help please reduced output on hot days

[billybee]

just an update, ive had some feedback from power one, he beleives that changing the internal wiring on the inverter to one string will improve things somewhat. he sent me two data sheets on 2 strings and one string and while i dont fully understand what it all means. it will make changes to (Load Factor/MPPT [%])(Maximum Power/MPPT [kW]) and (Inverter Reccomended Activation Voltage [Vdc]) thus uping my performance. so i will of corse have these changes made which looks quite simple to do and see what happens. ive also now got a thomitor on one of the panels. and the last few hours now the rains stoped. my roofs around 33'c and i'm peaking around 2.8 to 2.9 kw. but as theres still a lot of clould and the room where the inverter is, 25'c its not going to tell me much till we get a very hot day again. on a normal hot day by 10am the system upto 1600w by 10am and today it its been merky out side till affter 1pm the roof and the inverters had no real heat. so i dont expect to learn anything

thanks all and i'll let you know of any changer after the modifications made.

 

[Gavin A]

did the aurora guy mean running the inverter on single string mode, but still with 2 inputs?

if so, that would make a minor difference, but running it in one string of 12 panels will make a much more significant difference. This is easily enough tested out, as the installer can simply alter the wiring at the isolators to switch it over to running in a single string. Long term it's obviously be better not to have the extra cable run happening, but if you want to test the difference it makes, then this is dead simple.

 

[jason121]

i didnt think you could alter the power-one to single string, i ask that question at technical and they said no. But wonder why they provideded the two cable links with the inverter

 

[billybee]

yes thats what he's suggesting, even sent me details and pics of how to do it, at this time he's just sugesting making minor changes at the isolatiors moving 1 black and red and adding 2 wires linking them. i'm guessing that way as to totaly restringing them would problably mean scaffold back up and getting on the roof again. or could the cables coming in already be used for one string, or would this cause issues with cable lenth.

so does that mean that you think runing 2 strings on a single string mode isnt going to make a big diffrence.

when i first discussed having the panels installed i didnt want the inverter in the loft for a few reasons, the origanal plan was to run the panel cable down the wall to the spair bedroom and then the ac cable back out the same way and back into the meter. as the panels spair room and meter are all at the front of the house, i thought that would be easyer than going through several floors. but i was informed that the lenth of the cable from the panels could make a diffrence on output and the closer the inverter to the panels the better. in the end being 2 strings theres a lot of cable anyway.

 

[billybee]

i didnt think you could alter the power-one to single string, i ask that question at technical and they said no. But wonder why they provideded the two cable links with the inverter

well he sent me the pics and it looks very simple to do move two wires one red and one black.



> 1, move my black input 6 to number 5 and then put a black link wire from input 2 to input 6
>
> 2, move my red input 8 to input 7 and then put a red link wire from input 4 to input 8

that was it

http://www.power-one.com/sites/powe...y/tech-manual/manuale_inst_2011_multiling.pdf

page 12

big question is how much diffrence will it make and if i get scaffold back up and restring will that make a much bigger diffrence.

 

[jason121]

Remember you playing with DC so be careful nasty stuff if it bites you

 

[jason121]

i cannot believe you have peaked at 3.3kw on a fine day on a 3.0kwp install according to you graph

 

[jason121]

Also if you have two strings identical installed on a Power-one inverter. On the display were its shows both string outputs in watts and they are both the same there is not a problem with the installation or design

 

[billybee]

i used to play with DC in my job and sadly through some one else being stupid i got a nip of it. funny the smell of burnt flesh lol. even though i could easerly do it ive had the system in for 2 months and the second i change wires without the installers consent theres my guarentee gone. so we will leave wire changes to the perfesionals i think thats best.

i am a bit curious about why i have the 2 strings is this because the aurora has 4 lots of inputs and makes it seem normal to use them all. if you were to have had just one string would two of the inputs be left unused.

 

[billybee]

ive peaked above 3kw on about 10 days but never on a hot day only mixed days, thats what my read outs say anyway.

 

[jason121]

Most of use power-one because of shading the lowest voltage on an power-one is 130volts, so minimum number of panels = 4
so if there is partial shading on one tracker the other tracker wont be effected.

 

[billybee]

i dont think he is saying theres a problem with the installation or design. i think he's saying that theres no need for two strings and if i want the optimum out of my system one string is better. the sheets he sent me say that at the moment my Load Factor/MPPT [%] with two string is 75% each string and with one it would be 87%. aslo the Inverter Reccomended Activation Voltage [Vdc] is 179v with 2 stings of 6 where as its 200v with a string of 12. like i said earlyer i'm not 100% sure what it will do but quoting him.

