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    • CommentAuthorMartyn1981
    • CommentTimeJul 28th 2011
     
    I've been researching a solar pv installation for my main and lower roof, for a month or so, and was hoping to sign up this weekend, for an installation date in one weeks time.

    Small problem, the system I've negotiated is 2.405Kv main roof and 1.295Kv lower roof (separate inverters), just found out today that you need permission from the distribution network manager for installs larger than 3.68Kv (mine would be 3.70 in total). I appreciate that a line has to be drawn somewhere, so not having a go at the network.

    I think the figure is based on inverter output not panel output, so with efficiency losses it might be ok as it is so, so close.

    Does anyone know the specific rules? If I wait for permission could be weeks or months, so next week would be a bust, and I'd lose August, September and possibly October sunlight.

    Am I over thinking this? Any advice appreciated.
    •  
      CommentAuthorted
    • CommentTimeJul 28th 2011
     
    Unfortunately different DNOs around the country all interpret the rules slightly differently.

    It should be the output from the inverter that matters, and losses in the inverter taken into account.

    Your installer should know what happens in your area.
    • CommentAuthorMegacycles
    • CommentTimeJul 28th 2011
     
    What inverter are you using? That will dictate the maximum current to grid, theres quite a few now with a 16A limit for the G83 standard. If you use on of these that should satisfy the DNO.

    I spoke to the microgen person at S&SE before my install last year and they were fine with it being slightly oversize at 3.76kWp. They took the sensible attitude that its a peak power and most of the time the output will be much lower, I think they take a stricter approach now. Probably worth doing the same.

    Our grid voltage is always around 250V so our 16A inverter can actually deliver 4kW.
    • CommentAuthorbiffvernon
    • CommentTimeJul 28th 2011 edited
     
    Before you go anywhere near electrickery make sure you understand the difference between kW and kV. After that you will have no problem with your grid connection. :)
    •  
      CommentAuthorSteamyTea
    • CommentTimeJul 29th 2011
     
    Do you mean kVA ?
    •  
      CommentAuthorDamonHD
    • CommentTimeJul 29th 2011
     
    Hi,

    I've not had a problem with a DNO getting tetchy about going slightly over the 16A-per-phase limit. Mine at home and another in a different area have been quite happy to waive the formal limit in one case to just over 5kWp and in the other 9kWp.

    Just ask nicely, IMHO.

    Rgds

    Damon
    • CommentAuthorMartyn1981
    • CommentTimeJul 29th 2011
     
    Thanks everyone for your advice.

    I should have mentioned I'm in Cardiff so dealing with Western Power Distribution, they seem helpful, but ended up confusing me with, 'we'll have to inspect and if re-enforcement necessary may cost you around £2,000'.

    If my domestic supply has a 70A main fuse, why can't the system cope with more than 16A going the other way? Or should I be thinking of the whole area and sub-station?

    With regards to Biffvernon and SteamyTea - nice catch, can't believe I put Kv instead of KW, and then repeated it again twice!

    Seems silly to be rushing and panicking at this stage, but I've really got the bug now, and the 3.7KW would just about equal our annual electricity consumption (around 2,700KW p.a.)- so nice to think we are at least partly owning up to some of our responsibilities. If only we could bottle it and spread it out evenly.

    Megacycles - I'll be running two inverters one for the main roof and one for the low roof, not sure the specific model, but I think they will both be from the SunnyBoy range.

    Thanks again.

    Martyn.
    •  
      CommentAuthorted
    • CommentTimeJul 29th 2011
     
    WPD are reasonable and should be told the output from your system will be 3.5kW. (3.7 - 5% inverter loss)

    Have you looked at a dual MPPT inverter? No need to get two.
    • CommentAuthorMartyn1981
    • CommentTimeJul 29th 2011
     
    Hello ted, basically I'm getting mixed messages from two companies. One states that the DNO will need the nominal output of the system, so I'll need permission before proceeding, and this currently takes WPD about 10 weeeks.

    The other states that they've had no problems notifying afterwards (as with most systems) up to 4KW with WPD.

    The second company can install in 1 weeks time so I catch some sun this year. But if the first company is right, and it takes WPD 10 weeks to give clearance then I might as well wait till March (gambling on getting in before FITS changes).

    hence my dilemma, I'm not trying to be cheeky at all, just a little confused by it all now. maybe I should just chop out 1 panel and be done with it. Due to roof dimensions and a Velux, I've opted for 20 185W panels, as these give the most surface area of any combination I can come up with.

    Regarding the inverter, the company did suggest a twin model, but after checking they felt that a 13 to 7 panel difference was too great. All too magic for me!
    • CommentAuthorRobL
    • CommentTimeJul 29th 2011
     
    Where does the 16A limit come from ?

