The Definitive Solar Panel Wire Size Guide: Choosing The Right Wire Size

Graham Bogie

Choosing the right solar panel wire size is crucial when installing a safe solar panel system. Here’s everything you need for a comprehensive understanding of wire sizing to ensure everything runs smoothly.


Installing RV solar panels can be an exciting investment for off-grid adventures.

However, choosing the correct wire size for your system is crucial for its optimal performance, safety, and longevity.

Using the wrong wire size could mean decreased power production, potential safety hazards, and damage to your solar components. 

To avoid these risks, it’s important to understand how to choose the appropriate solar panel wire size.

This post provides a comprehensive guide to solar panel wire sizing to help you choose the right wire size for your system.

We’ll cover the importance of proper wire sizing, the risks involved when selecting the wrong size, and the different factors to consider.

We’ll also introduce you to some helpful tools to assist you in selecting the correct wire size and designing your setup.

By the end of this blog post, you’ll have all the information to select the right wire size for your solar panel system, ensuring its optimal performance and safety.

So let’s get started!

Why Solar Panel Wire Size Is Important

The wire is sized based on how much current it can safely transmit.

Push too much current through a wire, and it could lead to overheating and a potential fire.

Installing oversized wire is an unnecessary expense and takes up too much space.

Choosing the right wire size can prevent:

  • voltage drops,
  • overheating, and
  • power loss.

Selecting the wrong wire size can lead to the following:

  • electrical problems,
  • reduced system performance, and
  • potentially catastrophic consequences, including fires and safety hazards.

That’s why selecting the correct wire size for your solar panel system is essential.

Choosing the correct wire size ensures that your system can transmit the necessary amount of current with minimal loss of power or risk of damage.

What Solar Panel Cables Does A DIY Solar System Need?

A solar panel setup could have three or more minimum wire sizes depending on the number of panels, wiring configuration, and circuit length.

Let’s take a look at that in a little more detail.

What Solar Panel Wires Does A DIY Solar System Need

Wires Attached To Solar Panels

Most solar panels have wires already attached at purchase and are usually 10AWG / 6mm².

They are sized to handle more than the maximum current the panel can provide.

Extension Wires & Connecting Wires

There are several ways of connecting solar panels:

When you connect the solar panel in series, the solar array produces the same current as the lowest-spec panel in the array.

But when you connect solar panels in parallel, the configured solar array produces the sum of all the panel’s current.

Therefore, at the point the solar panel wires are joined, the wire size needed to transmit the higher current might need to be bigger.

With MC4 branch connectors, there are many ways to connect multiple panels in parallel.

There could be more than one connection before the solar charge controller; in theory, the current increases at each.

The maximum current transmitted to the solar charge controller will be the same, regardless of the configuration.

Therefore, it’s best to size any extension wires to handle the total current. It will help keep things simple, and you won’t need multiple wire gauge sizes.

Wire Connecting The Solar Charge Controller To The Battery

Finally, you need wires from the solar charge controller to connect to the battery bank.

Solar charge controllers can increase the current received from the solar panels to transmit to the battery bank.

Therefore, these wires should be rated for the maximum current the solar charge controller can produce.

From the diagram below, you can more clearly see how:

  • the wires might need to transmit a greater current when the same panels are wired in parallel, and
  • how a different size solar charge controller could produce a more significant current.
What Solar Panel Wires Does A DIY Solar System Need

Factors That Determine Wire Size

The appropriate cable size for a solar panel installation depends on several factors, including current and distance, i.e., circuit length.

For example, an increased distance between the solar panels and the solar charge controller will require larger wire sizes to reduce voltage drop over the wire.

There are also regulations we need to adhere to when installing a DIY solar system on a camper van or RV.

Electrical regulations vary from country to country. In some places, regulations are mandatory, and you may experience restrictions on use unless you adhere to them.

In other places, authorities issue only guidelines.

When calculating wire sizes, we use the most stringent standards – The National Electrical Code (NEC) or NFPA 70 – as they offer the most safety for our installation.

We also account for a maximum of 2% voltage loss over the entire circuit length.

Harvesting energy from the sun is challenging enough without wasting it!

How To Determine The Right Solar Panel Wire Size

This section will guide you through the steps to determine the correct wire size for your solar panel system. 

However, we understand that parts of this can be a technical process, so we’ve created an interactive Solar Design Tool to help you easily determine the right wire size for your installation. 

You can get a free download by subscribing, or if you prefer, you can buy it in our online store.

