Guide to Solar Cables

Reviewed by Stephen Bettles, Technical Support Engineer (November 2024)

Solar power is one of the most popular forms of renewable energy in the UK. How does solar power work? Photovoltaic panels convert sunlight into electricity. In Britain, these panels contribute to almost 16GW of power, generated from about 1.5 million solar power installations.

Solar arrays pose unique challenges when it comes to connection because they are exposed to extreme weather, moisture, and temperatures. This guide explains why special solar cables and solar cable management are required for the job and includes a solar cable calculator to help you determine the cable size you are likely to need to connect your solar panel system.

There’s a difference between solar cable and normal cable. Solar cables, designed to connect photovoltaic installations, are rugged enough to withstand the demands of the great outdoors such as extreme weather and temperature. Solar cables typically feature copper conductors coated with tin, which helps prevent oxidation and corrosion. They are also coated in types of plastic or rubber with strong resistance to heat and UV radiation.

Solar cables connect photovoltaic panels to each other and components such as inverters, batteries, and charge controllers. Their specifications meet the demands of the system, such as the output of the solar arrays and the electrical load. They are rated for DC, which is the type of power generated by solar panels.

Types of solar cable include PV wire, USE-2 wire, and THHN wire. Standards sometimes dictate the use of PV wire or USE-2 wire in a particular solar application. USE-2 wires are used in grounded solar arrays as underground connectors.

Both PV and USE-2 wires feature cross-linked polyethylene plastic (XLPE) insulation, which helps make them durable to withstand the elements, and resistant to sunlight, moisture, ultraviolet light, and ozone. For example, PV wire has an operating temperature of 90°C in wet environments and 150°C in dry applications. PV wire tends to have copper conductors, or copper conductors covered in tin. Unlike USE-2 cable, PV wire can be used in both grounded and ungrounded solar arrays. USE-2 solar cables are good in operating temperatures of up to 90°C and guard against both wet and dry conditions.

THHN wire is a little different, being a building wire that is often used in solar applications. It has some of the same capabilities as USE-2 wire – a voltage rating of 600V and a maximum temperature of 90°C in dry locations – but in wet conditions it can only operate at 75°C. THHN wire should never be used if USE-2 wire or PV wire is specified.

Solar panel cables also require connectors to connect the modules together. The solar industry has now largely settled on the Stäubli MC4 connector as the ideal choice for connecting photovoltaic panels. Other types of connectors on the market include the MC4’s predecessor, the MC3, and the Helios H4, SolarLok, and Radox designs.

MC4 connectors are designed to make wiring a solar array straightforward. The MC4s include male and female types, which snap together. The connectors lock so they will not become unplugged, which makes them particularly suitable for the outdoors. Unlocking MC4 connectors requires a special tool.

Solar panels can be connected in series or parallel using the MC4 connectors. Connecting the panels in series will increase the voltage of the circuit while current stays constant, and connecting them in parallel will increase the current while voltage is constant. Parallel installations of solar panels will require special MC4 multi-branch connectors to enable two sets of male or female MC4 connectors to be connected together.

Typically, two cables run from each photovoltaic module: one positive and one negative. Connecting modules in series usually means the female MC4 connector is used with each panel’s positive cable and the male MC4 connector is used with the negative cable. In a parallel design, the modules’ positive leads join at an MC4 multi-branch connector, as do their negative leads.

Just how long can solar panels be? Solar cables come in a wide range of lengths, with some manufacturers offering cables of up to 100 metres. While there is no maximum cable length for a photovoltaic panel, installers should consider the drop-off in voltage as cable length increases, which entails running a cable with a greater diameter. (See our solar cable size calculator, below.)

You may be asking, ‘How far can you run solar panel cables?’ An efficient solar photovoltaic array will use less cable, not more. Users may benefit from not installing their array further than 50 feet away, which minimises the drop in voltage associated with longer cables. Minimising the length of solar cable also means making sensible decisions about where batteries, inverters, and other equipment are located.

Solar panel cable not long enough? You could consider extending it, in which case you’ll also need to think about how to connect solar cables. Solar cables can be connected together using a specially manufactured waterproof connector or a solder sleeve.

If you’re wondering, ‘What size cable for solar panels do I need?’, we’ve got you covered with our solar cable size chart. The size of solar cable you need depends on the length of the cable and the power of each solar module.

Below is the minimum recommended cable size (in cross-section area of a two-core cable) for 24V panels with a voltage loss of less than 5%.

Source: Leading Edge Power

Solar power already enjoys considerable success in the UK – despite our somewhat erratic weather! That trend is only likely to continue in the future. Over the course of the rest of the decade, solar is expected to grow to form a fifth of the UK’s total electricity generation capacity. That surge is part of a global phenomenon: Solar is set to become the world’s biggest source of electricity by 2035.

Appropriately enough, for solar power, the future is bright.

Did you know RS carries a wide range of single core cable and cables and wires? Browse our range now.