Explain these comments on a Gary Does Solar video?

[Alan Ambrose]

In this recent video, there's a couple of comments that I'm not sure I quite get. Here's a link to the video:

 

 

Why Are The DNOs Limiting Your EXPORT And Even Your INVERTER SIZE?

 

https://youtu.be/Bvpl9pvg8zk?si=4rLhJ-me57Pcwabu

 

 

Here are the two comments (I've highlighted the relevant bits that were raising questions for me in bold):

 

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One detail - only grid tie need approval. If your system isn't capable of pushing power into the grid (that's not capable as opposed to "set to 0") then you sidestep it at the cost of no export revenue. Setting up a big non grid tie inverter and putting the house on that with the grid as an input (generator basically) lets you side step all the mess in the difficult cases. It's not usually the best option but if you are getting 3.6kW and especially if you are also refused G100 with a bigger inverter it's definitely worth doing the maths on houses where you want bigger batteries and inverters, and remember it also lets you avoid the MCS costs too. I am guessing plug in solar is going to make it even more of a circus especially if they got 250,000 G98s submitted the month it goes legal 😎 Our setup actually has some grid tie with grid tie batteries and solar, and some non grid tie with other batteries/solar that runs the heatpumps and some other bits. It was the only way to make this big old building work within the allowed G99.

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>>>

The inverter size limitation is to do with failure cases with export limitation. If they calculate that the export limit fails, and the resultant voltage would exceed legal upper limits at your house, and your inverter voltage shutdown protections also fails, then they impose a choice: 1. Stipulate Inverter size limits, 2. Provide a quote to the solar installer for reinforce the DNO’s network so that it can accept the higher inverter size (often many thousands of pounds). At my house, I have an 8kw inverter with a 5kw export limit. When exporting 5kw, the voltage is about 247V. So there is some headroom between the export limit and the upper legal voltage. There are two a get out clauses though: 1. Install a 3.6kW inverter, but with 7kW Maximum Power Point Trackers. That enables you to hookup 7kw of solar, and at maximum power: 3.4kw can be fed to a dc coupled battery, even though the AC output is limited to 3.6kW. Sunsynk offers such an inverter. 2. Don’t connect your inverter to the grid. DNO’s only have jurisdiction over connections to their network. They have no jurisdiction over off grid systems. You could have an 8kw+ inverter supplying your house off grid. Then you can choose whether your house is connected to the grid, or your inverter, using a changeover switch. There’s no opportunity for export, or charge up with cheap overnight electricity though.

<<<

 

 

The reason I'm asking is that I'm planning on having a lot of panels and inverter power and self consuming as much as possible. I'm planning on over capacity so that I can make the shoulder seasons (i.e. spring & autumn) mostly self-consumption too. I don't really care about the export - I'm guessing the rates will continue to fall until it's a waste of time.

 

 

 

 

[JohnMo]

Lots of panels on a G98 inverter, massive overclock is the way to go. Easy no permission needed, just a G98 notification.

 

Self consumption is fine in theory, in practice difficult especially in the summer, you just end with loads of hot water you can't use. Just go with Octopus and pay £250 and get the export (wish I did it 3 years ago), East Suffolk you will generate tonnes of energy even with a 3.68kW export limits.

 

My advise, self install as many panels as you can to stay within the max voltage limits of your inverter, it's cheap, spend £250 to get with octopus. Export everything you don't normally consume.

[Dillsue]

10 hours ago, Alan Ambrose said:

 Setting up a big non grid tie inverter and putting the house on that with the grid as an input (generator basically) lets you side step all the mess in the difficult cases.

This is basically an off grid setup with the inverter taking one or more energy sources to power the house. Intended to use batteries and PV with a generator as a backup. In terms of the inverter generating anything, and being regulated by the DNO, it only generates power to supply the house as so far there's no grid connected. Now swap the generator input for a grid connection and as far as the grid is concerned the inverter is only a load but no generation capacity on the point where the grid is connected.

 

10 hours ago, Alan Ambrose said:

it  also lets you avoid the MCS costs too

MCS isnt required for any installation works. If the video is suggesting otherwise then take it with a pinch of salt

 

10 hours ago, Alan Ambrose said:

 DNO’s only have jurisdiction over connections to their network. They have no jurisdiction over off grid systems. You could have an 8kw+ inverter supplying your house off grid. Then you can choose whether your house is connected to the grid, or your inverter, using a changeover switch. 

