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  • What makes a product high quality?  Obviously, a products' ability to perform its underlying function properly is the number one factor, and depending on what the product is, other aspects like aesthetics, ease-of-use, and brand determine how we perceive quality.  But when you really consider products that people perceive as "high-quality", the perceptions stem not just from how well the product works in the short term, but more from how well the product performs in the long run, its lifespan.  That's why, much like a car or a laptop, a solar panels' ability to perform better for longer largely determines its quality, as the longer it performs its function, the better return on investment it provides.  So a major question when considering what panels to install is then, what brand of panel is the most durable, and lasts the longest?

  • What Determines a Solar Panels Durability?

    When we talk about the durability of a product, we are generally referring to its ability to stand up to elements that are expected to degrade its performance.  So with solar panels, there are many potential elements that work against the performance of the panels: rain, wind, heat, humidity, temperature fluctuation, impact from trees, etc.  A good solar panel then is designed to resist these elements in order to maintain optimum performance.  
     

    How is the resistance to each factor determined?

    In order to meet certification standards, solar panel manufacturers must subject their panels to a series of tests in order to ensure that they are up to code for basic durability requirements.  The basic tests are as follows: the Damp Heat test (measures resistance to humidity), Thermal Cycling (resistance to temperature fluctuations), and Dynamic Loading (resistance to weight or pressure).  These are industry standard tests that every solar panel is subject to, so we can actually determine which company makes the most resistant panel by looking at the outcome of the tests.
     

    The Damp Heat Test (humidity)

    The standard certification test for the effects of moisture and humidity on panel efficiency is called the Damp Heat 1000 (DH1000) test, in which the panel is placed in a climate controlled chamber set at 185⁰F and 85% relative humidity for 1000+ hours, and the amount of power production degeneration is measured at different times (1,000 hours, 2,000 hours etc.). The test is meant to simulate environmental conditions in a very humid place like Miami, FL or Bangkok, Thailand.
     
    A Fraunhöfer Institute study in 2010 found that the majority of well-made conventional panels maintained at least 80% production until around 2,000 hours of exposure, where after the production dropped significantly.  On the contrary, SunPower modules maintained close to 100% efficiency well beyond 6,000 hours and even into 8,000 hours of exposure.   The significant difference in degradation is due to the current carrying copper layer in SunPower panels, which are equipped with more than enough bandwidth to carry the current, proving a large design safety factor.

  • The Thermal Cycling Test (temperature fluctuations)

    The standard industry certification test for panel resistance against temperature swings is the thermal cycling test, which places the product in a climate controlled chamber which swings from -40⁰C to 85⁰C 200 times. In a comparison of internal data and public data published about other companies results, SunPower found that the differences in thermal cycling results varied greatly from manufacturer to manufacturer.
     
    While all companies passed the certification standard of 200 fluctuations, one company had a 10% power loss at just 400 fluctuations, and then down another 25% after 500 fluctuations.  Two other companies had lost around 15% production at 1000 fluctuations, while the majority lost around 5-8% at that time.  SunPower however, lost only 2% production, even at 2,000 fluctuations, clearly dominating the competition.  This is because SunPower panels use a fundamentally different cell connection system than that of conventional panels: a stamped plated copper interconnect with three cell connections per side and integrated strain relief between cells.

  • The Dynamic Loading Test

    A major part of SunPower's design qualification is the Dynamic Loading Test, which alternately applies 50lbs of pressure per square foot to one side of a solar panel, then the other.  This 50lbs is supposed to simulate a 90mph wind, about the wind speed of a category 1 hurricane.  The point of this test is to measure a panels' ability to maintain efficiency through a lifetime of shipping, moving, and exposure to weather and impacts.   
     
    SunPower did a side-by-side comparison of the results of the Dynamic Loading Test when performed on SunPower panels and conventional panels.  After 1,000 cycles, the conventional panel had several broken cells in the middle and had lost about 4% production.  The shunt resistance, a key indicator of panel performance and integrity, had dropped 25%.  The SunPower panel, however, displayed no broken cells and immeasurable power loss in the same test.  This is due to SunPowers highly resistant build and strength.

  • So who makes the Most Durable Solar Panel?

    A major part of SunPower's design qualification is the Dynamic Loading Test, which alternately applies 50lbs of pressure per square foot to one side of a solar panel, then the other.  This 50lbs is supposed to simulate a 90mph wind, about the wind speed of a category 1 hurricane.  The point of this test is to measure a panels' ability to maintain efficiency through a lifetime of shipping, moving, and exposure to weather and impacts.   
     
    SunPower did a side-by-side comparison of the results of the Dynamic Loading Test when performed on SunPower panels and conventional panels.  After 1,000 cycles, the conventional panel had several broken cells in the middle and had lost about 4% production.  The shunt resistance, a key indicator of panel performance and integrity, had dropped 25%.  The SunPower panel, however, displayed no broken cells and immeasurable power loss in the same test.  This is due to SunPowers highly resistant build and strength.

  • About the Author

    Michael Powers

    http://www.terrawatts.com/

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    Michael is one of the founding partners of Stellar Solar. In 2001, he helped launch The Home Depot’s national solar energy program which is now offering home solar through hundreds of stores in nearly a dozen states. He is a writer and marketing professional with over 30 years’ experience in the fields of energy, market intelligence and leadership training. He currently serves as treasurer and board member of Global Energy Network Institute (GENI), a San Diego-based non-governmental organization that advocates linking renewable energy resources around the world using electricity transmission.