Using an inverter as off grid (so no g98/g99g100) with 4 pole changeover contactor - does the DNO need to be involved

[jimseng]

25 minutes ago, JohnMo said:

I thought that for a long time, after doing a self installation. But in the ended paid out £250 to octopus to get paid for export. No off set my bills with export payments. You will be surprised by how much slips to the grid even with active management to prevent it.

Do you mean there was a fee to Octopus to allow you to get paid for a non MCS approved install? The whole energy supplier side of things is another bit of research I have to do as I don't even have a DNO connection yet. Sometime in the new year.

[JohnMo]

1 minute ago, jimseng said:

Do you mean there was a fee to Octopus to allow you to get paid for a non MCS approved install? The whole energy supplier side of things is another bit of research I have to do as I don't even have a DNO connection yet. Sometime in the new year.

You pay a fee for the to due diligence on your install. You have to pass on documents about the electrical install and anything structural to prove it's fit for purpose. Once that bit through the register you export. So way cheaper than paying an installer the MCS tax. Octopus are the only company I could find that does this.

[-rick-]

3 minutes ago, jimseng said:

Do you mean there was a fee to Octopus to allow you to get paid for a non MCS approved install? The whole energy supplier side of things is another bit of research I have to do as I don't even have a DNO connection yet. Sometime in the new year.

 

Sounds like maybe a step back is in order. If you want to export you need DNO approval. AFAIK if you don't want to export you can get inverters and set them to not export and not worry about the DNO. eFIXX interviewed someone who got e.On to approve a non-MCS install for export too (though the whole install was don't by a qualified electrician).

[jimseng]

22 minutes ago, -rick- said:

 

AFAIK if you don't want to export you can get inverters and set them to not export and not worry about the DNO. 

That isn't how I understand it. My understanding is that to even fit an inverter that is capable of > 3.6k export, even if it is set to export nothing requires a G100 application and maybe even a witness and password to prevent the settings from being changed. Or a G100 limiting device between the meter and the inverter (costly from what I have found). If I am wrong then that would simplify everything. If there is an inverter that is incapable of exporting to the grid then I expect that would work. There is a Victron option of a 5Kw set to 3.6kw in firmware from the supplier, and therefore G98, but it then effectively becomes a 3.6kw inverter, all be it with a higher grid pass through, which, to me, seems pointless.

Edited Saturday at 11:53 by jimseng

[JohnMo]

Playing devil's advocate, not saying this is right or wrong - if you can set export to zero, such as all Sunsynk inverters, do you need to tell anyone anything? You aren't influencing the grid your system is off grid for exports, only importing to charge battery.

Edited Saturday at 12:22 by JohnMo

[jimseng]

Quote

do you need to tell anyone anything?

Maybe. I'm a bit of a stickler for rules in case it comes back to bite me. If I got investigated it might become tricky. I'm open to all suggestions though.

Quote

only importing to charge battery.

I will be using the grid power too, otherwise I would fit a battery charger and not connect the inverter to the grid at all, that would mean I wouldn't need to involve the DNO. I have thought about that route but I think it would be a bit limiting in the winter. I must admit I haven't done the maths yet as I'm not sure how much battery power I will start with.

Edited Saturday at 12:34 by jimseng

[JohnMo]

8 minutes ago, jimseng said:

I'm not sure how much battery power I will start with

We have 13kWh, with a 6kW inverter, all electric house, with ASHP (6kW). Last year we were on E7 tariff and for about 300+ days the battery got us through the day (charged on low tariff plus PV) the other days we imported peak electricity for some of the day. Now on Cosy (3x cheap periods) and expect to get closer to 365 days per year on battery without peak rate import.

 

Some other things to throw into the mix

Most hybrid inverter in a power cut will only power a couple of dedicated UPS circuits, not the whole house. AC coupled battery inverter will continue to run whole house without interruption (make model specific - GivEnergy AIO does for example).

Inverter size matters, to small and you import peak tariff rates. For example 3.6kW inverter, if draw is above 3.6kW that excess comes from the grid directly.

 

So need to understand functionality that is important you.

 

PV yield by month (summer stupid high, winter stupid low). Loads of PV may not make sense if your inverter just limits generation 6 months if the year.

