For my own sanity!

[CBR600]

All

I am sure I know the answer to this question but am being told black is white so bear with me.

If we fit TIC 5KWp of panels on a 3.68KWp max output inverter my understanding is that the 16amp per phase rule is not breached and DNO pre-approval is not required to connect to the grid.

I am being brow beaten and told by a colleague that the wording of the definition of DNC is such that it is effectively the TIC and that the maximum output of the inverter is not relevant because a larger inverter could be fitted at a later date - Therefore DNO approval is required. I think this is nonsense but starting to doubt myself due to the weight of opposition.

Help!

Andy

 

[Leesparkykent]

https://www.gov.uk/government/publi...echnologies#appendix-8-feed-in-tariffs-scheme

calculated by the modules and not the inverter.

 

[Worcester]

DNO approval is not needed for the 3.68kW inverter.

HOWEVER, you wil be paid the FiT rate based on 4-10kW rate band.

Different rules, different environments, one is the electrical connection, the other is how you get paid.

 

[CBR600]

Thanks chaps

I am aware of the FiT rate differences, it is the DNO issue I needed to clarify.

As I said my understanding is as you have confirmed Worcester, however I have been a lone voice recently and started to question myself.

 

[TedM]

Ask your colleague: is it the panels or the inverter that are type approved under G83? A: the inverter.

Therefore the inverter is the SSEG under the terms of G83 and it is the inverter to which the 16A per phase limit applies.

 

[SibertSolar]

Your colleague is most likely interpreting the definitions of TIC and DNC from Ofgem, where DNC is the total installed capacity of the plant minus the plant's losses. If you come at it from a wind turbine point of view, you can see that these definitions make sense as the "amount of wind installed" is nonsensical, leaving just the SSEG minus its losses. In a PV environment, however, we have a certified conversion of solar energy into DC electricity, then we have the inverter. Multiple loss points. In this case, there is a more obvious distinction between the actual potential capacity of the panels to produce power (based on their certified output at STC) and the actual certified output capacity of the inverter. From a grid connection point of view, the DNO is interested only in what the declared capacity is of the actual generator (as per Ted's post) which, if under 16A (3.68kW @ 230vac) per phase, doesn't require pre-notification as per G83/2 engineering standard. The TIC of the array (kWp) is what determines the FiT tariff, that's all it does, as you know. If a larger inverter is used in the future then pre-notification under G59/3 is therefore required (I know, some DNO's have allowed deviations but the point is that you will have to speak to them otherwise you're operating outside of requirements anyway!)

 

[CBR600]

I think you may hit the nail on the head there Sibert as this was part of the argument made to me. Just out of interest, are you saying from a ROOFIT application point of view the DNC for PV would actually be the TIC less the inverter losses rather than the peak capacity of the inverter, or would they still want the max AC of the inverter as the DNC. I would have thought that the latter would still apply simply because of the point you have made about fitting a larger inverter later on.

 

[SibertSolar]

Well, there you go, it's somewhat ambiguous depending on what documents you are filling in....from a FiT application point of view, do you try to adhere to Ofgem's definition of DNC, but then what is the "plant" and how do you determine losses? I stand to be corrected but in the interests of avoiding confusion, don't most installers put the total kWp as the TIC and the inverter's AC capacity as the DNC? It's all a bit twisted in my opinion

 

[SibertSolar]

Or do most people just put the TIC as the DNC too?

 

[TedM]

The FIT tariff is based on the TIC which DECC and OFGEM clarified last year is the kWp of the panels as defined at STC for PV - even though the regulations do not say that. DNC has no impact, but the vast majority (85%) of all PV systems registered have TIC = DNC.

 

[SibertSolar]

Thanks Ted, didn't realise they had actually come together and clarified that. So if a FiT application form also asks for a DNC value, it could just be left blank?

 

[CBR600]

I don't think you can leave it blank. We always put the DNC (on anything I am involved in) on the MCS cert. as the lower of the inverter AC max output or the TIC, which I think makes logical sense. As you say the DNC has no impact on tariff rates anyway.