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  • Question about Solar Panel Degradation over time

    Most of the solar panel manufactures warranty their panels for a couple of decades and list the output as being 80% or greater. I think its pretty common knowledge that the panels lose a certain amount of capacity every year, maybe something like 0.7% to 1% or so.

    What I'd like to know is if this degradation is a flat rate across the board or if there are environmental variables that come into play. Will solar panels in Florida degrade at the same rate as panels in Michigan? In other words, does environmental operating temperature have any affect?

    Does the 0.7% to 1% degradation happen evenly over 20+ years or is there some kind of curve where maybe they do most of their degrading in the first 10 years and then flatten our or something?

    Anyone know?

  • #2
    Short answer is no one knows much about it and data seems to be scarce.

    A bigger question no one talks about is how to verify performance in the case of a performance warranty claim, and, who pays for any likely testing to verify such a claim. Think about it: Your panel warranty is, say, 80 % at 20 years. You watch you output carefully, but don't know much about solar radiation or weather variability. But, you think after 10 years of keeping an eye on output, your array is at say 88 %, or > 1%/yr. So, you file a performance warranty claim. First question is: How do you know what your array's performance is ?And, what verifiable proof do you have to back up your statements ? The proof better be pretty solid, starting with testing you've done and a history of actual available solar radiation at the array's site. Next question: Is it all panels or just a few ? Do you even know ? Anyway, 20 years isn't up yet.


    What seems a matter of some common sense that may not be true is it's likely that 20 year old panels still on a wrapped pallet in a warehouse will probably perform better that identical panels that have been sitting on a roof for 20 years, but much more than that is hard to speculate about.

    What's likely is that, unless some abrupt failure occurs, it's next to impossible for Joe Homeowner to know how his array's performance is changing and harder to quantify.

    Fortunately, most quality solar equipment usually exceeds warranty requirements.

    Add: Most panel warranties state a certain extra 1st year loss of up to 5 % or so, but most of the time a lot of that is covered by a certain amount of conservativeness in the STC rating.
    Last edited by J.P.M.; 01-09-2018, 07:25 PM.

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    • #3
      There are some catches and what you may think is covered is not likely covered.

      Last thing you want to do is buy from a manufacture like SP or any other manufacture who's core biz is solar panels and renewable energy. Reason is very simple, most have already gone out of biz and their warranties are not worth the paper it is printed on. Companies like SP revenues are negative and bleeding cash. So if you are going to buy pick a manufacture like Kyocera, Panasonic, LG and other large companies that have been around a long time and solar is only a small fraction of their biz. Those guys will be around for a long time to honor warranties.

      As for the actual warranties, the devil is in the details. Example Kyocera has an excellent warranty, but very limited. Like all the warranty only applies to the original owner. So if you bought a home with solar, the warranty is void and worthless. Kyocera has a 10 year limited warranty from defects and failure. Excluded are cracks in the glass, and storm damage. You pay for all labor and shipping cost.

      Kyocera 24 Year Power Limited is very limited. 1st year is 97% and complete replacement cost. After 1 year is .7% to year 24. Here is the catch. Kyocera has the sole discretion using their own test criteria to determine if power output has fallen below warranty standards.

      Just about every manufacture has the same warranty full of loopholes. Bottom line is you are likely going to pay for the replacement cost if the company is still in biz. Most of the manufactures are Chi-Com. Most of the good good manufactures that will be around are Japanese and South Korea with a rare German and US manufacture here and there.
      MSEE, PE

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      • #4

        I guess counting on the company to remain in business for the warranty is one way of looking at it, but it wasn't my way.. not so much anyhow. I bought SolarWorld SW270 panels and paid 61 cents per watt for them. So long as my panels last ~3 years, they will have paid for themselves. My system as a whole has a 4.9 year payback so the balance was in wiring, permits, inverter and ground mount hardware.

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        • #5
          Something to think about: Unless it is sitting somewhere that stays cold, your inverter's electrolytic capacitors will fade out long before your panels do.

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          • #6
            Originally posted by BackwoodsEE View Post
            Something to think about: Unless it is sitting somewhere that stays cold, your inverter's electrolytic capacitors will fade out long before your panels do.
            Not all inverters have electrolytic capacitors though.
            OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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            • #7
              Originally posted by Murby View Post
              I guess counting on the company to remain in business for the warranty is one way of looking at it, but it wasn't my way.. not so much anyhow. I bought SolarWorld SW270 panels and paid 61 cents per watt for them. So long as my panels last ~3 years, they will have paid for themselves. My system as a whole has a 4.9 year payback so the balance was in wiring, permits, inverter and ground mount hardware.
              I hope you bought 3 or 4 extra panels as spare parts.......much better strategy than depending on any panel performance warranty.

              Shipping costs alone to send non-performing panels to a hopefully still in business manufacturer for testing would be a few times over the cost of a replacement panel. You absorb the shipping cost. As stated many times......solar panel warranties are not worth the paper they are written on.

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              • #8
                Originally posted by DanS26 View Post

                I hope you bought 3 or 4 extra panels as spare parts.......much better strategy than depending on any panel performance warranty.

                Shipping costs alone to send non-performing panels to a hopefully still in business manufacturer for testing would be a few times over the cost of a replacement panel. You absorb the shipping cost. As stated many times......solar panel warranties are not worth the paper they are written on.
                I have 20 identical spare panels sitting in a Faraday cage in my basement. Also have a Radian 8048 and Flexmax chargers in with them.

