help please reduced output on hot days

[Fronius]

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.

I doubt that 75C has been hit on the average panel so far this year. Asphalt can melt at 60C. I have a temp sensor on the underside of my array ( 33deg S-facing ) and have not been past 47C.

 

[cbw]

Front faces were in excess of that (47) on testing this week

 

[billybee]

well going of 47'c thats a 2% diffrence in output. now going of pvoutput im seeing anywhere from 7.5% to 14% diffrence in performance. also no taking into account other factors to get an 8% diffrence due to temps if 10'c is 15 then we be looking at over 100'c to do that

 

[Gary K]

I doubt that 75C has been hit on the average panel so far this year. Asphalt can melt at 60C. I have a temp sensor on the underside of my array ( 33deg S-facing ) and have not been past 47C.

Fair enough. I just pulled some figures to work with. I have to get a 3 piece ladder out to get to my panels but will get the laser thermometer out at some point.

 

[Gavin A]

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.

you're rarely running it at 100% though.

its maximum rated output is 3300W, its nominal output is 3000W, and you're seeing it running at 240oW in long periods of full sun. If you get a bigger inverter the annual output will reduce for no benefit.

 

[billybee]

thanks for the help and i will report back after the inverter change. but taking in what you all have said that is possibly a couple of % on temps maybe a little on having 2 strings rather than 1, compairing 2 similer systems in the same area facing the same way with the smae pitch. maybe his 10% bigger system could out perform me by 13 to 14% (not factoring in that my panels do have out put peaks the same as his bigger system) but in 50 days the avarage diffrence is 20% today i got 17340w he got 21171 and i think thats around 21% diffrence.

 

[billybee]

you're rarely running it at 100% though.

its maximum rated output is 3300W, its nominal output is 3000W, and you're seeing it running at 240oW in long periods of full sun. If you get a bigger inverter the annual output will reduce for no benefit.

am i reading the technical data wrong the way i understand it is above 35% of rated Output Powerthe diffrence is 95.2 to 96.8 on perfromance anything below 35% i could pick a bit up as 3.0 starts inverting at 160 and the 3.6 at 120 and lets be hounest if thats all i'm getting were talking a few watts. if the bigger inverter increases peak out but on hot days (which im beginning to doubt now) i could pick up 400watts an hour. losing another 1% would be 180w on my best day and i could get some back of the slightly earlyer start up and shut down.

 

[SibertSolar]

Sounds to me like you have modules with shoddy junction boxes/bypass diodes fitted, either that or the cells in use are particularly low grade. Could it be possible that one or more bypass diodes are kicking into reverse bias because of individual sub-string cells getting too hot maybe? I've never come across a-sun modules and don't know what/whose cells they use, does anyone have any links/spec sheets?

NOCT = Normal Operating Cell Temperature and 45degreeC is within the typical range of most poly cells.

 

[billybee]

http://www.a-sun.co.uk/download/ASUN250-MB_EN.pdf

 

[SibertSolar]

Ok, thanks. Looks decent enough tbh. Well, if it's not something related to a defect diode then perhaps it is down to a combination of all the temperature related factors already outlined by others above. Would be interesting to see a thermal image of the array when the apparent losses occur!

 

[billybee]

so if its + or - 2% at 45'c should i expect to lose 10% thata 20x 0.53% ish over that temp range.

 

[billybee]

i carnt really call them losses just dont get above 2450w on hot days and because its already arrange to change the inverter, ive got my fingers crossed that its the panels kicking to much amp out for the inverter and by uping the inverter that it also ups the reduced peak output by the same %. i will post when i get some results either way. if nothing changes then its back to asun for an expernation of them on why ther claiming the temps we've had shouldnt effect the peak out put. as they told me there tested and used in italy with no reported power drops and its hotter there than here.

 

[sambotc]

They obviously know something that everybody else doesn't then, and bearing in mind they have temperature coefficients printed on their spec sheet, i'd say they are not telling the truth.

 

[FB.]

