Do panels degrade over time?

[electricthot]

I have been led to believe that solar panels weaken over time. I have some panels in my array that are over 20 years old. I tried to test them for current output, and got very low readings. They are 53 watt panels, and I got less than .5 amps from them. When I test them, should I test them in circuit, or should they be isolated from the system? Also, when I tested them, my charge controller was in float mode--would this reduce output readings?

[J.P.M.]

I have been led to believe that solar panels weaken over time. I have some panels in my array that are over 20 years old. I tried to test them for current output, and got very low readings. They are 53 watt panels, and I got less than .5 amps from them. When I test them, should I test them in circuit, or should they be isolated from the system? Also, when I tested them, my charge controller was in float mode--would this reduce output readings?

The short circuit current of a panel is about proportional to the irradiance. Panels have been rated for a long time at 1,000 W/m^2 normal irradiance and at a panel temp. of 25 C. I'd find out what the Isc was on a new panel. Max. likely normal full sun irradiance under a clear sky is also about 1,000W/m^2. Assuming a panel can be moved, wait for a clear, cool and preferably windy day, point the panel directly at the sun around solar noon and measure the current. Divide that reading by the Isc you found and divide the result by ~ .85 or so. That'll give a real SWAG of how much a panel has degraded. Expect to be within maybe 10-15 %, +/- some.

[Mike90250]

..... Expect to be within maybe 10-15 %, +/- some.

Wow, I was going to propose about 2-4% drop per year, for poly or mono panels, 15% year for amorphous panels.

[J.P.M.]

Wow, I was going to propose about 2-4% drop per year, for poly or mono panels, 15% year for amorphous panels.

Sorry for being less than clear. Assuming a mono panel, that 10 - 15% was the estimate on the tolerance of the panel performance degradation number. So, if a 20 yr. old mono panel had a new & clean STC Isc of, say, 0.80 A, and it measured out at, say, 0.50 A or so, the performance degradation, after accounting for (very roughly) an operating temp. of ~ 55 - 60 C. or so at ~~ 1,000 W/m^2 POA irradiance,, goofs & giggles, etc., might be something like:

[0.80 - (0.5/(1-(58-25)*.005))]/[0.80] = (0.80- 0.60)./ 0.80 = 0.20/0.80) = 0.25, or 25 % loss of the original performance, +/- very approximately 10 or 15 % or so of that 25 % number, or maybe 25% +/- 3% or 4 % or so.

[littleharbor]

I was just reading an article about Kyocera solar panels yesterday. They found the average output degradation of their modules after 20 years was like 8.6%

[J.P.M.]

I was just reading an article about Kyocera solar panels yesterday. They found the average output degradation of their modules after 20 years was like 8.6%

That sounds reasonable, but probably not without some bias.

[littleharbor]

Found the article from Kyocera. Output degradation was actually tested at 8.3%. Pretty close for my feeble memory.

http://www.kyocera.eu/index/news/previous_news/news_archive_detail.L3NvbGFyX2VsZWN0cmljX3N5c3RlbXMvbmV3cy8yMDEyL0tZT0NFUkFfU29sYXJfTW9kdWxlc19UZXN0ZWRfdG9fU2hvd19Pbmx5X01pbmltYWxfUG93ZXJfT3V0cHV0X0RlZ3JhZGF0aW9uX0FmdGVyXzIwX1llYXJzX2luX3RoZV9GaWVsZA~~.html

[Guest]

Does most of the panel degradation happen in the first 2 years?

[peakbagger]

If I remember correctlymy Sharp polycrystaline panels came with a warning that they were overrated to account for "burn in" which was a very short term higher output when initially installed. The extra output rapidly faded away after few months exposure.

The interesting thing with my poly panels is the grain irregularities seem to be more apparent as the panels age. I have also noticed this on my Evergreens which are sort of halfway between mono and amorphous. I don't think it impacts the output but its definitely noticeable.

[littleharbor]

I'd be curious to see what peoples amorphous panels are outputting after 15 - 20 years, if they are still working at all.

[J.P.M.]

Does most of the panel degradation happen in the first 2 years?

Often and probably.

How much will vary with the panel, the weather and other things. Check your, or anyone's panel spec sheet. While not the primary purpose of a +/- tolerance on panel nominal output, or rating, a lot of burn in loss is probably covered by that tolerance (as are, perhaps, more than a few warranty claims).

Some product info will speak to first year deterioration, sometimes called a "burn in allowance", or other names. Most mfgs. know and account for it, often in that +/- tolerance. Like a lot of power equipment, the performance is often somewhat understated by a bit (but not too much).

I estimate my panels lost ~ 2-3% of their startup performance over the first year or so of operation. My educated guess is that the panels original "new & clean" performance was something like ~ 4% or so higher than the published nominal spec sheet STC value of 327 W, with a +5%/-3% tolerance.

On 52 months of daily operation and data, after burn in and annual degradation, I SWAG the array to be still putting out something like 1 % or so more on an annual basis than the original, nominal, new and clean performance would calc. that annual output to be.

Also, as best as I can give an educated guess, the annual performance degradation for my array's panels is something a bit less than the Sunpower published degradation - at ~ 0.3%/yr. or so, maybe a bit more, vs. the spec sheet value of 0.4%/yr.

Your results will vary, as will mine going forward.

[DanS26]

Found the article from Kyocera. Output degradation was actually tested at 8.3%. Pretty close for my feeble memory.

http://www.kyocera.eu/index/news/pre...GaWVsZA~~.html

I have 72 Kyocera panels. 36 of the 235 black and 36 of the 245 blue. I use a .71% degradation factor per year per advice from Kyocera for the model panels installed.

First set of panels installed in 2011 and I have compared actual output to expected output and the mean average is very close to expected output using the .71% factor. Weather could be a factor but as I build up more data over time the more confidence I have that the .71% is accurate.

[littleharbor]

Is this 0.71% degradation factor based on the STC or the NOCT ?

[J.P.M.]

I have 72 Kyocera panels. 36 of the 235 black and 36 of the 245 blue. I use a .71% degradation factor per year per advice from Kyocera for the model panels installed.

First set of panels installed in 2011 and I have compared actual output to expected output and the mean average is very close to expected output using the .71% factor. Weather could be a factor but as I build up more data over time the more confidence I have that the .71% is accurate.

Dan: Any SWAG on 1st yr. degradation ?

Thanx.

[DanS26]

Dan: Any SWAG on 1st yr. degradation ?

Thanx.

The two arrays are a matched set...the only difference is the panel rating. Both oriented due south and at the exact tilt. The blue array was installed exactly two years after the black array. After adjusting for the difference in power output (ie 235 vs 245 watts per panel) I can now calculate the degradation between the two arrays due to the 24 month difference in the age of the panels. I can do this because each array is connect to matching Fronius string inverters.

Using a TED Pro to monitor the output of each array I can make a comparison and calculate the degradation based on age of the panels.

Based on my experience the first year I did see a greater than .71% factor, but in subsequent years the difference has hovered right around the expected .71% difference. I can measure this difference real time based on power output (ie kW) and also by time...day, month, year & installation to date (ie kWh).

The difference to date is within .05% of the expected .71% factor