Portable Solar Panels & Extension Cables

You’re looking to position some portable solar panels at a distance from your van or RV or cabin. Mainly because it’s nice to live in the shade, while you position the solar panels out in the summer sunshine. This is a quick note to discuss what you need.

The first thing to understand is voltage drop. Some portable solar equipment companies supply 15-foot or 30-foot extension cables. Seems OK until you look into how much energy is lost in the wire between the solar panel(s) and your battery location. Some of these cables are #16AWG, some are #14AWG, and some are #12AWG. Hopefully the manufacturer provides you with this information.
Let’s look at the loss associated with placing a 200W panel at a distance of 30’…

A 200W portable panel provides usually just over 10A max at 18V in ideal conditions.
#14AWG Wire : 10.3% voltage drop
#12AWG Wire : 6.7% loss
This voltage drop due to resistance in the wire means that you lose as much as 10% of the energy you generate in the solar panel.
Not good.
In off-grid applications like cabins, we try to keep losses to less than 3%.

Is this a dangerous situation?
Usually, no. For example, #12AWG copper wire has a typical ampacity of 20A, meaning that it is capable of handling 20A of current. It’s only the length of the wire that is creating the amount of total resistance that is stealing your solar energy.
But, it is important to choose a wire size that is appropriate for the current it will be carrying for safety (code compliance), and then consider losses over the distance.

Why do companies undersize their accessory cables?
Two reasons:
1. Cost : The proper cable will cost over $200 and is quite a bit heavier & more difficult to transport through their sales channels.
2. Connectors : Common MC4 solar & many quick-connect electrical connectors are only able to accommodate up #10-#12AWG wire. Go any larger, and they start having to use different connectors and then makes sense of it all for their customers.

What Do You Need?

Let’s take the Goal Zero example.
Many folks with the fabulous Goal Zero Yeti battery packs are looking to place two of the Boulder 200W briefcase solar panels on a 30′ extension. Since the panels are wired together in parallel, this means as much as 20A pushed by 18V over the 30′ distance. A quick run of the voltage-drop calculator shows that #6AWG wire will provide just over 3% voltage drop… that’s close enough. The trick is to choose a wire size that keeps losses to a minimum without being as large as your arm or costing as much as your RV. #6AWG is not too large, and not too crazy on cost.

Next, you need to choose a wire type that can handle being coiled, stored, deployed, stepped on, driven over, exposed to intense sunlight, etc.
For lightweight needs, jacketed marine cable is a good choice. Marine cable is tinned which helps it to resist corrosion and oxidation.
For the toughest and longest life, look to SOOW cable, or “CabTyre” as it is often referred to. This is a flexible, heavy-duty rubber jacketed cable that is often used for outdoor power equipment.

Making Connections

If you are looking to use anything larger than #10AWG wire, then you will need to consider upgrading your connectors. MC4 connectors are good for #12 & #10 wire, so go to the Anderson SB50, SB120, and PP75 connectors when you need to get into #8 and #6 wire.

Need Help?

Send us a note with your wiring questions.

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