bkp_duke
Well-Known Member
The link I posted, it's an actual scientific study (actually, a group of studies, which holds more weight than a single study would).
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How much do systems degrade? A friend's system seems like 33% in ten years.
- Thread starter Southpasfan
- Start date
The link I posted, it's an actual scientific study (actually, a group of studies, which holds more weight than a single study would).
charlesj
Active Member
Here you go. With a little search here found the link posted on the forum:
No, that is not a peer reviewed paper but it is actually instrumented.
bkp_duke
Well-Known Member
Here's the problem with that - solar panels run MUCH more efficiently when they are cool, than when they are hot.
He should have taken temp measurements of the panel surface, cleaned them, and then continued the video until the panels heated back up to the same temp as the pre-clean temp.
Solar panel temp has a MASSIVELY larger influence on panel efficiency than does dirt. If you read this thread, others have pointed that out as well.
EDIT - and I don't know about others, but I don't have those kinds of issues with bird poop. Just dust. His cleaning of the poop was arguably the majority of the increase of his output
EDIT 2 - regarding efficiency of power with panel temperature - if you look over the last 30 seconds of his video, you can see as the panels are heating up, they are slowly but consistently dropping in output (and no, he's not shading them with his hand or anything like that).
I downloaded my solar production data from Enphase Enlighten (my monitoring service provider) and plotted the results for the 6 full years that I've had my system. The 6th year produced only 80.12% of the first full year. These are cells made in Taiwan and assembled into modules in the USA. They were installed in October 2012.
bkp_duke
Well-Known Member
Be interesting to know exactly what modules you are running.
There was a study done about degradation rates of different PV panels, about 5 years ago. The "High Quality" group showed an average of 1.2% loss per year, while all modules overall showed 1.7% loss per year.
https://sf-asset-manager.s3.amazonaws.com/95679/29/19855.pdf (page 4 of this report)
Lots of good data and explanation in that report.
Sunpower always advertises that their panel degradation rate is the best in the industry, until a few years ago there was little 3rd party data to support that, but it looks like NREL's study did back up that claim in 2018 with a 0.2% average loss per year noted on 264 installations, over an 8 year test period.
SunPower Closes Year with Industry's Lowest Solar Panel Degradation Rate, Delivering More Reliable Electricity to Customers Over Time
No, I don't work for Sunpower or own their stock. Just an observation that all panels may not be made equally.
charlesj
Active Member
Interesting. My data doesn't show that kind of consistent production drops after the first year. My year 3 was higher than yr 2 and year 5 was higher than year 2 as well but a bit lower than year 3.. Will see how this year turns out for me.
And I also have a chart for each month and they are all over the map comparing the same month over the years
Panels definitely see a lower efficiency rate depending on the type of dirt. I've been involved with cleaning of panels and when you get heavy Lichen, Bat poo, Bird poo etc.... these things will coat the panels.
There was a crew here in Queensland who were performing thermal imaging on panels to see the quality and current efficiency on used panels.
Pretty sure it was these guys Off Grid Solar System
Maybe email them for some data on the topic
There was a crew here in Queensland who were performing thermal imaging on panels to see the quality and current efficiency on used panels.
Pretty sure it was these guys Off Grid Solar System
Maybe email them for some data on the topic
A given month year over year has significant variation because of weather. The reason I put the bar chart of the annual total is that it shows the trend more clearly, having averaged out weather variation. Early on, I used to clean the panels. However, the effect was so short lived that it wasn't worth it.
I've never looked at the data this way before. This is actually motivating me to more strongly consider re-powering the array. What I mean by that is replacing the panels 1:1 with higher power panels of the same size and cell count. This will not only increase the rated wattage, but overcome the degradation too.
I've thought about this, too, but would need to change the racking or reduce the number of panels. My panels are only about 14% efficient, new panels are 19-20% quite a bit better (35-40% more power!). Would like to add 3-5 kW more solar, so have thought moving the existing array to a different part of the roof, and adding a new separate array, probably while redoing the roof at the same time, too.