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                • #9
                  Originally posted by Murby View Post

                  I have 20 identical spare panels sitting in a Faraday cage in my basement.
                  So we will be asking you every couple years, to bring some out and run a comparison. Now I am wondering, if
                  degradation would show up primarily as lowered Vmp, or lowered Imp? Affects how to run the test.

                  Anybody been checking Vmp vs temp over some years? Bruce Roe

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                  • #10
                    Originally posted by Murby View Post
                    I have 20 identical spare panels sitting in a Faraday cage in my basement. Also have a Radian 8048 and Flexmax chargers in with them.
                    I'd do a yearly swap out of the inverter & controller, to spread the aging across the units and to keep the electrolytic caps formed. (and to make sure some infant failure is weeded out while warranty is effective)

                    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                    solar: http://tinyurl.com/LMR-Solar
                    gen: http://tinyurl.com/LMR-Lister

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                    • #11
                      Originally posted by Murby View Post
                      I guess counting on the company to remain in business for the warranty is one way of looking at it, but it wasn't my way.. not so much anyhow. I bought SolarWorld SW270 panels and paid 61 cents per watt for them. So long as my panels last ~3 years, they will have paid for themselves. My system as a whole has a 4.9 year payback so the balance was in wiring, permits, inverter and ground mount hardware.
                      Paid for themselves against what ? If the goal is to maximixe return, comparing a breakeven point via payback analysis against alternate ways to meet a demand may be seen as a bit shortsighted. If my current means of meeting a demand is VERY expensive, my "payback time", however that's calculated, will always be shorter against the proposed method than if I had a less expensive delivery means to compare the proposed system to. That's where comparison of alternatives comes in. For example, will I be more money ahead in, say, 10 years by insulating, or offsetting those insulation savings with some other task ? And of those tasks, which of them is, in a SWAG, is the least expensive in long term use of assets ?

                      I appreciate DIY, and that the savings that can be realized can be pretty good, but it's usually more cost effective to not use some commodity like electricity or reduce the need for it, than to get more of it.

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                      • #12
                        Originally posted by bcroe View Post

                        So we will be asking you every couple years, to bring some out and run a comparison. Now I am wondering, if
                        degradation would show up primarily as lowered Vmp, or lowered Imp? Affects how to run the test.

                        Anybody been checking Vmp vs temp over some years? Bruce Roe
                        That might not be a bad idea for me to check that in such a way.

                        Comment


                        • #13
                          Originally posted by Mike90250 View Post

                          I'd do a yearly swap out of the inverter & controller, to spread the aging across the units and to keep the electrolytic caps formed. (and to make sure some infant failure is weeded out while warranty is effective)
                          Does an SMA SB6.0 US40 inverter have any electrolytic caps? And what is it about these capacitors that make them go bad just sitting in storage?

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                          • #14
                            Originally posted by J.P.M. View Post

                            Paid for themselves against what ? If the goal is to maximixe return, comparing a breakeven point via payback analysis against alternate ways to meet a demand may be seen as a bit shortsighted. If my current means of meeting a demand is VERY expensive, my "payback time", however that's calculated, will always be shorter against the proposed method than if I had a less expensive delivery means to compare the proposed system to. That's where comparison of alternatives comes in. For example, will I be more money ahead in, say, 10 years by insulating, or offsetting those insulation savings with some other task ? And of those tasks, which of them is, in a SWAG, is the least expensive in long term use of assets ?

                            I appreciate DIY, and that the savings that can be realized can be pretty good, but it's usually more cost effective to not use some commodity like electricity or reduce the need for it, than to get more of it.
                            Paid for themselves against what I would have paid the power company for electricity if I didn't have them.

                            Next in line are my home's windows. We just got through a cold spell where daytime temps hovered in the single digits and night time temps were -10

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                            • #15
                              Originally posted by Murby View Post

                              Does an SMA SB6.0 US40 inverter have any electrolytic caps? And what is it about these capacitors that make them go bad just sitting in storage?
                              I suspect most string inverters use electrolytics. There's really no substitute when it comes to sponging up large amounts of current for more than a few microseconds at a time. Polymer film caps are also used, and have long lifetimes and great ESR. But they are very expensive and bulky for capacitances in the thousands of microfarads. (Sorry I didn't capitalize your name, Mr. Faraday. Nobody does when you stick "micro" in front of it.)

                              The life-limiter for electrolytics, and also the key to huge capacitances, is the liquid electrolyte. It simply evaporates and eventually leaves the aluminum "plate" (actually a foil roll) high and dry. That's why 50-year old tube audio equipment has an atrocious hum; the power supply filtering isn't working anymore because there's no capacitance left to absorb the ripple current.

                              The hotter the capacitor is, the faster the electrolyte evaporates. It doesn't take many vapor molecules steaming out from a bath that is 15 degrees C below the water boiling point to slip out past the best seals you can possibly implement before it really adds up over 20+ years. Or, put better, really subtracts out. Like batteries, keeping them cool will really help.

                              As noted above, not all inverters use electrolytics. Most microinverters probably use film capacitors, which is good considering how hot those little boxes get sitting right behind their toasty solar panels.

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