Technology Roadmap

Anticipated trends in the c-Si PV industry

To keep up with the competition from conventional energy sources and oth­er renewable energy sources, the so­lar PV industry must continuously develop and provide effective and efficient power generation products. An international technology roadmap can help identify trends and define the areas of improvement.

VDMA recently released the 13th edition of its International Technology Roadmap for Photovoltaic (ITRPV) to inform suppliers and customers about the anticipated technology trends in the crystalline silicon (c-Si) PV industry and to facilitate discussions on the required improvements and standards. The roadmap emphasises the need for improvement in PV technologies and de­velopment of comprehensive solutions.

Renewable Watch presents the key highlights of the report including major market trends, developments in the cells and modules segment, and the future outlook for the solar PV industry.

Market overview

The PV module market showed a significant growth in 2021, reaching a capacity of 183 GW. This growth was realised despite challenges in poly-Si supply, logistics and material supply. The global c-Si cell and PV module production capacity at the end of 2021 is assumed to have further increased to over 470 GWp due to continued capacity expansions. The market share of about 95 per cent for c-Si and about 5 per cent for thin-film technologies is assumed to be unchanged.

The c-Si module market shift to mono-Si continued in parallel with the implementation of innumerable module products deploying more and more M10, and M12 wafer formats together with bifacial module technology. The weighted average price of c-Si modules increased in 2021 by about 10 per cent compared to the end of 2020 (close to 15 per cent without including annual inflation). Mono-Si based products experienced a significant price incre­a­­se while price premiums for bifacial and high-power modules nearly disappeared at the end of 2021. The spot market price for PV modules has increased for the first time in more than 10 years by about 10 per cent. End users outside China have had to bear the additional burden due to the surge in logistic prices for container shipments from Asia to the world.

Efficiency improvements in PERC technology and the deployment of large wafers in large modules resulted in higher average module efficiencies. The use of larger wafers enabled new module power classes of 600 W and above. In 2021, PV manufacturers continued the installation of new PERC cell and module production ca­pacities, capable of new cell formats. They also invested in the upgrade of existing production lines to increase cell efficiencies and enable the use the new wafer formats.

Cell technologies

The BSF cell concept will be phased out in 2022. Nevertheless, the matured concept of diffused and passivated p-n junctions will go mainstream with different rear side passivation technologies (PERC/PERL/ PERT/TOPCON). PERC/PERT/PERL/TOPCON will dominate the market over the next few years. The 2021 market share of PERC/PERL/PERT/TOPCON was found to be approximately 85 per cent. Heterojunc­tion (SHJ) cells are expected to gain a market share of about 10 per cent after 2024 and close to 20 per cent by 2032. The double-sided contact cell concepts will dominate the market.

Rear-side contact cells are not expected to have a significant market share, which is assumed to change from nearly 2 per cent in 2021 to 5 per cent in 10 years. Si-based tandem cells are expected to appear after 2024 in mass production.

Cells using n-type material have shown the highest efficiency potential among cell technology concepts. P- and n-type mono-Si cells with diffused p-n junction at the front side are expected to reach up to 24.5 per cent and 25 per cent respectively in the next 10 years. Cells on n-type using tunnel oxide passivated contacts at the rear side show higher efficiencies than all p-type cell concepts. Other n-type-based cell concepts like SHJ and back-contact cells are expected to reach higher efficiencies of up to 25.7 per cent in mass production within the next 10 years. Si-based single junction cell concepts are converging to a practical efficiency limit of about 26 per cent, close to the theoretical upper limit of 30 per cent. Tandem cells will overcome this limit. Mass production cell efficiencies of Si-based tandem cell concepts are expected to start at about 27 per cent. Their introduction in the market is expected after 2024.

