help please reduced output on hot days

[billybee]

first of all hello to everyone.

i need some advice on reduced inverter output on really sunny days.

ive had my system for about 7 weeks, its a 3.0kw 12 a-sun 250w panels the inverter is a power one aurora 3.0 and the system is on 2 strings. my probelm is on mixed cloudy and sunny days the sytems peak out put can hit 3300w (great) and in the day the systems produced 18kws. now on hot days like the end of may the system only peaks at 2400w and produces around 18kws as well. ive done a lot of reading on it and it seems to be the inverter and some safty feature when it his 8 amps inputfrom the panels. is this normal ive watching a few systems and most seem to be doing this. some deal with it better than others. any advice on why this happens would be good.

thanks all

 

[SolarCity]

Hot temperatures will mean that the panels heat up - this actually reduces the efficiency of the panel and this will result in a reduced yield. You will find that you're more likely to reach peak power on bright yet cooler days.

 

[Gary K]

I think you will find its the panels that are affected by the heat, rather than the inverter, on partly cloudy days, the panels cool in the shade and then briefly produce strongly before they warm up again. On the constantly sunny days the panels are constantly hot and the output is reduced as a result. The panels are rated to produce the stated output at 25'c but up on the roof they may be at 60'c or more, for every degree above 25 you may be loosing .5% of the output.

 

[billybee]

i spoke to a-sun and they say its not that. they say the panels are good upto 80 and at .5 for every degree that means the panels must be hitting 80+ and when this happens you can see the change from as early as 10.30 am (i'm a nerd compaired daily outputs) no on a normal mixed day by about 11.30am the panels hit about 1800w by 12.30 3000w which is the way it went yesterday but i checked yesterday and neather of the 2 lines i have got to 8 amps. today started simler to yesterday and by 12.10 id it 2700w then by 1.15pm sun shinning lovely it was back down to 2450w it stayed at this (give or take a few cloudy spells till 4pm. but i noticed both lines stayed on 8 amps consantley. now output is similar (bit more today) but when you compair the two days the main diffrence is between 12 and 4 where it seems to lose upto 700watts and hour of the top of the graph.

the reason i'm asking is i'm compairing to some very simlar local systems (i know you can never do exact comparisions) and i'm getting about 10% less perfromance than them and its hot days that are affecting me the most.

 

[Gary K]

I can not find anything on a-sun panels, are you sure that is the manufacturer? Is this system on any site, EG PV output

 

[billybee]

yes
sunshine please 3.000kW

panels are ASUN250-MB_EN

thanks the reason i blame the inverter is i'm watching a sunnyboy inverter and its doing better on hot days. i have a solotion underway but not sure if it will work.

sorry sytem isnt live feed another problem with the inverter lol

 

[Gary K]

yes
sunshine please 3.000kW

panels are ASUN250-MB_EN

thanks the reason i blame the inverter is i'm watching a sunnyboy inverter and its doing better on hot days. i have a solotion underway but not sure if it will work.

sorry sytem isnt live feed another problem with the inverter lol

What system are you comparing with - if it as being run with say Sanyo panels, that may well cause the 10% differance

 

[Earthstore]

Almost definitively the panels heating up, some panels work better when hot than others, you need to remember the cells are black, and behind glass, so the temperature will increase when in constant sunlight.

An easy way to test is when performance is down, spray the panels with a hosepipe to cool them down, and watch the inverter at the same time.

But if it cracks the panels do not blame me...

 

[billybee]

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).

 

[billybee]

Almost definitively the panels heating up, some panels work better when hot than others, you need to remember the cells are black, and behind glass, so the temperature will increase when in constant sunlight.

An easy way to test is when performance is down, spray the panels with a hosepipe to cool them down, and watch the inverter at the same time.

But if it cracks the panels do not blame me...

sounds a bid dodgy lol. may be better just to put a temomiter on roof and check temps on days that it happens. or find another system with asun panels (ive tryed) but a diffrent inverter and see if sililer things happen.

 

[sambotc]

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

 

[Earthstore]

There are so many things that affect panel temperature, roof type, dark slate would be hotter than say a fibre cement roof, type of mounting frame can make a huge difference, air flow around panels, a roof may have an obstacle in the way that reduces air air flow.

It is not just as simple to compare one system to another.

I am only trying to help by the way.

Added
It is the cell temperature that you will need, not just the roof temperature.

 

[billybee]

this is what i think, and something i read (but carnt find now) had a similer problem, it was something to do with the inverter cutting down to about 80% output, there was a solotion that aurora tech told him to do but i phoned and they wanted the installers electrition there to check things out in the service area. he came crashed the inverter waited an hour for there tech to phone. after a hour he found the way to put right what he'd done (googled on net) waited another hour for power one then had to go. he did look at my figures and agreed with the 10% below par.

now when i decided on what system i wanted i did always want a bigger inverter than the panels. i now everyone says the inverters perform best at around 96% but from say 50% to 105% theres less than a % diffrence in efficancy. so my soloution is going to be up the inverter to a 3.6 i'm hoping when i do this that when i hit 16 amps (8 each string) and the inverter cuts down i should then get about 2900w instead of 2400w. may work.

 

[cbw]

I was going with the 8 amps a string as above, am I missing something here?

Sounds GREAT to me, one I installed last week has been maxing out merrily from 08:30 till 18:00 for the last 2 days.

Graph looks great, one great big block with a flat line at 16A!

 

[billybee]

i know compairing is hard. thats the main reason i went for the one i did, i have a fiberboard roof and noticed when they installed with monts that had to be drilled though the boards that the panels are quite high of the roof, i also live on a hill so should be getting good air flow. the panels a copir with are on a terreced house same as mine chimley either end same as mine. i do know the only true way to compair is to have the house next door. with the same size system.

 

[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.