My System was installed Sep 21, 2016 and has operated nearly continually up to the present. I have only had to replace three optimizers over that time frame. I specified the system components and my son installed the system. Here is the degradation curve for the system over the past nine years. I have tried to adjust the data for weather conditions to remove that extraneous variability. The first six months of 2022 was unusually dry and probably accounts for the high production. The first half of 2023 were unusually wet and probably cause the low production that year. The shaded area are the 95% confidence intervals for the data.
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Interesting that you brought this subject up. I have been pondering about panel degradation as well and was looking at ways to arrive at this prediction. I am looking at the yearly production as you have had but looking at efficiencies since this takes account of yearly variations and as efficiencies are at the per panel calculation, I think this would be a possible option. To determine degradation, I think using the highest year efficiency as a denominator and using the yearly efficiency as the numerator, a ratio or percentage can be arrived from which (1) can be subtracted giving the percent degradation. For instance: my highest efficiency is 5.113 kWh/kW in 2018. 2025 has an efficiency of 4.637 kWh/kW. The ratio is then 4.637/5.113 = 0.9069. 0.9069 -1.0 = 9.3% degradation from 2018 through 2025. 9.3% degradation over 8 years is about 1.16% per year.
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Hi @lwsmiser. Thanks very much for providing the information on the system performance decline. My own system was installed in August 2018 and I have been paying close attention to its degradation. I was wondering though how the actual decline compares to the stated performance of the panels that you chose? About the same? Slightly better or slightly worse? I purchased LG panels at the time and they were at the costlier end of the market however they also had good specs and a much longer performance warranty that filled me with some confidence.
Regards Grannos
It matches the value stated by the manufacturer…0.05 to 0.10 %/year.
I used GROK to run the evaluation and asked it to normalize the data based on the annual weather effects to improve the estimate. Southern California does have a varying rainfall pattern over nine years. That removes part of the variability of the annual capture of solar energy. The two outliers offset each other so I was pleased with the results.
The main thrust seems that degradation is very small and over 20 to 25 year lifespan is fairly minor. What wonderful things they are and so reliable. Ours is 15 years old now and I can’t spot any noticeable changes in performance and only once did a cable connector need replacing - took 5 minutes.
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That is where I started but I asked GROK to consider how much rainfall was recorded for my area each year and to adjust the lost production due to clouds. In that way some of the variability was removed to give a better estimate of performance degradation. The results were almost exactly what the manufacturer indicated on the panel performance, 0.1% per year.