As stated use a changeover switch to choose if your house is supplied from the grid OR from an off grid system that the DNO doesn't regulate.

 

What's your concern about what is said above??

[Beelbeebub]

I get limiting the export for the reasons laid out in the video, but the idea of limiting the inverter seems to rest on the theory that the export limit might fail and the inverter pump out whatever it's maximum at that moment is. 

 

But that seems to assume that the export limit system (a current meter and some software) would fail. Irrc my system just shuts down if the current clamp isn't working. Surely the whole point of g100 export limit certification is to make system the design and implementation is as foolproof as possible. 

 

Moreover, if the DNO is worried that you 8kw inverter could lead to severe problems if it were to pump the full 32a or whatever instead of the 16a limit into the local grid, that implies the local grid is running very very close to it's margin, less than 16a in fact, which could easily be gobbled up tomorrow by a neighbour notifying a g98 install. 

 

What I'm getting at is: has anyone actually heard of a dno limiting the inverter size for a regular hybrid inverter install with g100 limit certification? 

[Dillsue]

1 hour ago, Beelbeebub said:

What I'm getting at is: has anyone actually heard of a dno limiting the inverter size for a regular hybrid inverter install with g100 limit certification? 

If a DNO does limit the inverter size then effectively they're saying they dont trust the ENA standards and/or the G100 certification/self certification process

[Beelbeebub]

1 hour ago, Dillsue said:

If a DNO does limit the inverter size then effectively they're saying they dont trust the ENA standards and/or the G100 certification/self certification process

Exactly, which makes a mockery of the whole idea of g100 certification. 

 

Maybe someone could bring out some sort of 2way breaker - 80/100a incoming (as per normal) but 16a outgoing (or whatever the dno says the limit is) that would provide an extra layer of protection. 

[Dillsue]

The other rationale for a DNO limiting inverter size could be customer tampering with G100 settings?? AFAIK G100 settings are supposed to be password protected with an installer/manufacturer password that the customer doesn't know. There's been several posts on here where people have said they'll lift the export limit above the DNOs approved limit as they have the installer password.

 

The battery inverter I've just installed has a single password that protects G100 settings and all "advanced" settings including TOU charge scheduling. Technically I shouldn't have access to the G100 settings but legitimately have access to the TOU settings so this inverter is poorly designed from a G100 compliance perspective.

[Beelbeebub]

Surely, if DNOs wanted to police the export limits to check nobody is sneakily upping their export limit, they need to check the meter measured export. It's stored in half hourly blocks long term and availible in minute to minute blocks as well

 

If some is exporting 2.5kwh in a half hour block they are certainly breaching their 3.6kw export limit. 

 

One strategy would be to cap export payments at whatever your dno limit is. Therefore removing any incentive to over export.

[JohnMo]

24 minutes ago, Beelbeebub said:

exporting 2.5kwh in a half hour block they are certainly breaching their 3.6kw export limit

That's misplaced logic. If your export limit is 3.6kW and you produce 3.6kW for one hour that's 3.6kWh assuming 3.6kW is exported.

 

24 minutes ago, Beelbeebub said:

One strategy would be to cap export payments at whatever your dno limit is. Therefore removing any incentive to over export.

How does that work, assume 12 hrs a day at 3.6kW output, so 43kWh export. To get that would be nice.

 

I must have better things to do on a Sunday, than answer this rubbish.

[Beelbeebub]

7 hours ago, JohnMo said:

That's misplaced logic. If your export limit is 3.6kW and you produce 3.6kW for one hour that's 3.6kWh assuming 3.6kW is exported.

 

How does that work, assume 12 hrs a day at 3.6kW output, so 43kWh export. To get that would be nice.

 

I must have better things to do on a Sunday, than answer this rubbish.

You are correct but if you read the post carefully you'll see I said half hour block (the standard time slice for the grid). 

 

If your export limit is 3.6kwh and you export any more than 1.8kwh (eg 2.5kwh) in a half hour block you have breached your export limit. 

