G100 export limiting

[Oldgreybeard]

The thread on the Solis inverter that veered into G100 and export limiting got me thinking. The export limit is the thing that seems to cause a fair bit of hassle, especially for anyone adding an additional inverter, even if it's going to charge batteries. DNOs treat battery inverters as if they are going to export their full power to the grid, even though most people won't normally have them set up this way. They take this view because they can all (I think) be set up to export via settings that the user can adjust (and there could be good reasons why exporting to the grid from batteries makes sense for some).

Years ago I looked into fitting a G59 (as it was then) export limitation device, but in the end I didn't need it and the DNO were OK with me not exporting more than 6kW to the grid. Recently I've been looking at ways to increase our PV generation by adding more panels. I have been thinking along the lines of just having the extra panels connect to the batteries, using DC, via an MPPT controller, really to avoid having to jump though hoops again with the DNO. We very rarely hit our agreed 6kW export limit now, I've not seen us come close to it since the batteries were installed a year or so ago, as by the time the batteries are charged the generation peak is usually over.

I've been thinking again about ways to fit a second PV inverter and avoid having to deal with the DNO again, and one way would be to just fit a G100 export limiting device. These work by isolating an inverter if the total export exceeds the agreed limit for 5s. In reality I doubt it would ever operate at all, so wouldn't cause any problems, but if the DNO ever enquired being able to point them at the box and prove that their network was safe from anything I was doing could be useful, as long as it's not too expensive. It also avoids any future hassle if I want to change thing or add more PV.

Having looked around, you can get approved DIN rail mount energy meters that have a programmable output that can be used to switch a contactor. Fitting one of these meters to the consumer unit, so it's metering the whole supply and having its programmable output controlling a contactor that can isolate the second inverter seems to be a way to make a useful G100 export limiting device that's independent from any inverter. The plan would be to programme the meter to switch off the second inverter if the installation exceeded the export limit for 5s. This looks to be fairly easy to do, from my limited reading of some datasheets.

The wiring up looks dead easy, just needs the meter CT to be fitted around the supply tail and the contactor wired to isolate any additional inverter(s). In theory I could then had as many extra inverters as I like without causing any issues for the DNO. If this isn't too expensive it may well be a useful way to avoid a bit of DNO hassle for anyone that already has one PV system and wants to add to it. I'll try and sift through the guff I've been looking through and see if I can put together an idiots guide.

[nowty]

OGB, simply implementing a G100 device does not avoid you from dealing with the DNO. If your already at 3.68kW of grid connected inverter power, then its either a G99 fast track or G99 application. Both of those applications are pre-install applications.

If its a G99 fast track application G100 is mandatory as its a largely paperwork exercise. If its a G99 application, then it depends on what the DNO what you can have or what you need to do.

If you install an OffGrid system or added capacity on the DC side, then there is no DNO involvement.

This is the general info for all DNOs when connecting generating equipment to the grid.
Plenty of guides, and flowcharts in there.
https://www.energynetworks.org/operatin ... y-networks

[Oldgreybeard]

OGB, simply implementing a G100 device does not avoid you from dealing with the DNO. If your already at 3.68kW of grid connected inverter power, then its either a G99 fast track or G99 application. Both of those applications are pre-install applications.

If its a G99 fast track application G100 is mandatory as its a largely paperwork exercise. If its a G99 application, then it depends on what the DNO what you can have or what you need to do.

If you install an OffGrid system or added capacity on the DC side, then there is no DNO involvement.

This is the general info for all DNOs when connecting generating equipment to the grid.
Plenty of guides, and flowcharts in there.
https://www.energynetworks.org/operatin ... y-networks

Yes, I understand that, already been through it back when it was G59, still have the scars, too, as the DNO (SSE PD back then) definitely weren't at all clued up on domestic single phase PV systems that were over 16A per phase. I've been through all the guides and have read G98, G99 and G100 through, just to be sure that there is still a read-across from back when I did the G59 application.

The key thing here is that the G100 certification of at least some battery inverters is a bit mythical (it can very easily be turned off - perhaps accidentally - by the user). There's also a need to go though the DNO process any time you change the system, for example, swapping an inverter requires that the DNO are informed and be reassured that the G100 limitation functionality is still present.

The advantage of doing it with a simple programmable meter and contactor is that you do it once and it then doesn't matter if you swap inverters a dozen times, as the G100 limitation device hasn't changed. I have three possible future plans, first to add panels along the east of the house as a walkway, then I might add some more along the top of a high wall, and finally I might add some to the garage roof. AC coupling would be easier to do, especially for the detached garage, as there is already power to it, and it's about 30m from the house, so running extra DC cables would be a hassle (and involve digging up the patio!).

[openspaceman]

It looks like their webserver is currently down.

