Cable sizing solar PV

[normanton]

Morning gents, just a quick one. I've posted this already on the Solar PV forum but thought I'd add it here too as VD and cable calcs are always a good topic of discussion.
So I have a Solar PV system to install this weekend, its a 10KW single phase system on a farm. I'm going to be running a 2-core SWA from the substation to the invertor, the cable is going to be buried and as you know there needs to be <3% VD. My cable calculations are coming back with results of up to 95mm for some reason, this can't be correct surely? Any constructive help would be much appriciated, Cheers, Lee

 

[whinmoor]

Shouldn't you be aiming for a volt drop of less than 1% as per the "Guide"? (page 44, section 2.3.1):

"The a.c. cable connecting the inverter(s) to the consumer unit should be sized to minimise voltage
drop. A 1% drop or less is recommended. However in larger installations this may not be practicable
or economic due to the very large size of cable resulting. In this case the designer should minimise
voltage drop as far as possible and must remain within voltage drop limits as prescribed by BS 7671.

Note: The recommendation for a 1% voltage drop is due to two reasons: firstly when generating,
the voltage at the inverter terminals is higher than the voltage at the supplier’s cutout – during
periods of high power output this voltage drop must be kept to a minimum in order to prevent the
inverter nuisance tripping on over voltage ; secondly the requirement ensures losses from the PV
system are minimised."

You could have a play with SMA's Sunny Design which may be helpful in determining the correct cable for your situation.

 

[normanton]

Shouldn't you be aiming for a volt drop of less than 1% as per the "Guide"? (page 44, section 2.3.1):

"The a.c. cable connecting the inverter(s) to the consumer unit should be sized to minimise voltage
drop. A 1% drop or less is recommended. However in larger installations this may not be practicable
or economic due to the very large size of cable resulting. In this case the designer should minimise
voltage drop as far as possible and must remain within voltage drop limits as prescribed by BS 7671.

Note: The recommendation for a 1% voltage drop is due to two reasons: firstly when generating,
the voltage at the inverter terminals is higher than the voltage at the supplier’s cutout – during
periods of high power output this voltage drop must be kept to a minimum in order to prevent the
inverter nuisance tripping on over voltage ; secondly the requirement ensures losses from the PV
system are minimised."

You could have a play with SMA's Sunny Design which may be helpful in determining the correct cable for your situation.

ideally yes, but the 1% is merely a recommendation. Lee

 

[Leesparkykent]

Post your calculations up.

 

[Gavin A]

ideally yes, but the 1% is merely a recommendation. Lee

a recomendation for the very good reason that it will stop your inverters from tripping out all the time in sunny weather.

 

[jason121]

100m of AC cable works out at 70mm single phase

 

[Worcester]

70mm spot on for 10kW single phase, we've had to run that before now, Try running it three phase 4 core, that's fun getting around corners, up stanchions and across portal frames

You will suffer continuous disconnects if you go for the 3% and clinet will be seriuusly p***d off with output during the peak production times.

We know, we had the DNO screw up with voltages on one site, so they gave us written direction to reconfigure a 50kW system to G83, else it would have cost them an arm and a leg in new transformers - the local one was already down at the lowest tapping, upstream was the problem..