Contents
Introduction
Background of the BIPV Market
Flexible Module Encapsulation Opportunities
Rigid Module Encapsulation Opportunities
The BIPV sector is likely to be the fastest growing part of the solar industry in the next decade, but researchers believe that demand patterns for encapsulation and substrate materials from this sector will be different from the traditional PV industry.
Even though glass will be the most widely used material for both encapsulation and substrates in the BIPV sector, special coatings may be required as the result of the use of novel absorber materials in BIPV. In addition, NanoMarkets (a leading researcher into PV markets) believes that in the emerging BIPV market there will be a considerable trend toward flexible PV because of its ability to offer lightweight installation and improved aesthetics. On the one hand this means new opportunities for suppliers of special metal substrates. But it will also require cost effective flexible encapsulation systems.
With all this in mind, it is important to quantify the new business revenues that will potentially be generated by novel substrates in the BIPV sector as well as by advanced multi-layer encapsulation systems, including the new breed of encapsulation system that makes use of atomic layer deposition (ALD).
As monolithic integration becomes more common in BIPV, specialist encapsulation systems will be required to protect the relatively delicate CIGS (Copper indium gallium (di)selenide), OPV (Organic Photo-voltaics) and DSC (Dye-sensitized Solar Cell) absorber materials that will be used in such products. So great are the opportunities for growth in this market, many leading suppliers of encapsulation products are viewing BIPV as a market for their products as well.
The PV market is undergoing dramatic change as the industry transitions from one of generous subsidies to one with dwindling subsidies, dramatically reduced prices, reduced margins, and anticipated massive consolidation.
As the PV module market shifts towards a commodity business model with associated mergers, and many players are weeded out of the panel area, which dominates the overall solar industry, there are many in the industry looking for new business models with greater opportunities for high margin growth.
One of the potential areas of high growth for solar PV is in building-integrated photovoltaics (BIPV). BIPV traditionally has been a smaller market due to high module cost and the fact that nearly all products were glass-based rigid products with either crystalline or polycrystalline silicon absorbers that were not particularly aesthetically pleasing.
However, that is not the case today. A new range of BIPV products are beginning to enter the market that can be flexible and can even cover curved facades. They are often available in custom shapes that can cleanly cover building surfaces. They are also more pleasing to the eye, with a uniform dark appearance.
This new wave of BIPV products represents an attractive opportunity for new encapsulation materials. The current materials for flexible modules are relatively expensive to manufacture compared to the glass used in rigid modules.
However, for BIPV applications, where product lifetimes are 20-30 years, they represent a good value proposition for high-end applications today, and will have much wider appeal as costs come down. The larger opportunities will be in the newest generation of materials, which promise to reduce costs without reducing product lifetimes.
BIPV encapsulation opportunities exist for both rigid and flexible modules:
- In the near term, the outlook is good for rigid modules, as they are the lowest cost solutions available today.
- Long-range growth, however, will be in the flexible area.
- The trend towards CIGS in flexible modules will also be a big driver for BIPV encapsulation growth.
CIGS encapsulation requirements are greater than those for a-Si (the current flexible BIPV absorber material), and module manufacturers are looking for the next advances in encapsulation materials for emerging CIGS BIPV applications.
While near-term opportunities for BIPV encapsulation are centered mostly on rigid modules, NanoMarkets’ research indicates that flexible module encapsulation will be the long-term growth area for high margin opportunities for new materials in BIPV applications. And although current flexible modules are mostly limited to a-Si modules with some CIGS-based modules now becoming more routinely available, flexible high efficiency CIGS module growth will drive the majority of growth for encapsulation in the foreseeable future in the flexible module area.
Flexible substrates and encapsulation have several inherent advantages compared to rigid substrates in BIPV applications:
- The biggest advantage of flexible modules is their ability to conform to curved façade surfaces.
- Another major advantage is module weight compared to rigid modules. Modern rigid modules weigh 10 to 30 kg/m2, while flexible modules are on the order of 3 to 5 kg/m2.
