Types of Solar PV Ribbon: Tabbing vs Bus Ribbon

Look closely at any solar panel and you will see thin silver lines running across each cell. Those lines are not decoration. They are the path electricity takes out of the module. Every cell generates only a small amount of power, and it is the Solar PV ribbon that links dozens of them into one working circuit.

Ribbon is a small component by weight and cost, but a big one for reliability. A poor ribbon can cause cell cracks, weak solder joints and power loss that appears years after installation. This guide explains what PV ribbon is, the difference between tabbing and bus ribbon, where low-temperature ribbon fits in, and how ribbon is made.

What Is Solar PV Ribbon?

PV ribbon, also called interconnect ribbon, is a flat strip of copper coated with solder. It is soldered onto the busbars (the main collecting lines) of a solar cell to carry current away, and to connect one cell to the next.

It has two parts:

• The copper core. Usually high-purity, oxygen-free copper (OFC) or ETP copper, chosen for high conductivity and softness.
• The solder coating. A thin layer of tin-based alloy on the surface, which melts during soldering and bonds the ribbon to the cell. This is why you will often hear it called tinned copper ribbon.

Together they must conduct current with minimal loss, bond firmly to the cell and tolerate decades of temperature swings, from cold winter nights to hot Indian summer afternoons on a rooftop.

Tabbing Ribbon vs Bus Ribbon

The two main types look similar but do different jobs.

Tabbing Ribbon

Tabbing ribbon for solar cells, also called cell interconnect ribbon, is the narrower of the two. It is soldered onto the front busbars of one cell, then runs under the next cell and is soldered to its rear busbar. Repeating this joins the cells into a string. This process is called module stringing.

Typical characteristics:

• Narrow width, commonly in the range of about 0.8 to 2 mm depending on the cell busbar design
• Thin, often around 0.08 to 0.25 mm
• Very soft copper, so it does not pull or crack the cell
• Supplied on spools for automatic stringer machines

Bus Ribbon

Bus ribbon is wider and thicker. After cells are joined into strings, the strings must be connected to each other and to the junction box. Bus ribbon does this job. It collects the current from the ends of several strings and carries it to the output terminals.

Typical characteristics:

• Wider, often in the range of about 4 to 6 mm
• Thicker, often around 0.2 to 0.4 mm, because it carries the combined current of an entire string or more
• Cut to length and laid across the module, then soldered at string ends
• Sometimes laminated with an insulating layer in places where it must cross other conductors

A Simple Way to Remember

Tabbing ribbon joins cell to cell. Bus ribbon joins string to string and out to the junction box. Both use the same basic construction, but their dimensions are designed around the current they must carry.

Feature	Tabbing Ribbon	Bus Ribbon
Role	Connects cells in a string	Connects strings and output
Width	Narrow	Wide
Thickness	Thin	Thicker
Current load	Per-cell current	Combined string current
Softness priority	Very high	High
Supply form	Spool for stringer	Spool or cut lengths

Dimensions vary between cell designs and manufacturers, so always match the ribbon to your cell and module specification.

Ribbon Width and Thickness: Why They Matter

Choosing ribbon width and thickness is a balance between electrical performance and cell protection.

Wider or thicker ribbon has lower resistance, so less power is lost as heat. But it also shades more of the cell surface, blocking some sunlight.

Narrower or thinner ribbon shades less and is gentler on the cell, but resistance rises if it is too small for the current.

Cell design drives this decision. A cell with more busbars can use thinner ribbon on each one, because the current is shared across more paths. This is one reason the industry has moved from three busbars to five, nine and beyond, and in many modern modules to very fine round wires in multi-busbar layouts. Flat ribbon remains the standard for many module lines and is still essential for the bus connections at string ends.

Low Temperature PV Ribbon

Standard ribbon uses a solder coating that melts at relatively high temperatures. Conventional tin-lead solder melts at around 183°C, and lead-free tin-silver alloys melt higher, in the region of 220°C. Soldering machines run hotter than the melting point to make a reliable joint.

That heat is a problem for newer cell types. HJT modules (heterojunction technology) use thin amorphous silicon layers that are sensitive to temperature, so high soldering heat can reduce cell performance. Thinner wafers are also more likely to bow or develop microcracks when heated and cooled quickly.

Low temperature PV ribbon solves this by using a solder alloy with a much lower melting point, typically based on tin, bismuth and sometimes silver, melting in roughly the 140 to 175°C range depending on the formulation. Benefits include:

• Lower thermal stress on the cell during soldering
• Reduced risk of microcracks and wafer bow, especially with thin cells
• Better compatibility with HJT and other heat-sensitive cell structures
• Lower energy use in the stringing process

The trade-off is that low-temperature alloys can behave differently over a long service life, so the ribbon must be properly qualified for adhesion and durability. Module makers should always validate it with their own cells, flux and stringer settings.

