help please reduced output on hot days

[Earthstore]

Chimney's.....
Do you get any shading at all?

 

[billybee]

yes thats mine nice clime till miday hits 8 amps 2450w's then an almost flat line till it hits where it would normally start to drop again. clouldy mixed day graph is a montine peak maybe a 2 hour period frome 1 till 3 where it can run around 3300w's. i dont no if a bigger inverter will help but i will certanly post any results.

 

[billybee]

tinny bit on the top string early morning and the top sting oftern takes about two hours to get level with the bottom string. but i spoke to the guy i'm compairing with and in his reply without even asking he gets the same on a morning. were both south at about 5 degrees west. were both terreced simler roof pitchs and have chimleys either end. the big diffrence is he runs and eversolar 4000. but a diffrence the other way is his panels 3.290kw have only ever gone above this 3 times and only by 2% mine and thats in 192 days. mine have gone above 100% panel output 10 times in 50 days.

 

[Gavin A]

The inverter will max out at 16A so 8A per string sounds right to me?

that's AC output and not related to the max DC input which is 10A per MPPT, so it's definitely not that.

If run in 2 strings the string voltage at presumably 6 panels per string will be right at the bottom of the voltage range for the inverter, which will account for a few percent of the performance loss. Run it in single string and the voltage would be around optimum.

 

[Gary K]

im compairing with a system 10% bigger than mine that produces 20% more on average its 10kms away ive got all the info of him and we are the same orintation 2 degrees diffrence in roof pitch he has 14 235w ET panels. why would sanyo cause as much as 10% diffrence i read up on a lot of panels and went for the asun on cost and performance. also ive looked at a few systems and not many of the panels can hit 10% above there rateings and mine have peaked at above 3100 quite a few times. its manley hot days the problems happens. i read something a while ago about aurora inverters on the net with a similar probem and the solution (carnt find it again).

Your panels loose .53% for every degree above 25'c compared with a 235w ET panel which looses .43% so thats 1% differance for every 10 degrees above 25'c so if the panels are at 75'c the ET panels are 5% more efficient if all other factors are the same.

Any one confirm this is right.

 

[Earthstore]

Go to the top of the class..
Your maths is spot on.

In the real world, the difference may even be higher.

 

[Gavin A]

If those figures for the percentages are correct, then the rest is right, although I doubt the panels will get to 75, more like 55-60 max most of the time in full sun, so around a 3-4% loss.

add that loss to the reduced inverter efficiency though and that's probably 6-8% reduction accounted for. Add in the -2% power tolerance, and you've pretty much got the reduction mentioned.

 

[moggy1968]

a sun are talking rubbish, all panels produce a curve type graph of temperature coefficient. As the panels get hotter, they lose volatge, thats physics, and ye canee change the laws a physics!
Temperature coefficient graphs are one of the things worth looking at when comparing panels and is one of the many differences between cheap imports and better quality panels.
A 3000 inverter is ideal for your system, a 3.6 will be inefficient and will become more so as the panels age and their efficiencies drop further.
As above, running 2 strings will reduce efficiency, all things being equal, because of the lower voltage, but given your slight shading may be the best for your roof, it depends how they have been configured.

 

[Gavin A]

Temperature coefficient graphs are one of the things worth looking at when comparing panels and is one of the many differences between cheap imports and better quality panels.

not necessarily - the cheapest panels we offer have one of the better temperature coefficients at 0.41% (obviously not in Panasonics range, but beats a lot of higher price panels)

A 3000 inverter is ideal for your system, a 3.6 will be inefficient and will become more so as the panels age and their efficiencies drop further.
As above, running 2 strings will reduce efficiency, all things being equal, because of the lower voltage, but given your slight shading may be the best for your roof, it depends how they have been configured.

ah yes, shading. Hard to say which is going to have most impact, but the lower voltage will certainly be causing the impact in peak sunlight levels.

 

[billybee]

can i ask where you got those figures just out of intrest. as i phoned asun and they recon its not that. also why would it be so presise the loose on my system. i could understand at 25'c geting 110% 3300w maybe at 30'c losing a bit and more as the temp goes up but it doesnt happen like that when its a mixed day and hiting over 3000w the only time it drops is with cloud (and ive checked this next comment) on a hot day like today when we have had some cloud cooling slightly is drops a little but still only goes back to 2450w. i asked asun is there a safty feature that says right panels are to hot run below max for safety and they say no. ive looked at the data sheet and it says above 45'c i can see the .53% but dont know where the 25'c is coming from. thanks

 

[Gavin A]

the panels are rated at STC (standard test conditions), which is 1000W/m2 of light at 25 degrees panel temperature.

the temperature coefficients are therefore related to the 25 degree point.

this is standard across all panels, manufacturers etc. 0.53% per degree though is the highest I've seen, so your panels will be impacted significantly more than others, as discussed.

eta - this isn't a safety feature, it's simply how the panels work.

 

[Gary K]

All manufacters rate their panels at 25 degrees its makes for easier comparison

 

[moggy1968]

Which panels are those Gavin?
It's a generalisation for sure, but certainly a factor, as with all things, some branded stuff is tosh while there is some good budget stuff about, I'm a big fan of Yingli for example

 

[billybee]

so can i ask what this NOTC 45°C +/-2% means. i do understand what you say about temps and take it on board but why would it cut down the out put on 6 days to neally exactly the same amount each day. wouldnt i expect to see some fluxuation in the peaks as 5'c change in temp would mean aprox 150w's change in peak output. there doesnt seem any middle ground its all or nothing so to speak. i'm getting the inverter changed next week and going off what your saying it shouldnt or wont make any diffrence. i'm a bit old fashoned and strongly believe that if you run something at 100% you shorten its life. so yes ive done the figures and i know i'll get a slight performance lose with the bigger inverter (could make things worse lol) maybe as much as 2% but it will confirm that its a panel problem if outputs stay the same. and if its down to amps i should see a higher peak on hot days.

i wish i could find some asun panels to compiar with on pvoutput.

 

[billybee]

i have the aurora portable device (not very good) it has to readings Vin1 and Vin2 which im guessing are my two strings and the on thing i can 100% conferm of that is that sometines when i'm hiting 3000w the amps on both are 8 and on hot days at 2450w the amps are 8 never goes above 8, hot days its constant cloudy mixed days it moves about.