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Can the supply co. refuse your output?

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  1. #1
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    Default Can the supply co. refuse your output?

    I once saw some reference to the supply company being able to not accept the output from your solar panels if their system is over supplied. Is that true?

    Reason I ask is sometimes - when there is plenty of sun and no cloud the output graph on the computer monitoring program goes to zero. Sometimes it flat-lines at zero for a while then comes back up mid to late afternoon , sometimes it doesn't come back. Yet the total output for the day reflects what would be expected. I know there are glitches in the program - this could be one but just curious as to if supply can be refused - if it is there should be an alert so the output power can be used in house. (seeing we are on NET )
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

  2. #2
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    no, your supplier cannot 'refuse' your output.

    what inverter(s) do you have?
    do you know if the output really is going to zero? does your inverter have an error log that you can interrogate?

    reason being, if it really is going to zero it could be because you are over-driving your inverter (more panels / W than it can handle on DC side relative to its capacity, the AC side impedence could be wrong, the AC side voltage too high or frequency too low.

    certainly there have been cases (particularly more rural) where you're too close to the street transformer - or too far away - or piss weak cabling - or the transformer on an incorrect tap setting - which cause inverters to drop out.

    but more logging / log interrogation necessary to diagnose.

    it should not drop to zero in a sunny day. that definitely is not 'normal'.
    a sunny day output-wise should look like this: http://pvoutput.org/intraday.jsp?id=...40&dt=20110128

  3. #3
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    The inverter is a SMA Sunny Boy 3000TL with 15 x200watt panels.

    I had noticed some oddities with the records previously and wrote to the company and got a reply that they know there are some "issues" with the software that was not affecting the output just the daily records. (eg missing a days total and adding it in two days later so the record shows zero one day and 30kwh 2 days later with all the other days showing 12-15kwh ) The issue at the moment is like yesterday the graph was curving up nicely when at 10:30 am it stopped recording at 2.5kw and nothing was recorded until about 3 in the afternoon and the graph just drew a straight line from 2.5 to zero at the 3pm spot - just looks weid on the graph but the total output for the day is showing at 16.3kwH so it's there, just not showing I guess - more software gremlins
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

  4. #4
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    Quote Originally Posted by Wombat2 View Post
    The inverter is a SMA Sunny Boy 3000TL with 15 x200watt panels.
    how are those 15 panels wired in? what make/model are the panels?

    Quote Originally Posted by Wombat2 View Post
    I had noticed some oddities with the records previously and wrote to the company and got a reply that they know there are some "issues" with the software that was not affecting the output just the daily records. (eg missing a days total and adding it in two days later so the record shows zero one day and 30kwh 2 days later with all the other days showing 12-15kwh ) The issue at the moment is like yesterday the graph was curving up nicely when at 10:30 am it stopped recording at 2.5kw and nothing was recorded until about 3 in the afternoon and the graph just drew a straight line from 2.5 to zero at the 3pm spot - just looks weid on the graph but the total output for the day is showing at 16.3kwH so it's there, just not showing I guess - more software gremlins
    that you elude to that bug so you have Sunny Explorer and bluetooth setup. good.
    (i've heard about it but not seen it myself - SB500TL here)

    does Sunny Explorer record any 'events' / warnings / errors during that time?
    suggest you look and confirm.

    i'm not yet convinced that you don't have a problem, but advise me on the cabling of your panels and make/model and i'll see..

  5. #5
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    Panels are Suntech STP200-18/Ud connected as a single array

    Software does have error display but I thought it was only 'live' -don't know if it keeps a history - will check. Can't do anymore as I am down in Brisbane till Friday and the software only starts after it establishes a bluetooth connection with the inverter.
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

  6. #6
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    Quote Originally Posted by Wombat2 View Post
    Panels are Suntech STP200-18/Ud connected as a single array
    so its one set of 15 panels in parallel???
    can you verify that?

    Quote Originally Posted by Wombat2 View Post
    Software does have error display but I thought it was only 'live' -don't know if it keeps a history - will check. Can't do anymore as I am down in Brisbane till Friday and the software only starts after it establishes a bluetooth connection with the inverter.
    the SB TL inverters are some of the best on the market.
    if it is going out-of-spec or disconnecting from the grid, yes there will be recorded events for that.

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    Quote Originally Posted by president_ltd View Post
    so its one set of 15 panels in parallel???
    can you verify that?
    Only one positive and one negative wire coming down from the roof so I guess so
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

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    Quote Originally Posted by Wombat2 View Post
    Only one positive and one negative wire coming down from the roof so I guess so
    no - i'd expect only one DC cable down to the inverter since it has only one MPPT so no point bringing down 2 runs and paralleling them at the inverter. there might be 1, 2 or 3 sets of panels in 'series' but then paralled up to one another in a junction or CB on the roof/ceiling.

    i'm after the actual string configuration. 15 panels - but is it setup in a. 3 x 5, b. (1x7 + 1x8) or c. 1 x 15.

    i think (b) is the most likely but if its (a) or (c) that may explain your problem.