Critical challenges in cell technologies

Metallisation pastes/inks containing silver (Ag) and aluminum (Al) are the most pro­cess-critical and most expensive non-silicon materials used in current c-Si cell technologies. Therefore, paste consumption needs to be reduced. The reduction of the remaining silver per cell is expected to continue during the next few years. The current study concluded about 13.2 mg per W as the median value in 2021 and about 12 mg per W in 2022 for standard PERC monofacial and bifacial cells as average in the M6 and M10 formats. A reduction to 7.5 mg per W or 60mg per M10 cell is expected to be reached within the next 10 years for PERC. New developments in pastes and screens must enable this reduction. This highlights the necessity of a close collaboration between suppliers and cell manufacturers to accept this challenge.

The silver price has been around $800 per kg since the beginning of 2020, a quite elevated level of 30-40 per cent above the average during the five years before 2020. This resulted in costs of 1.1 cents per W for a 23 per cent mono PERC cell. Bifacial p-type concepts consume about 10 per cent more silver. N-type cell concepts show significant higher silver consumption than p-type PERC – 40 per cent and 60 per cent for TopCon and SHJ concepts respectively. This is mainly due to the use of silver for the front and entire rear side metallistion. Because silver will remain cost critical due to the world market de­pendency, it is extremely important to continue all efforts to lower silver consumption as a means of achieving further cost reductions.

Technical issues related to reliability and adhesion must be resolved before alternative metallisation techniques can be introduced. Appropriate equipment and proce­sses also need to be made ready for mass production. Silver is expected to remain the most widely used front metallisation material for c-Si cells in the years to come.

Module trends

Today, most of modules are monofacial modules (about 70 per cent in 2022). Over the next few years, the share of bifacial modules will grow to about 60 per cent. Bifacial cells can be used in bifacial modules as well as in conventional mo­no­facial modules. Cell types such as PERC/PERT/ PERL/TOPCON as well as SHJ cells can capture the light from the front and from the rear side if the electrical contacts are designed accordingly. This cell types can therefore be perfectly used for bifacial light capturing. For bifacial cells, the market share of 50 per cent in 2021 is expected to increase significantly to 85 per cent over the next 10 years. It is expected that 20-30 per cent of bifacial cells will be used in monofacial modules. Bifacial modules will mainly be deployed in power plant installations.

An important parameter to characterise the performance of bifacial modules is the bifaciality factor. It describes the ratio bet­ween rear-side and front-side efficiency, measured under standard test conditions. SHJ cells have the highest bifaciality factor that is expected to improve to up to 0. 92. The bifaciality factor of standard PERC cells is expected to improve from about 0.7 in 2021 up to 0.76 over the next 10 years. Topcon cells show a bifaciality bet­ween SHJ and PERC.

Another trend in module technology is the development of modules for special markets and environmental conditions. It is still expected that the main market will be for standard modules. Modules for special environmental conditions such as tropical climate and desert environment, and floating solar modules will together account for up to 20 per cent over the next 10 years.

Future outlook

The price experience curve for the PV market has continued with its historic learning. The learning rate (LR) was calculated at 24.1 per cent. The PV industry can keep the LR up over the next few years with a com­bination of cost reduction measures and implementation of cell perfections, with improved wafer material, improved cell front and rear sides, refined layouts, in­troduction of bifacial cell concepts, impro­ved module technologies as well as the introduction of new cell technologies. The introduction of larger cell formats will contribute to PV system cost reduction.

Improvements in all fields will result in module area efficiency improvement. Today, mainstream p-type mono-Si based modules reach efficiencies of 21 per cent, which will increase to 22.5 per cent within the next 10 years. N-type modules including heterojunction provide the highest power modules with efficiencies of close to 22 per cent that will increase up to 24 per cent within the next 10 years. Si-based tandem cells and modules are expected in mass production around 2026, starting with module efficiencies of 26 per cent.

Net, net, the combination of optimised ma­nufacturing costs and increased cell and module performance will support the reduction of PV system costs and thus ensure the long-term competitiveness of PV power generation.

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