Microgeneration 6kwh limit

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.

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!

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

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

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 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.

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.

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.

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.

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.

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

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.

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!

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