If you’d prefer to figure it out manually, here are the steps to follow:

Step 1: How Many Solar Watts Will You Install?

Determining the total wattage of your solar array is the first step in calculating the ideal wire size you need.

The total wattage of the solar array is a factor in two critical parts of the solar system design:

  • wire sizes in a parallel configuration, and
  • solar charge controller size and, therefore, the required wire size to the battery bank.

You can use our RV solar calculator if you’re unsure how much solar you need.

We recommend sizing your wires and the solar charge controller for the maximum amount of solar you can fit on your roof.

Even if you don’t intend to install the maximum immediately, it will future-proof your system and save you a lot of money and hassle if you want to expand later.

So, for example, if you can fit 4 x 100w of solar on your roof but only plan to install 2 x 100w panels now, do your solar array wiring calculations based on 400w.

Then if you add panels later, you won’t need to increase the size of every other component change and change everything you install

Step 2: How Many Solar Panels Will You Install?

Understanding how many solar panels are included in the array is important.

The number of panels doesn’t directly affect the wire sizes, but you’ll need to use the number in later steps to calculate the voltage and current your solar array could produce.

It’s also a factor in determining the connectors needed.

Step 3: Will You Wire Your Solar Panels In Series Or Parallel?

When installing multiple solar panels in your RV camper, you need to configure them in either series or parallel.

Which you choose affects the wire size you need.

The solar panels are connected end-to-end in a series connection, with one panel’s positive terminal connected to the adjacent panel’s negative terminal.

This configuration increases the voltage output of the panels while maintaining the same current. That means you can generally use a smaller wire size.

Alternatively, in a parallel connection, the positive terminals are connected, and the negative terminals are connected.

This configuration maintains the same voltage while increasing the current output of the solar panels.

When wiring solar panels in parallel, larger wire gauges are typically required to handle the increase in current.

Step 4: Calculate Maximum Amps Of The Solar Array

For this step, you need to take a look at the back of the solar panels for the specification.

It’s a little confusing, but solar panel specifications have two different types of amperage:

  • ISC (Short Circuit Current)
  • Imp (Current at Maximum Power)

ISC refers to the maximum current that flows when the circuit is shorted. This value is used to determine the maximum current that a solar panel can generate in ideal conditions.

In other words, ISC provides a theoretical upper limit on the current that a solar panel can produce.

On the other hand, Imp refers to the current that a solar panel produces when operating at its maximum power point.

Maximum power point tracking (MPPT), a technique used by some solar charge controllers, seeks to keep the solar panel operating at this point, where it’s generating the most power.

In general, ISC is used to determine the safety of a solar panel, while Imp is used to determine its power output under real-world conditions.

When sizing wire and fuses for a solar panel system, ISC is the primary specification used to ensure that the components can handle the maximum current produced by the solar panel.

By understanding these two values and their significance in solar panel installations for RV campers, you can use the correct components and wire sizes appropriate for your system’s unique needs and conditions.

Follow the steps below to calculate the maximum amps of your solar array:

  • Find the short circuit current (ISC) rating of your solar panel. This can typically be found in the panel’s documentation or etched on the back.

Maximum Amps Of A Single Panel

  • If you only have one panel, the maximum amps of your solar array = the ISC of the panel.

Maximum Amps Of Multiple Panels Wired In Series

  • If you have multiple panels and wiring them in series, the maximum amps of your solar array = the ISC of the solar panels.

It’s more efficient to use identical solar panels. However, if you have mismatched panels, use the smallest ISC of all the panels.

For example:

  • If you have four solar panels with ISC ratings of 5 amps each, the maximum amps of your solar array would be 5A.
  • If you have four mismatched solar panels with 3 with ISC ratings of 5 amps each and 1 with 4.5 amps, the maximum amps of your solar array would be 4.5A.

Maximum Amps Of Multiple Panels Wired In Parallel

  • If you have multiple panels and wiring them in parallel, the maximum amps of your solar array = the ISC of the solar panels multiplied by the number of solar panels.

If you have mismatched panels, total the ISC of all the panels.

For example:

  • If you have four solar panels with ISC ratings of 5 amps each, your calculation would be 5A x 4 = 20A.
  • If you have four mismatched solar panels with 3 with ISC ratings of 5 amps each and 1 with 4.5, your calculation would be 5A + 5A + 5A +4.5A = 19.5A.

The result reflects the maximum amps your solar array could transmit to the solar charge controller.

Step 5: Calculate Solar Panel Wire Size

Armed with the maximum current, you can now figure out the smallest wire size you need.

