DNO restriction to 2Kw export

[RobEdwards]

Hi all, first time poster here looking for any advice on how I can get around SPEN limiting me to a 2kw export with our newly installed system.

 

Bit of a long story however the basics are I had a PV & battery system installed comprising of the following:-

 

20 Jinko 440w panels 

Givenergy 9.5kWh battery Gen 2

Givenergy 5kW Hybrid Inverter Gen 3

 

Our installer did a G99 application requesting a 5kW export which was rejected, an extract from their initial response is below:-

 

I've modelled the network for your application and have confirmed that a 5kW export would cause a voltage rise of 257.1V, just within the G100 stage 2 temporary excursion limit of 257.6V.  You can export limit to no greater than 2kW and stay with G100 stage 1 limits.  Your inverter is both G99 Type A and G100 type tested so should be no issue to do this.  There are two options:

1. Proceed with a quote for circa £320 + VAT using the 5kW inverter, export limited to 2kW.  This will require an updated SLD and G100 Form A.  A quote is required as this customer's earth loop impedance is above 0.18 Ohms and therefore detailed network modelling was necessary.
2. Go for a G98 connect and notify option.  No quote required and we'll cancel this application down.  This will likely cause voltage rise greater than 253V and may cause nuisance tripping if the customer has an electric vehicle charger.  However, network reinforcement would be initiated at no cost to the customer if a voltage complaint is subsequently received.

If you can let me know as soon as possible I can proceed with this application.

 

 

I'm presuming that the option 2 that was proposed above for a G98 would be for a 3.6kW inverter, not the 5kW that we've already had installed.

After a couple of emails as obviously I was surprised and disappointed (we'd been advised by the installer that if 5kW was rejected they would give us 3.68kW, on which basis I was happy to proceed with the install) we had these further responses from SPEN:-

 

G98 connect and notify is allowed without restriction but it can and sometimes does cause issues on on network, particularly in cases where the customer's property is a long way from the substation. We are then forced to retrospectively reinforce the network to resolve the voltage rise issues. G99 is an application based process for larger than 3.68kW and may result in a fast track confirmation or a quotation depending on the network feeding your customer.  In cases such as yours where the earth loop impedance is relatively high (0.41 Ohms), putting 3.68kW in would cause a problem and it would be wrong of us to to knowingly do this.  You can have 3.68kW for G98 as it's a non application process but you're not automatically entitled to a minimum of 3.68kW export under G99. 
 

and later

 

We could reinforce the network to reduce your customer's earth loop impedance by laying some new mains cable in the footpath and installing a new 2 way link box further down the street to reconfigure the network running arrangement.  This would allow a headroom of 8kW of connected 1ph DG without exceeding the 235V limit.  The problem is that this would cost circa £10,000 and your customer would be liable for 5/8 th's of this (£6,250). Under current apportionment rules for generation as detailed in our charging methodology statement (Statement_of_Methodolgy_and_Charges_for_Connection_to_the_SP_Distribution_plc_and_SP_Manweb_plc_Elec.pdf (scottishpower.com)), the customer will contribute to reinforcement if that reinforcement is at the same voltage level of connection (see point 5.18 on page 26).  We don't usually go into this level of detail initially because in almost every domestic case, the customer won't be prepared to fund this level of reinforcement.  It's also hard to justify spending money like this to reinforce the network for a single customer when it can be easily averted by controlling the export limit.  The customer still gets the benefit of the larger inverter for their own use but has to export slightly less.  The funds available for reinforcement can then then be directed towards the places that need them most.  I'll pass this on to our  reinforcement team to assess in general as they may wish to do something in the wider network for other purposes.  If your customer sees this is happening in the local area, they can apply for the export restriction to be lifted.

 

Obviously I'm gutted that this has happened, and I'm kicking myself for not researching further before we gave the green light. I didn't realise until this came about that with a G99 nothing should have been installed until approval from the DNO was given. Currently our export is capped at 2kW (that's been controlled by our installer) but with that limit for some reason it won't discharge at more than 1700w on the Givenergy app. 

 

Does anyone have any advice on how I could approach SPEN to get 3.68kW, or greater? Or any other way to navigate this situation?

 

Thanks,

 

Rob.

 

 

 

[AppleDown]

I can't give any specific recommendations for what to do here, but I'd be incredibly p*ssed with your installer. I've spoken to three different providers/installers for our build, and each one has stated they'd like to get a request in first before they go any further. Maybe there's something they can do for you on the final invoice.

[RobEdwards]

12 minutes ago, AppleDown said:

I can't give any specific recommendations for what to do here, but I'd be incredibly p*ssed with your installer. I've spoken to three different providers/installers for our build, and each one has stated they'd like to get a request in first before they go any further. Maybe there's something they can do for you on the final invoice.

 

Sadly I've already paid the full balance! They installed on a Thursday/Friday and commissioned everything with it exporting at full capacity. It wasn't until a couple of weeks later that they advised me of the DNO's restriction. I want to try and negotiate with the DNO before I raise any kind of complaint with them, although they know I'm frustrated with the outcome.

[Dillsue]

Seems to me your installer has been negligent in not advising you of the correct process. They've also broken the national rules by connecting to the grid without consent. I'd be looking for them to fit a G98 inverter for you FOC. If they are members of any trade bodies you probably want to make a complaint.

 

Once you've got a G98 inverter fitted, if the DNO decide to do reinforcement works to handle your 3.6kw export, then once those works are done you can reapply for G99 with a 3.6kw G100 export limit. Shouldn't be any reinforcement cost for you

Edited June 20 by Dillsue

[RobEdwards]

22 hours ago, Dillsue said:

Seems to me your installer has been negligent in not advising you of the correct process. They've also broken the national rules by connecting to the grid without consent. I'd be looking for them to fit a G98 inverter for you FOC. If they are members of any trade bodies you probably want to make a complaint.