Today was a great day to see the temperature phenomenon.
It was about 20'C, no cooling benefit of any breeze and a mixture of sunny spells and cloud.

There were cloudy spells with generation being just a trickle, and when the sun came out power soared to 3.5kW. Then gradually the power output declined (as the panels got hotter) and settled around 3.0kW. Then a cloud would block the sun again, power would drop to 700W again, the panels cooled, the sun came out again and the power jumped back up to 3.5kW.

So I reckon that I was seeing a 15% loss of power output due to temperature.

The power-derating temperature coefficient of my panels is 0.43% per degree Celsius. So a rise of 35 degrees in panel temperature would explain the 15% drop in power output.

With ambient temperature around 20'C, the panels would appear to have been reaching 55'C after being in strong direct sun for many minutes.

 

[billybee]

well i agree there, the only other thing is on cold days i offtern get the same diffrence out of the last 21 days from 4 to 10kw production ive been out performed on 17 days by upto 23% but in saying that i have beaten him 4 times so even though were 10km apart weather could play some part may be cloudy here and raining there. thanks for the help anyway

 

[billybee]

i'm not an expert like the members on here, but today here in durham has been simler, i dont no what size system you have so dont know if your 3.5 is the size off your system but mine 3.0kw and both the inverter and panel have maxed on occasion at 109% output and today i never got above 80% peak. i do fully understand the maths involved (i did ask for a-sun panels but am i little disappointed that this coefficent was not expained as a 0.09 diffrence per degree is a lot over 30 degrees) but its not enough for the overall diffrence. there has to be more than just that. and the biggest diffrence on the two systems is the size of the inverter.

sorry and he's also running a 4kw inverter with 3.3kws of panels witch i'm being advised against. lol

 

[billybee]

Today was a great day to see the temperature phenomenon.
It was about 20'C, no cooling benefit of any breeze and a mixture of sunny spells and cloud.

There were cloudy spells with generation being just a trickle, and when the sun came out power soared to 3.5kW. Then gradually the power output declined (as the panels got hotter) and settled around 3.0kW. Then a cloud would block the sun again, power would drop to 700W again, the panels cooled, the sun came out again and the power jumped back up to 3.5kW.

So I reckon that I was seeing a 15% loss of power output due to temperature.

The power-derating temperature coefficient of my panels is 0.43% per degree Celsius. So a rise of 35 degrees in panel temperature would explain the 15% drop in power output.

With ambient temperature around 20'C, the panels would appear to have been reaching 55'C after being in strong direct sun for many minutes.

the heat thing with what youve said above i can understand and agree with, cool down power up heat up power goes down and if that was happerning and mine was going up after some clould great, but mine never go back past the same output once it hits 2450 thats is best for that day (hot days) half an hour clould and it will drop but within minutes of clould clearing back to 2450 again and thats it.

 

[FB.]

well i agree there, the only other thing is on cold days i offtern get the same diffrence out of the last 21 days from 4 to 10kw production ive been out performed on 17 days by upto 23% but in saying that i have beaten him 4 times so even though were 10km apart weather could play some part may be cloudy here and raining there. thanks for the help anyway

Does your roof have the exact same slope, and the exact same facing?

My system is 3.75kWp (Kinve KV250-60M) and 3.6 inverter (Power One Aurora PVI3600 indoor model - in a cool downstairs utility room).
However, the 3.5kW output dropping (-15%) to 3.0kW as the panels got hot in strong sun is the main point I was making. The actual size of the system wasn't so important as the percentage drop-off in generation as the panels got hot.
System faces East-South-East on an unshaded 40-degree pitched roof.
Readings showing the above fluctuations and temperature degradation were around 10am-12noon.

 

[FB.]

the heat thing with what youve said above i can understand and agree with, cool down power up heat up power goes down and if that was happerning and mine was going up after some clould great, but mine never go back past the same output once it hits 2450 thats is best for that day (hot days) half an hour clould and it will drop but within minutes of clould clearing back to 2450 again and thats it.