    Our master house fuse is 60A - I can't see why it cares if power flows in or out of the house, so long as the current is below 60A so the fuse - which protects the downstream cabling to the consumer unit - is ok. It's easy to draw >16A for hours, not that I do, honest:-)

    I assume that there is some "contention" applied normally to power use - ie. it is assumed that a whole street doesn't draw 60A from each house at the same time. If the whole street had PV :-), then their power outputs would be synchronised & overload some common cable/transformer/fuse - is this it??

    RobL, confused
    •  
      CommentAuthorted
    • CommentTimeJul 29th 2011
     
    I've tried to find out why 16A was chosen as an export limit and it seems to be lost in the mists of time. Doubtless there is an engineer's report sitting on a dusty shelf somewhere. The issue is more to do with the local transformer though (which have all been designed to work with the expectation that current will only flow in one direction) rather than fuses together with concerns of local variability of voltage and harmonics, or at least that is the answer I keep being given.
    • CommentAuthorMegacycles
    • CommentTimeJul 29th 2011
     
    Ted

    I've been told by S&SE that anything additional to my existing 3.76kW PV system would have to be approved under G59/2, they seem to be rounding to 3.7kW if that helps Martyn.

    Now this sounds like expensive territory but I understand that anything less than 17kW per phase ( I want to add a further 16A) can use a simplified process which is hopefully cheaper and allows the use of g83 approved equipment. Any ideas of cost of application and does this eliminate the need for g59 switchgear/liabilites?

    There doesn't appear to be consistency between DNOs regarding connections >16A .
    •  
      CommentAuthorted
    • CommentTimeJul 29th 2011
     
    It's all down to the individual DNO's interpretation. You can only ask.

    There are changes afoot to address this - but moving very slowly.
    • CommentAuthorjamesingram
    • CommentTimeJul 29th 2011 edited
     
    while were on the subject of confusion , how about the definitions of TIC , total installed capacity and DNC declared net capacity . plenty of dicussion on navitron forum and elsewhere re. this, but no clarification from ofgem i believe ,
    Ted, you and others are suggesting, go for TIC=DNC
    and therefore using, say a inverter with max ac output 3.6kw and installing 4.3kW total panel output DC should fall in the < 4Kw FIT tariff band ( As DNC refers to max output of system post system losses)
    Most people I know consider it total panels DC output of system to be the figure for TIC and relavent to the FIT banding.
    Thought I'd bring it up on here just to make more people aware of the potential .
    Be great to hear of more example of installers registering sytems with TIC=DNC without problems and also any info on clarification for this issue from any of the relavent official bodies that govern FITs etc.
    •  
      CommentAuthorted
    • CommentTimeJul 29th 2011
     
    As I said on the Navitron Forum, if you analyse the data published by OFGEM for FiTs installations wou will find that 99+% have TIC=DNC. There obviously isn't a problem with that interpretation.

    I've gone into some detail on there too about my reasons for suggesting that this is also the correct logical interpretation based on the definitions, so I won't repeat that here.
  1.  
    Thanks Ted , good info as usual
    • CommentAuthorMartyn1981
    • CommentTimeJul 30th 2011
     
    Me again, gone completely paranoid now about the rules. I've tried reading the DTI and DNO regs, plus the G83 stage 1 and 2 rules. Now I'm unsure if 2 inverters is classed as a multiple installation requiring prior notification as the guidance keeps referring to a single generation installation.

    I'd almost relaxed after deciding to switch my lower roof from 7 185W panels to 5 245w panels, bringing the total system down to 3,630W, just under the rule. Now I'm getting concerned again.

    Really need to relax and get a life or have a large drink.

    Does anyone now the specifics regarding multiple installations - I'm sure it just refers to a company installing more than 1 sub 3.68KW system within a small area (one road say) but don't want to get tangled up in rules?

    Martyn.
  2.  
    Your system even with multiple inverters would be one installation
    • CommentAuthorMartyn1981
    • CommentTimeJul 30th 2011
     
    Thank you so much.

    Martyn.
    • CommentAuthorGavin_A
    • CommentTimeJul 30th 2011 edited
     
    use either of these inverters and there will be no problem, the limit refers to the peak AC output from the inverter, not the DC rating of the panels as western power should have made clear.

    the arora power-one 3600 inverter has dual peak point tracking, and is now limited by the manufacturer to 16amps AC (but check it's new stock as they've only just switched across to this for the UK)

    SMA sunny boy 4000TL with dual peak point tracking can be limited by password protected installer settings to 3680W AC peak output, so 16amps at the nominal grid voltage of 230V.

