The Maximum Cable Length to Use with your Solar Panels?

In some solar installations, you may have to use a longer solar panel to charge controllers than those that came packaged with your solar panels.

For instance, if you need to mount the solar panels away from trees or another obstacle that casts shade on them to get maximum power, you may need to extend the length of the solar panel cables.

What is the maximum cable length you can use? Are there any rules of thumb you can use in working out the size of the cable?

This post shares some information (tips) to help you choose a suitable length of solar panel cables, includes a reference chart you can use to select a cable length, and finally provides some alternative cost-efficient ways should you have to run unusually long and potentially costly cable lengths for your solar system.

How far Solar panels should be from the Charge Controller

This depends on the current (amps) from the array and the size of wire you plan to use (AWG).

To work out the length of cable to use, determine the current flow from the solar panels and cross reference this against the various cable gauges, refer to the chart attached to determine the maximum cable length to limit the voltage drop to 2% (recommended).

For example, if you have 300 watts of solar panel wired with an output voltage of 18V, then the current flow is about 17amps.

Checking against the table, you can run up to 22.5 feet (one way) of 4 AWG.

You could double the length you can use with 4 AWG cables to 45 feet by wiring the solar panels so that the output voltage is 36V.

The Dangers and Benefits of Using Shorter or Longer Solar panel cables

If you run longer cable runs then there’ll a higher voltage drop, power losses, and corresponding less power available to the charge controller.

You can use a shorter cable length of the same wire gauge as well. Power losses will be within the allowed limits.

You can use the table below as an indicative guide or refer to the table below.

AWG Wire Size141210864
Current carrying capacity (amps)152030405570
Solar panel Array Output current (amps)cable length one way (feet) cable length one way (feet) cable length one way (feet) cable length one way (feet) cable length one way (feet) cable length one way (feet)
14570115180290456
222.53557.590145228
41017.527.54572.5114
67.51217.53047.575
85.58.511.522.535.557
104.579.51828.545.5
1534.57121930
2023.55.5914.522.5
251.82.84.5711.518
301.52.43.569.515
402.84.5711.5
502.33.65.59
1002.94.6
Credits: Windynation.com

How to Use Existing Solar panel Cables over a Long Distance while Minimizing Voltage Drops

#1. Sse higher system voltages. For example, the recommended cable length for a 300-watt, 18V solar system while keeping the voltage drop to 2% maximum is 22.5 ft.

If you increase the system voltage to 36V, you can run up to 45 ft of cable one way while keeping the voltage drop to up to 2%.

The benefit of this approach is you do not necessarily have to invest in additional cabling – you simply have to connect the solar panels in a series configuration.

Alternatively, instead of running DC cables, you can use an inverter and extend the higher voltage AC (115V) to the appliance.

You can then keep the DC cables short and extend the AC cables while keeping the power losses to a minimum since the voltage used is higher (115V AC).

#2. Increase the thickness of the cable used

You can also choose to use a thicker cable (lower AWG), that allows you to use a longer cable run without increasing the voltage drop.

For example, you can only run cable lengths of up to 6 feet when using 8 AWG wire if your arrangement generates 30 amps (720 watts at 24 volts).

Using 4 AWG wire allows you to use up to 15 ft of cable while limiting the voltage drop to 2%.

Should you Extend or Run a New Continuous Solar panel Cable?

Moden solar cables have MC4 male/female leads that you plug into each other to extend cable lengths.

Do not exceed the recommended cable lengths to avoid excessive voltage drops.

Alternatively, you can use a single longer cable run instead of joining to an existing cable section.

You may also be interested in this post: Why your solar panel may not be charging the battery

Closing Thoughts

There is no hard and fast number for the maximum length of cable you should use to connect the solar panel to the charge controller as this depends on the solar system voltage and the wire gauge used.

Using a higher system voltage allows you to use longer cable runs for the same system wire gauge.

Alternatively, you can use thicker cables which increases the cost of wires and overall material cost of the solar installation.

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