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Microgeneration 6kwh limit

  • 07-02-2021 7:42pm
    #1
    Registered Users Posts: 651 ✭✭✭ buzz11


    Question in relation to the 6kw single phase micro-generation limit: Can you have PV panels that would have a peak greater than 6kw but with some of it on different aspects and therefore should never reach the 6kw limit?

    For example;
    South facing panels 5.4Kwp
    West facing panels 1.9Kwp


«1

Comments

  • Moderators, Sports Moderators Posts: 16,065 Mod ✭✭✭✭ slave1


    Yes, the limit is your Inverter so no problem hooking up 7.3kWp, that's what I have, 4.1SW and 3.3 NE hooked up to a 6kW Inverter.
    Due to shading I'll never be generating 7.4kW


  • Registered Users Posts: 2,721 ✭✭✭ graememk


    Also some have installed more but limited the export to 6kW


  • Registered Users Posts: 651 ✭✭✭ buzz11


    graememk wrote: »
    Also some have installed more but limited the export to 6kW

    where you panels greater that 6Kw, I presume any excess is used onsite e.g by way of battery charging or to an immersion heater etc


  • Registered Users Posts: 2,721 ✭✭✭ graememk


    buzz11 wrote: »
    where you panels greater that 6Kw, I presume any excess is used onsite e.g by way of battery charging or to an immersion heater etc

    No the inverters themselves can limit their generation. They physically won't export anymore than what they are set to.


  • Registered Users Posts: 1,627 ✭✭✭ quentingargan


    You also have to stay within the limits of the inverter for warranty. Many 6kw string inverters are limited to 6.5kw of panels, even with different orientation. I know that is daft, but that's the warranty.

    Some 6kw inverters, particularly battery hybrid ones, have a diffrerent topology and can take up to 8kw or more. Funny enough, one of the 3kw hybrid models can take 7kwP of panels under warranty, so even if you didn't bother with batteries, you could theoretically have 14kw of panels on two inverters. Your production would be much higher morning and evening and would flat-line at 6kw on sunny days, but that doesn't happen for as much time as you think, and panels are cheap...

    ESB doesn't recognise export limiting standards such as G100. Their limit is based on fault currrent - what is the max current in the event of a fault.


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  • Registered Users Posts: 651 ✭✭✭ buzz11


    Thanks for the replies, I'm still a bit unclear...am I right in understanding it as follows;
    • The 6Kwp limit applies to export situations only -- apart from planning permission restrictions, you can have as many panels as you wish.
    • If you are not exporting to the grid, then you need an appropriately sized inverter to manage the panel output
    • If you are exporting to the grid and have panel output greater than 6Kw then you really need two inverters, one to manage the export panel group and another to deal with the excess over 6kwp which cannot be exported

    Have I got that right?


  • Registered Users Posts: 1,627 ✭✭✭ quentingargan


    buzz11 wrote: »

    Have I got that right?
    'fraid not buzz. You can have a total of 6kw of inverters. Usually that will be a single one of 6kw. Many of these can take up to 8 or 9kw of panels, and to be honest, putting 9kw of panels on a 6kw inverter produces about 48% more than 6kw of panels would on the same inverter.

    If your system is producing more power than you are using at a moment in time, you will export the surplus, but ESB does not currently accept any export limiting and allow you have more than 6kw of inverters.

    If you really wanted more panels and had a battery system, you could build a system with only 6kw of inverters feeding the grid from a battery pack, but an infinite number of charge controllers charging the batteries that feed the inverter. But it'll cost yer!


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,862 CMod ✭✭✭✭ unkel


    putting 9kw of panels on a 6kw inverter produces about 48% more than 6kw of panels would on the same inverter.

    That figure of 48% doesn't seem to make sense. Would you mind explaining?

    You would have a lot more useful electricity in winter or on a cloudy day by oversizing the array, 50% more. But obviously in full sunlight most of the year the extra production over 6kW would be completely lost (0%) instead of going to FIT / battery / diverter / EV / even to the grid for free :p

    So overall I would expect the figure to be somewhere in the middle between 0% and 50%, not near one of these ends

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 1,627 ✭✭✭ quentingargan


    unkel wrote: »
    That figure of 48% doesn't seem to make sense. Would you mind explaining?