[FONT=&quot]Bottomline, your inverter is not in the optimized mode,[/FONT] [FONT=&quot]Assuming you have all panels on same angle and azimuth and no partial shading, you will get a significant improvement of yield having the panels wired as a single string of 12. The key is higher string voltage matching the inverters nominal input equates to max efficiency[/FONT]

 

[billybee]

well i may have some minor shading on the top string of the chimley but i dont no as several companys quoted and they all said no shading issues. i do early morning notice that one string can be producing 4 to 500 watts while the other is on 150 but depending on the day by 9am there the same and stay the same all day. i did think it was sun high just taking a bit longer to hit the top string. then noticed where the sun was in comparision two the chimley and though it could be shading the end panel or two till the hight got up.

 

[jason121]

Could like DC through a junction box before both isolaters making a single string then wire thru isolater

- - - Updated - - -

sorry link

 

[Gavin A]

[FONT=&amp]Bottomline, your inverter is not in the optimized mode,[/FONT] [FONT=&amp]Assuming you have all panels on same angle and azimuth and no partial shading, you will get a significant improvement of yield having the panels wired as a single string of 12. The key is higher string voltage matching the inverters nominal input equates to max efficiency[/FONT]

now do you believe me?

 

[moggy1968]

Thats why I gave up posting on this Gavin, I got the feeling I would be better off peeing in my breakfast cereal!

 

[billybee]

yes thats a simple solution and is it not just the same as these link wires he has sugested, now im not an installer and even though i neebed when the fitted them didnt see everything they did. but to hazard a guess one string is each panel conected to the next till you get to the last one and then them wires to the inverter. now if thats the case im guessing that at the moment and knowing the panels i have that one of my stings is longer (wires) than the other (ones always slightly less than the other (normanal) so if you just joined the two strings with a junction box it wouldnt make much diffrence compaired to linking them inside the inverter. now i'm guessing that by linking where as i have lin1 and lin2 now i will just have lin1 changing the way the system runs.

now going back to what gavin A said, if this linking works and perfromance is up, then the best way forward is to full restring to one that way the DC cable lenth will be a lot less helping perfromance even more. (this is going of several installers telly me the shorter the DC wires the less the looses will be) i'm sure someone on here would no what the diffrence is say between 5 and 10 meters of DC cable.

 

[jason121]

so are you saying Gavin that a 3kw install on a power one split 50/50 is not very suitable ?

 

[billybee]

i never disbelieved you gavin, i just felt that theres more to it than the sinle string issue. your info on the % loss due to heat was very interesting. i wonder now why do i have 2 strings and what diffrence 1 will make. i always new about losses due to cable lenth of part of the job i used to do. and because of this no what your saying about a complete change to one string is going to help even more. but i still think on very hot days due to where the inverter is that derating is kicking in and with a bigger inverter i could salvage this. but of what ive picked up on here i think now for what it will cost and for the gain on some hot days the possible lose on the other 250 cold days could out way the benifit. and thats down to this discusion thats the reason i contacted power one and i gave them some of you views.

i'm 10% down on the system i compair with due to 2 strings and the the heat rateing on my panels, possibly some derating issues and i dont no any data on cable lenths but i had a look on my roof earlyer and i seem to have a hell of a lot of loose cable. but that may have no bearing at all. the plan now is to get the links in and see what happens if theres an improvement that i need to discuse with my installer what do do next about restring the system. but i will say if it wasnt for the help on here wedensday a replacement inverter was going in and i was paying for the instalation cost and also towards the price diffrence of the inverters. i'm not now so thanks all

 

[Gavin A]

yes thats a simple solution and is it not just the same as these link wires he has sugested, now im not an installer and even though i neebed when the fitted them didnt see everything they did. but to hazard a guess one string is each panel conected to the next till you get to the last one and then them wires to the inverter. now if thats the case im guessing that at the moment and knowing the panels i have that one of my stings is longer (wires) than the other (ones always slightly less than the other (normanal) so if you just joined the two strings with a junction box it wouldnt make much diffrence compaired to linking them inside the inverter. now i'm guessing that by linking where as i have lin1 and lin2 now i will just have lin1 changing the way the system runs.

now going back to what gavin A said, if this linking works and perfromance is up, then the best way forward is to full restring to one that way the DC cable lenth will be a lot less helping perfromance even more. (this is going of several installers telly me the shorter the DC wires the less the looses will be) i'm sure someone on here would no what the diffrence is say between 5 and 10 meters of DC cable.

afaik you can't actually turn a 2 string system into a single string system via the link cables in the inverter alone.

you need to do this outside of the inverter, and then use the link cables in the inverter to switch the inverter itself from dual string to single string mode.

ie at the isolators you could run a link between the positive cable from string a into the negative cable from string b, then use the other pos and neg cables to connect to the inverter.

Obviously it'd be better to do this on the roof to shorten the cable run, but if it's 4mm cable then the losses will be relatively small.