Why Indian Solar Market Slowly Shifting To Half-Cut and MBB PV Modules?

India has been heavily dependent on import of solar PV modules and solar cells from China. With imposition of 40% BCD on imports of solar PV modules, the manufacturing of higher efficiency solar panels to fulfill the demands of system installers and developers. Though India has made a significant progress in solar PV manufacturing from 5.8GW in 2016 to 18GW in December 2021, but still a long way to go.

There is a high demand for high efficiency solar panels from project developers. Developers need solar modules above 400Wp for their projects to ensure high solar power generation efficiency specially to utilize a limited space in better manner. The other reason is the “cost reduction”, which is one of the key buying factors. Manufacturers have taken a step in this direction by coming up with Half-Cut Cell & MBB solar Modules. The names can be referred from the latest ALMM list.

These latest technology based high power output panel will cost similar to the traditional ones. So, what is most expected with these advanced technology based solar panels is high PV system performance and faster ROI. Therefore Half-Cut or multi-busbar technology contributes to lower energy costs along with improved system performance.

In general terms

Multi-Busbars Refers to Modules with 9-12 or 16 Busbars instead of conventional 3-5 Busbars.

Half cut Refers to modules with 120 or 144 Half-cut cells instead of regular 60 or 72 cells.

Now let’s enjoy the details

Benefits of using Multi Busbar (MBB) solar cells

1. Reduced resistive losses - Multibusbars on solar cells shortens the length of grid fingers and each busbar has to carry lesser current. This reduces the internal resistance of solar cells and consequently resistive losses. As we know if the current is reduced to half the resistive losses gets reduced by a factor of four.

P loss = I²R

But MBB technology helps reduce the chances of cracks transforming into hot-spots by allowing alternative paths for current to flow. Smaller distance between Busbars let the cracked part of the cell stay connected with the rest of the cell through nearby busbar.

4. Cost Savings with reduced silver usage –Metallization is the process of printing silver grid fingers and copper busbars on the surface of solar cells and hence a very important part in manufacturing of solar cell. Using multi busbar reduces the usage of silver paste as the metallization process will require less amount of silver coating on the front side. The reduction of silver usage by 45%-75% ensures high cost savings.

So we discussed about how solar panels with Multibusbars promise high efficiency, more reliable and long-lasting performance . Now we will discuss about Half Cut Cell solar panels.

Half-Cut Cell Solar Panel

Majority of the panels that we see in the market today are of either 60 cells or 72 cell configuration. But with advancement in technical applications we can double the number of cells without much increase in the size of the module. This technology is the cut cell technology, where cells are cut in two equal halves and one module is split into two smaller ones and are connected in parallel.

So it is more like two small solar panels in one frame. Most of the leading solar panel manufacturers in India like Bluebird Solar, Vikram, Waaree, Adani, Tata and some others have shifted to this modern technology. But most important thing is how cutting solar cells in half and splitting solar panels in two halves is beneficial?

Benefits of Cutting Solar Cells To Half:

2. Low power losses

By cutting the cell into half the current gets reduced to half and the length of the bubars also gets reduced to half. This leads to reduction in resistance, Thus reducing the power losses in connecting busbars by half.

The parameters above means:

• The generated voltage decreases by 0.31% with increase in 1 degree temperature above 25⁰C.

• The generated current increases by 0.05% with increase in 1 degree temperature above 25⁰C.

• The power generated decreases by 0.31% with increase in 1 degree temperature above 25⁰C.

• NMOT (Nominal operating cell temperature) is the temperature of cell in open circuit when

· Irradiance on cell surface – 800 W/m

· Air (ambient) temperature – 20^oC

· Wind velocity – 1m/s

The temperature of the cell may vary by +2 in summers and -2 in winters.

The temperature of solar panels can be calculated any time and at any temperature using this formula:

T_cell = T_Air + (NOCT-20)/80*S

where S is an insulation level in unit (mW/cm²)

Now suppose you have a solar panel of 400W and the solar radiation is 900W/m² , insulation level Is 90mW/cm², ambient temperature in summer is 40^oC, then

Solar panel temperature is : 40 + (46-0)/80*90 = 69^oC

Increase in solar panel temperature = 69^oC – 25^oC = 44^oC

Power generated efficiency becomes = 0.4% x 44⁰C = 17.6%

100% - 17.6% = 82.4%

If power generated from solar panel is 400W x 82.4% = 329.6W

In actuals the decrease in power due to rise in temperature is more than the theoretical calculations.

Benefits of splitting solar panels to half

1. Reduced impact of high cell temperature:

In months of June to August when temperature may range between 40^oC – 45^oC and efficiency of normal solar panels gets reduced due to rise in cell temperature. Then, use of half-cut cell solar panel can reduce the impact of rise in temperature on power output. The use of multi-busbars and split cells reduce the current passing through the busbars which further reduces the resistance. Also, due to short lengths of busbars, resistance in connecting busbars also gets reduced. This reduction in resistance in the cell leads to decrease in cell temperature and increase in efficiency of solar panel.

2. Better performance in shadow

Dividing the solar panels to two equal halves improves the shade tolerance. The solar panel split in two separate halves generates energy even if a portion of on half is shaded. In traditional solar panels when one cell is shaded the entire row within the series stop generating power.

In the illustration image above where we have a conventional solar panel with 3 strings of solar cells, a solar cell in Row-1 gets shaded all the cells in Row-1 will stop functioning. This way 1/3 of the solar panel becomes non-functional.

Now in case of half-cut solar panel we have 6 strings of solar cells. The by-pass diode are connected in reverse to protect the solar panels from shading. Now assume a cell in Row-1 gets shaded then cells within Row -1 will stop functioning. Rest of the 5 strings will work normally. So, only 1/6 of the panel got affected. The presence of copper bonding tape in the middle of solar panel increases durability of solar panel.

Are Halfcut Solar Panels Future Of Solar Industry

Half-cut cells are really great for improving the solar power energy yield of panels, but they are more challenging to manufacture. This makes it hard for traditional manufacturers to switch to producing half-cell solar modules, it is not as simple as just adding half-cut cells to a production line.

In many cases, traditional solar panels can still work for you, like if your roof has ample sunlight throughout the day.

But if you need every ounce of energy you can get because you live in a shady area or you want to maximize your net metering benefits, half-cut cells make sense. Ask for half-cut cells if you have a small surface area that needs to generate all the solar power it can. Otherwise, you should be fine with traditional panels even if you might need a few more of them on your roof.

Perhaps when the manufacturing of half-cut cells becomes more streamlined and easier to adopt, they will become cheaper and more widespread.