Advertising a system as 4kWp?

[sambotc]

Even though it is capped at 3.6kWp under G83, surely you would have to advertise it as 4kW or am I missing something?

 

[moggy1968]

well it's 4kw according to the FiTS providers!

 

[sambotc]

kWp or kW?

I've seen a lot of companies advertising as kWp but surely this isn't the case?

 

[Earthstore]

We get into the grey area of TIC or DNC,
According to "the rules" the amount of panels on the roof is the TIC, I am aware some people say different, as the inverter is an integral part of the system, this is the problem with the powers to be using generic forms for all types of micro generation.

I have gone quite in-depth into this (for other reasons),
so if they say TIC is the panels, then it is a 4KWP.

I hope this helps

 

[dansk]

we advertise as 4kwp, TBH its easier to sell, and 3.68kw is more of a technicality.

 

[sambotc]

Thanks earthstore, I realise when it comes to the fits it is as you say and have read the previous posts regarding this, but to a customer could it not be seen as misleading, the system will never peak at 4kw after all? (spanner in the works)

Then you get into the SAP calculations, should they be calculated as 3.6 or 4? if it was calculated at 3.6 then you would not see the gains 4 would have in lower light conditions though, so the figures would be even further out, so I would be inclined to calculate at 4, given the fact that SAP is nearly always outperformed in real life scenarios.

If the industry is sticking to that method then i'm not going to put myself at a disadvantage.

 

[sambotc]

Yeah I think 99% of companies do dansk, and it is more of a technicality really, just wondered what would happen if it went to a court or something silly.

 

[Earthstore]

How many 4KWP systems peak at 4KW, and if they do it is not for long, maybe once or twice in April/May time, they certainly do not run at 4KW all day long, before anybody says "mine peaks".

It is common practice to have a 3.6KW inverter with 4KW of panels, and over a full year they tend to produce more power than a 4KW inverter.

If you have 4kw on the roof, then use that for your SAP calculation.

 

[dansk]

well i always explained its capped due to g83 and ive not had any issues, i dont see any issues really, im not takng VW to court coz my mpg doest do what they state it does!

 

[sambotc]

Yes but technically speaking your car could do the MPG as proven in tests. Technically speaking your 4kWp will never peak at 4kW ever.

It's a hornets nest I would rather not disturb and the way I see it is as long as you sell the system informing the customer that it is capped at 3.68kWp I don't see it being an issue, but those window companies with useless salesman might be misleading their customers technically.

 

[Gavin A]

if it's got 4kWp of panels then it's a 4kWp system, though we also advertise the max AC output as well to avoid confusion.

 

[Gavin A]

Yes but technically speaking your car could do the MPG as proven in tests. Technically speaking your 4kWp will never peak at 4kW ever.

It's a hornets nest I would rather not disturb and the way I see it is as long as you sell the system informing the customer that it is capped at 3.68kWp I don't see it being an issue, but those window companies with useless salesman might be misleading their customers technically.

kWp is the standard unit for the rated output of the panels under standard test conditions only.

if it's outputing 3.68kW of AC, then the panels will certainly be generating 5-8% more on the DC side, so it'd be very wrong to advertise these systems as being 3.68kWp unless they only had 3.68kWp of panels.

The fact that a 4kWp system will usually run at more like 3.3-3.6kW AC output in full sunlight regardless of whether the inverter is limited or not is just how solar PV works, but the only way of actually comparing the systems is by listing the actual kWp array size. Otherwise you'd not know if you had 4kWp of panels or 3.68kWp of panels, and obviously one system should generate around 8-10% more than the other.

 

[sambotc]

In that context it makes perfect sense Gavin, thanks for the detailed reply.

 

[dansk]

hey my car will never do the mpg stated, my right foot is made of lead ha ha

 

[moggy1968]

you car will never achieve the quoted MPG because it's done under lab conditions, Same as solar

 

[dansk]

bingo!

 

[sambotc]

Personally disagree and I think it was probably exceeded earlier this year. Irradiance 1000w/m2 module temp of 25 and air mass of 1.5. Not sure of the air mass that time of year but the temp was fairly low and the sun was belting out down here.

Admittedly it won't happen very often, but i'm sure the STC is achievable, if it was set at 1500w/m2 then it would be a different story.

 

[Gavin A]

don't get me wrong, it will happen sometimes, but usually only for relatively brief periods as the panels will warm up in 1000W/m2 of sunlight unless there's a howling gale, or the air temperature is seriously cold.

Usually when it's cold the sun is at a lower angle in the sky, so for most roof mounted systems they're not peak.

Actually peak outputs tend to be found on clear bright breezy days in March / October when the air temperature is still relatively low, but the sun at mid day is relatively perpendicular to many arrays.

but over the entire year, it's only for a negligible amount of time that they would operate above 3.68kW AC output even if they weren't limited.

 

[screwdriver]

Are we also forgetting that a 16 amp capped inverter could output over 4kw with high local grid voltage and under 3.68 with a low local grid voltage , explain that one in your advertising literature!!!!

 

[langstroth2]

don't get me wrong, it will happen sometimes, but usually only for relatively brief periods as the panels will warm up in 1000W/m2 of sunlight unless there's a howling gale, or the air temperature is seriously cold.​

Funny you say that, today is the first time (since install Sep last year) I've seen my 4kWp system output getting to just over 4kw for brief periods - exactly because the sun is constantly going in and out behind clouds, and there's a very strong wind which is keeping the panels cool I think.

As you say in constant sunlight with little breeze it's more like 3400W ish.

I was aware of the expected output largely from reading forums such as this one, but you do see a number of posters on forums querying why their output never seems to get close to the array size.

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