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Grid connection limit?

edited 30 November -1 at 1:00AM in Green & Ethical MoneySaving
30 replies 6.7K views
butakobutako Forumite
8 Posts
MoneySaving Newbie
edited 30 November -1 at 1:00AM in Green & Ethical MoneySaving
I've read that there's a 16A * 240 = 3840kW limit for home Solar PV connection. Anything above which would need special permission, and my local solar installer said that may take ~1 month and is highly likely to be refused. Is that true? What are the rules? I'd like to get a 5kW installation, do I need to apply for permission or not?
My provider is UKPN, based in South-East London.
And, what would be a reasonable price for a 5kW installation do people think?
Thank you!
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Replies

  • CoastalwatchCoastalwatch Forumite
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    Hi Butako and welcome. Apparently in order not to obtain permission from your local Distribution Network Operator then the max size array is for 4 kWp. It depends which installer you ask as to whether permission is likely to be granted! I was fortunate that in my case(8.85 kWp) the Installer sorted it all without a problem whereas another said it was near impossible to arrange! Even with a 5 kWp array it is unlikely you would achieve much more than 4 kWp from it due to losses in the system. As written elsewhere an Inverter can be used that caps the output to below that figure so in theory permission isn't required as your system won't stress the local grid beyond what is allowed.Those occasions when conditions are all in your favour for the system to produce more are seldom and you would only be missing out on the odd 100w or two for small periods at these times. If on the other hand you have space to fit an even larger array then consider going for this also. As for cost then it depends on the complexity of the installation, for instance will scaffold be required, does any shading occur to the panels! As a base line if you can obtain an installation for around £1k per kW generated you're doing well. If however, shading is involved requiring Enphase or Solar Edge to mitigate the effects of this then another £1k may need to be added.
    Hope this helps I'm sure others will assist further and pass on their experiences too. Good luck!
    East coast, lat 51.97. 8.26kw SSE, 23° pitch + 0.59kw WSW vertical. Nissan Leaf plus Zappi charger and 2 x ASHP's. Still waiting for V2H and home storage to become available at sensible cost.
  • Dave_FowlerDave_Fowler Forumite
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    butako wrote: »
    I've read that there's a 16A * 240 = 3840kW limit for home Solar PV connection. Anything above which would need special permission, and my local solar installer said that may take ~1 month and is highly likely to be refused. Is that true? What are the rules? I'd like to get a 5kW installation, do I need to apply for permission or not?
    My provider is UKPN, based in South-East London.
    And, what would be a reasonable price for a 5kW installation do people think?
    Thank you!

    Strictly you can't output more than 16Amps to the grid without permission from the DNO. So you could have a 5kW system provided that the inverter output is capped at 16 Amps and then you would not need to ask for prior permission. The capping is not a major issue since during the summer months a 5kW system will rarely output anything like 5kW due to the heating effect on the panels. During the spring and autumn when the panels are cooler there would be times when the output could be higher, but it would not amount to a significant amount.

    Dave F
    Solar PV System 1: 2.96kWp South+8 degrees. Roof 38 degrees. 'Normal' system
    Solar PV System 2: 3.00kWp South-4 degrees. Roof 28 degrees. SolarEdge system
    EV car
    Lux LXP 3600 ACS + 4 x 2.4kWh Aoboet LFP 2400 battery storage. Installed Feb 2021
    Location: Bedfordshire
  • Martyn1981Martyn1981 Forumite
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    I apologise for any pedantry, but because there are quite a few different figures being posted here can I just clarify that the exact rule is 3,680W (based on 16A at a nominal 230V). It used to be just 16A, but that allowed for higher export in areas with higher voltage.

    So, there's no KWp limit, in so much as you can slap as much PV on your roof(s) as you like, but the inverter must be sized or capped at 3.68kW for automatic approval (after the install) from the DNO. If the inverter can, even if just theoretically, export more than 3.68kW, then prior approval is needed from the DNO.

    As Dave points out, 5kWp of PV in the summer will most likely only sustain about 80% on a sunny day, and higher peaks in, say, April and October, will be shorter, so upto 5kWp through a 3.68kW capped inverter is a reasonable compromise.
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • CoastalwatchCoastalwatch Forumite
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    Martyn1981 wrote: »
    I apologise for any pedantry, but because there are quite a few different figures being posted here can I just clarify that the exact rule is 3,680W (based on 16A at a nominal 230V). It used to be just 16A, but that allowed for higher export in areas with higher voltage.


