help please reduced output on hot days

[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

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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.

 

[Gavin A]

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

no. I'm saying that this 3kW installation on 50/50 split on this inverter isn't very suitable, and should only be done if on different roof faces or there was significant shading to one of the strings that the bypass diodes and shading function couldn't sort out well enough.

if the installer had used 50V panels, then 6 of these per side would be much closer to the peak efficiency point of the inverter than using 6 x 30V panels. Alternatively they could have used 8 x 190Wp 36V panels etc.

using the 30V panels though single string is the only way to get the most out of the inverter.

 

[billybee]

so Gavin do you think it would be worthwhile when the electrician comes to put in the link wires, would it be better for me just asking him to do this possitive to negitive thingy and converting totally to one string straight away. thanks

 

[Gavin A]

so Gavin do you think it would be worthwhile when the electrician comes to put in the link wires, would it be better for me just asking him to do this possitive to negitive thingy and converting totally to one string straight away. thanks

Presuming the shading is as minimal as you say, I'd just ask him to wire it into a single string of 12 panels in series.

Only if he says he can't get on the roof to do it would I mention the idea of him doing it via the cables in the loft / isolators, as it may well be simple enough to do with a ladder / roof ladder on the actual roof, and this is the best option.

 

[billybee]

when i spoke to the installer about the bigger inverter he did some checking and said he would recommend that with a larger inverter he would recommend going to one string. he said then that to do this i would have to put the scaffolding beack up. the way the panels are on the roof theres nowhere for a roof ladder so i doubt he would go for the ladder idea. i had the back of my roof repaired 2 years ago (got a new roof now) and the roofer at the time wouldnt go on the front without scaffold and the electric lines sleeving. so without a lot of expense i think your internal idea may be best.

im just of southish facing bottom row is 6 vertical panels (1 string) next row up is one panel vertical then the top row is 5 vertical i think the chimly witch i think on the east end is about 3 feet hight and may or may not shade the top of the end panel i doubt it ever casts enough shadow to hit more than one panel or a full panel. to be hounest i dont think i have any shading looking at where the sun rises i think its just the hight diffrence in the panels and its only happering very earley morning when the suns very low.

 

[Worcester]

I've just run the system through Power-One's sizing and design tool and it recommends installing these as a single string of 12.

Since all the wring is in place, (the DC losses are minimal) then it would be fairly easy to reconfigure it as a single string of 12 at the inverter end.

If that works out, then it would be simple enough to go into the loft and just join string 2 to the end of string 1, the length of cable coming into and out of the loft would be minimal.

That change over is very simple.