MBB (Multi-Busbar) Technology: Increasing Module Power and Reliability

· About Solar Panels,PV Technology News

The development of solar cells using cutting-edge technology is one solution to the growing demand for efficient solar panels. Solar cells can operate more efficiently with the help of this technology, giving you access to improved solar modules for residential and commercial use. Did you know that there are solar panels with busbars and multi-busbars? If not, you will learn about MBB technology today. What effect do dash line pattern busbars have on solar cells?

MBB  solar cells

MBB has grown significantly in recent years

Solar panel technology has advanced rapidly in recent years. MBB technology has also rapidly evolved from laboratory research to market scale production after 11 years of development.

The use of MBB solar cells is one of the most noticeable features of modern solar panel design. The industry standard for solar panels has recently increased from 2BB to 6BB. Several manufacturers have stepped up their game, increasing panel sizes to 9BB and even 16BB. They are particularly interested in PERC Solar Cell panel designs that make the most of the front-side busbar. As a result, multiple busbars are extremely useful when building solar panels with efficiency in mind.

MBB is gaining popularity and will most likely spread. Others are being replaced by popular MBB. Busbars with multiple ribbons and wires improve cell metallization connections, reducing cell spacing and improving solar cell performance. When compared to ribbon technology, the shorter finger length and increased light in-coupling reduce electrical and optical losses, saving approximately 2.4 g for the 60 cell module.

MBB+half-cut is becoming increasingly popular in the market. Higher-end products, which are more than the traditional 5BB whole piece, have both half-cut and MBB advantages. The most common are 9BB+half-cut, 12BB+half-cut, 10BB+half-cut, and so on. It is the product with the most potential in the back, as well as the most recent high-end product with new technology.

In recent years, screen printing technology, wafer size, and wafer cost have all improved. As a result, silver paste costs more, technical complexity of multi-busbars decreases, and cost performance improves.

What are Busbars used for in Solar Panels? What exactly does MBB Solar Cell mean?

Busbars are typically printed flat and soldered flat. Busbars carry generated current to cells, whereas ribbons carry current away from cells. MBB in the front of the solar cell transfers current from the fingers to the environment via connecting ribbons. The multi-busbar can improve the bifacial property of PERC cells (the ratio of front power to rear power). By utilizing the multi busbar technique, the solar cell exhibits the following characteristics.

  • The cell's shading towards the rear side has decreased. 
  • There is a small rear aluminum fingers print. 
  • The bifacial light-harvesting function has been improved.

Busbars are rectangular strips of solar cell printed on both sides. Both sides of solar cells have a narrow, rectangular busbar. Electricity is transmitted by the entire solar cell strip. This strip separates cells, allowing photons to pass directly to the solar inverter and be converted into alternating current (AC). Front conductivity and back oxidation are improved with silver-plated copper busbars.

The efficiency of solar cells influences the number of busbars. MBB solar cells have multiple busbars, which reduces series resistance. Solar cells made of MBB, particularly 5BB cells, are in high demand.

Thinner wires are preferable because metal electrodes obstruct the cell and reduce light area, and silver is costly. Thinner wires have a smaller conductive cross-sectional area and higher resistance losses. Because a solder strip connects the module cells to the main grid, grid wire changes necessitate soldering process changes. The grid wire must strike a balance between shading, conductivity, and cost.

Multiple Busbars-MBB Round-wire Busbars Fingers

How does MBB function?

The following steps will explain how MBB works:

  • The fingers collect the generated current and deliver it to the busbars. The fingers are ultra-thin metal grids that run parallel to the busbars.
  • Tab wires collect the current from a single string of cells. Soldering is commonly used to connect tab wires to busbars.
  • Bus wires carry electricity from the cells to the junction box. Parallel bus wires connect a collection of interconnected cells.

Busbars collect the current from each string of cells, and the combined current is sent to the inverter.

MBB's Operating Principle:

The MBB method actively reduces resistive losses by lowering the current flowing through the fingers and busbars. We effectively shorten the space between busbars by printing more of them on a wafer, resulting in a shorter path for current to flow through the fingers. This length reduction significantly contributes to a reduction in series resistance losses. Because resistive power loss (Ploss) is proportional to the square of the current (I) multiplied by the resistance (R), halving the current reduces resistive losses fourfold.

