Type of Wire Used for Solar Panels? (Best + Installation)

Today we look at the best wire to use for solar panels. The difference will protect you and your panels and produce a better return. Cables with very thin insulation are usually colored sheets to identify the wire’s voltage and wattage.

The monocrystalline solar cells have a “back” contact, made of metal with a lower resistance than aluminum. This type of contact allows for better electrical current flow from the back of the cell to the front, allowing for slightly higher efficiency when converting photons into electricity.

Below are some of the key points that I’ll cover, plus more you’ll need to know;

  • Can you use THNN wire for solar panels?
  • Do solar Panel wires have to be in conduit?
  • What wires should you use for solar panels?

Let’s find out which cable is the best for your solar system.

Wiring under solar panels

Why Is The Right Solar Cable So Expensive?

The best metals for electrical wire cables are Silver, Copper, and Aluminum. Silver is the best but also very expensive and would not be commercially viable for installing domestic solar systems. Copper is the best alternative and much more affordable than Silver.

Use a solar cable that carries the Underwriters Laboratory (UL) markings defining it as suitable for use in external photovoltaic installations. These cables must be:

Aluminum wire is often available in the market as a low-cost alternative. Copper-plated aluminum is also available to seduce the frugal buyer but should be avoided at all costs.

If you are running a short-term trial setup, you can use lower-cost wire just to prove your test of concept, but for long-term installations, pure Copper wire is the best.

Solar cables are bundles of thin strands of pure copper wire to provide flexibility and maximum current carrying capacity (lowest resistance). Stranded wire conducts the flow of electrons better than a single solid wire strand of the same gauge.

Types of Cables

The wire is produced to various thicknesses and rated by the Amperage at a certain diameter (gauge) and temperature.

The bigger the diameter of the combined strands of copper wire, the less the resistance the electrons will have from the solar panels to the charge controller.

The design of your solar installation will consider how far the solar panels are from the charge controller and how much the voltage drop will be over such a distance.

Many online calculators will assist you in determining the correct gauge wire for your design. The cost of the wire increases as the diameter gauge required increases.

See also: How to install solar panels (Detailed Step-By-Step Guide)

Which Solar Cable To Choose

As a rule, always go for a heavier gauge wire. The initial investment will be higher, but the payback will be in system efficiency.

An inner protective coating of the copper wire strands affords an additional layer of protection and flexibility. It prevents moisture ingress and ensures that the bundle of stranded wire is compact.

An outer Silicon-based plastic sleeve protects the wire against UV radiation and must be fire retardant and not be attractive for rodents to gnaw at.

Extreme temperatures and the relentless attack of the sun on the cabling require you to select the correct gauge UL-rated PV cable at the outset. The most commonly used wire gauge connecting the solar array to the charge controller is 10 AWG.

In Marine installations, the option of using Tinned Copper wire affords additional protection against corrosion.

Buy the thickest gauge UL-rated PV-specific wire you can afford for your project. Look at ways to limit the distance from the solar array to the charge controller to save money, but don’t go cheap on the solar cabling.

Can you use THNN wire for solar panels?

No,THNN wire has a much larger insulating layer on the conductor, which isn’t needed for the lower voltage of a solar panel application.

That insulation would block too much electrical current flow for it to be helpful in a solar panel set. THHN wire has a small insulating layer on the conductor, and that insulation is fine for lower voltage solar panel setups.

This could cause some problems, though. The solar panel voltage is around 15 volts, but the power company’s grid has 120 or 240 volts of alternating current.

This means that there will be a significant difference in electrical potential between your home wiring and your solar panels, which would cause electricity to arc through the air from one wire to another if the insulation is not thick enough to prevent this.

(This arcing causes sparks, which can be disastrous if they ignite something flammable.)

Can I use ACSR wire for solar panels?

No. The ACSR wire has aluminum conductors, but those conductors are much thicker to make up for the lack of electrical current flow from an aluminum conductor compared to copper.