 

Once you've got a G98 inverter fitted, if the DNO decide to do reinforcement works to handle your 3.6kw export, then once those works are done you can reapply for G99 with a 3.6kw G100 export limit. Shouldn't be any reinforcement cost for you

Yes I'd definitely agree with your comments regarding their negligence. At no time did they advise me of either the potential for the application to be restricted below 3.68kW or the fact that G99 should be installed after acceptance.

 

I've had further dialogue with SPEN and they've advised that as far as the 5kW inverter goes, we are where we are and there is no scope to get approved for any export over 2kW unless we contribute towards reinforcement. Obviously this isn't financially viable so that option is off the table.  I'm cautious that I don't want to cut off my nose and install a 3.6kW inverter with a G98 as I'm sure that it won't have any of the negative effects on the DNO's network that they have suggested and reinforcements funded by them won't happen. 

[Dillsue]

SPEN previously said-

In cases such as yours where the earth loop impedance is relatively high (0.41 Ohms), putting 3.68kW in would cause a problem and it would be wrong of us to to knowingly do this.  

 

If you go for G98/3.68kw then it's hard to see SPEN doing nothing after youve sent in your G98 notification. Once they've remedied the problem then there shouldn't be a problem getting 3.68kw export via a G99.

 

If you don't think any of the problems will happen then put in a 3.68 G98 inverter and get a qualified spark to test/witness there's no problems and let SPEN know the sparks findings. 

 

What's the issue with a 2kw limit?? Once you've charged your battery you may not actually have that much over 2kw to export for much of the year. If you're concerned about export payments then you may not be loosing out on too many £s over the year.

Edited June 21 by Dillsue

[RobEdwards]

3 hours ago, Dillsue said:

SPEN previously said-

In cases such as yours where the earth loop impedance is relatively high (0.41 Ohms), putting 3.68kW in would cause a problem and it would be wrong of us to to knowingly do this.  

 

If you go for G98/3.68kw then it's hard to see SPEN doing nothing after youve sent in your G98 notification. Once they've remedied the problem then there shouldn't be a problem getting 3.68kw export via a G99.

 

If you don't think any of the problems will happen then put in a 3.68 G98 inverter and get a qualified spark to test/witness there's no problems and let SPEN know the sparks findings. 

 

What's the issue with a 2kw limit?? Once you've charged your battery you may not actually have that much over 2kw to export for much of the year. If you're concerned about export payments then you may not be loosing out on too many £s over the year.

Before the installer limited our inverter we were exporting around 30kWh on a good day, that was in early June. Now at best we are getting 15kWh. I realise that won’t be the case for the whole year however it will certainly add up over the summer months.
 

[Dillsue]

If you don't want to go the temporary G98 route and you think your loosing a significant amount of export income, then you could add more battery capacity to capture any daytime excess and then export a steady 2kw when the sun goes down.

[Jinglish]

Just out of interest when your installer did the G99 application was it the SGI-3 fast track? Since your inverter is registered as "Compliant" this should have been the route taken.

 

If you go down the G98 route then you're only loosing out on 1.32kW during peak generation.

 

I suggest you model this up in something like OpenSolar which can give you a good indication of cost vs reward but in any event sounds like this is the only sensible route forward.

 

Keep up posted and good luck!

[Ferdinand]

First of all, Welcome to Buildhub, Rob.

We try to help you turn slightly less grey than would otherwise be the case.

On the question, it is some time since my solar was put in (2016), but can you do anything to reduce the 'earth loop impedance' number to circumnavigate the issue?

I am not sure whether this is defined here as looking from your installation to the network, or the other way round.

Could you affect the number, for example, by improving the earthing of your domestic network?

(This probably needs input form someone like @ProDave.)

[sharpener]

On 19/06/2024 at 16:50, RobEdwards said:

A quote is required as this customer's earth loop impedance is above 0.18 Ohms and therefore detailed network modelling was necessary.

 

Don't understand this. My Onsite Guide says it is appiicable for impedances outside the customer's installation of 0.35 ohms for TN-C-S, 0.8 ohms for T-N-S, 21 ohms excluding the customer's earth electrode for TT. IIRC these are the usual design assumptions for domestic wiring.

 

So I don't see why an external earth impedance of 0.18 should be necessary for a generator putting out 5kW which is only about 1/4 of the max load of your typical house.

 

Can someone explain what the DNO is trying to achieve here? What kind of faults do they envisage? Would converting the installation to TT help?

[Antonb182]

The response you received is almost identical to the one I got a few days ago. I'd be interested to know which route you took and how it went. I'm probably not going to export, but it might be helpful for future dealings with them (from my own perspective) if you took the G98 with the aim of them reinforcing the network (and they did). Did you make a decision yet?

 

Also, and I know this is a very noob kinda question...on the G100 form, power station capacity is just the max that I can supply to the network, correct? so a 6kw inveter tied to a 10kwh battery with max output of 5kw), power station capacity would still only be 6kw? I only ask because the SPEN guy seems to be changing his mind and leading me on a merry dance. 

[Dillsue]

Depends if the battery output is regulated by the inverter and if theres PV hooked up to the inverter. If theres 6kw of PV hooked up to the inverter and the battery can separately output 5kw then total is 11kw potential export.

 

Power station is your premises with one or more generators within the premises.

[sharpener]

See also this thread.

Clearest explanation of the myriad G99 options I have found recently is here https://connections.nationalgrid.co.uk/downloads/24747.