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Data and monitoring: Poor performing PV systems, system or weather?

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      CommentAuthorSteamyTea
    • CommentTimeMar 13th 2012
     
    Just been looking at some weather data and it seems that the last 3 months down here (Cornwall) have been rather dark. Has anyone else noticed this, maybe through the output from a PV or ST system?
    Thoughts, anecdotes or data welcome.
    Thanks
    • CommentAuthorpmusgrove
    • CommentTimeMar 13th 2012
     
    You need to come east to Somerset. It must be lighter up here as the results for the past few weeks have been great.
    • CommentAuthorcbatjesmond
    • CommentTimeMar 13th 2012 edited
     
    I've just had my best January and February (see the second graph courtesy of www.bdpv.com):
    http://www.ccandc.org/cgi-bin/pv?START=20120301&END=now
    Of course (1) these months are 1/5 and 1/4 of the best months and (2) I rarely get what the PVGIS thinks I oughta.
    December 2011 was also my best December but at 30kWh nothing at all to boast about.

    ETA: I've just updated this page with monthly production for 2010 and 2011 also courtesy www.bdpv.com.
    (And fixed spelling :0)
    •  
      CommentAuthorDamonHD
    • CommentTimeMar 13th 2012
     
    For Jan and Feb PVGIS predicts 2.8kWh/d and 5.4kWh/d respectively for my system and I generated 2.4 and 5.1, so a little down, but not horribly so.

    Rgds

    Damon
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 13th 2012
     
    Somerset may be brighter, nearer the drought, I have only looked at my end so far, slowly working my way up.

    Chris, forgotten about your data, I shall book mark it. Have also forgotten the size of your system.
  6.  
    Posted By: SteamyTeaSomerset may be brighter, nearer the drought, I have only looked at my end so far, slowly working my way up.
    Come to sunny Tyneside :-)

    Have also forgotten the size of your system.
    Full details should be on the page linked from the second graph. But it's (only) 1.72kWp.

    I do like the BDPV site even though I begrudge having to type the numbers in by hand:

    * the PVGIS estimate gives an independent benchmark of sorts.

    * they facilitate comparison between users (I think I suffer compared with those nearest me from having a small system, with little economy of scale).

    * when you do compare, they automatically scale the values so that you see what the other installations would have achieved at your site.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 13th 2012 edited
     
    Thanks Chris
    Shall have a play tomorrow, just sorting out some charts to pop up.
     
    These are for Plymouth, the 1983-2005, min and max are from the Nasa/Noaa site.
     
     
      Plymouth 12-2011.jpg
      Plymouth 01-2012.jpg
      Plymouth 02-2012.jpg
    • CommentAuthorEd Davies
    • CommentTimeMar 13th 2012
     
    ST, it's because it's winter. It happens every year. Haven't you noticed the pattern yet?
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 13th 2012
     
    Never winter down here, just rains less :wink:
    • CommentAuthorskyewright
    • CommentTimeMar 13th 2012 edited
     
    West, but not South.

    Here, insolation has been way down on PVGIS's view of average, both as measured by PV production and by weather station pyranometer. February's PV was 68% of PVGIS's estimate. The pyranometer only managed 60%.

    January was not too bad overall, mainly because a few very good days at the end of the month dragged the average PV up. On the 21st it was still down at 64% of "average", by the 26th that had improved to 75%. Given that, finishing at 92% seemed not so bad!

    December only managed 62% PV.

    So yes, it's been a cloudy few months, and March is continuing in the same vein (though we did have a couple of good days just over a week ago :bigsmile: ).
    • CommentAuthorJeff B
    • CommentTimeMar 13th 2012
     
    Steamy Tea - similar story here in west Wales. Little rain but constant cloud cover. It won't surprise me if our small children here are starting to develop rickets. Derek Brockway our friendly BBC Wales weatherman reckons it has been the gloomiest winter since 1995.

    Our local Met Office weather station (Abersoch) recorded just 25 hours of sunshine in December - the lowest since 1942! January had 59 hours (average for January = 57). February had 68 hours (average = 78).

    Our PV system (3.9 kWp) generated 33 kWh in December, 54 kWh in January and 103 kWh in February. The total since April last year is 2758, so the three months December, January and February generated just 7% of the total. And before someone says "what do you expect, it's wintertime" let me say that on the only two blue sky days we've had this month so far (4th and 5th March) we generated 10.1 and 12.8 kWh respectively! Today and yesterday, both overcast days, managed 1.7 kWh each.
    • CommentAuthorBeau
    • CommentTimeMar 14th 2012 edited
     
    I think it has been a particularly dreary winter in West Devon but it has improved massively this month.

    3.76 kW system
    We produced 198kWh between installation at the end of October -1st of February this is 52% of PVGIS estimate and by comparison we have produced 162kWh in the last 2 weeks.
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 14th 2012
     
    So it seems that it is weather. Shall have to see if I can find more information.
    My feeling is that it has been dull, but it is easy to forget previous years.
    • CommentAuthorBeau
    • CommentTimeMar 14th 2012 edited
     
    ST

    I think it is weather. I have lived here for 36 years and I have always been able to handle our wet cloudy winters but this year really has got to me like never before. I know this is totally unscientific but it is my view. The other awful year I think was 2000 when we had 100 consecutive days of rain but I think the sun came out between the rain..

