Connect with us

solar panel power loss

Discussion in 'General Electronics Discussion' started by Johnny5, Sep 21, 2010.

Scroll to continue with content
  1. Johnny5

    Johnny5

    8
    0
    Sep 10, 2010
    Hi! I have 5 kw solar production on the roof, I am only seeing around two thirds max at full sunlight, panels are clean but producing 3.2 kw does anyone know why such losses occur.

    the panels are around thirty feet from inverter dc input is around 300vdc. are there losses due to running 4 conductors in same conduit or is it heat possibly at panels, I was told that it is normal to run at those watts but I wonder if anyone knows if anyone knows why this happens?
     
  2. darkman1969

    darkman1969

    18
    0
    Jun 23, 2010
    3.2Kw from a 5Kw solar system does not seem too bad to me from what i have seen. I am in the planing stage of getting a Solar energy system installed and now know the rating the solar panel makers list is the absolute max power the panel can produce. In the real world, 60-70% of rated power is not bad.

    Regards
     
  3. trobbins

    trobbins

    83
    0
    Jun 15, 2010
    It depends how you are measuring your power. For starters, you may not have 'one sun' insolation conditions, even though you think it is pretty sunny. Yes you loose a bit of power in the dc cables, and in the grid-connect inverter. Also, the pv panels reduce their output as their temperature rises - they can get pretty hot - which is why they are usually mounted where fresh air can cool their rear side. You may also not be at a time in the year, or day, where the panels are perpendicular to the sun. And they may be a bit dusty!

    Ciao, Tim
     
  4. shrtrnd

    shrtrnd

    3,781
    499
    Jan 15, 2010
    Another thing that people don't talk about, probably because it's not politically correct in today's 'go green' mentality; is that solar panels have a limited life expectancy.
    How old are your panels, their output degrades with time. 13 to 15 years is peak efficiency. Considerable degredation after that.
     
  5. Resqueline

    Resqueline

    2,848
    2
    Jul 31, 2009
    As darkman says, unless the inverter is "intelligent" and keeps searching for the maximum power knee point then you get substantially less power than the panel label.
     
  6. trobbins

    trobbins

    83
    0
    Jun 15, 2010
    shrtrnd - crystaline silicon (single and multi) are fine for well past 20yrs for well made panels - amorphous Si continuously degrades but cycles - not sure about more recent Cd tels and others?

    MPPT algorithms are pretty good nowadays - they probably stay within a percent or two of max, as long as the insolation level is constant - otherwise they have a short delay effect if radiation level is bouncing around a lot.
     
  7. shrtrnd

    shrtrnd

    3,781
    499
    Jan 15, 2010
    Hmmm, ok Trobbins, who are these 'well-made' panels?
    I'd like to investigate this.
    I live in the Arizona desert, the sun kills 'em quick here.
    I'd guess they might survive longer in less hostile environments, but not by much.
    I keep reading the technology is getting better, but that's kind of a subjective claim.
    I'd sure like to know who makes 20+ year solar panels that can output anywhere near
    their newly manufactured specs. I want me some.
     
  8. trobbins

    trobbins

    83
    0
    Jun 15, 2010
    Manufacturers back in the 80's were able to get it pretty right (links below), showing an acceptable drop of measured output after 15 yrs. I note BP Solar are claiming 0.4% degradation per annum nowadays - however care is required comparing difference between field and accelerated test results - but I would suggest that those manufacturers using time proven techniques and quality materials would get it right, which may not be the case for all manufacturers. But, a larger percentage of panels are being sold into large PV installations, where warranty is extending out to 20 years.

    uaelani.jeeran.com/uae/PVCAR2.doc
    http://www.telepower.com.au/PVsec96a.PDF
    http://www.telepower.com.au/Solar96.PDF
     
  9. davenn

    davenn Moderator

    13,711
    1,911
    Sep 5, 2009
    I would like to see test evidence for that too

    everything I have read/heard so far indicates a signif falloff in output after 10 years and substantial after 15 yrs

    its one of the big things that puts me off going solar is the huge cost of replacement...
    yopu never get to actually save real money cuz just as you get to that point of money saving after paying for the initial install wham you're buying new panels
    QUOTE....
    9. Discussion
    A comparison of the results of the testing
    programs of the a-Si and the c-Si modules found that
    although the c-Si material is more stable over time, it
    does undergo a loss of power as modules age. A major
    cause of this power loss is degradation of EVA, which
    varied between manufacturing techniques and the
    exposure environments. The average power loss
    approximately 0.7% per annum. This can be modelled
    to a drop of 90% over 15 years [3].
    ENDQUOTE

    So in 15 years time its only putting out 10% of what it did when new CRAP!!

    cheers
    Dave
     
    Last edited: Sep 22, 2010
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
    2,809
    Jan 21, 2010
    0.993^15 = 0.8999

    So a drop TO 90% after 15 years, not a drop OF 90% after 15 years.

    I have had quotes from people promising (actually guaranteeing) 80% after 20 years. The panels are more expensive and they tell me the panels actually put out more than 100% when brand new, so they're under-rating them to extend their rated life.