You can do calculations as you would for THHN wire to ensure your wires have enough wattage capacity for your application (in this case, a solar panel system).

The cables also have different insulation, usually a colored sheet to identify the wire’s voltage and wattage.

Can you use Romex wire for solar panels?

No. For several reasons, mainly because all conductors have some resistance, so if you’re wiring up your house with Romex (which has NM-B insulation), there will be too much electricity loss through heat generation, which could cause problems including fires if they get bad enough.

Plus, the thin NM-B insulation isn’t meant to withstand the heat of a solar panel system, so it’s likely to deteriorate over time.

Also, not all types of NM-B have the same fire-resistance rating. For example, when exposed to flames, Romex is only rated for about 3 minutes.

If you use Romex in a solar panel wiring setup, your wires will probably melt and catch on fire after being exposed to sunlight for just a few minutes.

Solar panel cables

Can I use regular cables for Solar panels?

Don’t use standard cables. They won’t handle the high currents associated with solar panel systems because they’re not rated for outdoor installation and direct sunlight exposure.

Use cables specifically made for outdoor installation, such as MC4 connectors or copper grounding lugs, to guarantee they will last a long time.

If you have access to a welder, you might also want to consider sealing all of your connections with metal-to-metal adhesive because it’ll prevent corrosion from forming over time (even if just marginally).

That being said, many people don’t bother to seal their wires together, and sometimes it doesn’t matter as much as you would expect because stainless steel wire is already corrosion-resistant.

What wires should you use for solar panels?

MC4 connectors are the most commonly used wires for solar panels because they don’t need to be in conduit, and you can use any old house wire for them.

(Although it’s probably best to stick with THHN or THWN wire, which is what most professionals would do, especially when wiring your home.)

Other MC4 cables are available but are usually more expensive than standard insulated house wires like THHN, THWN, etc.

You can also use non-insulated MC4s if you want to install the wires alone without having anything else surrounding them except air, like on top of your roof where there would be nothing nearby that could catch fire even if the insulation were to get knocked off.

How much wattage do solar panel wires need?

This depends on the number of panels in your setup, their total wattage requirement, and the distance between them. You can find these specs on the panels, usually right around the outside of one of the corners.

If you’re doing a small panel or two to power some lights or charge your electronics, then probably 15-20 amp rated THHN wire would be enough for that distance.

Still, if you have more than that or are planning to expand so eventually you’ll have more solar panels in the future, you may need something with a higher amperage capacity.

It’s best to get wires with more wattage capacity than required, though, because it will give you wiggle room when working with electrical calculations, figuring out how long your wires need to be between different parts of your setup, etc.

What Is The Most Commonly Used Solar Wire?

The UL specification 4703 applies to solar cables and is specific to the wiring up of the solar panels in either series or parallel and the connection to the charge controller. The wire is designed to withstand exposure to UV and for underground installation.

The most commonly used size conductor in domestic installations is 10 AWG. For future expansion or upsizing, the conductor Amperage, 6 AWG, and 8 AWG are also used. The smallest diameter conductors in compliance with UL 4703 are 18 AWG.

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The wire bundles are double insulated with cross-linked Polyethylene and are rated to withstand 90 degrees Celsius in wet and 150 degrees Celsius in dry conditions.

The insulation is resistant to sunlight, ozone, Ultra Violet light, flame, and moisture and is not tasty for rodents. The cable is available in maximum voltage ratings of 600 V, 1000 V, and 2000 V.

Your solar system installer can purchase in bulk and will be able to give you the best pricing and quality for the system.

The installer will also provide you with an installation warranty and will thus ensure that they use the correct size and type of solar cables.

Romex cable wire

Upsizing Cables For Your Solar Installation

Installing a solar power system at home or in commercial properties makes sound financial sense. As the cost of PV panels and components has reduced to a level where solar power has the lowest cost per kW/h of any form of energy, the payback period is less than five years.

