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#4476723 - 08/01/17 05:02 PM Solar panel degredation
OVERKILL Offline


Registered: 04/28/08
Posts: 36422
Loc: Ontario, Canada
This topic has been touched on a pile of times in numerous threads but we haven't really had a formal discussion about the phenomena.

We are I believe, all aware that solar cells produce less and less over time. The amount of degradation however, does it vary between brands? Do all of the high quality cells degrade at the same rate? Do newer cells degrade less than older technology cells?

Our local solar farm is 10MW and 200 acres and is cited by our PUC as producing 14,300MWh of electricity a year. This facility had 1/3rd of its panels replaced recently because they were underperforming significantly. However, there's no mention of the incremental decline in performance of these panels as the facility ages.

Cue example B:

The Webberville 35MW solar farm in Texas

Originally Posted By: Wikipedia
The 35 MW Webberville Solar Farm, located in Webberville, Texas, is a photovoltaic array in Texas. It is made up of 127,728 Trina Solar solar panels[1] mounted on single-axis trackers, covers an area of 380 acres (150 ha), and was built at a cost of $250 million.[2] It is expected to generate 61 GWh in the first year of operation,[3] and 1.4 billion kWh over its 25 year life. Operation began on December 20, 2011, while ribbon cutting by Austin's mayor, Lee Leffingwell, was held on January 6, 2012.[4] The project was constructed by RES Americas, who will operate the plant for five years. SunEdison in 2012 sold the plant to MetLife and Longsol Holdings, but will operate the plant for 20 years upon the expiration of the responsibilities of RES Americas.


Actual generation output of the facility has been as follows:



With the first year actually besting the target of 61GWh, but there has been a steady decline in output since that first year, with 2016's output putting us at 44GWh. Now, how much of this is due to weather and exposure and how much of it is due to the degradation of the panels? I don't know. December of 2012 seems to stand out as an anomaly at 7GWh with subsequent Decembers hovering around 3GWh. Averaged over the 5 years of operation however, the general trend is a reduction in output of 5GWh a year. It will be interesting to see, going forward, if that trend is maintained. This makes the claimed output of the facility over its lifetime questionable.

To expand further: the claimed 25 year output is 1,400GWh. Based on 61GWh a year, we end up with 1,525GWh, so obviously there is some degradation factored into that number, as the average based on the aforementioned figure is 56GWh a year. However, looking at the trend in our table above, that number appears to be highly optimistic. Our average presently is already <56GWh and if the trend continues, that figure will steadily decline.

Now, using our above provided figures, if the facility produces 1.4 billion kWh in 25 years, and had a installation cost of 250 million, this requires $0.178/kWh for 25 years to break even. So it would be interesting to see what kind of rate they are being paid for their generation. This is actually more than the break-even cost on my local example, which is paid a handsome $0.42/kWh.

This also, I believe, demonstrates that solar panel pricing still has a significant way to go in terms of unit cost, not even factoring in the degradation over time, and further still if we do.

If the above is typical, then this also touches on the issue of output for a given capacity of solar generation going the opposite direction of demand. While demand, particularly with the electrification of the transportation industry should be trending upward, actual output of these installs will be going the other way. This is not the case with other modes of generation.
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#4476875 - 08/01/17 07:50 PM Re: Solar panel degredation [Re: OVERKILL]
czbrian Offline


Registered: 04/10/15
Posts: 154
Loc: Houston, TX
The panel manufacturers provide a degradation warranty of around .5% per year so there must have been a defect in those panels. The prices of construction have come down significantly since then as well. Im guessing 250 million can get you at least a 150 MW AC solar farm now in the US based on some recently constructed solar farms my company manages. I dont have any actual figures available on degradation due to the limited time frame.

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#4476880 - 08/01/17 07:52 PM Re: Solar panel degredation [Re: OVERKILL]
madRiver Offline


Registered: 07/11/15
Posts: 3532
Loc: New England
Interesting topic, curious on the obsession on power generation?

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#4476882 - 08/01/17 07:54 PM Re: Solar panel degredation [Re: madRiver]
OVERKILL Offline


Registered: 04/28/08
Posts: 36422
Loc: Ontario, Canada
Originally Posted By: madRiver
Interesting topic, curious on the obsession on power generation?


It's a hobby of mine.
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#4476895 - 08/01/17 08:03 PM Re: Solar panel degredation [Re: madRiver]
Garak Offline


Registered: 12/05/09
Posts: 24574
Loc: Regina, Saskatchewan, Canada
Originally Posted By: madRiver
Interesting topic, curious on the obsession on power generation?

If you paid Ontario electrical rates, you'd be obsessed, too.
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#4476902 - 08/01/17 08:09 PM Re: Solar panel degredation [Re: Garak]
OVERKILL Offline


Registered: 04/28/08
Posts: 36422
Loc: Ontario, Canada
Originally Posted By: Garak
Originally Posted By: madRiver
Interesting topic, curious on the obsession on power generation?

If you paid Ontario electrical rates, you'd be obsessed, too.


