10kw vs 10.08kw

[EWebster]

Hi all,

We're quoting for a 10kW system, our first over 4kW.

My question is, will we get away with putting 10.08kW on the roof and still qualify for the 10kW tariff, given that the actual maximum generating capacity of the array will be more like 9.7kW after inverter efficiency is taken into consideration.

I know we can do this with 4kW systems, to reduce it to 3.84kw (16A), but not sure about the G59 standard calcs.

Many thanks,

E.

 

[TedM]

Depends entirely what is written on the paperwork for the 'installed capacity'. I would put 9.7 kW - because that is what it is.

 

[cookiemonster]

i've always thought for FIT think panel output and for G83 / G59 think inverter output.

 

[SolarCity]

i've always thought for FIT think panel output and for G83 / G59 think inverter output.

Agreed. Have you installed systems just over 4kWp before and allowed for the efficiency of the inverter to bring you down to <4kWp - I think this is a huge mistake, although I'm prepared to be proved wrong.

 

[TedM]

OK, I see I'll have to convince you otherwise by digging out my arguments based on the definitions of TIC and DNC.

 

[EWebster]

Agreed. Have you installed systems just over 4kWp before and allowed for the efficiency of the inverter to bring you down to <4kWp - I think this is a huge mistake, although I'm prepared to be proved wrong.

Yes, I have done that, as that is the official line from UK Power Networks. As long as the maximum output, after inverter efficiency is taken into consideration, is LESS than 3.84kW, they are happy and the feed-in-tariff will apply.

 

[TedM]

This is the definition of TIC:

“Total Installed Capacity” means the maximum capacity at which an Eligible Installation could be operated for a sustained period without causing damage to it (assuming the Eligible Low carbon Energy Source was available to it without interruption), a declaration of which is submitted as part of the processes of ROO-FIT Accreditation and MCS certified Registration;

A grid-tied PV system can only 'operate' with an inverter controlling MPPT to generate a current. Without an inverter there is no current generated - therefore the 'Eligible Installation' must comprise both the panels and the inverter.

Therefore the inverter output must be the TIC.

And for virtually all domestic grid-tied PV systems the DNC will equal the TIC as well.

(The exception of TIC=DNC would be any system where power was fed to a circuit between the inverter output and the total generation meter - but there really shouldn't be any of these.)

 

[SolarCity]

Is the FITs rate based on TIC?

 

[TedM]

Yes, it is.

 

[SolarCity]

Thanks for the info, Ted. I have always worked on the rule that the FITs tariff brackets were interested in the total capacity of the panels fitted. Are we confident that this isn't just a grey area created by poor definitions? And a grey area where the energy suppliers eventually clarify and therefore leave some homeowners on the reduced tariff rate?

 

[TedM]

I'd love to be able to offer a cast-iron guarantee (and get clarification of the definitions) but when I've raised this with OFGEM all they say is "talk to MCS about it".

The best I can do is to point out that more than 99% of all pv systems registered for FiTs so far have TIC=DNC.

 

[Worcester]

Fits has nothing to do with the Panels per se, they are the power source, the SSEG is the inverter.

I know it's weird, all the DNO's want to know is what inverter and don't care about the panels, and the MCS registration website only asks about which panels are used!

However FITS bandings are about power output, take AD for instance, It doesn't care how big your digester is (power source) just what it outputs, same with hydro, how big a flow have you got from your river (head/ flow rate) it's just the size of the turbine. (you could hook a turine up to the thames or a mountain stream)

 

[SolarCity]

So do you agree with Ted's assessment, Gordon? That we can install, for example, 4.1kWp of panels and as long as the inverter is rated at 3.9kWp then this will define the FITs band?

 

[Worcester]

I agree with Ted in principle that it could be done, just waiting for the opportunity to go for it. I would also like to push the East/West output and see if I can get some agreement on that to push the limit up (which is more that panels x inverter efficiency, because we can also factor in reduced 'fuel supply' due to design )

 

[BruceB]

FWIW I agree with Ted also. I routinely put in more than 4kWp of panels (where there is space and client can afford it) but make sure that the TIC is 4kW or below in order to get the best FIT rate. I'll dig out the arguement about TIC/DNC etc that I posted on another forum and put it here.