 

The half hour time slice means it is much harder to hide any over export with any inevitable lower export periods eg clouds going over sun for 10 minutes and the system is already working at that resolution. 

 

If you do this for every half hour slice you can discourage over exporting because there will be no financial benefit and you might get a visit from the DNO. 

 

 

[dpmiller]

isn't the export limit more about overvoltage in the local grid, in which case it could be a near-instantaneous issue...

[-rick-]

42 minutes ago, dpmiller said:

isn't the export limit more about overvoltage in the local grid, in which case it could be a near-instantaneous issue...

 

Inverters have overvoltage protections built in. They shut down when the voltage gets too high and there are at least some saying that the limits imposed on inverters are too strict so they are likely to turn off too early.

 

Doesn't mean there might not be problems with significantly excess provision on a local network but the protections for safety are already there. The inverter size limits are I think it's a way to prevent existing installs having to shutdown due to new installs. Given the benefit of solar outside of peak production I feel if these are the reasons they should be reassessed.

 

It's feasible for a standard to be made so that inverters scale back their output gracefully rather than trip off. If that could be done then I'd guess the whole approval process could be significantly simplified (and people would be more likely to install bigger systems that might be limited in peak but net produce a lot more outside the peak).

[SteamyTea]

On 26/04/2026 at 21:25, -rick- said:

It's feasible for a standard to be made so that inverters scale back their output gracefully rather than trip off.

I think it does that because as it approaches the max voltage (253V) less current will flow. 

There will be variations because local grid voltages will vary.

 

[-rick-]

10 minutes ago, SteamyTea said:

I think it does that because as it approaches the max voltage (253V) less current will flow. 

 

Not sure that's right with switching inverters unless programmed to do so. Got anything to back it up?

 

Their internal voltages will be higher than the grid limit, their limitation will come from the voltage seen on the grid line. So they should be able to output the full current up to cut off.

[SteamyTea]

1 minute ago, -rick- said:

Got anything to back it up?

 

No data, but when I was installing them I often noticed that the cooling fans went to full power as the voltage limit was reached. The power meter also showed a decline.

We almost exclusively fitted SMA inverters.

[-rick-]

Just now, SteamyTea said:

but when I was installing them

 

Is there anything you haven't done?

[SteamyTea]

4 minutes ago, -rick- said:

 

Is there anything you haven't done?

Loads, but still time.

[billt]

On 26/04/2026 at 21:25, -rick- said:

It's feasible for a standard to be made so that inverters scale back their output gracefully rather than trip off. 

 

In principle it's quite easy, unfortunately the grid would need to be re-engineered.

 

My system is off grid and AC coupled using SMA inverters. The master battery charger/inverter changes the mains frequency as the batteries become fully charged and the PV inverters reduce their output accordingly until they stop producing completely. All (!) you would need to do is make the grid change frequency when too much power is being fed into the grid.

 

Of course it wouldn't work as there will be too much local variability in over production as well.

[-rick-]

57 minutes ago, billt said:

My system is off grid and AC coupled using SMA inverters. The master battery charger/inverter changes the mains frequency as the batteries become fully charged and the PV inverters reduce their output accordingly until they stop producing completely. All (!) you would need to do is make the grid change frequency when too much power is being fed into the grid.

 

Changing grid frequency is how the overall grid responds to load as frequency directly affects power generated due to the spinning generators that make up most of the grid.

 

Software driven inverters have more flexibility. They are not constrained by big rotating turbines and generators. So I believe it is possible to inverters to choose how many amps to export independently of the frequency and therefore have a configuration option to have a voltage level where output is tapered off that is set below the max voltage trip.

 

Given our grid runs quite close to the upper limit in many places the scope for this currently may be limited, but there are plans to change the acceptable voltage range of the grid (https://www.efixx.co.uk/Articles/Proposed-Changes-to-UK-Mains-Voltage-Limits-Explained) and if that happens the the average grid voltage might drop. This would give more room to inverters to generate in the first place, but might also give room for regulations to support sensible production reduction above say 250V to produce a more stable grid when lots of inverters are online at peak times.

 

Wouldn't hold my breath for it though (would seem like the sort of thing that would already have been proposed to align with the voltage change if it was going to happen).