LOL! True, that's primarily what spurred my interest.
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#4477000 - 08/01/17 10:09 PM Re: Solar panel degredation [Re: OVERKILL]
JHZR2 Offline



Registered: 12/14/02
Posts: 41767
Loc: New Jersey
A few things Ive not yet come to understand:

1) panels will get dirty, and that slight amount of dirt can affect performance in a minor way, but that minor way can add up.
2) the sun has cycles, and may have varying levels of irradiance (is that the right term?) per year.
3) weather patterns may vary from year to year, and are difficult to normalize against.
4) is there a standard where a light source calibrated to a certain amount of lumens/m2 is used to measure and verify a panel's output? When this is done, is the power converter performance verified too to ensure that isn't the source of loss?
5) power electronics have varying efficiency with temperature, are we sure they are considered for apples to apples assessment?
6) is ambient and panel,temperature the same year by year?
7) is esr of the interconnects verified year after year?

Without all these and more verified and fully understood, it's not clear to me how the panels can be assumed to be degrading nad the definite root cause.

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#4477020 - 08/01/17 10:43 PM Re: Solar panel degradation [Re: JHZR2]
OVERKILL Offline


Registered: 04/28/08
Posts: 36422
Loc: Ontario, Canada
Originally Posted By: JHZR2
A few things Ive not yet come to understand:

1) panels will get dirty, and that slight amount of dirt can affect performance in a minor way, but that minor way can add up.
2) the sun has cycles, and may have varying levels of irradiance (is that the right term?) per year.
3) weather patterns may vary from year to year, and are difficult to normalize against.
4) is there a standard where a light source calibrated to a certain amount of lumens/m2 is used to measure and verify a panel's output? When this is done, is the power converter performance verified too to ensure that isn't the source of loss?
5) power electronics have varying efficiency with temperature, are we sure they are considered for apples to apples assessment?
6) is ambient and panel,temperature the same year by year?
7) is esr of the interconnects verified year after year?

Without all these and more verified and fully understood, it's not clear to me how the panels can be assumed to be degrading nad the definite root cause.


A quick google yielded:

What is the lifespan of a solar panel?

Originally Posted By: Engineering.com
The National Renewable Energy Laboratory (NREL) performed a meta-analysis of studies that examined the long term degradation rates of various PV panels. They found that the 1% per year rule was somewhat pessimistic for panels made prior to the year 2000, and todays panels, with better technology and improved manufacturing techniques, have even more stamina than their predecessors. For monocrystalline silicon, the most commonly used panel for commercial and residential PV, the degradation rate is less than 0.5% for panels made before 2000, and less than 0.4% for panels made after 2000. That means that a panel manufactured today should produce 92% of its original power after 20 years, quite a bit higher than the 80% estimated by the 1% rule.


*snip*

Quote:

What Causes Degradation?
Crystalline silicon modules located in extreme climates showed high degradation rates. For very cold climates, panels subjected to heavy wind and snow loads suffered the most. On the other hand, panels in similar climates that were installed in a facade, eliminating the snow load, had very low rates of degradation. At the other extreme, panels in desert climates exhibited large decreases in production over time - close to 1% per year - mainly due to high levels of UV exposure. Panels in more moderate climates such as the northern United States had degradation rates as low as 0.2% per year. Those panels could retain 96% of their production capabilities after 20 years.


I'm guessing that middle bit may be a contributor in what we are seeing with the panels in Texas.

A far more detailed paper exploring this, being the foundation for the above can be found at the US Department of Energy


Generally it would seem that in more northernly climates that the %0.5 figure cited by another poster is a good rule of thumb, however the study linked from the Department of Energy goes into detail as to why that may not always be the case. It also I believe covers all of your questions with respect to dirtiness, testing protocols, standards, electronics and their degradation, interconnect corrosion, temperature.....etc.

Assuming we use the extremely pessimistic 1% figure, our Texas system should only have degraded by 5% since its install, yielding an overall drop of ~3GWh. So obviously there are other factors in play here to create what appears to be the trend demonstrated in the table.
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#4477111 - 08/02/17 05:53 AM Re: Solar panel degradation [Re: OVERKILL]
PimTac Offline


Registered: 03/04/17
Posts: 4232
Loc: Soviet State of Washington
Just to throw in another angle, besides degradation, how high are the chances for damage to occur to the panels from adverse weather like hail for example? If the cost/value is figured over 25 years, that's long enough to be exposed to many weather events.
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#4477193 - 08/02/17 08:27 AM Re: Solar panel degradation [Re: PimTac]
OVERKILL Offline


Registered: 04/28/08
Posts: 36422
Loc: Ontario, Canada
Originally Posted By: PimTac
Just to throw in another angle, besides degradation, how high are the chances for damage to occur to the panels from adverse weather like hail for example? If the cost/value is figured over 25 years, that's long enough to be exposed to many weather events.


Good point! As touched-on above, severe weather can impact the life of the panels and was a factor in why our local farm needed 1/3rd of its panels replaced from what I recall.
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#4477241 - 08/02/17 09:20 AM Re: Solar panel degradation [Re: OVERKILL]
SeaJay Offline


Registered: 03/05/15
Posts: 1083
Loc: New York City
There are very, very few mechanical items that will operate flawlessly for 25 years without maintenance or repairs at some point in time.

