If you’re setting up an off-grid solar system, you might need to extend the cables from your solar panels to the charge controller, particularly if you need to position the panels away from shaded areas for them to generate as much power and for as long as possible.
Wondering about the maximum cable length permissible?
This post provides tips and a calculator to help you choose the optimal cable length that minimizes power loss from your solar panels.
The Optimal Solar Panel Cable Length
The maximum cable length for solar panels to a charge controller depends on:
- The current (amps) flowing from the solar panels. Higher amps necessitate shorter cables for a specified wire size (AWG).
- The arrangement of your panels—connecting them in parallel versus series can affect the permissible cable length.
Use the calculator below to ascertain the suitable wire size for a given voltage drop (3% or 10%) relative to wire length.
Example Calculation
Let’s take 400 watts of solar panels made up of four 100-watt panels connected in parallel, each with an optimal operating current of 4.91A (as per panel specifications).
The combined current from these panels would be 19.64 amps (4.91A x 4). For a total cable length of 45 ft (22.5 ft one-way) from the solar panels to the charge controller, the calculator indicates that for a 3% voltage drop, you should use 6AWG wire.
If a 10% voltage drop was acceptable for your requirements, then 12AWG wire would work as well.
The Dangers of Exceeding Recommended Cable Length
1. Appliances Might Not Work Properly
Using longer cables than recommended for a given current and wire size (AWG) leads to a higher voltage drop. This can result in insufficient voltage reaching your appliances causing them to fail to operate as expected.
To determine this using the calculator, keep the acceptable voltage drop and current flow (amps) fixed, and adjust the cable length to determine what wire size is needed to maintain the voltage drop.
2. Increased Costs of Wiring
Longer cable runs necessitate thicker, more expensive wires and can be more challenging to work with, especially when connecting to charge controller or inverter terminals.
Related Questions
What if you wanted to know the maximum cable length you can run for a given wire size (awg)?
Worked Example: Maximum Cable Length with 10 AWG Wire
There isn’t a straightforward answer as it depends on:
- The output current from your solar panel array,
- The wire size (AWG),
- And the cable length.
With above calculator, select the output current and increase the length of wire incrementally until the wire size drops below 10 AWG.
Using the calculator as an example, assuming a current of 5 amps and limiting voltage drop to 3%, the maximum recommended return length of wire to use is 50ft.
2. What if you already have the voltage drop problem at the appliance and the cables have been installed already?
To address voltage drop issues, consider: increasing the voltage output from the solar panels (check if your charge controller can handle increased voltages).
For example, with four 100-watt solar panels connected in parallel (yielding an output voltage of 20.4V and combined current of 19.64A), and a one-way cable length of 22.5 ft, you would require a 6AWG cable for a voltage drop limited to 3%.
If connected in series for an output voltage of 81.6V (and limiting current to 4.91A), then a 10AWG cable would suffice for maintaining a voltage drop within 3%.
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 amps that the cables are handling, the wire gauge used, and acceptable voltage drop.
To increase the distance of the wires from the solar panels to charge controllers, use thicker cables or increase the system voltage. Make sure the charge controller can handle the higher voltage.
Note too that thicker cables increase the investment cost in cabling.
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