What's your opinion on + 4kW peak?

[ktech]

Just wondering on what everyones opinion is on installing more than 4kW (peak) is. We have for quite a long time installed more than 4kW on the roof. This is based on the fact that the inverter is limited to G83 and therefore will not exceed the 16A per phase limit but makes it all the more possible for acheive nearer 4kW at good times of the year and increase winter production.

My interest came again when I noticed that 'Appolo Solar' (Wakefield) said that the reason they did not install 250W panels was that these are subject to a -0 +5% tolerance and therefore a 250W x 16 panel array would exceed the limit and therefore be subject to the +4kW tariff. Rubish in my opinion but wondered what you thought?

We did come across this in the December rush when we got offered a batch of 255W LG panels and questioned the +4kW limit (in terms of 16 panels). We got forwarded an email from the EST stating that this was not a problem. Personally I have 5.4 kWp installed that is declared as 3.68kWp (West and East facing roof, 4kWp West 1.4kWp East - never exceeds 4kw output but benefits from morning and afternoon irradiance).

 

[Earthstore]

There has been a thread on this a while ago, and my take on this is check with your DNO and FIT provider if they will except DNC (declared net capacity) and not TIC (total installed capacity), which some believe it is the panels only, yet others except that the inverter is part of the system, so if G83 makes the TIC 3.68KW.
It appears to be a very grey area, and there seems to be different opinions on this.
But this is how I see it.
I hope this helps.

 

[ktech]

Followingour conversation this afternoon please see below information:

‘The‘cut-off’ output for an array is 3.68KW through the inverter. There are lossesthrough the DC cable and inverter so as long as the residual energy at thispoint is no more than 3.68KW it is G83 compliant and will get the 43.3p. Belowis an earlier response I got to a similar query:

Too many people still think that the feed-in tariff boundariesrelate to the peak DC rating of the panels. If you read into the definitions,and realise that in other contexts e.g. G83/G59 connections terms, the SSEGunit specifically refers to the inverter, not the panels, and as the meter ismeasuring the AC output, and the payments are made based on the AC output, thenit makes sense it refers to the peak AC output.

In all other circumstances TIC (total installed capacity) and DNC(declared net capacity) also refer to the AC output. I think the confusionarose because PV systems sizes are usually talked about in terms of their peakDC rating (e.g. 4kWp), this is for ease of comparison. But setting the FITboundaries on this basis wouldn’t make any sense as everything else is basedaround the maximum AC output of the inverter.

So, 4.5kWp (or up to 5kWp with unfavourable orientation) wouldstill be eligible for the 43.3p rate, as long as the inverter is limited to3680W AC.


Cheers
Malcolm

Malcolm Potter
Project Manager
tadea

 

[Gavin A]

I'm currently involved in a dispute with certain parties over this. can't really say more in public though, but will try to post something in the private place later this week or next about it... put it this way though, I've just agreed to cough up for a lawyer to check over our interpretation of the legislation on this, and providing they agree with us then I'm not planning to back down on it.

 

[ktech]

As previously stated we quite often install +4kW systems and declare at 3.68 so how come you have had to go to the lawyers? Surely once declared that is it job done?

 

[ktech]

I think that the declared capacity is what is important not only to the DNO but for FiT as this is the output (AC) that would not be exceded. Apart from the Solar PV Police (if they even exist) why would this be a problem?

 

[Gavin A]

As previously stated we quite often install +4kW systems and declare at 3.68 so how come you have had to go to the lawyers? Surely once declared that is it job done?

can't really go into it on the public forum, but let's just say that the energy company on one installation ain't playing ball, and neither is anyone else.

If you could possibly forward me the energy saving trust email you mention though I'd be much obliged.

<engage stealth mode>

 

[ktech]

Hi, The email I got forwarded from Zenex originates from the TADEA Ltd on behalf of the Energy Saving Trust.

From: Mary Flynn [mailto:[email protected]]
Sent: 20 October 2011 17:34
To: Ben Harrison
Subject: Array size and FIT

DearBen,

Followingour conversation this afternoon please see below information:

‘The‘cut-off’ output for an array is 3.68KW through the inverter. There are lossesthrough the DC cable and inverter so as long as the residual energy at thispoint is no more than 3.68KW it is G83 compliant and will get the 43.3p. Belowis an earlier response I got to a similar query:

Too many people still think that the feed-in tariff boundariesrelate to the peak DC rating of the panels. If you read into the definitions,and realise that in other contexts e.g. G83/G59 connections terms, the SSEGunit specifically refers to the inverter, not the panels, and as the meter ismeasuring the AC output, and the payments are made based on the AC output, thenit makes sense it refers to the peak AC output.