Then it sounds as if a shadow is cast across one or more of your panels, and the whole panel goes offline until much later in the day, when the sun has gone behind the panels or is much weaker.
A whole panel can be shut down with just a few cells shaded (if they happen to be just in the right places). So if you have two panels with some shaded cells, your maximum generation could be down from 3.0kW to 2.5kW.
However, although a panel can shut down with just a few cells shaded, it does depend on which cells.
I previously posted a sketch of the typical layout of bypass diodes, which I will repost here - just one cell shaded in each third of the panel will effectively take that subsection of the panel out of production:

 

[moggy1968]

or a dodgy panel?

 

[Earthstore]

or a dodgy panel?

That makes real sense, if a cell or two is over heating then it could be shutting down the panel as it warms up in bright sunlight, maybe time for a thermal imiging camera to see if there are any "hot spots".

 

[billybee]

to answer some questions
roof pitch is ni on the same possibly a degree or two diffrent. according to what he told me we facing within a degree or two the same way. its not the drop thats my concirn its that it doesnt get high enough to drop (hot days) going of the inverter size and panel i'm loosing more like 20% of my peak and going of what the inverter and panels have peaked at could be over 25%. to get a drop you need a peak.
i do get a shadow i think early morning as the top string is always lower than the bottom for an hour or so. but if its shading or faualty panels i would expect one string to be better than the other later in the day. after about 10am and for the times i get 2450 (hot days) both strings are on 8 amps and about 1200w. so if its a faulty panel there must be 2 one on each string.
i know nothing about thermal camers, i'm changing the inverter next week and if that doesnt work will have to put a thermiter on the roof to check temps. sounds possibly heat is the problem. but its the way they react.
could we be looking at vaultage from the panels. mine is about 560v (inverter) and ive noticed a system with a sunnyboy inverter has much better outputs on hot days, sunny boys 700v also the eversolar i'm compairing with can run at 680v.
thanks all

 

[moggy1968]

to answer some questions
. but if its shading or faualty panels i would expect one string to be better than the other later in the day. after about 10am and for the times i get 2450 (hot days) both strings are on 8 amps and about 1200w. so if its a faulty panel there must be 2 one on each string.
thanks all

unlikely I would say, but then,I've seen unlikely before!
The only thing that deviastes me away from temperature is the consistency of the top reading. Otherwise I would say yep, 99% sure it's temp.

 

[Gavin A]

to answer some questions
roof pitch is ni on the same possibly a degree or two diffrent. according to what he told me we facing within a degree or two the same way. its not the drop thats my concirn its that it doesnt get high enough to drop (hot days) going of the inverter size and panel i'm loosing more like 20% of my peak and going of what the inverter and panels have peaked at could be over 25%. to get a drop you need a peak.
i do get a shadow i think early morning as the top string is always lower than the bottom for an hour or so. but if its shading or faualty panels i would expect one string to be better than the other later in the day. after about 10am and for the times i get 2450 (hot days) both strings are on 8 amps and about 1200w. so if its a faulty panel there must be 2 one on each string.
i know nothing about thermal camers, i'm changing the inverter next week and if that doesnt work will have to put a thermiter on the roof to check temps. sounds possibly heat is the problem. but its the way they react.
could we be looking at vaultage from the panels. mine is about 560v (inverter) and ive noticed a system with a sunnyboy inverter has much better outputs on hot days, sunny boys 700v also the eversolar i'm compairing with can run at 680v.
thanks all

I've already explained in detail where your system is underperforming and what you can do about it.

replacing the inverter with a higher rated inverter will make it worse not better. The problem IS NOT the inverter limiting the output, it is a combination of your panels poor temperature coefficient plus the system being run in 2 strings of 6 panels that's right at the bottom of the efficiency range for the inverter, a problem that is compounded at higher temperatures as the string voltage also drops at higher temperatures.

this is not guess work, there's no magic involved in these systems, it's all in the data sheets for equipment you're using.

