Kwp vs. actual performance?

[Lev]

Hello everyone, wanted to get some advice to understand if there is an issue with my setup...

I have a Growatt 3000-S inverter, connected to 10x 285W solar panels. The system is performing pretty well, while orientation could be better (it is SE) my roof does not have any shades and has a good angle.
What I`ve noticed, I`m running pretty far from the peak performance. Typically on a hot day I max out around 2200 Wh, colder days slightly higher. See an example from the past days (was around 15C, so not really a HOT day)


However, when some clouds comes in for a short period, - and assuming that cools down the panels even for just a few minutes - it goes up easily to the peak performance, however it does not sustain it for long. It went up to 2800 below and after the next cloud it went back again above 2500.



I understand panel`s performance will drop with higher temperature, however wondering this level is justified what I`m observing? It is still around 15C with some nice wind and the panels performs below 80%. The product sheet does not indicate this high of temp coeff.
Could there be an issue with just 1 panel which overheats and draws back the whole system? Anything worth to check?

Thanks in advance,

 

[MisterSandals]

The product sheet does not indicate this high of temp coeff.

The coefficient is normally around .35% per deg C. Rated at 25C (77F)

Could there be an issue with just 1 panel which overheats and draws back the whole system?

You have not mentioned how your 10 panel array is configured.

Anything worth to check?

Do you have a DC clamp meter? With that its easy to check the current each panel is producing.

 

[Lev]

Thanks!
So coefficient does not justify at the moment, panels are unlikely to be around 90 deg C... especially in April with relatively cold weather.
The 10 panels connected together, I do not have optimizer installed. Hence I do not see individual performance of the panels.
I don`t have a DC clamp, but sure can get hold of it, however panels are difficult to access and hard to get to the roof. I may need to ask the installer to do that, but trying to understand first if I MAY have an issue or it`s the expected performance of the system.

 

[WYtreasure]

Hey Lev, Welcome to the party.

You may have an issue with any number of things. Panels will only produce @100% when optimum conditions exist. When the panels are not directed exactly at the sun, at solar noon, you have no hope of achieving peak performance. Add a bit of air pollution, a bit of dust and the occasional Goose droppings and you have lost some power.

Is your roof a very dark color? Some solar energy goes right through many panels and could be heating your panels.

Your installer should know, and have informed you of what your peak performance should be.
MisterSandals pretty well summed it up. I just like to blab and wanted to welcome you.

What is Kwp?

 

[Lev]

Hey Lev, Welcome to the party.

You may have an issue with any number of things. Panels will only produce @100% when optimum conditions exist. When the panels are not directed exactly at the sun, at solar noon, you have no hope of achieving peak performance. Add a bit of air pollution, a bit of dust and the occasional Goose droppings and you have lost some power.

Your installer should know, and have informed you of what your peak performance should be.
MisterSandals pretty well summed it up. I just like to blab and wanted to welcome you.

What is Kwp?

Thanks WYtreasure!

Understand, not chasing the maximum performance, as you`ve mentioned every system is different a bit - not to mention those goose drops.... However why I`m puzzled is the fact that this behavior is very consistent - after a 2 min cloud period, the performance shoots up like 30% compared to pre cloud condition and then it drops back slowly. In this case, there is not difference in angle, pollution, dust, etc... but only panel temperature (I guess).

kWp - kilowattpeak - theoratical max performance of system

 

[WYtreasure]

Digital Infrared Thermometer Gun​

I have one of these and get surprising temps of cloud bases. Perhaps it will surprise you at how fast your panels heat up.
I use mine to see if electrical connections are getting hot too.

 

[iamrich]

This might be a silly question, but are you using all the power the system can produce? I have a similar setup, and mine never produces max because the panels only produce a little power in the morning, but by the time the sun is ready to really push power, my batteries are already topped off.

 

[wattmatters]

This might be a silly question

It's not silly but that inverter model is a grid-tied non-hybrid inverter. If there is a battery it would be independent of the inverter.

Provided the panels are unshaded and getting full sun at an optimal angle and the temperatures are cool, the system should be able to generate close to its maximal output.

However, and this is where the fun starts, there are a range of possible reasons for a system to not generate maximum output, some of them have been mentioned already.

Panel temperature and panel orientation are the two most common factors which may inhibit a solar PV system reach the full potential output of the array.

There are tools to check for both, e.g. an infrared temperature monitor, while there are online tools which can model the expected performance of a given system, e.g.

Solcast API Toolkit

toolkit.solcast.com.au

Some other possibilities:

The grid voltages are high when exporting power and the inverter may have to limit output.
The local power distribution company will typically have a requirement on how these settings are to operate for grid tied inverters. For instance mine has two settings which kick in as voltages rise. One is Volt-Var mode whereby the inverter generates a reactive power component from its output to help mitigate voltage issues. Another is grid voltage dependent power reduction (GVDPR) mode, where the inverter simply reduces output in an effort to bring grid voltages down.

Does your system have a power export limit?
In many areas there is a cap on the power which may be sent to the grid and systems need to be set up to manage this. Normally it would be pretty obvious in the charts and you'd and see a capping/flat lining of output around the middle of the day. Usually it requires separate metering compatible with the inverter to be able to manage production so as to remain within export limits. For a 3kW inverter, unless the export limit was unusually low, then I don't think this is the case in this instance but it's worth keeping in mind.

Is the array is correctly wired?
I have seen arrays where some panels were simply not included in the string!

Are the panels old or damaged in any way?
Panels naturally degrade over time and lose performance. Something like 0.5% per year.
Panels can also have non-visible damage which also affects their performance. Look for hot spots with thermal imaging, or check the open circuit voltages and short circuit current of each panel.

 

[wattmatters]

However, when some clouds comes in for a short period, - and assuming that cools down the panels even for just a few minutes - it goes up easily to the peak performance, however it does not sustain it for long. It went up to 2800 below and after the next cloud it went back again above 2500.

There are two effects in play, one is the cooling effect, and what you observe suggests than temperature is playing a bigger part in your array's performance than you might think.

The other is the cloud edge effect - this is a rather ephemeral phenomenon which will cause the array to briefly produce an output quite a bit higher than they are rated for. It's a well known and studied phenomenon.

 

[iamrich]

inverter model is a grid-tied non-hybrid inverter.

I missed that part.

 

[Lev]

Thanks everyone for your replies and suggestions. I should not have any limits on the output as I can see it goes up or even exceeds the rated power after cooling effect, I just found it low as it runs almost 25% lower on a regular continuous sunny day.

 

[WYtreasure]

Thanks everyone for your replies and suggestions. I should not have any limits on the output as I can see it goes up or even exceeds the rated power after cooling effect, I just found it low as it runs almost 25% lower on a regular continuous sunny day.

Hey Lev, just out of curiosity, what is your approximate Latitude & elevation?
I'm still curios about temps on your roof, in case you get a chance to share those numbers.