Help about string configuration

[goc555]

Hello everybody,
this is really useful forum i ve learned a lot from you guys!

I am writing from Croatia and soon I will instal my first PV. But I have some doubts, maybe you can help me.
System is:
KACO Powador 12.0 TL (2 MPPT, every can hold 2 strings, range 200-800V) and
52 Luxor 190W modules (Vmpp=36,18V, Impp=5,71 A)

1. Is it better to have 4 strings with 13 modules, or two strings with 17 modules on one MPPT and one string with 18 modules on the other MPPT?
2. Is it better to have 5 m of DC cables and 5 m od 3-phase AC cables, or 8 m DC, and 2 m of AC?

Thank you!

 

[sharpener]

Hi,

1. Conventional wisdom would suggest you should divide the panels equally between the two inputs, this will minimise the stresses in the input circuits of the inverter and so give you slightly longer life and greater reliability. 13 panels will give you 470V which is right in the middle of the tracking range (it will be more in very cold weather).

2. Again it is usual to minimise the DC cable runs as there are more cables and they are more expensive. But I can't see 3m making a lot of difference if the cables are correctly sized.

HTH

 

[jerriais]

http://kaco-newenergy.de/de/binary/1/external/page/download.xml?file=kcp_2_9_6.exe

Here you will find the software that can answer all your questions about different types of Kaco inverters, hope this is helpful. Good luck with your system and I hope the Croatian government is more helpful towards solar than here in the UK, and I'm sure you have a bit more sunshine.

 

[bumcrack]

You will probably get better inverter effeciencies with longer strings, but....

a string of 18 will put you over 800v, once you have applied a safety factor of 1.25. This will limit the choice of DC available isolators, unles you use something like a PKZ-SOL12, page 17, here:

http://www.moeller.net/binary/pdf_kat/w7622en.pdf

 

[goc555]

Thank you for answers.

I already used KACO software and there is 'ideal' for both of configurations, so it did not help me much.
I can agree that should be conventional to divide panels equally but I am afraid that I will have to low voltage. For e.g. 4 x 13 panels 470V per string and maybe it won't work on not-so-sunny day, and on the other side there is 2x17 615V per string, and 1x18 651V string.
I'm quite new in this field so maybe I am saying something stupid... sorry about that

About our governments... I'm reading what is going on in UK, and must say that you are really in difficult position at the moment. In Croatia FITs are quite OK for now, but procedure to get into FIT system is completely nightmare!! There are tons and tons of paperwork and it take about 8 to 10 months to finally get the final contract! :/

 

[sharpener]

I don't know about the particular panels you have got but you will probably find from the data sheet that the voltage does not reduce much in low light levels. It is the current that reduces proportionally to the irradiation.