Losses Nearing Zero

ITRPV Predicts 100% Cell-To-Module Conversion Ratio In 2015

Losses Nearing Zero

Multicrystalline modules will reach the benchmark of a 100% cell-to-module performance ratio by the end of 2015, while 60-cell panels…

  • Concepts improving module performance independent from cell level are becoming widespread
  • Cell to module performance ratio for multi to reach 100% bench market in 2015, while mono attains this level in 2019, indicates 6th version of ITRPV
  • Half-cut cells used for 30% of modules made in in 10 years
  • Module configuration based on 60 cells continue to lead in near future, 72-cell modules will be part of mainstream in long run
  • ITRPV points to IEC draft standard for testing PID to avoid over testing

 

When talking about efficiency improvements, you naturally look at the cell. But it is worth to look at the module as well, as quite a bit of the gains for cells can be lost when assembling them into a panel. However, compared to increasing cell efficiencies, optimizing the module format or avoid optical and electrical losses are rather low hanging fruits. According to the 6th edition of the International Technology Roadmap for Photovoltaics (ITRPV), multicrystalline modules will reach the benchmark of a 100% cell-to-module performance ratio by the end of 2015. When it comes to the module, ITRPV sees also improvements regarding the shape and number of cells.

Losing on losses

The cell-to-module power ratio is a pretty good metric for developments at the module level. It simply tells how much of the cell efficiency is lost after the blue silicon slices are packed into a panel.

ITRPV expects multicrystalline modules will reach 100% in 2015. This is impressive and indicates how advanced module manufacturers are today, especially since this ratio has already reached 99%. For mono, however, the level is still at 96% (which has a lot to do with pseudo-square mono cells usually being used, which leave some unproductive space in the panel). While ITRPV 2015 anticipated monocrystalline modules to reach 100% in 4 years,  multi would climb up by 2% points to 102%. The developments are taking a faster pace for multicrystalline compared to the progress anticipated in the previous roadmap, which assumed it to reach 100% by 2016. Progress got delayed with mono, which was expected to reach the same level in 2018. On the other hand, the previous document projected consistent growth, reaching 104% for multi and 103% for mono within 10 years – by 2024, while the current roadmap is a bit more conservative in the long run,forecasting multi to attain slightly over 103% and mono to reach  101.5% in 2025. These improvements are supposed to come from better light management, such as employing grooved or colored ribbons and encapsulation materials with improved UV-performance. As for monocrystalline, the shift from pseudo-square to full-square wafer formats can also result in a big leap in module performance. However, the 2015 roadmap underscores that pseudo-square wafer formats will dominate the market, while the full square wafers are expected to account to 20%, rising from their current share of 2%.

Lean growth on the long run: The short-term expectations for the cell-to-module performance ratio given in the current 6th ITRPV roadmap closely match those of the previous 5th edition from 2014. The difference is that the current roadmap provides a more conservative forecast in the long run, as can be see in this comparison chart.

Lean growth on the long run: The short-term expectations for the cell-to-module performance ratio given in the current 6th ITRPV roadmap closely match those of the previous 5th edition from 2014. The difference is that the current roadmap provides a more conservative forecast in the long run, as can be see in this comparison chart.

 

Half cells to reduce losses to one fourth

Modules built with half-cut cells is another concept to improve output. Technically, this design requires just one change. Instead of using cells as they are coming out of the cell line, the square silicon slices are cut into two pieces. The module making follows the same traditional course. The logic behind cutting cells into two pieces is that they both have the same voltage like a full cell, but the current – which is a function of the surface area – gets divided accordingly. Consequently, the internal electrical losses, which are in the second order of current flowing, are reduced to 1/4th for a half cell compared to full cells. The flip side of the concept is the additional process step of slicing cells. More than that – this step negatively affects the throughput of the stringing tools, which process only half the cell size in the same period of time it usually solders a full cell. In consequence, the throughput of the stringer is decreased by 50%. It still makes sense – the 6th ITRPV expects the market share of modules using half-cut cells will grow from 2% in 2015 to around 30% in 2025.

Half cell fashion: According to ITRPV’s 2015 roadmap, half cut cells, with the advantage of reducing electrical losses, are expected to become prominent – reaching a 30% market share in 10 years.