    Pedantry! Surely not.:)
    East coast, lat 51.97. 8.26kw SSE, 23° pitch + 0.59kw WSW vertical. Nissan Leaf plus Zappi charger and 2 x ASHP's. Still waiting for V2H and home storage to become available at sensible cost.
  • Exiled_TykeExiled_Tyke Forumite
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    A further thought. I was talking to an installer yesterday about this very problem. I was told that there are now reasonably priced devices designed to limit export. This means that generation could go above the 3.68kW and used for domestic consumption or battery storage without upsetting your DNO. (He also said that charges for requesting higher outputs vary considerably and he's known of charges up to £300)
    Install 28th Nov 15, 3.3kW, (11x300LG), SolarEdge, SW. W Yorks.
    Install 2: Sept 19, 600W SSE
    Solax 6.3kW battery
  • silverwhistlesilverwhistle Forumite
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    Not a situation I'm in but I'm sure it would interest many here, so can you give us any more information and perhaps define "reasonably priced". :-)



    With the advent of more electric vehicles there is much more potential for home usage even with bigger installations, or just heat the swimming pool to a higher temperature..:D
  • Exiled_TykeExiled_Tyke Forumite
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    Sorry no more info at present as the comment was made 'in passing'. But it's something I'll be exploring further as I'm interested in adding another 1kW to my 3kw system (and hopefully in time some batteries). I can only promise to let you know as and when I know more.
    Install 28th Nov 15, 3.3kW, (11x300LG), SolarEdge, SW. W Yorks.
    Install 2: Sept 19, 600W SSE
    Solax 6.3kW battery
  • Hi - I've just joined the MSE forum. It's seems to be the best place for discussion on solar in the entire web. Feel like I've searched all of the web over the last 3 weeks of solar research.

    I'm intending to add solar panels now and a battery later. Most installers that I've spoken to are saying I can't go over 4kw limit even though I've got plenty of room on my roof for more. None seem to know you can oversize the inverter much more than 4kw. Anyway I'm thinking of going with 4kw for now and adding more panels later on. Does that cause any issues later on?

    Also thinking I will add batteries later too. Specifically the Solaredge Storedge system which is DC coupled but allows charging from the grid. I haven't found any other DC coupled system that does that.

    One installer has mentioned that a DC coupled battery is more problematic than AC coupled. Specifically he says:
    1 - "AC coupled is more straight forward and the DNO much prefer these."
    2 - "With AC Coupled, charging from the grid is much easier, downloading power to the grid in the future is also much easier, changing and setting the profile is much more straightforward as well. "
    3 - "The DNO and Feed in Tariff company (your energy provider) want to know that when discharging the battery with DC Coupled systems it doesn’t effect the generation meter, (they will want to come check more often) with AC coupled they know it can't. "

    Does anyone have experience of DNOs being unhappy with DC coupled battery ? Anyone got any comments on any of the above points.
  • Martyn1981Martyn1981 Forumite
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    iotum wrote: »
    Anyone got any comments on any of the above points.

    Hi and welcome to MSE.

    In simplistic terms, you can add as much PV to your roof (and elsewhere) as you like, but you need prior permission from the DNO if the system is to be capable of exporting more than 3.68kW.

    So 4kWp, 5kWp, 6kWp etc through an inverter capped at 3.68kW is ok.

    Less simplistic, if all the PV is going on one roof/orientation and will therefore all be peaking at the same time, then a 3.68kW inverter is going to cap generation at peak times from around 4.5kWp onwards* so you might want to investigate getting DNO approval.

    *Systems tend to fall to around 80% in warm weather and strong sunlight, perhaps 70% in hot still air (June/July). They can peak higher, even 100%+ especially in cold clear skies (April & October) but all of these peaks will be short, and capping not significant.

    If you've got the room I'd go for it all in one go. Extensions don't get any FITs, and FiT ends next Mch, so it might be worth doing it all now, earn more back, then use that to save up for a battery when prices fall ...... eventually!!!!!
    Mart. Cardiff. 5.58 kWp PV systems (3.58 ESE & 2.0 WNW)

    For general PV advice please see the PV FAQ thread on the Green & Ethical Board.
  • Thanks Mart.

    I'd be splitting it over 2 roofs. Can fit 10 panels SSE facing and rest can go on a WSW facing roof. So I reckon that would work quite well as it would spread the production curve out over the afternoon / evening.

    The challenging bit seems to be getting solar installer sales people to understand oversizing. I've been told the limit is actually 4kw - not 3.6kw and that MCS won't let them go over the 4kw limit. They seem to think that if I wanted more than 4kw I'd need to have a higher wattage inverter and put a modbus meter on it to limit export. But the SolarEdge SE3680H can take well over 5kw according to the spec sheet.
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