    I have noticed that my parents PV system that is at 15 degrees has percentage wise out performed our system at 36 degrees in the cloudy weather. I presume the light gets refracted down vertically so in these conditions a 0 degrees system might be best?
    • CommentAuthorskyewright
    • CommentTimeMar 14th 2012 edited
     
    Had a chance to check the insolation records now. I added a pyranometer to the weather station at New Year 2010/2011. Here's a summary of figures since then quoted as %age of the figure suggested by PVGIS Climate-SAF as local average insolation on a horizontal surface:

    Month 2011 as % of PVGIS
    Jan 109%
    Feb 94%
    Mar 76%
    Apr 91%
    May 74%
    Jun 94%
    Jul 108%
    Aug 88%
    Sep 91%
    Oct 75%
    Nov 92%
    Dec 67%
    Year 89%

    Month 2012 as % of PVGIS
    Jan 84%
    Feb 60%

    Looking at the 1m soil temp, the minimum this year has been 6.0C, and the temp was only below 6.5C for about 3 weeks. Minimum last year was 5.5C, and it was at that level for 2 months (and below 6.5C for approx 4 months).

    Edit: 1m temp is currently (i.e. 14th March) at 7C. In 2011 that wasn't seen till the start of April.

    HDD for Jan & Feb have been about 0.5HDD/day down (i.e. warmer) compared to 2011. The Jan & Feb kWh/HDD/day figures were slightly up :cry:; I think that is probably at least partly down to lack of solar gain - we may not get much sun here in the NW even in a good year, but what there is arrives at a low angle so it penetrates well into the house? Another factor is probably that getting the storage heating charge regime right is always that bit harder when temps are at the warmer end of the "heating on" range.
    • CommentAuthorJeff B
    • CommentTimeMar 14th 2012
     
    We have been down here in Pembs almost exactly 5 years (moved 31st March 2007) and IMO this winter has been the dullest by a country mile. Could it be that just by having PV panels tends to focus the mind more on the amount of sunshine (or lack of in this case)? This prompted to me to take a look at the Met Office data for our area for the last 5 years:

    Month Sun (hrs) Aver* Max* Min*
    Dec 2007 74 50 88 25
    Dec 2008 74 50 88 25
    Dec 2009 69 50 88 25
    Dec 2010 79 50 88 25
    Dec 2011 25 50 88 25

    Month Sun (hrs) Aver* Max* Min*
    Jan 2007 58 57 98 24
    Jan 2008 55 57 98 24
    Jan 2009 91 57 98 24
    Jan 2010 86 57 98 24
    Jan 2011 81 57 98 24
    Jan 2012 60 57 98 24

    Month Sun (hrs) Aver* Max* Min*
    Feb 2007 88 78 133 44
    Feb 2008 133 78 133 44
    Feb 2009 56 78 133 44
    Feb 2010 101 78 133 44
    Feb 2011 68 78 133 44
    Feb 2012 68 78 133 44

    *1942 – date

    [Please excuse variations in column widths - can't seem to copy & paste a table here?].

    As can be seen Dec 2011 had the lowest number of sunshine hours since 1942, Jan 2012 was about 5% above average (previous three January’s all well above average) and Feb 2012 was about 11% below average. (Previous February’s show huge variations e.g. Feb 2008 figure was the highest since 1942 at 170% of average and Feb 2009 was only 70% of average).

    So, yes I concur with ST and Beau - this winter has been duller indeed.

    On the plus side, whilst we haven’t had those cold, crisp sunny days this winter, at least it has been incredibly mild and hence I expect our wood pellet consumption to be significantly down this winter compared to the last two!
    • CommentAuthorSteveZ
    • CommentTimeMar 14th 2012
     
    My 4kWp system has been in operation since the end of January 2012, here in North East Cornwall. The total for February was 166.5Kwh and so far for March (14th) the figure is 133.6kWh. The variation on a daily basis has been quite wide, from 2.5kWh to just over 15 per day.

    Given that 3/4 of the system faces East and 1/4 South, both on a 30° inclination, and the South is shaded late in the day by the ridge, I am pleased so far with the figures. It is a SolarEdge system, so is unlike most of the others reporting, and will be fascinating to see if the extra expense was worth it :confused:
    • CommentAuthorpmusgrove
    • CommentTimeMar 14th 2012
     
    What does SolarEdge have that the others do not?
    • CommentAuthorSteveZ
    • CommentTimeMar 14th 2012
     
    Hi pmusgrove. The main difference is the way it does Maximum Power Point Tracking (MPPT) Each individual PV panel has its own SolarEdge PowerBox which keeps the voltage constant and varies the current according to the irradiation level on that panel. The Inverter is fed a constant voltage as a result, which makes the circuitry in the SolarEdge Inverter more straightforward, and more reliable, I hope. The plus is that each panel gives out its own maximum power all the time, which is good, the minus might be that the losses in each PowerBox and in the inverter might reduce the final output figures more than a good string inverter. We will see............
    • CommentAuthorcbatjesmond
    • CommentTimeApr 1st 2012 edited
     
    Posted By: SteamyTeaSo it seems that it is weather. Shall have to see if I can find more information.
    My feeling is that it has been dull, but it is easy to forget previous years.

    Following my best ever December, January and February: ta-dah, my best ever March -- http://www.ccandc.org/cgi-bin/pv?START=end-1w&END=now" > even beating the PVGIS estimate.
    • CommentAuthorJeff B
    • CommentTimeApr 4th 2012
     
    Poor performing PV systems, system or weather?

    Below please see graph of PV output from our system for the month of March. Spot the sunny days! Nothing wrong with the system me-thinks!
      PV data March 2012.gif

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