# Forum Home Renovation Solar Electrical Systems  Panel output?..?

## mattski2008

Hi Solar People,
I have had my 2.6KW system up and running for about 2 months now and my average daily generation is around 16KWh. My system has 14 x 190W panels which equals 2660W.
My query relates to the instantaneous output of the panel which you think would be less than 2660W but a few times I have checked and the inverter is reading over 2700W. My understanding was that this rated output of the panels would be lower due to system losses and such. My only explanation is that maybe they installed 200W panels??? Maybe i'll get up on the roof and have a look....

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## president_ltd

A few points: 
1.
Panel power numbers are based on a standard calculation of solar irradiation being 1000W/m2 (or something like that) @ 25C ambient.
If the ambient temperature is lower you get more power.
If the solar irradiation is higher you get more power. 
Former certainly happens in the morning.
Latter can happen when clouds are around and the sun is going in/out of clouds and its 'bending' the light (concentrating it) such that solar irradiation is actually higher (temporarily).
Google "cloud burst pv solar" or similar, you can read it up. 
2.
New panels often generate more than their rated value.
190W panels are closer to 195W to start with. The rationale behind this is that over time they decrease and from memory its something like that at +15 or +20 years they are rated to be "no worse than 80% of the rated capacity."
One way they ensure this is by labelling them as less power than they actually are. 
Our 180W panels generated closer to 185W to start with.  2.5 years on, they're still often above their rated capacity but I'm sure after a few years they won't be anymore. 
3.
You're reading 'instantaneous kW' numbers off the inverter. You don't say what the make/model of the inverter is, but some brands show you the DC-side kW numbers and not the AC-side.  
Indeed you'll see instantaneous bounce around a fair bit, a lot more than you think.
What really matters is the kWh/day numbers.
There normally are losses of around 20% from rated capacity.
Per pvwatts (PVWATTS v. 1) you can expect 2.66kW of panels in Brisbane to generate 3718kWh/annum or an average of 10.18kWh/day.
We are of course closer to the peak production - December should be ~337kWh/month or an average of 11.23kWh / day.
Generating more than that is fantasitc - but not likely to last.  :Smilie:

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## mattski2008

Thanks for your response. All of that makes sense. I suppose of the two months it has been on we have only had 3 or 4 rainy days which as you say is not likely to last. I guess I will may hay while the sun shines?>..??.?

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## president_ltd

BTW one of the best comparison tools is pvoutput.org.
you can compare your output to others around to (or anyone on there for that matter). 
for your system, generating at 16kWh/day for 2.66KW of panels = an efficiency of >6 kWh/KW which is not unexpected during the sunniest days and longest days.
e.g. Melbourne today almost achieved that here myself (may yet - sun is still up but the clouds are now over). see 'el presidente's palace 4.860kW | Live Output - not bad for a 38C day.  :Smilie:  
my all-time high is 7.248 KWh/KW generated (see 'el presidente's palace 4.860kW then click on 'efficiency' to sort by that).
Likely you're seeing this kind of thing too.

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## Sir Stinkalot

Your panels may have positive tolerances such as 190w +2% or whatever, you will need to check the specifications of the panels.  
Other panels may have a varied tolerance, say +/-2% which obviously isn't do good for solar. 
Cheers 
Stinky

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## Smurf

Over short periods (minutes) there can be various reflection of light off clouds etc. It's more than you might expect, and will push practically any panel well over its' nominal output. 
I've seen a 1.02 kW (DC side) system go to 1.21 kW (DC) due to this with my own eyes. It happens.

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## mattski2008

Thanks for all the responses!!. Thought I was going mad!  I definitely won't complain though.

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## Wombat2

I'm on the Sunshine Coast - after nearly 2 years on 3 Kw solar I've noted some trends. 
November is our best month for high output - can touch 18Kw in a day but usually 16-17Kw drops off in the winter months to 12Kw on a good day ( wish we could change the angle ) Yearly average is around 11Kw 
Provided we hit 8.5Kw in a day we break even financially at our current use/cost/rebate 
Hope that doesn't dampen you eurphoria too much  :Wink 1:

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## mattski2008

Just got my bill recently..... Generated 887kw @ 50c = $443. 
Usage dropped to 7Kwh/day.... cost me $156................... so I made $287 this quarter.. any profit is good.. I think I will save it up until I have enough for a solar hot water then watch it soar!!

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