    both situations would be compliant with g83/1 rules, and no advance permission would be required. Many staff at DNO's are clueless about inverters etc, and for a time we had problems because they were taking the peak DC panel rating from our systems diagram, and ignoring the peak AC output stated on the form, so we've taken to clarifying this in the comments section of the appendix 3 notification form, and removed the peak rating of the panels from the diagram to avoid confusion - since then we've had no problems, and YEDL are accepting 4000TL's limited in this manner no problem, we'll find out shortly if SSE accept it straight off or need an argument first.
    • CommentAuthorGavin_A
    • CommentTimeJul 30th 2011
     
    Posted By: Martyn1981Regarding the inverter, the company did suggest a twin model, but after checking they felt that a 13 to 7 panel difference was too great. All too magic for me!


    what panels?

    the difference in voltage makes no difference on the 4000TL as long as it's inside the voltage range, and I'm fairly sure it's not an issue on the aurora either. The only problem would be if the voltage / power on the 13 panel system was outside the voltage range of the inverter, which is possible depending on the panel type.

    we install a lot of these systems
    • CommentAuthorGavin_A
    • CommentTimeJul 30th 2011
     
    2 or more inverters could be regarded as g83/1 stage 2, ie requiring an application depending how you choose to interpret the regulations. We've never had a problem doing it as stage 1 with multiple inverters if it's under 16amps total, but if you're worried stick to the single dual MPPT inverter and you've no worries.
    • CommentAuthorCWatters
    • CommentTimeJul 30th 2011
     
    I'm considering submitting a planning application for a system around the 3-5KW range so this is an interesting thread.

    I'm waiting for a reply from my DNO to tell me if there are any restrictions in my area. Meanwhile what would be a reasonable maximium "DC rating of the panels" if you are limited to 16A out of the inverter?

    It's going to be a ground based array so is there a standard panel size I can use for a planning application? eg dimensions that wouldn't limit me to one supplier? For example are panels all a multiple of the standard 400mm rafter pitch these days?
    • CommentAuthorMartyn1981
    • CommentTimeJul 30th 2011 edited
     
    Gavin A, not sure if this makes a difference, but when I'm referring to two roofs, they are both in alignment. The main roof and the lower roof both point identically (about 110deg) the lower has about half the slope of the main. So the inverter would be getting power from both until around 3 or 4 ish when the main roof starts to overshadow the lower.

    So not 13 or 7, it should be all 20 then 13 + part of 7 later on.

    Forgive my ignorance if you already realised this, it's just that other people have told me about single inverters that switch between the stronger signal, but I would need one that processed both simultaneously.

    PS Panels are Yingli 185W (their size means I can better fit my roof layout).

    Thanks.

    Martyn
    • CommentAuthorGavin_A
    • CommentTimeJul 30th 2011
     
    CWatters

    panels mostly come in either 800 x 1600mm or 1000 x 1650mm ish sizes

    with standard mono/poly panels we work on around 4.3-4.5kWp being the max sensible size for a 16amp ac system, with around 15% reduction in performance from the temperature of the panel in full sun (eg 50 deg operating temp), and 5-6% losses from the inverter and cables meaning a 4.5kWp system would usually not operate at more than around 3.6-3.7 kW ac for longer than a few minutes at a time anyway most of the year.

    I'd suggest looking towards the low end of this range or possibly even slightly lower than that, for a ground mounted array though as you'll be getting far more airflow around the back of the panels than on the roof, so they'll operate at a cooler temperature in peak sunlight, and be optimally angled etc.

    You can go higher than this, but the system will suffer from peak lopping by the inverter.
    • CommentAuthorGavin_A
    • CommentTimeJul 30th 2011
     
    Martin, ah... the 7 panels of yingli 175's wouldn't produce enough voltage for either of the inverters I mentioned, so please disregard my previous advice, I now understand why the installer opted for 2 inverters.

    you'd need something like the sunny boy Sb1200 for the smaller array, and 2000HF or SB2000 for the bigger if using SMA / Sunny boy inverters.
    • CommentAuthorMartyn1981
    • CommentTimeJul 31st 2011
     
    Thanks Gavin, nice to know that what the installers are saying matches the thoughts of others on this forum. I'm learning fast, but regarding such issues as 1 or 2 inverters I have to take their word for it.

    Martyn.
    • CommentAuthorCWatters
    • CommentTimeJul 31st 2011 edited
     
    Thanks Gavin. Can I ask how many panels that size would be needed for around 4kW? 16 or so ?
    •  
      CommentAuthorDamonHD
    • CommentTimeJul 31st 2011
     
    You need very roughly 8m^2 of roof space for 1kWp of (mono/poly) panels. Maybe 2 or 3 times that for thin-film.

    Rgds

    Damon
    •  
      CommentAuthorSteamyTea
    • CommentTimeAug 1st 2011 edited
     
    Draw your own conclusions from the best solar resource on the mainland

    Whoops, wrong thread.
   
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