OFC Copper Core and Yield Strength

Two properties of the core strongly affect how well a ribbon performs: purity and softness.

• OFC Copper core. High purity means high conductivity, which keeps resistive losses low. It also improves consistency, so every metre behaves the same way on the stringer.
• Yield strength. This is the stress at which the ribbon starts to deform permanently. A lower yield strength means the ribbon is softer and more flexible. During soldering the ribbon heats up, then cools and contracts. A stiff ribbon pulls on the cell as it cools, causing stress and cracks. A soft, well-annealed ribbon bends and absorbs that movement. This matters most for large, thin cells, where there is little margin for error. Manufacturers typically specify a maximum yield strength for this reason, and module makers should ask for it in the datasheet.

PV Ribbon Manufacturing Process

Understanding the PV ribbon manufacturing process helps you judge quality when comparing suppliers. In general terms, it works like this:

• Copper preparation. High-purity copper rod is drawn down to wire of a controlled diameter.
• Rolling. The wire is flattened between rollers to the required width and thickness. Tight tolerances here are crucial, because uneven ribbon causes uneven solder joints.
• Annealing. The flattened strip is heat treated to soften it and reduce yield strength, making it gentle on cells.
• Cleaning. The surface is cleaned so the solder bonds properly.
• Solder coating. The strip passes through a molten solder bath, which leaves an even coating, often in the range of 15 to 25 microns per side, though this varies by product. Coating thickness and uniformity directly affect soldering quality.
• Slitting and spooling. The finished strip is wound onto spools with consistent tension, ready for automatic stringers.
• Inspection and testing. Checks typically cover dimensions, coating thickness, tensile and yield properties, solderability and surface defects.

Each step affects the end result. Rushed annealing leaves ribbon too stiff. Uneven coating causes weak joints. Poorly controlled dimensions lead to jams on the stringer line.

What About "Energy Ribbon"?

You may come across the term energy ribbon in market listings. It is not a single standardised product name. Often it is used loosely for PV ribbon in general, and sometimes for light-capturing ribbons that have a textured surface designed to reflect light back onto the cell. If a supplier uses this term, ask for the exact dimensions, coating and mechanical specification so you know what you are buying.

How to Choose the Right PV Ribbon

Here are practical checks for module manufacturers and procurement teams:

• Match the ribbon to the cell. Busbar count, busbar width and cell technology (PERC, TOPCon, HJT) all influence the right choice.
• Check the solder alloy. Choose standard or low-temperature coating based on your cell type and stringer profile.
• Ask for yield strength data. Softer is generally better for thin cells.
• Confirm tolerances. Width, thickness and coating should stay consistent along the whole spool.
• Inspect the spool. Look for even winding, no kinks and clean, bright surfaces.
• Run a trial. Test on your own line before committing to bulk orders. Peel strength and electroluminescence images reveal problems early.
• Check storage guidance. Ribbon should be kept dry and sealed so the surface does not oxidise.

Common Problems and Their Causes

• Cell cracking after soldering: often caused by ribbon that is too stiff or soldering temperatures that are too high.
• Weak or uneven joints: usually linked to inconsistent solder coating or poor surface cleanliness.
• Stringer jams: commonly traced to dimensional variation or poor spooling.
• Power loss over time: can result from undersized ribbon, poor joints or thermal cycling fatigue.

Most of these start at the ribbon stage, which is why quality control at the supplier matters so much.

Frequently Asked Questions

What is the difference between tabbing ribbon and bus ribbon?

• Tabbing ribbon connects individual cells into strings. Bus ribbon is wider and thicker, and connects strings together and to the junction box.

Why is PV ribbon coated with solder?

• The coating melts during soldering and bonds the copper core to the cell busbar, creating a conductive, durable joint.

What is low temperature PV ribbon used for?

• It is used mainly with heat-sensitive cells such as HJT, and with thin wafers, to reduce thermal stress during soldering.

What is the best copper for PV ribbon?

• High-purity OFC or ETP copper is commonly used because of its conductivity and softness.

Can one ribbon type be used for every module?

• No. Dimensions, alloy and softness should be matched to the cell design and the stringing process.

Final Thoughts

Ribbon rarely gets mentioned in a solar brochure, yet it carries every watt a panel produces. The right choice of tabbing and bus ribbon, soldering alloy, dimensions and softness decides whether a module delivers its rated power for twenty-five years or loses output early. For modern cells, especially thin and heat-sensitive ones, those details matter more than ever.

If you are a solar module manufacturer looking for dependable interconnect ribbon, the team at Koprex can help you select the right type, size and coating for your cells and stringer line. Share your cell specification and monthly requirement, and Koprex will guide you to a suitable option.

Need quality PV ribbon for your module line? Contact Koprex today for specifications, samples and pricing.