In all other circumstances TIC (total installed capacity) and DNC(declared net capacity) also refer to the AC output. I think the confusionarose because PV systems sizes are usually talked about in terms of their peakDC rating (e.g. 4kWp), this is for ease of comparison. But setting the FITboundaries on this basis wouldn’t make any sense as everything else is basedaround the maximum AC output of the inverter.

So, 4.5kWp (or up to 5kWp with unfavourable orientation) wouldstill be eligible for the 43.3p rate, as long as the inverter is limited to3680W AC.


Cheers
Malcolm

Malcolm Potter
Project Manager
tadea
Email: [email protected]
Tel: 01642373028 Fax: 01642 564221 Web: www.tadea.com

Want to save a packet by doing even more?Then call the Energy Saving Trust advice centre on 0800 512 012.

The Energy SavingTrust advice centre North East is managed by TADEA Ltd on behalf of the EnergySaving Trust. TADEA Ltd is a company limited by guarantee registered withcompany number 04452865 in England and Wales.TADEA Ltd registered office is 18bManor Way, Belasis Hall Technology Park, Billingham TS23 4HN.

 

[ktech]

We have taken from this to offer either a 4kW install or a 'Solar MAX' offering of a +4kW install (upto 4.5kW or 11kW for 10kW declared systems). This gives us the edge on many installers and helps seal the deal on occasions.

 

[Earthstore]

I spoke to DECC on this very matter (twice), and they insisted that TIC is the panels, not the Inverter, and if you read through some of their very complex documents, it states that it is what the system can produce less any losses.
As this is generic for all types of generation, ie anerobic digesters use some power to produce their maximum output the TIC would be the maximum power, and the DNC is what is produced after losses.
In the documents that I read (well until I got bored) none of them stated DC or AC, just KW.
As I stated, a very grey area, and if I was nuetral, there is an argument for either.
It may well depend on who can prove whether one rule over rides another.
Why cann't this damn industry be black or white???

 

[nowty]

I have read many threads on this and I have read the official definitions of DNC and TIC. My own opinion is the panels are irrelevant as the suns output in the UK can get to well over the standard 1000 w/m3 at times and some panels which are MCS compliant have net positive tolerances, some of 5 or even 10%. Also the defenition talks about output (with unlimited renwable source being available) which can surely only be the AC output from the inverter.

Various people have contacted DECC, DNO’s and FIT providers all whom have given different interpretations. It also seems that depending on who you talk with in all these organisations you can also get a different answer from the same organisation.

The only argument I can see for the panels being relevant is how DECC came up with the FIT rates in the first place based upon their targeted rates of return. Their consultation docs speak about ranges of kw/hrs per kw installed, circa 850 in favourable locations. Of course if you look at PVOUTPUT you can clearly see some people near the south coast of England (including myself) are generating over 1000 per kw installed. If you then put up 5kw of panels then even a 3.6kw limited system is going to produce 5000+ units a year therefore pushing the envelope up to and over 1250 per kw installed (TIC definition of 4kw not the actual 5kw you have on the roof). Which I am sure DECC won’t like as it burns up the FIT subsidy faster than they calculated.

But if the total yield is DECCs argument, then what about trackers ?, they produce circa 20% more than a fixed installation so whats the difference between having a 4kw tracker or a 5kw fixed installation ? They are both likely to yield roughly the same yearly total with the same 3.6kw compliant inverter.

I also belive that in the near future we will see even more complexity as systems could be designed with batteries or super capacitors to soak up excess DC power (over 4kw) and release to the inverter as a cloud passes to keep up the max TIC ouptut of the system.

 

[SolarCity]

Good luck with that Gavin. I think the case is rock solid.

DNC and TIC as far as PV is concerned is more or less the same. It refers to the maximum capacity at which an Eligible Installation could be operated for a sustained period without causing damage to it.

If you're inverter is capped at 16A then it is operating at a maximum of 16A and 16A must therefore be the TIC.

 

[BruceB]

I support the view that for simple solar PV where kWp installed is greater than nominal output of the inverter then TIC = DNC = inverter output. I am confident in my interpretation of the legislation as it stands.