[Beelbeebub]

Isn't the issue that a local grid may be very spread out so the voltage at the transformer needs to be (say) 249v to ensure thr person at the farm miles away gets at least 220 (or whatever the lower limit is) in the worst. 

 

Which was fine when everybody consumed. The local voltage could be set high at the transformer and would never go higher as everyone consumed. 

 

But if the people next to the transformer are exporting, they need to push the voltage above 249 to export, and if there are too many people too close the voltage could go above 253v.

 

If the grid lower the transformer voltage to 245 to give headroom, they endup only supply 216 to the poor sod at the end of the line. 

 

The solution is to reduce the voltage drop between transformer and the end of local network ie new cables. 

 

 

[joth]

18 hours ago, billt said:

On 26/04/2026 at 21:25, -rick- said:

It's feasible for a standard to be made so that inverters scale back their output gracefully rather than trip off. 

 

In principle it's quite easy, unfortunately the grid would need to be re-engineered.

 

It's also unnecessarily complex, from the grid operators view. Scaled over 10s or 100s of houses, the current system of individual inverters just shutting off when hitting the threshold has the system wide effect of gracefully reducing the amount put into the grid (as each inverter shuts of one by one, converging to a stable number exporting during periods of strong sun and low consumption). It just sucks for the individuals that get hit by it first as they don't get to self-consume any of their solar if the inverter has safety shutdown.

 

What can be very frustrating is if the inverter is on a long AC line within the property (after the meter) then it may see >253V even though the grid itself outside the property is no where near that. It would be tempting to say either allow the inverter to exceed 253V so long as it is export limited (to zero export) or if there's a voltage sense at the meter tails.

Of course, this is messing with a safety system, and also risks damaging other equipment in the home if that starts seeing > 260V, so a terrible idea in practice. The answer here is move the inverter as close to the meter as possible, and ideally have dynamic export limitation (to do near-zero export when it sees the grid is over 250V) and then it will never need to trip over 253V while still satisfying the home's own demand.

A DC-coupled battery also helps capture what would otherwise wasted solar, oc.

 

 

 

[-rick-]

2 minutes ago, joth said:

It's also unnecessarily complex,

...

2 minutes ago, joth said:

The answer here is move the inverter as close to the meter as possible, and ideally have dynamic export limitation (to do near-zero export when it sees the grid is over 250V) and then it will never need to trip over 253V while still satisfying the home's own demand.

 

Huh? This is what I was proposing which I think you just called unnecessarily complex? Am I misunderstanding something?

[-rick-]

22 minutes ago, Beelbeebub said:

If the grid lower the transformer voltage to 245 to give headroom, they endup only supply 216 to the poor sod at the end of the line. 

 

This is exactly what's being proposed by the grid (see the link I posted earlier). Reducing the minimum acceptable voltage to 207V.

 

Modern equipment shouldn't really care about the voltage being that low (the minimum voltage in Europe is 207V and almost all electronics we have bought in the last 30 years have been designed to work in that market). Link suggests a 4% reduction in resistance heating output, slightly dimmer lights. Most tricky issues being non-inverter driven motors and UPSes with to high a brown-out setting (likely can be adjusted).

[Dave Jones]

On 22/04/2026 at 20:47, JohnMo said:

Lots of panels on a G98 inverter, massive overclock is the way to go. Easy no permission needed, just a G98 notification.

 

Self consumption is fine in theory, in practice difficult especially in the summer, you just end with loads of hot water you can't use. Just go with Octopus and pay £250 and get the export (wish I did it 3 years ago), East Suffolk you will generate tonnes of energy even with a 3.68kW export limits.

 

My advise, self install as many panels as you can to stay within the max voltage limits of your inverter, it's cheap, spend £250 to get with octopus. Export everything you don't normally consume.

the problem with self install is no MCS paperwork. Octopus wouldnt accept any export from me (for payment) without it.

[joth]

8 minutes ago, -rick- said:

...

 

Huh? This is what I was proposing which I think you just called unnecessarily complex? Am I misunderstanding something?

Fair point 🤣

What I was trying to say was it would be unnecessarily complex to try and design something elaborate into the standards requiring "intelligent" collaboration across a system of inverts communicating with each other, when you can achieve it within the existing pretty dumb standard.