Max length of run?

[nick611]

Can anyone help with this..2500w of panels. 6mm cable. Max length of run?

 

[Earthstore]

I think you are trying to do your sums the wrong way around here, You have your panel specs, and your cable distance, what you need to work out is your cable size.

If you do have some losses on the DC side do you see this as a problem?

 

[nick611]

Not sure really voltage fluctuates anyway. So i dont know how inportant it would be. Could you enlighten me?

 

[yellowvanman]

Can anyone help with this..2500w of panels. 6mm cable. Max length of run?

You need to find the Isc of the panels - written on the back!

 

[Earthstore]

Not my area of expertise, but on your panel spec you should have the voltage,
multiply this by 11 (if you are running on one string) then you will have your DC voltage.

When you say the voltage fluctuates do you mean the AC or DC?

 

[nick611]

have been told by inverter suppliers that i can run 100 meters but i am close to if not over this. what problems could this cause ?

 

[nick611]

Not my area of expertise, but on your panel spec you should have the voltage,
multiply this by 11 (if you are running on one string) then you will have your DC voltage.

When you say the voltage fluctuates do you mean the AC or DC?

not mine either. i can give you max runs on low voltage 230/400 circuits all day long but not sure of my figures on the dc side of things.

 

[Earthstore]

I would guess that you would have a small drop in performance, if your total panel voltage was say 200VDC and your inverter start up was say 175VDC then it may strugle to start up the inverter, or may not start it up quite as early in the mornings,
That said I am sure you are not cutting things that fine?
What inverter are you using?

Added;You say you have voltage fluctuations, this may cause you a problem, what are they from and to?
Also your AC cable(inverter to supply) needs to be under a 1% loss.

 

[Gavin A]

really long.

66m before you hit the 1% volt drop threshold, but it's only 1.5% at 100m which can be acceptable in some circumstances.

ps sunny design is your friend for this sort of thing.

 

[nick611]

really long.

66m before you hit the 1% volt drop threshold, but it's only 1.5% at 100m which can be acceptable in some circumstances.

ps sunny design is your friend for this sort of thing.

thanks gavin. what circumstances are these?

 

[Earthstore]

Just one other point, make sure when you install these DC cables that they are secured and safe, they are high voltage DC and the last thing you want is for them to get chaffed.

 

[Gavin A]

thanks gavin. what circumstances are these?

where it's not cost effective or practical to move up to 10mm2 cable. TBH I'd only consider it for bigger systems, never go above 6mm2 on something that size, though I guess I've also never gone above a 66m run for a system that size either.

 

[nick611]

ok gavin thanks. its a case of neccesety im afraid the length of run. and in reply to earthstore cables are run on cabletray and in flexible conduit labelled pv every four meters. thanks lads

 

[Worcester]

Some of our runs have been nearly 200m round trip on 6mm2, though at nearly 1000V (big strings ) Voltage drop is your enemy. As they guys say, Sunny Design is your friend here (it's free) V=IR Voltage Drop = Max Current (Isc) x Resistance (Ohms/m x length in m) Ideally you want as low as possible. At the end of the days it's effiiceincy losses and if cloase to the startup voltage of the inverter will have a bigger impact.

 

[moggy1968]

bear in mind also that the performance of panels diminishes over time, and also voltage drops with temperature so you need to be comfortably above the start up voltage to make sure the system still works in 10 years time and on a hot day!