MBB is distinguished from "more-busbars" by its cross-section and function. MBB sends current away from the cell via thin, rounded copper wires rather than flat busbars and soldered ribbons, which cause shading and resistive losses. MBB wires actively transfer current from fingers to interconnecting ribbons located outside the front surface of the solar cell. Cell ribbons are unnecessary. The figure below depicts how the rounded cross-section of MBB improves solar cell performance.

the enhanced optical performance of using rounded wires over flat Busbars.

Diagram representing the enhanced optical performance of using rounded wires over flat Busbars.

As bifacial technology spreads around the world, MBB may improve PERC cell bifaciality. Bifaciality is defined by the front-to-rear power ratio. MBB allows us to print smaller rear aluminum fingers, reducing shadowing on the back side of the cell and increasing light harvesting from both sides. MBB also reduces microcracks and increases the likelihood of cracked areas remaining electrically connected to the rest of the cell, thereby improving performance and reliability.

Worldwide market share trends for more and multi-busbar (busbarless) technology

Worldwide market share trends for more and multi-busbar (busbarless) technology

5BB 9BB 12BB solar cells

The Benefits of MBB Technology

1. Manufacturing technology is maturing, and the reliability of PV modules is improving.

Scientists are looking into MBB solar panels to increase the energy of solar cells. Busbars improve the efficiency and dependability of solar cells. Despite its high cost, silver is used in most solar panel wiring due to its high conductivity. New techniques are being developed to help reduce the reliance on silver in solar panels without sacrificing performance. Reduce costs while increasing output! Silver is reduced by using a multi-busbar solar panel design. The cost of screen-printed Ag front-side metallization. The 3BB cell design was improved with new busbars. Busbars conserve Ag paste while increasing module efficiency. Tin soldering Ag/Al pads on the backside reduces silver. Busbars facilitate solar cell output.

Solar cell busbar number change process

2.Reducing the possibility of hidden cracks

Module dependability has been improved. Even if the multi-grid cell contains hidden cracks and fragments, the increased grid density and small spacing allow it to maintain superior power generation performance. The weld strip spreads out uniformly across the cell after welding, relieving stress on the cell's encapsulation and improving its mechanical properties.

Experimental power gain and theoretical simulated power gain of multi-busbar components

3. Increased efficiency (less shading from welding tape, more light)

Because of reduced electrode resistance and shading, the module power increases by 5-10%. The majority of multi-busbar cells are designed with 9/12 busbars, which increases the current collection capacity of the busbar and effectively reduces the module operating temperature, improving the module's long-term power generation performance by 2.5% and power by 5-10W.

4.MBB solar panels are more visually appealing than standard solar panels

When we design the cell, the area of the main grid lines is the same regardless of how many main grids there are. As a result, the more main grids there are, the thinner the lines are and the better they appear from a distance.

5. Weather adaptability

MBB cells are a well-known design trend in solar panels. MBB cells reduce the size of the solar cell and are more resistant to overload and environmental factors. It also prevents microcracks in cell bus bars. MBB are more dependable and long-lasting under cracking conditions than regular cells.

6. Optical efficiency

5BB modules use rectangular plates, whereas MBB modules use circular ribbons, which reduce shadowing and repeatedly reflect incident light, as shown in the Figure, increasing optical performance and, as a result, power generation. However, the cross-section and purpose of MBB and the more bus bar method are distinct. Bus bars are typically printed flat, and because they require soldered flat ribbons to transmit current from the cell, they suffer from higher resistive losses. MBB are spherical, thin copper wires that, unlike ribbons that span the solar cell, transport electricity from the fingers to connecting ribbons located outside the front surface of the cell.

flat welding strip VS MBB cells

Although MBB technology has many advantages, it does have some drawbacks, such as a more complex manufacturing process than the traditional 5BB process. Its price has risen by 0.5-1 euro cent per pound. However, experts are working on the most efficient and cost-effective ways to reduce its price.

Maysun Solar is dedicated to providing our clients with advanced, differentiated, and cost-effective products like shingled, bifacial, and half-cut 9BB 10BB 12BB large-size and high-efficiency