- Flexible modules also have an aesthetic advantage over rigid modules, which contain iconic but unattractive silicon wafers or polysilicon modules in rectangular framed modules.
In contrast, the latest flexible BIPV products can be ordered in custom shapes for application to cover an entire façade with very inconspicuous seams and thin-film absorbers that present an attractive uniform exterior surface.
While flexible thin-film-based modules have many advantages over rigid modules for BIPV applications in theory, several practical issues have greatly limited flexible BIPV adoption:
- Reliability issues
- High cost, and;
- Poor efficiency have limited the appeal and use of flexible BIPV to date.
The limitations of current encapsulation materials are at the heart of all of these concerns. From an efficiency perspective, until recently, flexible BIPV has been limited to a-Si, which has less stringent encapsulation needs for oxygen and moisture penetration than high efficiency CIGS modules. And because flexible BIPV has generally been limited to a-Si, the efficiency has been capped for these modules around 8-9 percent.
Dyadic systems
Recently however, higher efficiency CIGS-based modules offering 10-13 percent efficiency have entered the market. These new CIGS modules use dyadic encapsulation systems that provide protection that will pass a 30-year reliability spec, however these are currently very expensive to produce. The need from an encapsulation perspective is to develop materials with equivalent hermetic seal and long-term reliability as in the dyadic systems, but at a lower cost.
The current dyadic systems incorporate two or more alternating layers of polymer and thin ceramic. Multiple layers are used to eliminate pinholes and provide a material that will last many years in outdoor environments. Vitex Systems was early to the game in dyadic barrier technology, but it recently went out of business. Firms such as Dow, Fujifilm, DuPont, and 3M are actively working on dyadic and other barrier concepts to improve the encapsulation solutions available.
Borrowing from the semiconductor industry: One promising area for encapsulation beyond the dyadic systems that may provide similar performance and lower cost is the use of multiple, very thin layers of silicon oxy nitride and silicon nitride using the plasma-enhanced chemical vapor deposition (PECVD) or atomic layer deposition methods common in the semiconductor industry.
These systems have already shown some success in greatly improving OLED (Organic Light-emitting diode) barrier performance, and are used in volume manufacturing as a protective overcoat in semiconductor devices before packaging. It remains to be seen if such systems, which provide such good encapsulation on chips up to a centimeter on a side, can be scaled to provide pinhole-free protection over areas of multiple meters – the sort of scale required for PV panels.
Another barrier system that has shown success in the lab is ultra-thin TaN/Si3H4. TaN is the current barrier used in the semiconductor industry to encapsulate copper metallization in 130 nm and below technologies. Leveraging semiconductor barrier technology and infrastructure for BIPV encapsulation as has been done in other PV processes and seems a likely path to improved materials without re-inventing the wheel. Atomic Layer Deposition (ALD) is another technique used in the semiconductor industry that has shown promise for depositing high performance barrier films.
Potential of flexible glass
In addition to new encapsulation systems based on semiconductor barriers, other flexible encapsulation technologies include thin, flexible glass such as the lines developed by Corning and Schott.
Part of their promise is the likelihood that such materials would retain many of the properties of thicker glass, such as dimensional stability, heat tolerance, and impermeability, while permitting roll-to-roll processing and limited flexible applications. These types of materials are not viable options yet, however.
Advances in organic systems: While pinholes are still an issue for most organic polymer-only encapsulation systems, several organic-based encapsulation materials are still being investigated. A transparent poly(ethylene naphthalate) (PEN)-based ultra-high barrier material has been demonstrated in the lab as a possible organic encapsulation material for organic- based flexible PV modules. It remains to be seen if a single layer organic material can be deposited pinhole free and meet all of the BIPV reliability metrics, but work continues in this area in the lab and in prototypes.
Flexible substrates
Along with top layer encapsulation, flexible BIPV requires high quality flexible substrates. Flexible substrates have, up to now, fallen into two general categories: metal foils and polymer films:
- Metal foils like aluminum and stainless steel have taken the lead in flexible PV, because they are generally more heat resistant and less easy to deform than polymers while still offering good flexibility. They also offer a higher level of barrier protection for the back side of the PV cell versus polymer films.
