What Cable Size For 300W Solar Panel?

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A 300 watt solar panel can provide a lot of power, but only if wired properly. The cables running through the solar panel, charge controller, battery and inverter have to be sized right to produce the best results.

10 AWG is the ideal wire size for a 300W solar panel. You can use this for a cable up to 5.5 feet long, but for longer wires you have to go with 8 AWG gauge.

Solar Panel Wire Size Calculator Guide

If you want to avoid manual calculations, just buy a 300W solar panel kit like the Eco Worthy Solar Power System which includes the cables, connectors, solar panels and everything you need to set up a basic solar system. If you want to do the calculations, read on.

Solar panel watt hour / VMP = amps (maximum current)
Solar panel maximum current = minimum AWG wire size

A 300 watt solar system has a VMP of 18 volts. The highest possible current is 16.6 amps as shown below.

300 / 18 = 16.6

We round this off to 20 amps, and the smallest wire size you can use is 12 AWG. The maximum distance is 3.5 feet, meaning the cable has to be 3.5 feet or shorter to remain within the 2% voltage drop.. For best results we recommend 10 AWG as it lets you use a longer cable.

The longer the cable you want to use, the thicker the wire gauge has to be. The following are for a 12V 300W solar system with a maximum current of 16.6 amps. Double the cable lengths if you are using a 24V 300W solar system, and quadruple it if you are on a 48 volts.

Cable Length AWG Wire Size For 12V Solar Systems

Maximum Cable length AWG Wire Size
3.5 Ft 12
5.5 Ft.10
9 Ft.8
14.5 Ft. 6
22.5 Ft.4

The longer the cable, the greater the performance loss. You can avoid this by using thicker AWG wires but those are expensive. This is the reason why the distance between solar cables are so important.

If you use a thin long wire the losses will increase. The size guide given here allows you to maintain voltage drops to within 2%, but those losses can reach 4% or more if you use long thin cables.

How to Minimize Solar Panel Cable Losses

There are two ways, use a thicker wire or switch to a 24V system. Either one will keep losses to a minimum.

If you haven’t set up a solar system yet, decide if you want to go with 12 or 24 volts. Each has its pros and cons and your set up determines what should be used.

If you already have a 12V solar system, use 10 AWG. If you are using a longer cable use the other sizes recommended earlier. Here is a guide to AWG wire sizes to help you out.

What is important is you pick the right wire size. Undersized cables will generate significant losses. This not only wastes the solar panel’s potential but also dollars too.

Ill fitting wires are vulnerable to overheating and could start a fire. Think of a wire carrying current the same way a hose holds water. The larger the hose diameter the more water can pass through.

The same principles apply to solar cable cables. A 300 watt solar system generating maximum current needs a thick enough wire to ensure the power passes safely.

The longer the cable, the greater the resistance. High resistance levels reduces the power that can get to the system, which is why we recommend short, thick wires.

More about Cable Sizes

Solar panels greater than 50 watts typically use 10 AWG, but again this is for 12V systems. 24V PV modules can handle twice the cable length so you can use a larger wire.

Earlier we pointed out that a 12V 300 watt solar panel has up to 18 VMP. Using the same formula solar panel watts / VMP we can determine the minimum AWG size for any 12V solar panel size.

Suppose you have a 500W solar system. If it has a nominal 12V rating its current is good for up to 18V. 500 / 18 = 27.7 which we round off to 30 amps.

A solar array with a 30A capacity can use a 10 AWG for a distance of 3.5 to 6 feet. From 6 to 9.5 feet you have to go with a 8 AWG.

If you have several solar panels in a parallel connection, an AWG combiner set is recommended. This is ensure the current goes safely into the charge controller. The rule of thumb is you can always go one wire size bigger but never smaller.

Solar Panel, Battery and Charge Controller Wires

The wires for the battery and charge controller have to be at least the same size as those used on the solar panel. We recommend you use larger wires for the battery and charge controller if you have an inverter connected to the system.

Inverters may require more power than a solar panel. If that is the case you have to make sure the wires are large enough to handle the demand. Just like with solar panel cables, undersized wires for the inverter, controller and batteries result in underperformance. If you don’t have an inverter, the charge controller and battery wires can be similar sizes.

If you find all these confusing don’t worry. Complete solar panel kits like the ACOPOWER 300W RV Solar Power Kit are now available. They have the wires bundled so you don’t have to worry about the size. Even if cables are not included, the package will tell you what the optimum AWG size is.

When we talk about wire and cable sizes, it speaks of the length and diameter. The key points are the shorter and larger the diameter, the easier current can move through. The opposite is true, a long cable with a small diameter impedes the flow of current.

The wire size for a 300 watt solar panel – or any solar system – is determined by the maximum current and voltage. In most cases 10 AWG is good enough for up to 30 amps per PV module.

If you join several solar panels in parallel, you have to combine 3 to 8 wires to meet the demand. All the wires have to be the right gauge to ensure the system can handle the current.

Important Points to Remember about 300W Solar Panel Cables

  • A 12V 300W solar system works best with a 10 AWG wire. The cable length can be up to 5.5 feet. If you want to use a longer cable, get a thicker AWG wire like 8.
  • The lower the gauge number, the less resistance and more current goes into the wire. This is what you want in a solar system.
  • The cable and AWG sizes recommended here are designed to limit power losses to 2%. That is the highest percentage acceptable for solar systems today.
  • The cables connecting the battery bank and solar controller can be the same AWG size as the solar panel. Use a large cable if you have to install an inverter.
  • The 300 watt solar panel used in the examples here have a 12V nominal rating. A 24V or 48V solar array will produce different results and require other wire sizes.

You also have to consider the number of batteries in the system. A bank consisting of several batteries requires multiple wires. Each wire needs to be the appropriate size as well. As we pointed out, the battery and charge controller wire gauge can be the same as that of the solar panel.

If you are going to buy the solar cables separately, make sure to do so from a reputable manufacturer. And we cannot emphasize enough how important this is. A low quality solar panel is not only going to waste the panel’s potential but can even start a fire.

Lastly, make sure the wires are all secure. The MC4 connectors and other components have to be top notch as well. All these will ensure the system runs as you would expect.


Connecting wires and cables is hardly fun, but it is essential to get optimum results from solar power systems. By using the right wire sizes for your solar panel, you can be assured the components perform at peak capacity.