(Another) Cable question

[MikeD]

We're due to have our 3.84KW system fitted soon, and from reading other posts here I'm a bit concerned about the losses due to the DC cable from panels to inverter.

We'll have 16 panels arranged as 2 rows of 8, each panel providing 30v at the top of the power curve. So that's 240vdc per array.

The distance to the inverter is 12m, which seems like quite a long way.

Can anyone tell me, is that going to work, and what thickness of cable should be fitted to keep the losses to a minimum ?

[Automan]

If each bank has its own cables to the inverter the current would only be 8amps max.

No skin effect with DC energy so I would have thought the standard 4mm cable used would be fine...

Power lost in cables would be the current squared x resistance of cable.

Automan.

[MikeD]

Thanks Automan.

I should have said, it's 2 arrays of 8 panels per array because we've got twin MPPT inputs on the inverter.

Pardon my ignorance, but is that 4mm dia of copper for each core then ?

[EccentricAnomaly]

Pardon my ignorance, but is that 4mm dia of copper for each core then ?

No, 4 mm² cross-sectional area for each core. Leaving out the "squared" bit is a common shorthand.

[MikeD]

I make that a total resistance of 0.08 ohms (using 24m of wire as there's 2 cores)

P=I^2 * R

So about 5W loss (at full power) per array, so 10W in total.

Assuming the maths is right, then 3.84KW at the panels becomes 3.83KW at the inverter . I can live with that.

Cheers guys

[BruceB]

Download Sunny Design and model your installation in that.  It includes cable loss calcs.
Regards
Bruce