I am increasingly thinking I shall go down the route of connecting 1.5kW of array to a charger and only charging a battery unless. As the panels will operate nearly flat I cannot see them peaking.

Has anyone any experience of the growatt batteries, the manual says the capacity can be doubled up but is this by simply connecting a second battery in parallel (after getting the SOC correct?? Can a pylontech battery be used as the second battery or will there be voltage difference issues?

[cojmh]

Hi OGB,

What you say makes sense to me, but I was under the impression that any G100 export device had to be certified and not able to "tampered with" by us users.

So whilst it makes sense, I don't know if it will satisfy the DNO.

I am interested as this is possibly something I am going to have to do myself.

[Oldgreybeard]

Hi OGB,

What you say makes sense to me, but I was under the impression that any G100 export device had to be certified and not able to "tampered with" by us users.

So whilst it makes sense, I don't know if it will satisfy the DNO.

I am interested as this is possibly something I am going to have to do myself.

I can't find any clear definition as to what the anti-tamper clause in G100 really means. All it states is this:

A means of ensuring the applied settings are tamper proof will need to be demonstrated. A
copy of any additional settings associated with the ELS shall be displayed on site alongside
any EREC G59 or G99 protection settings.

and this:

G100 requirement:
Once installed and commissioned, the scheme settings should not be capable of being
readily altered by the Customer and should only be changed with the written agreement of
the DNO.

For our Sofar inverter all the settings, including the G100 one, can easily be changed by the user. I change the settings fairly often, albeit just to switch from time-of-use mode to auto mode (depending on the weather forecast), but it's a doddle to change the other settings, in fact I have to scroll past most of them to get to the mode setting (no idea why it's on the second screen).

It would be very easy to make a tamper proof G100 relay. The meters I've been looking at have their switched output programmed by connecting them to a laptop and using a bit of free software that comes with them. The settings can't be altered without connecting the meter to a laptop, so once installed inside a consumer unit they would be pretty much tamper proof. Certainly this would be more tamper proof than either the Sofar or Solis inverters, and probably a few others, too.

[patrickl]

[Long time lurker on The Old Forum, so very glad to have discovered the new place! Liking the vibe!]

Can the G100 certification requirements be avoided if the system is built as the equivalent of an always online UPS / classic generator fed off-grid configuration, feeding an isolated consumer unit? i.e. grid -> charger -> batteries | inverter -> isolated distribution board. In this setup, there could never be any export, as the inverter is not connected to the grid. This arrangement would suit people like me just fine, as I don't claim FITs.

A tangential issue that is relevant to my plans, which possibly include adding some battery storage - what do you do if it's not possible to physically locate a hybrid inverter near to the grid supply, which seems to be the default assumption afaics, in terms of current sensors/import-export monitoring? Are there any budget end systems capable of supporting some sort of remote sensing - ideally powerline, as running a signalling cable isn't that practical?



Thanks!

P.

[nowty]

[Long time lurker on The Old Forum, so very glad to have discovered the new place! Liking the vibe!]

Can the G100 certification requirements be avoided if the system is built as the equivalent of an always online UPS / classic generator fed off-grid configuration, feeding an isolated consumer unit? i.e. grid -> charger -> batteries | inverter -> isolated distribution board. In this setup, there could never be any export, as the inverter is not connected to the grid. This arrangement would suit people like me just fine, as I don't claim FITs.

Thanks!

P.

You are effectively talking about an OffGrid system which does not need any DNO permission.

[Oldgreybeard]

Yes, no problem at all with setting up a non-grid tied island, at least in theory. Not something I've ever done, but what you'd be doing would be setting up an off-grid system with the grid only providing DC charging. Main issues are the same as those with off-grid systems, mostly things like managing the peak load so the inverter doesn't shut down if there are short duration high power appliances turned on. It's not unusual for us to see around 6kW or so for a short time with the oven and hob on, for example.

[patrickl]

You are effectively talking about an OffGrid system which does not need any DNO permission.

In one of your threads, Nowty, you say (I think) that you originally started out this way - I seem to remember you started out scavanging from first gen Growatts? - but wouldn't do it that way again. Is that for the reasons outlined by OGB or is there some other pitfall?

Now that, afaics, new signups to off-peak tariffs are a non-starter (I'm on 22p/kWh until Oct 23 with Octopus, having timed the switch from agile pretty much perfectly), I would only be time-shifting solar. In the shoulder months, I can't see how that is going to help much as PVGIS predictions show solar generation to be 25% of total daily (24h) consumption if I upgrade to 6.5kWp in an East & South split. I guess there is some marginal benefit to the ability to offset heavy loads, but that's difficult to model with the data I have and intuitively feels 'small'.

Sorry for the thread hijack. (The need to place the inverter a distance away from the incoming grid supply whilst capping export as required by DNO is the driver here)

Thanks for the replies so far,

P.