 

[billybee]

now this is what i think happens and i'm pritty sure that i'm going to be told i'm wrong but here goes.

the way my data is stored only gives watt ouput for previous days so till we get a mixed day i carnt conferm this 100%

my portable device gives me vin1 and vin2 for each you get vaults (pritty steady around 160 to 180) next amps which is always changing and lastly watts that changes with the amps.
now ive looked at it a lot and ive never seen it go past 8A on each vin so thats got to be its max, now yesterday it read 180v 8A and aprox 1200w on each line. that was my peak for the day. a couple of days ago on the mixed day my system peak for a short time at 3276w and i think the ampage peak would have had to of been 8. there is another reading which is larid witch seems to be the two combined.

so if on two days one hot peak of 2450 and one mixed 3276 and both peaks were pushing the same amps out heat must effect the ampage level. now i read somewhere before i got the system, of a guy who had an aurora and on hot days was having similer problems. i beleve he said it was a safety feature that cut the inverter production down when the ampage got to much.
so heres what i hope, the new inverter is bigger so when the drop happens i hope that rather than it cutting down to 2450 it will only drop to 2850 of corse this will only happen if its the inverter ampage and not the panels. also ive found the artical i red link below.
now my installer is being good about it, and we've agreed that if i pay the cost diffrence of the inverter and pay for the electrition he will change it. he also suggested that i put the new inverter to one string but a carnt afford it as it means scaffold again. id probably be better changing the make of inverter to an eversolar or sunny boy but thats down to cost and loosing my little potable monitor (wasnt cheep)

thanks all

info re Power-One Aurora grid inverter « Alternative Technology Assn Forums

 

[Gavin A]

the ampage you refer to is the peak ampage rating of the panels.

I'm banging my head off a brick wall here though, so I'm out of this thread, you can choose to follow my advice or just guess yourself.

 

[SibertSolar]

Put all the panels on 1 string and see what the difference is in performance.....As Gavin has suggested, if the Vmpp of the string falls below the min MPPT voltage of the inverter input then the inverter's power handling and efficiency will be impacted. It wont stop working but it will not operate at an optimum. Worth putting all panels on one string/input to verify that?.....

If that doesn't make a difference then we're back to looking at potential defect cells and/or diodes. Or you could just go ahead and change the inverter but I doubt that will help.....

 

[billybee]

i'm going to email the installer about the strings and ask why it was put onto 2 rather than one. see what he says. and take it from there. i am going to change the inverter still, as at the moment i have 12 panels (due to cost) the bigger inverter will give me the option of adding 2 more panels maybe at a later date. i will post with what happens either way if only to help with feedback. i think the problem i'll get with the strings is he'll no be keen on paying for scaffold to change them to one rather than 2 but i'll await his reply.

thanks all for the help and info.

 

[FB.]

An oversized inverter will tend to not operate at its optimum, and therefore have more DC to AC conversion losses. Each size of inverter tends to be optimal for panels of about the same rating. So by adding a bigger (more expensive?) inverter, things are likely to get worse - especially on dull days when a big inverter's internal power consumption may use up most of what the panels supply to it, resulting in little or nothing coming out as AC power.
Technically, if you add panels at a later date, you're supposed to get whatver FiT is being paid at the time, on a pro-rata basis. Your total installed capacity and declared net capacity will also no longer match your MCS certificate and not be what was originally approved by the DNO and your FiT provider - and I hear that some DNO's are looking to further reduce what is allowed to be installed on a property without consulting them.

 

[sambotc]

billybee, I strongly suggest you listen to the advise of the above posters, they do this day in day out and know their stuff. With all due respect you seem to have convinced yourself you know what the problem is but it doesn't make much sense.

You've been given the advise, it's up to you whether or not you take it on board, but arguing the facts with very credible installers and designers is not going to do you any favours, and your installers are obviously not aware of the facts that have been outlined in the above.

I'm off to un subscribe as its clogging up my inbox!