost nothing about their sites. Nothing useful, anyway.

That all changed when website analytics came along – a new technology came along that allowed web owners to monitor their site traffic as much as they wanted. Any time they wanted. Web sites suddenly became a business proposition, not just an enthusiasm for a few hobbyists.

Google Analytics was created in 2005 with the acquisition of Urchin (an earlier type of analytics software). Flash forward to 2007, when Google got into the solar business and opened a 1.65 megawatt photovoltaic power array. The largest commercial system in the world at the time.

Just like web sites before Analytics, Google would soon learn how little it actually knew about its solar array.

After its panels were up for 15 months, Google cleaned them (as in, wiped dirt off) and documented its efforts in a report called “Getting the most energy out of Google’s solar panels.”

On several sections of its array, solar energy output doubled after the cleaning. Eight months later, energy output went up 37 percent after another cleaning. But here comes the money graph:

It would be difficult to detect manufacturer defects or accidental damage by data analysis alone, unless the damage impacts more than ~20% of the solar panels on a given building. Example: There have been few occasions when some of the solar panels were damaged by delivery trucks accidentally hitting the support beams that hold up the solar panels.

Since these accidents did not damage a sizable portion of the solar panels, the damage went undetected for a while. Losing 50 percent of your power is real money, even for Google.

“Just like the web prior to Analytics, Google had to admit it really did not know what was happening in its array — because it had no way to monitor when good panels went bad,” said Mark Yarbrourgh, a city councilman in Perris, California who pioneered the use of solar in public buildings. “But neither does anyone else. Arrays malfunction and no one knows because they do not use monitors at the panel level.”

Unmonitored, solar panels go bad in all sorts of ways. Panels degrade anywhere from 0.5% to 9.5% a year in efficiency, depending on the manufacturer, says Sandia Laboratories in a study for the Department of Energy.

How will you know what your panels will do? Warranty Week Magazine says you won’t. Not really:

“and yes, it really is guesswork.”

Dirt plays even more havoc. If not dirt, a bird dropping, or a baseball, or a golfball, or a rock, or a squirrel chewing a wire, or a Texas oak thick with pollen, or heat on the roof, or poor soldering. Or a shadow — all worse than you think, says the National Renewable Energy Laboratories:

“ The reduction in power from shading half of one cell is equivalent to removing a cell active area 36 times the shadow’s actual size.”

“One bird, one truck of dirt, one flowering tree can destroy your solar production, and you would not know for a long time,” Yarbrough said. “Welcome to the Christmas Tree Effect: Hurt the panel a little, hurt production a lot. It is amazing how many people put up solar for great reasons, but really do not watch their systems. As a result, a lot of people lose a lot of money because many, many systems are not producing the power its owners were promised. And few know.”

“If your solar array produces a megawatt of power, that means it is composed of 3000 to 5000 panels,” said Ray Burgess, CEO of Solar Power Technologies. “If some panels go bad, you need panel level monitoring to find the bad panels. But most systems monitor power at the system level, but as Google found out, that is that useful for detecting catastrophic failure, but not much else.”

Thus the need for small wireless monitors throughout the array.

“Now that we have cost effective monitors from a company in Austin, that is going to change the world, just like Google Analytics.”

Leading the solar monitor business is Burgess and Solar Power Technologies of Austin, Texas. The company is introducing monitors and other devices to give solar array owners unprecedented control over their panels. If you have 3500 panels and a few start breaking, you better have something better than “guesswork” to optimize your array. Says Burgess,

“As we travel the country talking to panel owners about their systems, we are constantly amazed at how many systems that are producing power far below their capacity, and some not producing power at all. Monitors on the panels can change that and let you know what is really happening with your system. And where it is happening. Saving system owners thousands of dollars a month.”

Just like Google Analytics.

[Image Credit Dave Dugdale, Flickr]


▼▼▼      5 Comments     ▼▼▼

Newsletter Signup
  • Rob Bryan

    I doubt the future of solar installation design is in strings. I think it will most likely be micro inverters (at least for residential an dsmall commercial). The microinverter converts the output of each panel to AC at the panel. A decrease in output of one panel does not affect the performance of the rest of the array. Each panel can be monitored individually through a web based monitoring service. Here is one that we are probably using in a new installation- http://enphase.com/
    Some pretty cool technology. Available now to you and me.

  • pete oesterle ve3hoh/w3

    Each panel can be monitored by reading its individual output current with an ammeter probe inline with that panel’s output. That reading can be compared to it’s immediate neighbour’s current using comparative output current graphing techniques to see what the difference is between panels.
    It can be a wiring mess sampling every panel’s output. To get a solar array , you need a lot of panels that are comprised of a lot of individual cells.
    It could turn out that one of those cells in one of those panels could be bad.
    How accurate and how localized do you want the data?
    It can be done.
    Find tha bad panel with low or diminishing current and replace it.

  • http://www.learningdslrvideo.com Dave Dugdale

    I am so glad that you liked my Flickr photo so much that you included it on this page.

    Dan, I enjoy when people use my photos that I work hard on, but as I noted on Flickr below each photo I let people use my photos on the condition that they provide me credit to my learningdslrvideo.com site.

    Please add my link when you can.

    • Jen Boynton

      Hi Dave, I’m the one that selected the photo. Sorry I missed your caveat when I chose it; I’ll update the link right away. Thanks for making your photos available for reuse! We really appreciate it.

  • JonathanRCole

    Another important point to remember is that designing solar arrays in large fields without adequate access for easy cleaning or with only dangerous access possibilities means that expensive cleaning techniques are required. With cleaning best practiced three or four times a year, that can add considerable expense to a PV system over the long haul. Installers that assure their customers that panels are “self-cleaning” are perpetrating a fraud on the purchaser.