    80% after 20 years equates to a little more than 1% per annum, so I suspect that those panels are not even using the best quality materials to start with.
     
  11. Johnny5

    Johnny5

    8
    0
    Sep 10, 2010
    The maximum output that ive seen is 4.6 kw after hosing them off. The biggest factor in increased wattage is cooling the panels somehow. I imagine it would extend the life as well.

    I'm getting good insolation due to roof pitch which in my case is perfect right around spring and fall due to angle. The Inverter is a new Sunny Boy I would imagine it monitors max wattage at given power .

    I dont have them but now they have panels with inverters built right in and they match the grid. you just tie into your net meter and watch it spin backwards.I am still curious about losses in dc current. If I find info I will re-post.
     
    Last edited: Sep 22, 2010
  12. trobbins

    trobbins

    83
    0
    Jun 15, 2010
    You can calculate the DC loss if you can determine the average length of cable between the panels in the string, and if you can estimate the MPP current, and if you know the gauge of wire used (I2R).

    The power measurement in the grid inverters has an error tolerance that you have to add in too - SMA have a doc on that aspect.
     
  13. davenn

    davenn Moderator

    13,711
    1,911
    Sep 5, 2009
    no the text says a drop OF 90% over 15 yrs
    quote ... This can be modelled to a drop of 90% over 15 years ... endquote

    how can that be read any other way ?
    Dave
     
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
    2,809
    Jan 21, 2010
    I think it can be read as they don't understand English, or mathematics, or possibly both. :D

    Can you point me to the source of that quote?
     
  15. shrtrnd

    shrtrnd

    3,781
    499
    Jan 15, 2010
    Why do I have a problem believing BP's claims, when they're pushing 'going green' in publicity ads? Looking for government subsities. And what are they going to say after 20 years? Oops, we made a mistake, but oh well, those claims are 20 years old, and we didn't have all the data?
    Actually though. I have been reading claims about the cells getting better, so I'll be looking into them. Arizona heat is probably a worst case scenario (the cell output is greatly diminished, the hotter the cells get).
    A lot of people here got suckered in, buying rooftop sheets with tax breaks. It takes 15 years to get your money back in energy savings, and that's about the time it takes
    before their present efficiency dropped so far as to make them require replacement or removal.
    I'll be checking into this again with newer models. But everything I've seen lately, still makes the cost effectiveness of solar cells for power, a losing proposition.
    Thanks for the input. If trobbins is still out there, I'd be interested in hearing what companies (by name) are putting out the best gear lately.
     
  16. trobbins

    trobbins

    83
    0
    Jun 15, 2010
    Most of the big names have a range of panels - they all know how to make top notch stuff - it's just that you need to sell panels, so they all have a variety of more budget oriented panels - you have to sell to keep in business, and competition drives the price point for sales down. The likes of BP Solar were a major source for the panels in use in Australia telecom and have had huge experience on what ages and deteriorates.

    Davenn, the text is obviously a contextual typo error - if you read the rest of the article you may better appreciate that. There were product from a few manufacturer's tested, some of the panels exhibiting degradation down to the low BP Solar levels talked about nowadays.

    Steve, they understand English, and mathematics, very well. The quote comes from the links I put in earlier.

    Shrtrnd, it is reasonable to extend the economic lifetime of panels out past the 80% rated output timeline, there is often no disadvantage to letting them continue producing power in this mppt age. Like finding 52 matchsticks in a box marked with a quantity of 50, all the produced panels have to exceed their rated levels (aka battery capacity).

    There can also be an aesthetic bias against old panels - it was not unheard of that techo's were replacing 'old looking' panels for new panels after 15-20 years, only to be told to put them back again because they had in fact only degraded to 90 odd %.
     
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
    2,809
    Jan 21, 2010
    I found the quote.

    I will offer another suggestion. They didn't proof-read their paper very well.

    It's pretty obvious from the context that they should have used wording suggesting a drop TO rather than OF that magnitude.

    It also fits in very well with some friends of mine who used ex-telstra solar panels that were removed after 15 years of telstra use and then gave them an additional 15 years or so (maybe longer) of service as their sole electrical power source until their inverter died and they decided to get new panels as well.
     
  18. shrtrnd

    shrtrnd

    3,781
    499
    Jan 15, 2010
    Ok trobbins, I'll have to look into the latest and greatest.
    Hey, Hope Johnny 5 got the answers he wanted.
     
  19. Johnny5

    Johnny5

    8
    0
    Sep 10, 2010
    I got more than expected actually. Funny how davenn thinks how a drop so great is actually acceptable and worth the investment....lol just kidding dave,

    I think Ill just keep a mister going on these suckers and watch stalagmites grow! hmm
     
  20. trobbins

    trobbins

    83
    0
    Jun 15, 2010
    Steve, many people wanted to remove Telstra's PV panels - it got so bad that Telstra tried many different techniques over many years to ebb the flow of panels into the hands of others - the one I thought most innovative was using an orange coloured backing to the cells (tedlar layer). Orange was the corporate colour of Telstra, and very niticable from the road and the air at long distances!

    Ciao, Tim
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-