  9. #9
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    I think they are 10 and 5 - I'll have to get up on (and in) the roof on Friday and check

    edit: that's about 5pm in July - so don't worry about the shade from next door - antenna is pointing almost due south
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

  10. #10
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    Quote Originally Posted by Wombat2 View Post

    I think they are 10 and 5 - I'll have to get up on (and in) the roof on Friday and check
    if its as you describe, there's a yield problem right there..
    the 5 panels in parallel is the problem case. to balance the voltage it would have to be 3x5. but that means yield loss due to falling out of MPPT tracking range at peak power.

    fire up Sunny Design software (downloadable for free from sma.de) and you'll see.

    it recommends you drop a panel to have 2x7 or add a panel and have 2x8.

    there's simply no way to connect 15 panels into a single MPPT without it being mismatched. if you had 1 more panel (3x6) or 2 MPPTs as like what you'd have on a SB4000TL or SB5000TL then maybe.

  11. #11
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    why would 1x15 be a problem - Sunny Design says it's OK ( as I read it )
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

  12. #12
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    Quote Originally Posted by Wombat2 View Post
    why would 1x15 be a problem - Sunny Design says it's OK ( as I read it )
    look closer. if you put in 15 x Suntech STP 200-18U/d on page 1 then on the page 2 put SMA3000TL it magically downsizes it to 14 panels.
    which is fine.

    on that 2nd page turn it back into 15 and see what it says. big red letters. INVERTER DANGER.

    now i think its unlikely that its 1 string of 15 panels in series.
    but with 1 MPPT its not as if you can 'balance' 15 panels in any way.

    well - you can. (2x5) + (1x5).
    but if you do that then Sunny Design will tell you "yield loss" based on falling outside the lower MPPT voltage.

  13. #13
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    Did you change the min PV temperature to 0 (default is -10 which throws things out a bit)
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

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    Quote Originally Posted by Wombat2 View Post
    Did you change the min PV temperature to 0 (default is -10 which throws things out a bit)
    nope, left it at default of -10C. i guess that's the difference.

    ok - if you accept it will never get to lower than -5C then the Voc gets to 542V at most.
    pretty close to the 550V where the magic smoke is let out.

    but agree 15 panels in series does in fact work - provided thats how its cabled up.
    that you have two orientations of panels isn't ideal. but should still be pretty much ok.

    i guess next step is to take a look at Sunny Explorer logs on the day and see if its actually cutting out. or just misreporting.

    if you have a linux host handy you could look at exporting your live data to pvoutput.org & comparing with others in your area.

  15. #15
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    Well I fired up the Sunny Explorer program and the are no error reports for the 21st or any days. The internal graph is still showing as I described so I exported the full data set for the day to Excel and the full data appeared to be there and when I plotted it in a graph lo and behold the perfect curve. Guess it is a software gremlin in the Sunny Explorer program
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

  16. #16
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    good to hear.

    you might want to consider exporting live data to pvoutput.org then you'd have a benchmark for comparing systems around yours to your own.

    this really is the ultimate in seeing if there is an issue with your system as you can compare with others around you so its similar atmospheric conditions & cloud conditions.
    e.g. i regularly compare my system with SolarDave who is just a couple of km away.
    see Compare Live
    if our systems are more than a couple of % different then its a sign that one of them has gone awry.


    if you have linux skillz u can use sma-bluetooth from sma-bluetooth - Project Hosting on Google Code
    or if you have windows / Sunny Explorer use PV BeanCounter from pvbeancounter - Project Hosting on Google Code

    i use the former as don't have a windows host near my inverter but do have a linux box as my fileserver / mythtv frontend/backend / dns hosting.

  17. #17
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    I worked out the graph drops to zero when the connection is lost

    The bluetooth link is weak at best being 'critical' most time - this morning while watching it went to 'none' while watching it and almost straight away a message popped up saying reconnect - never seen that before - and the graph had dropped to zero - so guess that's the answer to that.

    Last week after exploring the bluetooth connection strength I found out there are 3 classes of bluetooth. I wrote to SMA and got this reply:

    While it is true that the Bluetooth range for the SB 3000TL is 100m, another condition must also be met for a quality connection to be made. This is the range sufficiency of the Bluetooth on your laptop. Do you know what class your Bluetooth system is? It sounds to me like it is a class 2 or 3 Bluetooth device, which has a maximum range of about 10m. I would consider investigating this and possibly get a class 1 Bluetooth dongle (USB device) which has a range of 100m.

    Another option is to use a Bluetooth repeater which can be purchased from your supplier. This essentially acts as a middle man for your Bluetooth network, and strengthens the signals. However this option is more pricey than the first.
    Digging further I found that Class 1 has a range of 100m - Class 2 10m and Class 3 1m

    Seeing the computer is just on 10m from the inverter I guess the above explanation from SMA is on the mark.

    I have since ordered a Class 1 dongle from the States - $7 plus $5 postage for the same brand as one selling here for $42 ( and Jerry Harvey wonders why people shop on line )

    I'll let you know what happens.
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

  18. #18
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    David,

    I am just about to have a Sunny Boy inverter installed, and was wondering about a suitable bluetooth dongle. Can you share where yours came from?
    Life's too short for dull sandpaper

  19. #19
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    From the US eBay ( sometimes has a better range than local eBay)
    Bluetooth v2.0 EDR Class 1 USB Mini Adapter (eBay item 320484662850 end time 02-Apr-11 14:59:27 AEDST) : Computers Networking

    I offered $US7.00 and it was accepted - he's increased his postage since I bought it.
    David L
    "A dedicated amateur will always do a better job than a slap dash professional"

  20. #20
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    Cool, thanks. Let us know how it works when it arrives.

    Peter
    Life's too short for dull sandpaper

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