Half cell fashion: According to ITRPV’s 2015 roadmap, half cut cells, with the advantage of reducing electrical losses, are expected to become prominent – reaching a 30% market share in 10 years.

More 72-cell modules

It is worth to improve the cell-to-module ratio, even if the power rating difference is only a few percentage points. But in the end, most aspects of the module output are attributes of cells – even the size and net power rating, which depend on the number of cells. As for the size, the 2015 roadmap emphasizes that module size differs depending on application. But although utility-scale power plants dominate most markets, ITRPV assumes that the 60-cell module configuration owns the lion’s share of 80%, which it believes will eventually drop to just above 50% by 2025 as the other dominant 72-cell configuration is becoming more popular – and will then grow from today’s more than 15% share to about 40%. The 80-cell module is not expected to gain a meaningful acceptance – and will have just a 2% share in 2025. The previous roadmap, however, was very positive on the prospects of modules with 80 cells, expecting them to reach 10% market presence already in 2021. The other module sizes using 32, 36, 48 cells, which are mainly designed for niche applications, are also expected to stay a small minority, at about 5% in 2025. 

Power output matters

Today the 60 cell module configuration is considered the basis for comparing power ratings. PV panels using 60 cells based on the different variants of multicrystalline cells currently have a module power rating of about 270 W, with a negligible difference. But by 2025, modules made of high-performance multicrystalline cells are expected to reach 310 W, while ITRPV believes that standard multicrystalline based panels will deliver close to 300 W. Modules using monocrystalline p-type cells are forecasted to improve from about 20 W today to 320 W in the next 10 years. N-type mono modules – at the same level as p-type today – are expected to reach more than 330 W, a gain of 40 W in 10 years. Heterojunction modules, which are only being offered on a large scale by Panasonic today but which many consider the next step in cell/module production, are expected by ITRPV to grow their power ratings dramatically – from about 295 W in 2014 and close to 310 in 2015 to about 365 W by 2025. That would be a growth of nearly 18%. Even back contact modules are not anticipated to improve its power rating that much (only 15%). Of course, these products already have a very high base level of 330 W, which is expected to increase to 380 W by 2025 –  so in absolute terms that would be even a 50 W power rating gain over 10 years.

High on n-type: ITRPV 2015 expects a strong gain in module power for panels based on all n-type wafers. Hetero-junction, back contact and standard n-type module are anticipated to gain 18%, 15% and 14%, respectively, by 2025.

High on n-type: ITRPV 2015 expects a strong gain in module power for panels based on all n-type wafers. Hetero-junction, back contact and standard n-type module are anticipated to gain 18%, 15% and 14%, respectively, by 2025.

 

Miscellaneous module aspects

When looking at module quality, you also have to look at defects  – in particular microcracks and PID.  Many companies advertise their modules being PID-free, same is true for micro-cracks. The 2015 ITRPV recommends using the relevant IEC 62804 draft standard for PID testing (which was published shortly afterwards – in Aug. 2015) as such a common platform avoids “over testing.”

ITRPV emphasizes that silicone as a replacement for adhesives in order to attach the module frame to the laminate, would further strengthen its dominance – increasing its share from the current 75% up to 90%in 2025. The target of accomplishing the electrical interconnection in the junction box with welding instead of the current practice of soldering, which the 2014 ITRPV version considered to take place between 2015 and 2017, is now pushed back by 2 more years – from 2017 to 2019.

Overall, concepts that boost performance of solar cells in modules independent from the cell level are expected to improve even further although they are already very much advanced and widespread. In addition to employing innovative interconnection technologies and encapsulation materials (both which are covered in different articles), the half-cut cells concept is expected to enjoy increased acceptance. As for the cell dependent characteristics, no big change in developments is recorded in power output (which in average grow 5 W per year), while the 80-cell module configuration is not considered to be an attractive future design anymore. However, it would be interesting to know how ITRPV has based its breakdown and forecast for 60-cell or 72-cell modules. The 72-cell variety is usually used for big PV power plants, which dominate the market today, but many forecasters see rooftop solar to gain market shares. In any case, the hot news is that multicrystalline modules are reaching a 100% cell-to-module performance ratio. That’s pretty efficient.

 

About The Author

Shravan Chunduri

Shravan Chunduri is Head of Technology at TaiyangNews.

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