Solar Panels - is this correct

Darthbane_

SOLAR PANELS- i have had some solar panels installed in jan/feb 2021 which look great .. But ! i have noticed on the side of the inverter that it says 4200kw .. but ive had 5.84kW installed on the roof which is what i asked for ? 16 x 365W= 5.84w

i have asked my installation company and they say its where i live in England and a calculation that every solar panel supplier users? im i being fob off? because now my panels are 262.5w each instead of 365w ? ( i understand that the sun is brighter on certain days .. but when the sun is at its best i will only produce 4200w)

David

[Deleted User]

Depends on a lot of factors really - solar panels don't always achieve their rated output.

Are all the panels facing the same direction? What direction is that? Angle of the roof can also affect max output.

At high temperatures, solar panels can lose efficiency, on the hottest sunniest days they might only achieve 70-80% of rated output so they may never reach rated capacity.

South coast will receive 30% more solar power in full sunshine than Northern areas for example so if you are located more northerly you might never see them run at full power.

The wattage rating is usually specified at 1000w/m2 solar intensity at 25 C which also may never actually occur.

Invertors run more efficiently at over 25% of rating so some people do under-rate the invertor to get the best out of the typically cloudy days in the UK. Also invertors have a minimum startup voltage that increases with rating, if it is too high, it won't even switch on for the typical cloudy winter days despite the panels generating a small amount of power.

Have you got a monitoring device to see if it ever reaches 4200 watts and therefore getting 'clipped' by the invertor?

Heedtheadvice

I read the OP (very quickly) but differently do I think so a clarification is needed!

The OP understood the quotation(?) was for 16x365watt panels to be installed. Actual installation is 262.5w panels and feels he is being fobbed off...rather than questioning the actual outputs.

Is that correct @Darthbane_ ?

Tallmansix gives you a technical overview but is that what you want?

The higher rated panels will in theory produce a higher output compared to the lower rated panels under the same conditions. But that is far from the whole story as per spec referred above. Also the inverter must then limit the max output (a condition of grid connection....it is a grid connected system???) unless permission has been granted for a higher power connection. 4kW is the approximation of that max.

It would therefore seem that higher output panels are of no use but they also reach output levels at lower level of light. Against that it is marginal that the extra cost is worth it.

My system is 16 lower power panels south facing quite northerly uk lattitude. The installation had the standard calculation for panels of that power, orientation and lattitude that was the requirement by the regulations. The annual output has exceeded the prediction by a few percent and it is only in full sunshine around the middle of the day in late March, April and May that is achieved owing to climatic and angular direction of sunlight etc.

It is never quite straight forward but you should be getting soon on parts of good days a peak output of what was quoted. Plus with FIT payback time of 8 years (just a rule of thumb mind you with FIT, export and other savings) is on course to recoup the £5.5k outlay.

Bought from a reputable local supplier not from the cowboy who first arrived!

But...what was actually quoted?........and for comparison what was the cost?

ComicGeek

Firstly what does the MCS certificate state the system size as?

There is a maximum system size of 3.68 kW whereby the DNO doesn't have to give permission - the installer has to inform the DNO of the installation, but at this system size permission is granted retrospectively. 

Anything above this would need prior permission from the DNO, and isn't guaranteed. Also could be costs charged by the DNO. Have a look at this site, which gives a good guide to the process https://blog.spiritenergy.co.uk/homeowner/dno-permission

My guess is that they are trying to get round the G99 application by limiting your system to 16A. While you would still be getting the benefit from the additional panels out of peak hours, you wouldn't get any peak output above the inverter limit. Ultimately it's chopping of the peak generation, and I would be looking at what proportion is now wasted money and taking action against the installers (unless this has been clearly explained to you and you accepted it). 

Chino

Heedtheadvice said:

Actual installation is 262.5w panels and feels he is being fobbed off...rather than questioning the actual outputs.

No, I think the OP is saying that he/she thinks that their 365 W panels are being limited by the 4,200 W invertor to 4,200 W / 16 = 262.5 W.

Heedtheadvice

You may well be correct. That is why I asked for more information.

But it seems the OP has gone.....

Darthbane_

Hi 
 Sorry ive replied late ..

Chino said:

Heedtheadvice said:

Actual installation is 262.5w panels and feels he is being fobbed off...rather than questioning the actual outputs.

No, I think the OP is saying that he/she thinks that their 365 W panels are being limited by the 4,200 W invertor to 4,200 W / 16 = 262.5 W.

That is correct .. my monitor even now is flat lining at 4200 w in March-April at mid day  ComicGeek said:

Firstly what does the MCS certificate state the system size as?

There is a maximum system size of 3.68 kW whereby the DNO doesn't have to give permission - the installer has to inform the DNO of the installation, but at this system size permission is granted retrospectively. 

Anything above this would need prior permission from the DNO, and isn't guaranteed. Also could be costs charged by the DNO. Have a look at this site, which gives a good guide to the process 

My guess is that they are trying to get round the G99 application by limiting your system to 16A. While you would still be getting the benefit from the additional panels out of peak hours, you wouldn't get any peak output above the inverter limit. Ultimately it's chopping of the peak generation, and I would be looking at what proportion is now wasted money and taking action against the installers (unless this has been clearly explained to you and you accepted it). 

i have G98 is that the same ? ( as i have one of those ) Sorry but im that clever on this ... but i can see real elderly people not even having a clue when they purchase these things..
   

Heedtheadvice

Apologies as I am one of those real elderly you mention so I haven't a clue.........?

Are G98 and G99 the same? No!

Your clarification of what you actually have installed as panel power capability and your G98 statement really makes it certain that you have a system installation as generally described by Comic and Chino. G98 limits you to 16amp current generation which translates approx just under a nominal 4kW power (depending upon generation voltage and that is a little variable).

That is usually achieved by inverter self control irrespective of the maximum that the panels are able to generate. That is by design and type testing to meet G98, quote:

"This “summary” guide is written for the developers of distributed generation or storage projects which are covered by Engineering Recommendation (EREC) G98.  This covers Project that are:

• Projects with a capacity of 16A per phase or less (if there are multiple generation or storage units connected at

the same premises, then 16A is the maximum combined capacity per phase); and

• Projects connected at low voltage (230V single phase, or 400V three phase); and

• Technology which is type tested under the requirements of EREC G98.

"

So you have it would appear a system that complies with G98, a maximum output limit and all is fine........

.....except you are not getting as much maximum output as you expect and it might not agree with what you believe you contracted the installer to provide. Those are the issues you need to address not the engineering. It would not be worth the effort and cost to now convert to slightly higher output given the need to have a different inverter and to go through the aporoval and compliance process. Peak power generation may well be higher but that will be just a small fraction of overall generation.

Maybe you are just too young to understand? Maybe you need to learn how to do online searches (often incorrectly called googling) and you will find that document that I extracted and quoted text from https://www.google.com/url?q=https://www.energynetworks.org/industry-hub/resource-library/g98-distributed-generation-connection-guide-(single-premises).pdf&sa=U&ved=2ahUKEwjnu_ecz4fwAhUKhlwKHTvBA9MQFjACegQICBAB&usg=AOvVaw2we55TI3RkGiD5NFz8xkDM.

p.s. perhaps we should not be ageist so I apologise in advance.........

Fellwalker

You're lucky OP. When I got mine fitted the installers all said they could only fit a maximum of 4kw of solar panel generation ability. Living in the North East and having panels facing east and west, we have never in 4 years had more than 3.1kW generated.
It is still on track for an 8 1/2 year payback.