However it is not a done deal. If the DECC, the regulator and the industry were to 'gang up' and interpret it a different way then it could take a court case or two to change their mind, which for a customer or contractor is an expensive and uncertain business. And then the Government could change or 'clarify' the legislation. From DECC's and the industry's perspective I can certainly see advantages to them of pushing through the kWp interpretation. I have not researched what alternative complaint/arbitration routes surround the FIT legislation but there may be some, rather than rushing to the courts.

Regards
Bruce

 

[SRE]

EST aren't the regulators and while they do good work they aren't the people who determine the output. Just because one of their subcontractors (which is what tadea is) says that this is correct doesn't mean it is. Unless you hear it from the horses mouth ie Ofgem/Decc then I wouldn't take anything as given.

 

[methley]

Interesting discussion. However, if the TIC is taken as the system (inverter output) what happens in the scenario where you have installed 4kw of modules on a G83 inverter, and then want to add more modules, keeping the G83 inverter? What info do you give to your FIT provider? Would you even bother notifying them? They will see the system output increase over the year so they will notice something has changed, and as they only see Kwh figures from your TGM (not peak outputs) from their point of view the capacity of your install has gone up...

Edit: the MCS cert contains an estimated annual generation figure which will not longer be true...

 

[SolarCity]

Interesting discussion. However, if the TIC is taken as the system (inverter output) what happens in the scenario where you have installed 4kw of modules on a G83 inverter, and then want to add more modules, keeping the G83 inverter? What info do you give to your FIT provider? Would you even bother notifying them? They will see the system output increase over the year so they will notice something has changed, and as they only see Kwh figures from your TGM (not peak outputs) from their point of view the capacity of your install has gone up...

Edit: the MCS cert contains an estimated annual generation figure which will not longer be true...

I'm not sure I know what you mean. If you install more panels then you will still need to inform both the DNO and the supplier.

The discussion here is regarding the 4kW threshold and where it actually lies.

 

[TedM]

The confusion arises from disparate views from both the legal and the technical (electrical engineering) viewpoints. There is a small area where the two can coincide and, to me, that is where TIC is the inverter AC output.

Whether that was the original intention of the definitions is not easy to say. But I would submit that if DECC/OFGEM want PV panels alone to define the capacity of TIC then the definitions will need to be re-written.

 

[Gavin A]

Whether that was the original intention of the definitions is not easy to say. But I would submit that if DECC/OFGEM want PV panels alone to define the capacity of TIC then the definitions will need to be re-written.

this is the crux of it. The law is what is written on paper, not what someone at DECC now might wish had been written. They are of course free to go back to parliament and change it if they want to, but up to that point everyone should operate on the basis of what is written into the legislation.

tbh it's also the only basis for determining it that makes any logical sense, and determining it in the other way could easily be open to legal challenge for unfairly discriminating against people with east / west roofs who'd be getting paid a lower rate for a system that was only capable of generating the same amount of electricity over the year as a 4kWp south facing system, that also cost more to install than the south facing system. Not 100% sure on that, but I'd think there would be grounds for that somewhere in the law.

 

[SolarCity]

But I would submit that if DECC/OFGEM want PV panels alone to define the capacity of TIC then the definitions will need to be re-written.

Totally agree. And therefore I think Gavin is in a very strong position.

 

[BruceB]

Interesting discussion. However, if the TIC is taken as the system (inverter output) what happens in the scenario where you have installed 4kw of modules on a G83 inverter, and then want to add more modules, keeping the G83 inverter? What info do you give to your FIT provider? Would you even bother notifying them? They will see the system output increase over the year so they will notice something has changed, and as they only see Kwh figures from your TGM (not peak outputs) from their point of view the capacity of your install has gone up...

Edit: the MCS cert contains an estimated annual generation figure which will not longer be true...

The answer must be:

a. you go by the legislation, ie has the system been expanded (has TIC changed), in determining whether MCS needs to know; and

b. you go by your FIT contract in determining whether you have made a change of which your FIT supplier requires notification.

 

[SolarCity]

Another side to this is that we are supposed to be advising our customers as experts on the subject. By designing to current legislation then we are maximising the potential benefit to the customer and should be advising them accordingly.

Incidentally, I have never installed more than 4kWp of panels but I actually believe I have badly advised some of those whose potential could have been more - particularly with regards to east/west split.

 

[moggy1968]

yes, think I'm in the same boat. I have thought about increasing panel numbers like this but shied away from it due to the lack of clarity on the matter.