However, it’s important to understand two things here:

  1. The wires attached to solar panels tend to be 10AWG / 6mm². When extending wires, never connect them to a smaller wire size. Always use at least a 10AWG / 6mm² wire.
  2. The cable length may affect the wire size you need, so you don’t lose too much voltage.

The mathematical calculation is complex. However, this is all done for you if you’re using our Solar Design Tool.

Otherwise, use our wire size calculator. But remember to use a minimum of 10AWG / 6mm² in a solar array.

Step 6: Calculate Solar Array’s Maximum Voltage

Calculating the right solar charge controller size is crucial to achieving optimal solar power generation in your RV camper.

Again, our Solar Design Tool will work it out for you, or you can use our online Solar Charge Controller Calculator.

If you’d prefer to work it out manually, follow the steps below to calculate the maximum voltage of your solar array:

  • Find the Open-Circuit Voltage (Voc) of your solar panel. It should be printed on the panel’s back panel.

Maximum Voltage Of A Single Panel

  • If you only have one panel, the maximum voltage of your solar array = the Voc of the panel.

Maximum Voltage Of Multiple Panels Wired In Series

  • If you have multiple panels and wiring them in series, the maximum voltage of your solar array = the Voc of the solar panels multiplied by the number of solar panels.

If you have mismatched panels, total the VOCs of all the panels.

For example:

  • If you have four solar panels with Voc ratings of 24.3 volts each, your calculation would be 24.3A x 4 = 97.2V.
  • If you have four mismatched solar panels with 4 with Voc ratings of 24.3 volts each and 1 with 19.6, your calculation would be 24.3A + 24.3A + 24.3A +19.6A = 92.5A.

The result reflects the maximum voltage your solar array could transmit to the solar charge controller.

Maximum Voltage Of Multiple Panels Wired In Parallel

  • If you have multiple panels and wiring them in parallel, the maximum voltage of your solar array = the Voc of the solar panels.

It’s more efficient to use identical solar panels. However, if you have mismatched panels, use the smallest Voc of all the panels.

For example:

  • If you have four solar panels with Voc ratings of 24.3 amps each, the maximum voltage of your solar array would be 24.3A.
  • If you have four mismatched solar panels with 3 with Voc ratings of 24.3 volts each and 1 with 19.6v, the maximum amps of your solar array would be 19.6v.

Step 7: Determine MPPT Solar Charge Controller Size & Amp Rating

Now you must select a charge controller that can handle your solar panel array.

Here are the main factors on the charge controller’s specification to consider:

  • Max. PV Input Power should be able to handle the total wattage of your panels from Step 1
  • Rated Charge Current should be greater than the maximum amps of the solar array calculated in Step 4
  • Max. PV Input Voltage should be able to handle the maximum voltage of your solar array calculated in Step 6
  • Nominal Voltage should match your RV’s system voltage (usually 12v but sometimes 24v or even 48v)

Step 8: Calculate MPPT to Battery Wire Size

Armed with the rated charge current of your chosen solar charge controller, you can figure out the smallest wire size you need to connect it to the battery bank.

However, it’s important to understand that solar charge controllers are limited to wire-size terminals. Most will go up to about 4AWG, but models will vary.

The mathematical calculation is complex (it’s the same as for the solar panel cables). But, again, if you’re using our Solar Design Tool, this is all done for you.

Otherwise, use our wire size calculator.

Selecting the right wire size for your solar panel installation is an essential step that cannot be overlooked. 

Choosing the correct wire size ensures optimal performance, safety, and longevity of your solar panel system.

Throughout this guide, we’ve explored various aspects of solar panel wiring, from the types of wires needed to the differences between ISC and Imp values. 

We’ve also provided practical step-by-step guidance on calculating the wire and solar charge controller sizes needed for your RV camper’s solar installation.

Always remember that ensuring your system is safe and efficient is critical, as any faults could jeopardize the safety of your family and your RV camper.

Do you have any questions about your camper’s solar panel installation? Use the comments below to reach out – we look forward to hearing from you!

Graham Bogie

Graham Bogie - Expert in RV & Campervan Electrics - Mowgli Adventures

Graham is a seasoned marine electrical engineer with two decades of experience designing customized electrical systems for plant machinery and converting campers and overland vehicles. His expertise has led him to author the reputable Campervan Electrics Handbook and become the chief designer of our Campervan Electrical Design Service. As a knowledgeable figure in the field, his YouTube channel, blog, Facebook group, and newsletter, offering electrical advice and product reviews, reach more than a million users each year.

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