    You would have a lot more useful electricity in winter or on a cloudy day by oversizing the array, 50% more. But obviously in full sunlight most of the year the extra production over 6kW would be completely lost (0%) instead of going to FIT / battery / diverter / EV / even to the grid for free :p

    So overall I would expect the figure to be somewhere in the middle between 0% and 50%, not near one of these ends
    In practice, a 6kwPV systems spends very little of its time at bang on 6kw. I used PV-Syst to do simulations of 6.5kw of panels and 8.91kw of panels on the same 6kw inverter, all based on 30 degree south facing in Dublin. This is the result. It shows a 1.9% loss in KwHrs per KwP


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,862 CMod ✭✭✭✭ unkel


    Any link to the site you use, Quentin? I've tried

    Linky


    But it doesn't let you limit the size of your inverter

    Not that I don't believe you, but I like to see these things for myself :p It would solve a big problem that I thought I would have later on this spring / summer when I plan to install significantly more PV and would need to replace my inverter or add an inverter. Replacing my 3.6kW inverter with a 6kW one (easy enough to DIY) would be infinitely better than to have to get an electrician to install an additional inverter

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



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  • Registered Users Posts: 1,627 ✭✭✭ quentingargan


    unkel wrote: »
    Any link to the site you use, Quentin? I've tried

    Linky


    But it doesn't let you limit the size of your inverter

    Not that I don't believe you, but I like to see these things for myself :p It would solve a big problem that I thought I would have later on this spring / summer when I plan to install significantly more PV and would need to replace my inverter or add an inverter. Replacing my 3.6kW inverter with a 6kW one (easy enough to DIY) would be infinitely better than to have to get an electrician to install an additional inverter
    PV-Syst isn't free I'm afraid (quite the opposite...).

    Here is the simulation for 9kwP into 6kw inverter. You will see on the last page that inverter losses due to "over inverter nominal power" is 2.3% of total energy.

    I also enclose a similar pair of simulations on 15KwP of PV into a 10kw and 15kw inverter. In this case, the industrial roof pitch is 15 degrees, so the lost power is lower.


  • Registered Users Posts: 3,911 ✭✭✭ mp3guy


    'fraid not buzz. You can have a total of 6kw of inverters. Usually that will be a single one of 6kw. Many of these can take up to 8 or 9kw of panels, and to be honest, putting 9kw of panels on a 6kw inverter produces about 48% more than 6kw of panels would on the same inverter.

    If your system is producing more power than you are using at a moment in time, you will export the surplus, but ESB does not currently accept any export limiting and allow you have more than 6kw of inverters.

    If you really wanted more panels and had a battery system, you could build a system with only 6kw of inverters feeding the grid from a battery pack, but an infinite number of charge controllers charging the batteries that feed the inverter. But it'll cost yer!

    As usual, more confident misinformation around solar PV on boards, pervading and misleading countless people no doubt.

    This is incorrect, source: I'm on a domestic single phase connection, have 10.24kWp of panels and 9.2kWp of inverter power across two inverters that dynamically limit the export to 6kWp. SEAI don't care and the ESB provided written confirmation via email that this was acceptable.


  • Registered Users Posts: 105 ✭✭ Coltrane


    mp3guy wrote: »
    As usual, more confident misinformation around solar PV on boards, pervading and misleading countless people no doubt.

    This is incorrect, source: I'm on a domestic single phase connection, have 10.24kWp of panels and 9.2kWp of inverter power across two inverters that dynamically limit the export to 6kWp. SEAI don't care and the ESB provided written confirmation via email that this was acceptable.


    I have the same situation as mp3guy.


    But Quentin is I suspect also correct! In Ireland, two conflicting interpretations of the law are often practised at the same time.


  • Registered Users Posts: 3,911 ✭✭✭ mp3guy


    Coltrane wrote: »
    But Quentin is I suspect also correct! In Ireland, two conflicting interpretations of the law are often practised at the same time.

    This is definitely true.


  • Moderators, Sports Moderators Posts: 16,065 Mod ✭✭✭✭ slave1


    mp3guy wrote: »
    As usual, more confident misinformation around solar PV on boards, pervading and misleading countless people no doubt.

    This is incorrect, source: I'm on a domestic single phase connection, have 10.24kWp of panels and 9.2kWp of inverter power across two inverters that dynamically limit the export to 6kWp. SEAI don't care and the ESB provided written confirmation via email that this was acceptable.