 

[babba]

If we stuck all the past and future threads about this subject together, they could reach the moon and back before this is sorted out

 

[it'llneverwork]

Very interesting thread!

I've been asked the question by a client that has 50kW TIC, and is asking whether he can add to it to generate more on days with low insolation, given that the CL48 installed can be capped to 50kW AC.

Also our sparks are asking about TIC and DNC, and what to advise customers to put on FIT forms - whether to go with the G83 3.68kW or the DC/panel rating at 4kW.

No definitive answer it would appear.... much like everything in our industry at the moment!

 

[wstevew]

If you have 4kwp east and 4kwp west and they switched half way through the day what is the capacity?

Equivalent to a moveable array.

 

[Ian-LS]

That would have to have an above 4 kW inverter so therefore wouldnt be eligible for <4 kW PV FIT rate. The capacity should be whatever the inverter is rated at, but as been discussed there is no clear guidance and what the TIC should refer to. Logially it should be the lesser of the panels and the inverter.

 

[wstevew]

Why would it require an inverter greater than 4kW if it only has 4kWp of panels connected at any one time.

 

[Ian-LS]

ok just run this through sunny design and with a 3600 TL it predicts you will lose 7% of your output through the inverter limiting it to 3.68 kW. I would suggest that 8 kW with 4 kW on each roof would be over the top if trying to claim it is a < 4 kW PV System. I suppose yuou could argue you are gaining more than 7% in increased generation by using 8 kW of panels

I suppose in theory it could work but I doubt any installer would quote on this basis

 

[wstevew]

The point I was making was if 8kwp of panels is not allowed to be connected to a 3600TL for the <4kWp FIT. What if you had a device to physicaly disconnect one array and connect the other at the optimum time on an east west split.

That way only 4kwp of panels would be connected at one time. Its an expensive tracker.

 

[SolarCity]

You wouldn't need to. As long as you got your voltages and current within the accepted range of the inverter then you could stick 8kWp of panels on a 3600TL inverter.

 

[wstevew]

Yes but if 8kwp of panels on a 3600TL was considered >=4kWp for FIT purposes. how could they object if only 4kWp at any one time is connected. Its like having an array you can move.

 

[nowty]

The point is some people including myself think that 8kw of panels on a 3600TL is perfectly legal for <=4kw FIT purposes as the tech defenition seems to be the inverter output.

However if it turns out (through the courts, etc) that >4kw of panels on the roof is not legal for <=4kw FIT purposes then your idea of a switched system will probably also be illegal for the same reason, i.e. you have got more than 4kw on your roof. The fact that it does not make sense is irrelavent.

 

[Ian-LS]

If you put 8 kwp on a west/east roof that would generate approx 6000 kwh per year so surely this would get flagged up by ofgem or your energy provider as it would be a lot higher than any other 3.68 kw declared system.

I would also say that really with east/west splits you should only put on a system that would generate as much as a 4-4.5 kwp system in a south facing roof. So that would mean 3kw on each roof taking it up to a 6 kw pv system which would be sensible imo.

That said until the tic and dnc situation has been clarified i cannot quote for greater than 4 kw pv systems and quote at 21p/kwh fit rate.

 

[moggy1968]

I was thinking of about 20 panels (5kW) for an East/West roof on 3.6 inverter split equally between the 2

 

[BruceB]

I have done almost exactly that with an additional x3 panels facing south on a soladin 600 and the DNO (WPD) agreed, albeit after a spirited discussion, that it fell within the G83 16A limit. It took some 3D trig to prove it though.

 

[Gavin A]

I was thinking of about 20 panels (5kW) for an East/West roof on 3.6 inverter split equally between the 2

we've done this several times, one of which we've installed remote half hourly monitoring on, so will have a lot of data for once we hit peak summer.

 

[saggers]

What was the outcome of this debate?

 

[TedM]

Do you mean the TIC definition part or having a switched 8kWp system?

On the TIC definition BruceB was pretty much spot on with his post of 19/03/2012. DECC/OFGEM provided clarification that TIC (on which tariff bands are based) is calculated for PV by Wp of a panel times the number of panels.

Their clarification was the subject of a FOI request by myself which you can read here: https://www.whatdotheyknow.com/request/determination_of_method_of_calcu

Regarding a switched 8 kWp system - I don't think there was any specific resolution. Now, of course, the lowest FIT band is 10 kW so it would be a moot point in any case.