 

Do you have power cuts, if no no benefit having something that powers whole house.

[Beelbeebub]

How many panels are you wanting? 

 

AFAIK most inverters can't handle more than 2x (often 1.5x) panels being connected to them. 

 

So if you fitted an g98 device with a hard max output of 3.7kw you couldn't fit more than 7.2kw peak of panels (16ish). 

 

You would also have the situation where any load greater than 3.7kw (eg kettle and toaster) would require grid import. Even on a sunny summer day when your panels could output 7kw.

 

Unless you want a limited system I'd suggest you pretty much need to have a higher power inverter with software export limits. 

 

That means you need an export limited device.

 

This has the added advantage that, should your infrastructure be upgraded, you can increace your export very easily without having to replace your system. 

 

The worst case is you fit a sigenstor or SolaX or whatever, make an application and they come back and say "2kw max", and you set your inverter to 2kw max export. 

 

Can I also ask why you want low voltage batteries? The trend is to move to high voltage systems which are more efficient especially at the higher inverter powers. 

 

At 8kw your batteries, connectors and inverter will need to handle 160A plus.  

 

 

 

Edited Saturday at 13:12 by Beelbeebub

[Beelbeebub]

Doh! Pretty much beaten too it by @JohnMo ! 

[Beelbeebub]

I'd also say with a high power inverter (eg 8kw) you can wire your whole house from the inverter and be immune to power cuts.

 

Depending on manufacturer the cost of the high output inverters is not much on top of the low output ones. 

 

Eg a solax 3.7kw plus a battery is £2,975 whilst the 8kw version is £3,050. At that price difference it's an absolute no brainer to go for the 8kw unit and export limit it.  

[jimseng]

Quote

Eg a solax 3.7kw plus a battery is £2,975 whilst the 8kw version is £3,050. At that price difference it's an absolute no brainer to go for the 8kw unit and export limit it.  

Exactly. A 10kw Sunsynk and a 16kWh Fogstar battery is around £3.5k all in. That is a G100 / 2  compliant system. With the 60 amp pass through I think I would struggle to max it out, unless I really try.

[Dillsue]

5 hours ago, jimseng said:

That is a question I have mused over. Passing the ac output of the G98 device to the ac input of a slave device set to zero export. Or a generator input. But in order to live with the system, a high ac passthrough is important to me. I don't want to split my loads into on and off grid if I can help it. That is why I am looking at a 10kw system for an all electric house. 3.6kw isn't enough for my long term ambitions.

I should add that grid export is not relevant to me as it is a a self install. Off peak battery charging and lots of battery capacity is important. 

My comments were on parallel wired G98 devices where they are all connected direct to the grid. If you are series wiring then it's only the final device connected to the grid that needs to meet the DNO specs

[Dillsue]

4 hours ago, JohnMo said:

Not exactly sure, but you cannot have a G98 approved inverter that does G100 management - can you? If it's G98, it's G98, not something else as well. Otherwise it's a G99/G100?

?? You suggested 3 G98 devices in parallel with 1 as master and retain the G98 certification which isn't possible.

[Dillsue]

4 hours ago, -rick- said:

If you want to export you need DNO approval. AFAIK if you don't want to export you can get inverters and set them to not export and not worry about the DNO. eFIXX interviewed someone who got e.On to approve a non-MCS install for export too (though the whole install was don't by a qualified electrician).

If you connect any generator to the grid, the DNO gets involved whether you intend to export or not. It's a legal requirement covered in the National Terms of Connection that everyone with a grid connection is signed up to via your electricity supply contract.

 

If the generator is a PV inverter with a G98 cert you tell the DNO after you've connected it. Anything else you ask for permission BEFORE you connect regardless of whether you've set it to zero export.

 

Eon won't have approved a system for export as only the ENA/DNO can do that. Eon may have agreed to buy any exported electricity 

[Dillsue]

4 hours ago, jimseng said:

That isn't how I understand it. My understanding is that to even fit an inverter that is capable of > 3.6k export, even if it is set to export nothing requires a G100 application and maybe even a witness and password to prevent the settings from being changed. Or a G100 limiting device between the meter and the inverter (costly from what I have found). If I am wrong then that would simplify everything. 

