The Solar Power Expert Blog

How to Wire Solar Panels

by Chris - June 28th, 2011.
Filed under: Equipment. Tagged as: , , , , , .

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Properly sizing the wire for your solar panels will play large role in the efficiency of your overall system. This article will help you select the right wire gauge for your solar project.

There are many problems associated with improper wire sizing. If the wire is too small and the current capacity of the wire is exceeded, it will cause a voltage drop and rob the load of the voltage it needs to function correctly. That voltage drop also means that energy that would otherwise go into the load is being wasted in the form of heat along the wire. In extreme situations, the wire can heat up enough to cook the insulation. Continuous heating will turn the insulation brittle and it will begin to flake off or melt off.

Over sizing wires comes with its own set of problems. The biggest factor is weight and cost. Copper is both expensive and heavy. While a wire does not seem that heavy to you, a bundle of wires add up in weight very quickly. That being said however, I am a big fan of overkill. If you don’t mind the extra weight and cost, larger wire will make your system more efficient. It’s also perfectly acceptable to oversize your wire if you are planning on adding capacity in the form of extra solar panels in the future. Just be sure to plan it out so that your wire can handle the extra current in the future.

When using the tables below to calculate the current carrying capacity of copper wire, be sure to factor in the return path. The electricity has to flow from the source to the load and back again. The return path needs to handle the same amount of current. Also, be sure to add a few extra feet to ensure room for error. It’s not a big deal to have a few extra feet of wire, but you really don’t want to have too little wire. Adding pigtails and extensions will increase resistance and create additional failure points in your design.

Wire Resistance Chart

In order to determine the proper wire size, you need to know what you’re connecting. If your connecting an insensitive load, such as a pond pump, battery, or light, your system can handle a voltage drop of up to 10%. These kinds of loads will not be as sensitive to voltage drops or noise. However, other loads such as computers, microcontrollers, or other device with timing electronics will be more sensitive and should operate as close to nominal voltage as possible. For these electronics you should plan for a 3% voltage drop or less.

Round Trip Wire Length (in feet)
Current (Amps) 10 20 30 40 50 60 70
5 18 18 18 16 16 14 14
10 18 16 14 14 12 12 10
15 18 14 12 12 10 10 8
20 16 14 12 10 10 8 8
25 16 12 10 10 8 8 6
Wire AWG for 10% Maximum Voltage Drop

While amperages under 5 amps can use 18 gauge (AWG) wire, you should take a moment to consider the mechanical strength of the wire. Many ‘old school’ experts recommend not using any wire smaller than 16 AWG, because 18 AWG and smaller wires do not have much mechanical strength. Remember that the bigger the AWG, the smaller the diameter of the wire.

Round Trip Wire Length (in feet)
Current (Amps) 10 20 30 40 50 60 70
5 18 14 12 10 10 10 8
10 14 10 10 8 6 6 6
15 12 10 8 6 6 6 4
20 10 8 6 6 4 4 2
25 10 6 6 4 4 2 2
Wire AWG for 3% Maximum Voltage Drop

Buying Wire

Before purchasing the cheapest wire you can find, you should give some thought to the quality of the wire you buy. While it is true that copper wire is copper wire, it’s also true that corrosion is a constant headache.

If your project is going outdoors, as most solar projects will, then you’ll probably want to invest in wire that has a good reputation for withstanding the test of time. Ancor is a well respected brand in marine grade wire. The insulation has been extensively tested to resist sunlight, cold, heat, abrasion, acid… and the list goes on. Additionally, the wire is tinned which prevents corrosion of the actual copper underneath. This is a high quality wire that will last.

On the other hand, if you’re looking to for budget wire, speaker wire is the way to go. This wire is designed for indoor use, so it wont’ stand up for long in the outdoors. However, if you’re looking for inexpensive wire for a quick project, this is best to keep costs down.

There are tricks you can use to improve the weatherability of the wire – such as tinning the ends of the copper, using shrink tubing, and anti-corrosive grease. However, this wire will probably not hold up to UV radiation from sunlight for very long.

For more information…

The 3% and 10% voltage drops are rules of thumb and originate from The 12 volt Bible for Boats. While this book focuses on 12 volt systems, the wire resistance chart above are based on current and are equally applicable to solar systems of any voltage.

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