baker array output

Do solar panels produce less as they age? 

Or more to the point, will solar panels lose power over time in western Washington?  Possibly not, according to what we have observed with PV systems at our home.  We have three arrays and for this article we’ll be looking at the oldest one.

Laboratory testing and field measurements of solar panels by the the Jet Propulsion Laboratory and National Renewable Energy Laboratory show that solar panel output can lose 0.4% - 0.7% relative to the previous year.  It is important to note that it’s not the same as absolute degradation of the original output per year, which would be faster.   That said, we have not observed any appreciable decrease in output from the panels at our house.

In September 2005 we installed (32) 190 watt panels made by Sanyo Electric (now Panasonic), model HIP 190BA3, on our south-facing roof at a 30 degree slope.  There is a hill and trees to the east of our house, so our panels receive an average of 83% of the total possible sun per year in Seattle.   3 years later we added one more panel for a total of (33) giving the array a DC power rating of 6,270 watts.  At 83% solar resource, the expected output is 5,985 kWh per year.

In late April 2012 we began monitoring the array with an eGauge so we have continuous data from that time that show the output varying somewhat from year-to-year, but not decreasing overall.  This array has only been cleaned once, and several years ago a 57 foot maple tree fell on our roof, bending one of the panels.  Since it was still working after this event, we have left it bent, rather than risk breaking it trying to straighten it out.  So we haven’t given any special attention to these panels, typical of most of our customers.

Although this is not a scientific study, you could conclude that it is possible that solar panels in Seattle never degrade more than the increase in sun due to climate change, or that they are degrading so little as to not be noticeable. Not all photovoltaic panels are created equal, so this is testiment to the technology that Sanyo developed (the HIT cell) and to their manufacturing abilities, and there are other brands, such as SunPower that are showing this kind of steady output as well.  This is great news for solar energy system owners.  A properly designed, manufactured, and installed solar panel can provide the same amount of energy from the sun for decades. 

If you want to see how solar technology can benefit you, click here.

About the author


Started Puget Sound Solar in 2001 with 30 years of construction contracting experience, and a desire to turn Seattle on to solar energy. Achieving NABCEP certification in 2004, Jeremy believes that our customers often follow a path similar to the one he took, starting out with solar daydreaming, then progressing to education on the subject, and eventually leading to action. In addition to leading the company he also does some teaching and speaking engagements about various aspects of solar energy, and experiments relentlessly with various solar, energy efficiency, and electric vehicle projects.

Jeremy Smithson

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