- Going forward, the growth in substrates will likely be in polymer films, as they are lighter weight and cheaper than metal and are optically clear in many cases. The biggest hurdle to wide adoption of current polymer materials is lower deposition temperature requirements. Currently, only the polyimides are compatible with current thin-film PV deposition conditions for flexible substrate materials.
Another advantage of polymer substrate films is that they can be made extremely thin and should become a much smaller proportion of total TFPV device cost over time, especially if process development allows cheaper, less temperature-tolerant plastics to be used. Metal foils are, however, a mature product, but one that has a lot of potential for thinning—and thus cost reduction.
While the reliability challenge is large for BIPV, the 30-year lifetime also represents a significant span of time to allow for depreciation of cost, even if the upfront cost is relatively large:
- BIPV encapsulation materials not only need to protect the module, but also need to be compatible with the lifetimes of the underlying construction materials with which they are associated.
- Early degradation of a thin-film PV device within a BIPV product may lead to either a very costly replacement of both the PV module and the building material, or a panel that remains non-functional for an extended period due to the high cost of BIPV replacement.
The confidence that reliable encapsulation systems can bring to BIPV products—by extending their actual and expected lifetimes—enhances the value of those products. In turn, the value added from a robust encapsulation system yields revenue opportunities for the firms supplying them.
The near-term market for rigid BIPV encapsulation will be dominated by the same materials as many rigid modules of today, namely glass. Glass will continue to be the king for the foreseeable future. Compared to other options, it is inexpensive, provides a hermetic seal and thick tempered modules are robust to weather and wear.
Current rigid module encapsulation comes in two main forms:
- The first is very similar to rigid panels for rooftop or solar farm applications. These modules, in many cases, amount to more robust adaptations of current module designs with heavier glass and more robust edge seal designs to meet 20-30 year lifetime specs for BIPV applications.
- The second is transparent a-Si modules that have had some penetration in skylight and window applications, but have been hampered by the low efficiency of a-Si absorbers.
However, Rigid BIPV modules in general have been limited by several constraints:
- For façade applications, the rigid nature limits their use to flat surfaces.
- The weight of rigid tempered glass-based cells can be up to 30 kg/m2. Extra weight equals extra cost for integrating such modules.
- Less of a factor is the uniform rectangular module size and framing, which limits their ability to cover a surface in an inconspicuous manner.
- Efficiency can also be an issue with c-Si and polysilicon based modules. While such modules are very efficient in solar farm applications with direct sunlight, the efficiency drops off precipitously in BIPV applications when the majority of incoming light is reflected.
While current semi-transparent a-Si BIPV modules are of low efficiency, there may be an opportunity for growth for encapsulation and substrate providers if a suitable transparent substrate and rear conductor can be found that would allow the transition of BIPV transparent modules from a-Si to CIGS.
Currently, most CIGS modules have molybdenum as the back conductor. Highly conducting optically transparent films containing carbon nanotubes, metal dispersions and extremely narrow metal grids have been explored for such applications, and may represent significant opportunities going forward if they can be integrated into transparent BIPV CIGS modules.
About NanoMarkets
NanoMarkets is a leading provider of market research and industry analysis of opportunities within advanced materials and emerging energy and electronics markets. Since the firm’s founding, NanoMarkets has published over one hundred comprehensive research reports on emerging technology markets. Topics covered have included OLED displays, lighting and materials, thin-film electronics, conductive inks, transparent conductors, renewable energy, printed electronics and other promising technologies. Our client roster is a who’s who of companies in specialty chemicals, materials, electronics applications and manufacturing.
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This information has been sourced, reviewed and adapted from materials provided by NanoMarkets (NanoMarkets Report: Substrates and Encapsulation for BIPV).
For more information on this source, please visit NanoMarkets
Date Added: Feb 3, 2012 | Updated: Feb 13, 2012