    Good stuff, I've just gone from 4.1kWp to 7.4kWp and therefore maxed out my inverter (6kW Solis). I have an idea for another ~4kWp and either micro inverters or another dual MPPT inverter so will probably end up like yourself and need to think about dynamic limiting export too....another thread


  • Registered Users Posts: 1,627 ✭✭✭ quentingargan


    mp3guy wrote: »
    This is definitely true.

    There may indeed be multiple realities within ESB. My information comes from a number of discussions I had with the Head of Protection in ESB Networks. He was adamant that their current determining factor was fault current. What could go wrong if everything failed - if it meant more than 25A could be exported, that was that.

    I know industry groups are lobbying for G100 standards of export limiting to be accepted, but I knew of no site where this had been accepted without witness testing, and usually a G10 relay to back up the grid limiting in the inverter.

    I would be interested to know what was said in writing by ESB. It could be a useful precedent.


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,862 CMod ✭✭✭✭ unkel


    Is there any benefit in having more than one inverter? Quentingargan has stated that the overproduction of undersizing an inverter is barely lost at all. And I can see lots of cons of having more than one.

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,862 CMod ✭✭✭✭ unkel


    I would be interested to know what was said in writing by ESB. It could be a useful precedent.

    Aye, would be good if you could share that here, mp3guy. Maybe just a screenprint of their reply obviously with your personal details removed?

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 1,627 ✭✭✭ quentingargan


    unkel wrote: »
    Is there any benefit in having more than one inverter? Quentingargan has stated that the overproduction of undersizing an inverter is barely lost at all. And I can see lots of cons of having more than one.
    Just if you have multiple orientations, or too many strings with mismatched panels.

    On the 6kw limit, from HERE

    Micro-Generator is a source of electrical energy which operates in parallel with ESB Networks LV System and rated up to and including:

    25 amperes (6kW) at low voltage [230 volt] when the connection is single phase
    16 amperes(11kW) at low voltage [230/400 volt] when the connection is three ph

    If you wish to connect a generator with an output greater than that for micro-generation, go to ​connect a wind farm or other renewable generator.



  • Registered Users Posts: 3,911 ✭✭✭ mp3guy


    unkel wrote: »
    Aye, would be good if you could share that here, mp3guy. Maybe just a screenprint of their reply obviously with your personal details removed?

    My installer did the communicating but forwarded me the email, I won't be sharing it publicly online. All it took was emailing the Network Services Bureau at [email protected], stating I'm putting in 9kW of inverters with an export limit of 6kW and will NC6 be accepted in this case (as opposed to having to go with NC5).


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  • Registered Users Posts: 3,911 ✭✭✭ mp3guy


    unkel wrote: »
    Is there any benefit in having more than one inverter? Quentingargan has stated that the overproduction of undersizing an inverter is barely lost at all. And I can see lots of cons of having more than one.

    Features really. If you could have one giant inverter with batteries, EPS, 4 MPPTs, huge peak output power you'd be laughing, but I don't think they exist. Oversizing on individual inverters is dead handy e.g. with east/west arrays where it won't explode in the Summer but you get that long tail of production in the Winter.


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,862 CMod ✭✭✭✭ unkel


    Just if you have multiple orientations, or too many strings with mismatched panels.

    Hope I'm not hijacking the OP, but it is kinda relevant here. I have 5 * 290W Amerisolar panels on my high roof and 5 * 355W Longi panels on my kitchen roof, all south facing and in series connected in one string. Would you consider that too mismatched, as the output would only ever be a max of 10 * 290W or so?

    If I need to separate them out and I would add say a 12 * 360W Longi string (south facing on my shed that will be built soon), could I put that in series with the 5 * 355W Longi string, so I could use a dual MPPT 6kW inverter (7545kwp in total)
    mp3guy wrote: »
    My installer did the communicating but forwarded me the email, I won't be sharing it publicly online.

    Any reason for not sharing, if you hide any personal / identifying details?

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 1,627 ✭✭✭ quentingargan


    unkel wrote: »
    I have 5 * 290W Amerisolar panels on my high roof and 5 * 355W Longi panels on my kitchen roof, all south facing and in series connected in one string. Would you consider that too mismatched, as the output would only ever be a max of 10 * 290W or so?