If I repower mine, I would want to stay under the 1.0kW increase rule for staying on NEM 1.0. I would DIY it to use exactly the same number of panels, microinverters and rack mounting. The alternative is doing nothing or adding a completely new array on the available SE facing roof area, kissing NEM 1.0 goodbye.
charlesj
Active Member
Yep, the same month over the years shows how weather patterns change over the years. May was my best month for the 1st 3 May years.
Year 4 was bad, 7th month in that year. This year May may come back to #1 slot, too early to tell. First year May produced 717kWh. This may was 691kWh, a 3% drop from year 1.
My annual production doesn't show a good enough degradation pattern year to year in 7 full years of production.
If you re-power will you keep your present inverter? If so, you might get more clipping, produce closer to full capacity and extend this capability.
I have considered doing this with a few of my panels that are more affected by shading. The only problem now is finding a black panel around 270W and a 1.8" frame to match existing frames and hardware. Kyocera had one but no longer in business.
charlesj
Active Member
I don't have a fancy graph such as miimura posted but the numbers in sequence by production in mWh and year. Cannot correlate this to
degradation that happens but how weather patterns are changing overall:
2013 6.68 mWh
2015 6.33 mWh
2018 6.27 mWh
2014 6.24 mWh
2017 6.18 mWh
2016 6.08 mWh
2019 6.06 mWh
Much easier to make heads out of this than my earlier post.
The very 1st year of operation, 2012 went on line midday 30 Mar.
degradation that happens but how weather patterns are changing overall:
2013 6.68 mWh
2015 6.33 mWh
2018 6.27 mWh
2014 6.24 mWh
2017 6.18 mWh
2016 6.08 mWh
2019 6.06 mWh
Much easier to make heads out of this than my earlier post.
The very 1st year of operation, 2012 went on line midday 30 Mar.
FWIW, my install is a bit of an anomaly because the panels are mounted nearly flat (my mistake, I did the install myself) so dirt accumulates on the bottom row of panels. I just went up on the roof today to clean them (I just dust with a "California car duster", easier than dragging a hose up there), and power is up about 10% compared to yesterday at the same time of day. But as I said, this is an anomaly, your typical roof install is mounted steep enough that you shoudn't see more than 5% unless you live in a very dry and dusty area (central California comes to mind, have seen some really dirty solar panels out there).
If I used a hose, power would probably go up another few percent.
Hi miimura,
FWIW, I live in the same town as you, so to rule out any local or regional weather variations from year to year, might be useful for me to share my system data. Also my system is different size and orientation than yours I'm sure, so can only compare relative year-on-year, month-on-month changes. BTW mine is 4kw array with microinverters, but I lose some morning and afternoon production due to shading.
My system is about one year younger, so I don't have 2013 data. Mine shows similar higher production in 2014 March to June, compared to other years, as yours does, for example.
My degradation seems to be about 1% per year, so over six years I've gone from 5.0MwH to 4.7MwH. Your degradation, if it is that, does seem a lot more pronounced than mine. Could it also be that your panels overperformed the first two years, and are now settling to a slower, more expected degradation?
At this point I have to assume that my panels are truly degrading, especially in light of your system for comparison. I may also download the individual inverter production data and see if there are any that are significantly deviating from the average of the system. I should also look up what the warranted degradation is. Panels currently sold by the same company have a 83.1% 25 year linear production warranty. Clearly my slope is not up to that level of warranty.
charlesj
Active Member
I would not count out that last year was a bad weather year even in your area. Mine was the worst in 7 full years of operation and is last so far.
I did notice that 2018 your system is healing, not degrading.
My 2018 also exceeded 2016 and 2017 production. I must have washed it a lot in 2018.
Down here and where I live, fog is an issue and varies.
In 2015 August was my best month for production while in 2012-2014 it was in 5th place for each year. .
I am still positing that weather changes, monthly and yearly, makes it very difficult to gauge system degradation from production data we have.
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