4 KW or Under

[davethrell]

Hi Guys - We are fitting a PV system to a large south facing roof in Cumbria but one installer says 3.99KW and the other says go for 4KW - do we still get full 41.3p at 4KW.

And why do prices vary so much?

Thanks

 

[BruceB]

Under the legislation, the full FIT applies for less than or equal to 4kW.
The FIT is also 43.3p, not 41.3p.
And it is the output of the inverter which is the critical figure not the amount of panels.

 

[DomB]

And it is the output of the inverter which is the critical figure not the amount of panels.

..there does seem to be two "Declared Capacity" figures on any given G83 compliant system tho'; one that is declared to the the DNO & one that is declared on the MCS certificate - they are not always the same. They're not even the same between DNOs.

Taking UK Power Networks as an example DNO, they're asking us declare the capacity as "The kWp of the array x the efficiency of the inverter". So that might be 4kWp x 95% = 3.8kWp.

The MCS certificate however asks us to declare "the kW peak (kWp) capacity of the system once it has been installed. E.g. a PV array which has ten 200W [panels] will be a 2kW system". For a 4kWp system this would obviously be 4kWp.

EOn, for one, are interested in what is on the MCS certifcate - which, in this case would be 4kWp..

 

[BruceB]

Its worth getting your head around TIC and DNC and not always assuming that the DNO, MCS or FIT suppliers know better than you.

 

[DomB]

Aye, it seems "Declared Capacity" could mean TIC to some & DNC to others.

Fair dues to EOn, they ask for both numbers on their forms. Altho' when customers ask their tech support what to put down for those numbers they're told to put what it says on the MCS certificate for both! The MCS database's Help documentation implies it wants TIC to be declared on the certificate.

British Gas also ask for "Installed Capacity", which I'm guessing is TIC.

It seems the people paying the FiTs (and therefore I guess the FiT system?) is more interested in the TIC..

 

[BruceB]

It seems the people paying the FiTs (and therefore I guess the FiT system?) is more interested in the TIC..

Because it is TIC that determines the FIT rate,

 

[DomB]

Cool. so @davethrell, the critical figure for your FiT rate is the total capacity of the solar panels (10 No. 200W panels = 2kW).

But your installer also needs to consider your particular DNO's calculation method so he doesn't overstep their electrical requirements (I've bumped into this before installing 4kW with Scottish & Southern. They maintain their own list of inverters that can be installed with 4kW & not all G83/1 inverters are on there, for example the Aurora 3600 isn't :angry_smile.


Soz if that's what you were alluding to, BruceB

 

[BruceB]

No you have lost me.

The FIT rate is decided by the TIC. You need to understand the statutory definition. It is not the sum of the installed panels.

The MCS form asks for the DNC. The advice they then give in the help document is:
"For the declared net capacity field, enter the kW peak (kWp) capacity of the system once it has been installed. E.g. a PV array which has ten 200W will be a 2kW system, therefore enter in 2.00 you will not need to enter the units, only enter the figures."
.....which is NOT the DNC

Say you have a panel capacity of 4.2kW on a 4kW inverter. The TIC and DNC according to the statutory definitions is 4kW and the owner should get the less than or equal to 4kW FIT rate. If you were to put 4.2kW on the MCS form, representing the installed panel capacity, I am willing to bet the owner would struggle to get the 4kW rate. So I would put the DNC which is what they ask for and assume their advice is wrong.

Regards
Bruce

 

[solarfred]

Cool. so @davethrell, the critical figure for your FiT rate is the total capacity of the solar panels (10 No. 200W panels = 2kW).

But your installer also needs to consider your particular DNO's calculation method so he doesn't overstep their electrical requirements (I've bumped into this before installing 4kW with Scottish & Southern. They maintain their own list of inverters that can be installed with 4kW & not all G83/1 inverters are on there, for example the Aurora 3600 isn't :angry_smile.


Soz if that's what you were alluding to, BruceB

The DNO knows that the 3600 is not capped to 16 amps which is their benchmark for inverters under G83/1. It will be capped in the very near future AFAIK.

 

[DomB]

Thanks BruceB; Now I'm not following; We're saying that the MCS certificate defines the applicable FiT rate and the FiT system is based on TIC - but that we should put the DNC figure on the MCS cert?

 

[irishjohn]

The feed in tariff is determined from your MCS cert. When creating the MCS cert you choose the MCS approved panels from the list (so they know the output of the panels). You also state on your FIT application the panels (size and number of) and total generated. You cannot install greater than 4KW and expect to receive the 4kw rate, if you do this is fraud. The installation will also need notifying under G59 and the DNO will have something to say about it. The generator is a combination of the collectors, not what comes out of the invertors.

 

[BruceB]

I think you need to get your mind around the legislation and show that you understand TIC and DNC before you make such bold assertions. A quote from TedM in another thread seems relevant:

"The FiTs bands are based on TIC. The 50kW MCS limit is based on DNC.

It would solve a lot of problems if the FiTs bands were based on DNC which, in my opinion, they should have been in the first place. In fact, for small systems, there is no point in having any distinction between TIC and DNC. There should only be Installed Capacity and that defined as the output from the inverter. Basing capacity on DC when the system pays for AC generation is plainly ridiculous.

That FiTS bands are based on TIC is clearly shown in the tariff tables in the Standard Conditions: http://www.decc.gov.uk/assets/decc/w...dification.pdf

See Annex 2 from p22 onwards."

Regards
Bruce

 

[liquidity]

...I've bumped into this before installing 4kW with Scottish & Southern. They maintain their own list of inverters that can be installed with 4kW & not all G83/1 inverters are on there

Can you post the list please?

 

[BruceB]

Thanks BruceB; Now I'm not following; We're saying that the MCS certificate defines the applicable FiT rate and the FiT system is based on TIC - but that we should put the DNC figure on the MCS cert?

Yes, because that is what they ask you to put on it. The reason it does not cause a problem is that for small PV systems TIC = DNC.
Regards
Bruce

 

[irishjohn]

Yes, because that is what they ask you to put on it. The reason it does not cause a problem is that for small PV systems TIC = DNC.
Regards
Bruce

Now you are saying that a 5kw TIC = 5kw DNC.

So having 4.5 kw installed and changing the inverter settings to output 4kw does not equate to 43.3p and from your comment you now agree?