    If I need to separate them out and I would add say a 12 * 360W Longi string (south facing on my shed that will be built soon), could I put that in series with the 5 * 355W Longi string, so I could use a dual MPPT 6kW inverter (7545kwp in total)

    It is hard to say exactly how MPPT tracking will deal with different panels on one string, but Amerisolar 290 Max power point current is 9.07A. That would throttle back the Longi from 10.27A, losing about 12% of their power in the process.

    Very little difference between 355 and 360 in the same type of panel. But you can't put 17 panels in series on most single phase inverters. Your limit there is

    Open circuit voltage * No. of panels * 1.15 temperature coef <600V


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,862 CMod ✭✭✭✭ unkel


    So the max I could lose is 355W * 12% * 5 panels or just over 200W and that only at full output in full mid day sunshine, in summer. I can live with that loss :D

    So keep those 10 panels on the one string and then all the new panels on the other string. Get a 6kW dual MPPT inverter. Paying even €100 extra for a triple MPPT inverter would not be worth my while.

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Registered Users Posts: 3,911 ✭✭✭ mp3guy


    unkel wrote: »
    Any reason for not sharing, if you hide any personal / identifying details?

    Just don't think a plain screenshot of a redacted email between a PV installer and ESB representative is actually more useful to anyone than being able to contact the ESB themselves. Also not interested in contacting the involved parties and asking can I post their email online, redacted or not.


  • Registered Users Posts: 1,627 ✭✭✭ quentingargan


    unkel wrote: »
    So the max I could lose is 355W * 12% * 5 panels or just over 200W and that only at full output in full mid day sunshine, in summer. I can live with that loss :D
    Not just in full midday sunshine. Your smaller panels would always throttle back your larger ones. The current passing through would decrease on all panels proportionally, though the MPPT voltage shifts a bit as well.

    If you already have a 3kw inverter for example, you can always add a second 3kw one and have four MPPTs altogether.


  • Moderators, Category Moderators, Motoring & Transport Moderators, Regional East Moderators Posts: 58,862 CMod ✭✭✭✭ unkel


    The issue is that I can replace my current inverter myself, quick and easy job, no costs involved, no materials needed. And to install a new one it's nearly impossible to find an electrician who would do it and then I'd be looking at €200 + materials, even if I did most of the work myself, so nearly €300 in all. I'll pass on that!

    "Wind is Ireland's oil" - An Taoiseach, 25/05/2022



  • Moderators, Sports Moderators Posts: 16,065 Mod ✭✭✭✭ slave1


    Numbers gotta make sense, glad to see this point being made.


  • Registered Users Posts: 5,155 ✭✭✭ Ubbquittious


    In theory if the meter doesn't ever see less than -6kW going through it you should be alright. Doubt anyone will be calling to your house and inspecting your setup in any great detail.

    Makes sense that there would be some limit to the size of the array for the inverter but once it isn't possible for the max current/voltage to be exceeded it should work whether the power is coming from an oversize array or from millions of hamsters running in hamster wheels. Though I'd guess it would be possible that certain times of the day on good sunny days too much current would be available for short periods when the sun is shining at just the right angle.

    Should be possible to come up with some form of current limiting circuit to put between the inverter and panels. They probably put the warning on the inverter so they can skimp on panel-side current limiting circuit. I have a charge controller kicking about that has a similar warning not to exceed certain size panels even if it's within the voltage range. Must mean that it doesn't have any self-limiting feature built in or the manufacturer believes it's not reliable

    Stellantis: All the sh1t brands under one roof



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  • Registered Users Posts: 2,721 ✭✭✭ graememk


    It is hard to say exactly how MPPT tracking will deal with different panels on one string, but Amerisolar 290 Max power point current is 9.07A. That would throttle back the Longi from 10.27A, losing about 12% of their power in the process.

    Very little difference between 355 and 360 in the same type of panel. But you can't put 17 panels in series on most single phase inverters. Your limit there is

    Open circuit voltage * No. of panels * 1.15 temperature coef <600V

    So I currently have 20 longi 360w. On a dual string solis 6kw inverter.

    Could that be pushed to 24 or even 28 panels?
    12 or 14 on each string?

    It's on low angle roof (walkable), split 50:50 north east/south west.


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