You're understanding is correct

[Dillsue]

3 hours ago, JohnMo said:

Playing devil's advocate, not saying this is right or wrong - if you can set export to zero, such as all Sunsynk inverters, do you need to tell anyone anything? You aren't influencing the grid your system is off grid for exports, only importing to charge battery.

And if the person doing that was your neighbour and their son inadvertently reset the limit to max export that subsequently pushed the grid voltage up high enough to trip your PV would you be happy? If the same excess voltage tripped another neighbours medical equipment, would they be happy? It's all regulated for good reason and I'm sure you know whether it's right or wrong

[JohnMo]

1 hour ago, Dillsue said:

?? You suggested 3 G98 devices in parallel with 1 as master and retain the G98 certification which isn't possible.

Why? The units I spoke about are only parallel at the battery, so no different to adding more battery capacity, that all DC. The other connection is a CAN connection. The unit already has an inverter larger than 3.6kW, but is still certified as G98. With a master inverter you only have one inverter controlling stuff.

[JohnMo]

53 minutes ago, Dillsue said:

son inadvertently reset the limit to max export

Why would you let your kids f*CK about with stuff like this? But with the Sunsynk inverter you can set export limits, it's either allowed to export or it's not, there are no settings for 1kW or 10kW, just the default G98 setting 

[jimseng]

4 hours ago, JohnMo said:

But with the Sunsynk inverter you can set export limits, it's either allowed to export or it's not, there are no settings for 1kW or 10kW, just the default G98 setting 

Not sure I fully understood this. Can you expand? When I briefly looked through the manual today it seemed you can set the export to any KW value, but it was a fairly cursory browse through. I'm talking about the Sunsynk 10 / 12k inverter. If I do want to try and export at some point Then it likely going to have to be the 2k limit under a G100 application with anything other than a G98 certified inverter.

[JohnMo]

16 minutes ago, jimseng said:

Not sure I fully understood this. Can you expand? When I briefly looked through the manual today it seemed you can set the export to any KW value, but it was a fairly cursory browse through. I'm talking about the Sunsynk 10 / 12k inverter. If I do want to try and export at some point Then it likely going to have to be the 2k limit under a G100 application with anything other than a G98 certified inverter.

I was previously talking about the combined AC coupled inverter battery from Sunsynk, that was G98 approved. I suggest 3x units. They are G98 approved and the only possible options are to allow export or not allow export at all. @Dillsue said that wasn't possible to couple several units together and retain G98 certification, which I am not convinced is correct.

 

The bigger G99/G100 hybrid inverters, you can set any export limits you want. But @Dillsue is concerned your kids or his kids will mess with settings and you will shutdown the local grid. Not sure about that either.

[jimseng]

27 minutes ago, JohnMo said:

I

The bigger G99/G100 hybrid inverters, you can set any export limits you want. But @Dillsue is concerned your kids or his kids will mess with settings and you will shutdown the local grid. Not sure about that either.

Actually, re reading the manual I'm still trying to get my head around how to set an export limit, but I am getting there.

Luckily I don't have kids. I'm not convinced I will let any into my new house. They are noisy, sticky things that leave jam and muddy footprints everywhere. 

[Dillsue]

7 hours ago, JohnMo said:

Why? The units I spoke about are only parallel at the battery, so no different to adding more battery capacity, that all DC. The other connection is a CAN connection. The unit already has an inverter larger than 3.6kW, but is still certified as G98. With a master inverter you only have one inverter controlling stuff.

My mis understanding then. Originally you said 3 x AC coupled battery inverters connected in parallel which I took to mean they were all connected to the grid.

[Dillsue]

7 hours ago, JohnMo said:

Why would you let your kids f*CK about with stuff like this? But with the Sunsynk inverter you can set export limits, it's either allowed to export or it's not, there are no settings for 1kW or 10kW, just the default G98 setting 

In this context "their son" is anyone who doesn't understand what the regulation is for and inadvertently or intentionally removes the export limit without considering the implications. That's a potential spin off from by passing the regulation which was being hinted at

[SteamyTea]

6 hours ago, jimseng said:

Luckily I don't have kids. I'm not convinced I will let any into my new house. They are noisy, sticky things that leave jam and muddy footprints everywhere. 

My mother, who is 96, will agree with you there.