Why is solar panel cable so expensive ?

[AntarcticPilot]

Thanks guys , something' I'm still confused about is that I note that some people have significantly higher voltage panels , how does that work with 12volt batteries or am I missing something? Is there an advantage to going higher voltage ?

A nominally 12V battery actually varies in its voltage during the charge/discharge cycle, going as high as around 14V when fully charged to about 11.5 V when as flat as a pancake. In order to charge your battery, you need a voltage higher than the current value for the state of charge of the battery; otherwise, nothing will go into the battery. It's easier to obtain this from a voltage source that exceeds the highest voltage of the battery, and the job of the charge controller is to regulate the solar panel voltage to a voltage appropriate for the state of charge of the battery. PWM and MPPT controllers both do this; MPPT is more efficient.

 

[Zing]

Why is solar panel cable so expensive relative to normal cable ? Is it the covering to stop degradation . My set up will only be set up and used when on anchorage or when not plugged in to shore power so do I need to use it ?

I just bought a batch of cable for a new installation from 12V planet. I found their product to be better and cheaper than what I could find from my usual suppliers at RS and Farnell. I liked the double UV resistant insulation. Very much a good idea I think.

 

[William_H]

Voltage, potentially It depends how long the run is from panel to controller and what nominal voltage you expect from the panel configuration. It's the volt drop from an undersize cable that is the risk

Size of wiring from a solar panel to controller is a lot less significant than you might think. A solar panel functions with significant internal or source resistance. So a 10w panel giving 20v open circuit and .5 amp short circuit has an apparent internal resistance of 40 ohms. A 100w panel 4 ohms. So when you use a cable that has perhaps .05 ohm (.5 v drop at 10 amps)resistance the relative resistance of panel to cable becomes insignificant even in a 100w panel.
So in practice almost any wire size will be OK. Of course being on a boat heavier wire is more robust against corrosion damage etc.
If you are using a PWM controller then panel is effectively connected to the battery so the difference 20v to 14v of battery 6v is wasted in panel internal resistance so half a volt of cable loss is nothing. Using an MPPT controller means perhaps that power lost in cable can be power lost to end battery charge.
Note however that if you are buying solar panel cable it may be made for domestic PV systems where voltage can reach near 400v so more insulation required. ol'will

 

[coopec]

Maybe this would interest some people?

Solar cables and wiring: sizing and AWG explained

 

[Farmer Piles]

Thanks , over about 3 metres would it be significant ?

If it's only three metres surely the difference in the cost of the cable is minimal compared to the cost of the installation and the general cost of running a boat. Personally, I feel it's always best to use the proper stuff in circumstances like this. You know that it is fit for purpose and should there be a problem further down the line your insurance is far more likely to stump up if the recommended materials are used.

 

[arcot]

Two commonly types of conductor are used for solar panels....
Copper
Copper Clad Aluminium

 

[penfold]

If salt gets on copper plated aluminium you'll be able to hear the fizzing.

 

[noelex]

A 100w panel 4 ohms. So when you use a cable that has perhaps .05 ohm (.5 v drop at 10 amps)resistance the relative resistance of panel to cable becomes insignificant even in a 100w panel.

So in practice almost any wire size will be OK. Of course being on a boat heavier wire is more robust against corrosion damage etc.

Agreed, a 2.5% voltage (or power loss) at 10A is fine especially as the output will frequently be lower than this. However, the voltage drop is always worth calculating. Some solar panel wiring runs are long and voltage drop caused by insufficient cable size does sometimes become a problem. The voltage drop between the panels and the controller should be calculated separately from the voltage drop between the controller and the batteries as in most systems the voltages, currents and wire run lengths are different in these wires. This often necessitates different sized cable.