Discuss Panel Performance Loss over Lifetime, reflect in k/Wh/ROI figures. in the Solar PV Forum | Solar Panels Forum area at ElectriciansForums.net

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EPiSolar

I'm just trying to get some clarity on the above. We currently develop EPiSOLAR, software for people involved in Solar PV sales. At the moment we don't include any figures for panel degradation over lifetime, I've been in contact with MCS who have referred me to RECC who have been unable so far to enlighten me as to whether we should include a percentage degradation over lifetime.
We're keen for our software to comply with all requirement as set out by MCS and RECC so our users also comply.
I would appreciate feedback on this and an idea of realistic degradation over time.
We are aware that this will differ between manfacturers and that it is unlikely to be linear year on year.
Any advice greatly appreciated.
 
Need to refer to datasheets for each panel as it varies between brands. 0.5-0.8% annual degradation would seem reasonable as an average but it's not easy to measure. Some panels may degrade a bit more in the first year but if they are positive tolerance, that would make them about the same power as on the badge.
 
None of the standards expressly mention including panel degradation in the calculation of system performance. Anyone at MCS should have been able to tell you that off the top of their head.

See:
MCS MIS 3002 section 4.3 http://www.microgenerationcertification.org/images/MIS 3002 Issue 3.1 Solar PV 2013 02 22.pdf
The PV Guide section 3.7 http://www.microgenerationcertification.org/images/PV Book ELECTRONIC.pdf
RECC Consumer Code section 5.3 Consumer Code - Scheme - Renewable Energy Consumer Code (RECC)
RECC guide http://www.recc.org.uk/pdf/guidance-on-the-presentation-of-performance-estimates.pdf (I think this is out-of-date)

The RECC Consumer Code section 5.3 does say:
take account of predicted variations from the calculated output, for example, to allow for shade from buildings, aspect, distance from the measurement location, variations in fuel moisture and quality, and any other factors that apply);
which could be interpreted to include panel degradation as 'any other factors' if you wanted it to.
 
Since the panel manufacturers are supposed to warrant the degradation as part of the MCS approval for the panels, in our ROI calculations we always include a 1% compounded degradation per year, so after 25 years the output is 78.57% of that at the beginning.

Although some panel manufacturers warrant a flat degradation, others do a stepped one, meaning that immediately after install you could lose 10% and then 10 years later lose another 10% (80% of original output) so each panel is different. So, to be precise in that instance for year 2 you should reduce the output and hence return by 10%, keep it flat for nine years and then drop it by a further 10%.

As whinmoor has said since almost all the panels we provide come with a +ve tolerance on the output, by taking a compounded 1% figure and ending up after 25 years at 78.57% we believe that we are offering a conservative figure to our customers. We don't tailor it for specific panels.

Why 25 years not 20? We don't include FiT or export after 20 years (of course some people could well be selling export till then on the 'open market', especially if they have ended up with smart meters) the panels will however continue to offer the savings on expenditure at least for their warranted output period.
 
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Thank you for the replies, we're considering what to do next!!
We were asked by a customer who felt that by showing degradation between panels, their customer would see a clearer argument for choosing a more expensive panel over a cheaper one.
I had asked both MCS and RECC about this but they couldn't give a straight answer. I work on the sales side but I'm looking into things in depth to ensure we are up to speed and able to produce a product that does everything it should.
I've come across a fair amount of grey area's so far!!
 
all panels degrade over time to some extent, so it's obviously misleading to run 20 year performance estimates that make no allowance at all for this fact.

The grey area should be what level of degradation should be allowed for, personally I think it's safest to stick with manufacturers guarantees, although I can see an argument that the average degradation rate will be significantly better than the warranty as the manufacturers will need a decent margin of error to avoid ending up paying out on the guarantee.
 
The panel degradation that the manufactures claim is for the guarantee only. They should be higher than reality to protect themselves against claims and the step in output is just for claims. The real degradation depends on too many factors to be able to precise so I would use 1% per year cumulative and state that on the performance estimate. manufacturers I have spoked to have said that the degradation can be much lower than this, it depends on the quality of the backing sheet, location, installation and maintenance; like everything in life I guess.
 
Panels which remain functional seem to average only 0.2% to 0.5% loss per year over a couple of decades.

But I suppose the handful of panels which fail completely might drop that average to what seems to be a commonly-accepted 1% per year if they don't get noticed (they may not be noticed because the power flows through their bypass diodes so the others continue to function almost normally and variation in weather could mask the loss of a panel).

Accumulation of dirt probably knocks up to 5% off output after the first year, but most panels have a "plus" tolerance of about 10W, such that a 250W panel would be in the 250W-259.9W output range when flash-tested at the factory and therefore the "plus tolerance" probably balances the accumulation of dirt. In other words: a panel labelled 250W may produce up to 259.9W and drops to 240-250W after reaching a dirt equilibrium (a balance between the cleansing of rainfall and the regular accumulation of dust and bird poo).
 
Would this be a pertinent time to flag the issue of PID (potential induced degradation)? Anyone come across this as yet here in the UK? Granted, it tends to be more applicable to larger scale installations....
 
Would this be a pertinent time to flag the issue of PID (potential induced degradation)? Anyone come across this as yet here in the UK? Granted, it tends to be more applicable to larger scale installations....
ye gods man what have you done there's worms escaping from that can all over the thread now.

PID is an issue that's definitely concerning me in terms of something that could come back to bite us at some point if it turns out that any of the panel / inverter combinations we've used are particularly susceptible to it.

Correct me if I'm wrong, but I understand it to mainly be an issue with higher DC string voltages and TL inverters impacting on certain panels... so probably less of an issue for domestic, but potentially a major one for commercial installs where all of ours have been run at maybe 6-700V operating voltages using TL inverters, so really it's a bit of a waiting game to see if any of the panels we used do end up being impacted by it.

I understand that SMA have got an add on unit for their tri-powers that's supposed to rectify the situation to some degree at least.

Think I might need to start properly monitoring the generation figures, and particularly the peak output levels on some of our systems to see if there is any evidence of any issues emerging.

I suspect it might well be an insurance job if it turns out that one of our main panels is affected.
 
Haha! My apologies, don't panic!! Difficult to provide a definitive response/answer in a few sentences, and I'm on my phone rather than laptop, but I wouldn't worry too much as there are a number of factors that need to come into play in order for it to become a concern, and there is evidence out there to show that it is entirely reversible...
 
I was looking into OPID only the other day, and (a bit like Gavin) came to the conclusion that we are just installers and can;t be chemical and physice experts as well. It;s good to know that research is going on put there - the MW plants of course have far more cause to worry about this then we do.

Personally I'm going to let the experts do their research, monitoring etc and then present their findings and solutions - Am I worried about it? Nope, nothing I can do about it!
 
Nope, nothing I can do about it!
well, nowt we can do about systems already up, but we can ensure we're specifying panels that are specifically tested and warranted by the manufacturers (or independently tested ideally) to say that their panels aren't affected by the issue.

That way it'd be down to the manufacturer if there were a problem, or at least we could show that we'd done everything we realistically could do to ensure it wasn't a problem.
 

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