For a five-year payback on a thirty-year investment, you will be making a healthy return on investment.

Most of the budget will be for the solar panels, charge controllers, inverters, and battery banks but do not neglect to buy the best solar cables to join the system up. Poor quality cable or undersized cables can destroy your solar panels or even your house due to overheating resulting in fire.

Get professional advice and installation assistance. All solar system contractors are fully qualified and certified installers. Let a professional guide you with the design and the installation.

Plan for the future expansion of your solar power generation capacity upfront. Do not use the minimum gauge PV wire for the installation.

It is always more expensive to rewire than to go bigger from the beginning.

Do solar Panel wires have to be in conduit?

No. If you want to use THHN or THWN (or even ACSR) wire, they need to be in conduit because of the potential for arcing and sparking between wires that could ignite flammable objects nearby.

This is more critical than regular house wiring because solar panels are installed up high on your roof where there’s nothing but the air that could easily catch fire.

Suppose you’re using MC4 connectors, though. In that case, a conduit isn’t necessary because those connectors have a positive lock that only allows them to touch the panel connector’s negative part.

So no electricity will flow through them if they accidentally come into contact with each other or else grounded like your roof or suspect roof.

Solar panel cables along a wall

How do you hide solar panel wires?

There are a few options to consider, but most people just let them hang down their roof where you can see them or attach them to the house with some mounting brackets.

You could also run the wires through PVC pipe if you want them concealed underneath your shingles…but this is probably best suited for larger jobs because it might be hard to make all the connections with long runs of wire inside PVC pipe.

Keeping your links short will help reduce resistance and increase efficiency, which is essential with solar panels since they’re relatively expensive equipment that needs to produce as much wattage as possible.

Also, using Romex (NM-B) wire isn’t recommended for this kind of wiring job because it’s more likely to catch fire than other types of wiring insulations.

Can you run solar panels inside your house?

Yes, but only if you use an inverter. Standard solar panels don’t produce AC power like household outlets, so you can’t use them directly without one.

An inverter turns DC power from the solar panels into usable electricity that can run any appliance you could otherwise plugin at home: TVs, lights, computers, toasters, space heaters, etc.

Solar panel setup engineers controlling a solar system

How do you protect solar panel wires?

If you’re wiring together your solar panel system, then it’s best to use junction boxes (weatherproof or not, depending on where you live) for all of the connections that need to be made.

You’ll probably want to use some conduit if you plan on running wires inside the walls/attic of your house, etc. Conduit is just tubing with openings at each end so you can feed wires through it and seal up both ends with plastic/metal caps.

The gap between these two cap ends is where you can slide in another piece of conduit filled with more wires, which creates a network for carrying electricity throughout your entire system.

It might also be advisable to use thermal insulation to wrap around the actual solar panels if you live in a hot climate.

Do I have to install a solar charge controller?

Yes, you do. And this component is essential if you want your batteries to survive many years with multiple charge/discharge cycles.

Not all solar panels come with built-in charge controllers, meaning you’ll need an external one to regulate the flow of electricity into your batteries (keeping them from overcharging and causing damage).

Using an inverter instead of directly connecting your solar panel system to household appliances is also better for the battery bank because it reduces how much current gets drawn at any given time.

If your inverter were constantly drawing 120 volts @ 100 amps, 24 hours per day, things would eventually degrade even further than if you hooked it up directly to the battery bank.

Man soldering cable in a workshop

What gauge wire should I use for solar panels?

It depends on the total wattage required by your solar panels, how far apart they are from each other, how long the wires need to be between them and the solar controller/inverter unit, etc.

If you’re doing a few panels, then 14-gauge should be good enough for that distance (or even 12-gauge if you want to save money), but it depends on your setup.

When you lay out all of these different factors, it ends up being an electrical wiring calculation problem; so, hire an electrician or do some research online about using Ohm’s Law to help figure things out (you can find examples in various places).


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Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

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