Busbar

A busbar is a conductive metal strip or bar used inside solar panels, inverters, and electrical distribution equipment to collect, carry, and distribute electrical current. In solar modules, busbars are printed or soldered onto photovoltaic cells to transport the electricity generated by the semiconductor material. In electrical systems, busbars serve as central connection points for AC or DC power distribution.

Busbars play a critical role in improving electrical efficiency, reducing resistance losses, supporting higher current flow, and ensuring reliable energy transfer across a solar PV system. Their design and number significantly influence module performance, shading behavior, durability, and long-term reliability.

For designers working in tools like Solar Designing, understanding busbars helps in evaluating module selection, performance modeling, and long-term degradation characteristics.

Key Takeaways

A busbar is a conductive strip used to collect and transport electrical current in solar cells and PV system components.
More busbars generally reduce resistance and improve module efficiency.
MBB (multi-busbar) technology provides higher durability and lower shading losses.
Busbars appear both inside solar modules and in electrical distribution hardware.
Understanding busbar design helps optimize system performance, module selection, and long-term reliability.

What Is a Busbar?

A busbar is a strip of copper, aluminum, or silver-coated conductor that collects electrical current and channels it to the next component in the electrical path. In solar PV applications, busbars appear in two main places:

Inside solar cells → where they collect electrons generated by sunlight.
Inside electrical hardware → such as combiner boxes, inverters, switchgear, and distribution panels.

In solar modules, the number and layout of busbars determine how efficiently current moves across the cell surface, how shading impacts output, and how durable the module is under thermal cycling or micro-cracking.

Key related concepts include Solar Panel, Stringing & Electrical Design, and Module Degradation.

How a Busbar Works

1. Conductive path for electrons

As sunlight excites electrons within a solar cell, those electrons must be collected and transported efficiently. Busbars act as low-resistance highways carrying these electrons toward the cell tabs.

2. Current flows from cell → tab → string

Busbars link to cell tabs or ribbons, which connect one cell to the next in series.

3. Reduced resistance = higher module efficiency

More busbars shorten the path electrons must travel, lowering resistive losses.

4. Structural support for the cell

Busbars reinforce the cell structure and reduce the risk of micro-cracks spreading.

5. Integration into the larger PV system

At the system level, busbars in combiner boxes and panels carry current from multiple strings into inverters—see Stringing & Electrical Design.

Types / Variants of Busbars

1. Traditional 2BB and 3BB Busbars

Older modules typically used 2 or 3 busbars, but shading sensitivity and efficiency were limitations.

2. 4BB, 5BB, and 6BB Busbars

Modern modules commonly feature 4–6 busbars:

Lower resistance
Improved performance in partial shading
Reduced hotspot risk

3. Multi-Busbar (MBB) Technology

MBB uses 9–20 thin wires instead of wide busbars:

Higher surface conductivity
Better current collection
Lower silver consumption
Improved durability

Often found in high-efficiency and half-cut cell modules.

4. Wire-Based Busbars (Round Ribbon Busbars)

Round wire busbars capture more reflected light and reduce shading.

5. Busbars in Electrical Distribution

In BOS components (combiners, inverters, AC panels), busbars are:

Thick copper or aluminum bars
Rated for hundreds of amps
Used for power routing and safety isolation

How Busbars Are Measured

1. Number of Busbars (BB Count)

Typical ranges:

3BB
4BB
5BB
9BB (MBB)
12BB+ (advanced MBB)

2. Busbar Width (mm)

Affects shading and efficiency.

3. Resistivity

Measured in micro-ohm-centimeters depending on material.

4. Current-Carrying Capacity

Important for distribution busbars in combiner boxes and inverters.

5. Contact Resistance

Lower resistance improves module efficiency.

Typical Values / Ranges

Practical Guidance for Solar Designers & Installers

1. Prioritize modules with 9BB or MBB technology

They offer better shading tolerance and lower resistive losses.

2. Consider busbar shading impact

More busbars = thinner wires = less shading compared to wide 3BB ribbons.

3. Use busbar specs during module comparison

When evaluating module options through Solar Designing or proposal tools, reviewing BB count helps assess performance characteristics.

4. Pay attention to micro-crack propagation

MBB modules exhibit better tolerance due to distributed current pathways.

5. Ensure correct busbar ratings in BOS components

In combiner boxes, AC panels, and inverters, busbars must match current and temperature ratings.6. Review datasheet cross-sections

For accurate stringing, performance modeling, and module placement, confirm busbar count and type.

Real-World Examples

1. Residential High-Efficiency Module

A homeowner installs half-cut MBB modules with 12 busbars, resulting in improved performance in partial shading and reduced mismatch losses.

2. Commercial Flat Roof System

A 500 kW design uses 5BB modules, balancing cost and efficiency while ensuring reliable performance across multiple array sections.

3. Utility-Scale Solar Farm

A 100 MW plant selects 16BB MBB modules to minimize resistive losses and enhance long-term reliability under thermal cycling and mechanical stress.