What's your opinion on + 4kW peak?

[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.