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#4477277 - 08/02/17 09:59 AM Re: Solar panel degradation [Re: SeaJay]
OVERKILL Offline


Registered: 04/28/08
Posts: 36422
Loc: Ontario, Canada
Originally Posted By: SeaJay
There are very, very few mechanical items that will operate flawlessly for 25 years without maintenance or repairs at some point in time.


This is true, which is why the cost per kWh of the installation needs to be considered. If your break-even cost is $0.20/kWh, not including land tax, maintenance, repairs....etc then that's concerning. On the other hand, many wind farms have break-even costs of $0.02-0.03/kWh, so even accounting for repairs, maintenance, land taxes....etc they have the potential to be inexpensive generators (their contracted rates are a whole other subject).

This ties into the OP because that amortization, generally based on the life of the panels (25 years or so) must account for the progressive decline in performance of the installation, which is a rate that, according to what has been linked already, varies depending on a myriad of factors including location, weather, the types of cells, the interconnects.....etc. Given a fixed install price and reasonable exposure, a farm that degrades at 1% a year is going to be significantly more expensive per kWh than one that degrades at 0.2% for example.

The other issue is that most "traditional" generators don't have relatively fixed lifespans for the whole works. If you are doing turbine upgrades on an HE dam, you aren't replacing the entire dam for example.

Ultimately, improvement in panel life expectancy and output as well as significantly lower procurement costs are what are needed, and that seems to be the trend.
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#4477488 - 08/02/17 02:12 PM Re: Solar panel degredation [Re: OVERKILL]
sleddriver Offline


Registered: 02/06/10
Posts: 4599
Loc: Central Texas
Very interesting post OK. That facility isn't too far from here. Austin pols have never met a green project they didn't like, regardless of the cost. They've fallen head-first into many of them. One reason my e-bills are so much higher than fellow BITOGer living in Cedar Park.

Re: Panel Degredation. Rarely mentioned is the fact that optics plays a huge role and I'm not talking about lenses or mirrors, rather transparency. Lay a piece of glass on the ground at a 30 angle here and check it every 2 days. With a simple light meter, you could measure the amount of light passing through at a given time.

Who is in charge of cleaning 127,728 panels on a weekly? monthly? basis? Dust, dirt blow in (even from the middle east) from local farms, dirt roads, traffic. Ever seen how much dirt blows up from a single car driving down a dry, dirt road where it hasn't rained in 3 weeks? Dirty panels don't produce as much electricity.

Re: Weather. They're about 30N of the equator, average rainfall is ~ 33"/yr. Elevation about 500-800' above MSL. Hot & humid climate with large puffy clouds when high pressure is not in place. PV arrays will drop in output as their temp increases, lowering efficiency. 3M experimented in the 80's with water cooled arrays to combat this and heat water. Not sure if this is done anymore.

Point being this location is not high, dry desert like West Tx at all.

The reason no mention has been made re: incremental decline in performance is because it would be embarrassing to the pols who approved it.

Finely, silicon purity & manufacturing. Lots to this, but there's a reason silicon is a semiconductor. The emphasis is on the 'semi-' part. It still has resistance, and power is dissipated through this resistance as heat. Further, we're talking about DC here...not AC. Big difference when it comes to power generation & transmission.

It's also not a battery. Many see PV's far too simply as 'solar-powered-batteries'. Not even close...

Yet another issue is the very, very low-density of the energy source. Not efficient to begin with.

Yet another example of why some ideas don't scale well.
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#4477837 - 08/02/17 10:14 PM Re: Solar panel degradation [Re: OVERKILL]
JHZR2 Offline



Registered: 12/14/02
Posts: 41767
Loc: New Jersey
Originally Posted By: OVERKILL
Originally Posted By: JHZR2


...

Without all these and more verified and fully understood, it's not clear to me how the panels can be assumed to be degrading nad the definite root cause.


...

So obviously there are other factors in play here to create what appears to be the trend demonstrated in the table.


My point exactly. Lots of other phenomena may affect the output, not just the panels....

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#4477862 - 08/02/17 10:43 PM Re: Solar panel degradation [Re: JHZR2]
OVERKILL Offline


Registered: 04/28/08
Posts: 36422
Loc: Ontario, Canada
Originally Posted By: JHZR2
Originally Posted By: OVERKILL
Originally Posted By: JHZR2


...

Without all these and more verified and fully understood, it's not clear to me how the panels can be assumed to be degrading nad the definite root cause.


...

So obviously there are other factors in play here to create what appears to be the trend demonstrated in the table.


My point exactly. Lots of other phenomena may affect the output, not just the panels....


Certainly, but there's what appears to be a trend with the reduction in output if you look at the table. So while degradation may be a factor in this, as another poster pointed out, it would be above the warranty threshold on the panels, so what else is going on? It isn't desirable, that's why I'm interested. Obviously there is a degrading trend in output, and if it isn't from the actual panels themselves losing efficiency, there's something else creating the trend.
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