Solar modules with increased break resistance

1st February 2013

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TULiPPS Solar BV is the first company to use special 2-mm/0.08 inch, single-layer toughened solar glass from Ducatt NV (Lommel, Belgium), produced via the patented tempering process developed by LiSEC Group (Hausmening, Austria).

This ultra-thin ultra-clear glass provides frameless COSMOS solar modules from TULiPPS with increased break resistance, light transmittance, and energy-generating efficiency/unit area while also reducing module weight and overall costs (Watt-peak installed). 

LiSEC is the market leader in high-quality glass-processing equipment, supplying systems to the world’s largest flat-glass producers.  The company has invested considerable research and development effort to perfect its new tempering process and to build automated processing systems that achieve new levels of performance in very-thin, very-light, and highly robust glass, which is ideally suited for solar applications like cold-bent parabolic reflectors or glass/glass PV modules.  

Eliminating traditional roller-based processes, LiSEC equipment can temper flat glass down to 0.9 mm/0.04 inch, achieving uniform microstructure, unrivaled density and bending strength (120 MPa/17,404 PSI and respectively equivalent to ~10,000 PSI  surface tensile strength) plus superior optical properties.  Since the glass surface is not touched during tempering, roller 'waves' that can distort optics are eliminated and sheets can be coated on one or both sides prior to heat treatment without risk of damage.  LiSEC’s tempering process also reduces energy consumption 40 per cent versus competitive systems.

Ducatt is one of the world’s only dedicated solar-glass manufacturers and specialises in producing ultra-clear, ultra-thin, ultra-light low-iron solar glass that does not sacrifice strength. 

The company has just completed a €50-million ($68-million USD) investment in a best-in-class dedicated solar-glass furnace/manufacturing line as well as glass processing and tempering lines – the latter exclusively outfitted with state-of-the-art equipment from LiSEC. 

The new tempering line has been optimised end-to-end for quality and speed to produce ultra-clear (95 per cent transparency with minimal reflectivity), ultra-thin (down to 2mm), and ultra-strong (fully tempered) rolled solar glass. This special glass helps reduce shipping costs and facilitates module installation.  Plus, its exceptional clarity means that it can help improve any module’s energy-generating efficiency by 4 per cent. 

This new thinner glass offers distinct benefits to manufacturers, installers, and owners of PV modules in terms of transparency/energy-generation, break resistance, and lower weight.  However, as often happens when a breakthrough is made and technology makes a significant advancement, an industry’s specification and certification systems are often inadequate to properly quantify and qualify the performance benefits gained with the new technology. 

Worse, measured or calculated values obtained from these specifications often contradict what the eye can clearly see with regard to how much better a technology performs during testing vs. older products. This is the case with very-thin tempered glass.

The first problem is that currently the term 'fully tempered' glass – which is required for use in solar PV modules to ensure safety of workers during installation and maintenance – refers to the physical properties (strength) of single-layer ESG/safety glass, but it also refers to a 'fracture' image.

The new thinner glass (in cross-sections lower 2.7 mm/0.11 inch) behaves differently and produces a different fracture image than thicker “classic” tempered solar glass. 

By conventional measurement, it resembles only heat-strengthenedglass; however, in physical testing, it behaves like fully tempered glass, and in fact provides far superior break resistance if properly supported in the testing apparatus.  And that bring up the second challenge: the test set-up itself.

Since this new glass is more 'bendable', it must be allowed to move in order to absorb and dissipate energy during an impact event. Module designs where the new thinner glass is rigidly constrained on all four edges can prove problematic. The same is true when the glass is rigidly constrained in a test fixture (rather than being mounted onto a stable supporting device) during laboratory evaluation. One of the strengths of the new COSMOS module design from TULiPPS is that it is frameless and the glass, while supported via a tough energy-absorbing composites underbody, is allowed to move, dissipating energy wave patterns that would cause breakage in conventional rigid aluminium-framed module designs. Since most testing facilities have little experience analyzing this new thin glass, they may not realize they need to modify test fixtures to get a more realistic view of how the glass behaves and the design of modules in which the glass is likely to be installed.

Still another testing challenge is that the industry’s commonly used measurement device for determining the strength of flat glass is a Strainoptics laser GASP non-destructive measurement system[1].  This device actually measures residual surface stresses rather than strength itself.  Because cooling conditions for 2-mm glass are different from that of 4-mm glass owing to different skin/core/skin relationships, the residual stress distribution between the two glass samples will vary considerably. The stress-level differentials between both types of glass are also quite dissimilar, and there is question as to whether this measurement system will have value when used to evaluate performance of the new thinner glass.

Another challenge is simply one of nomenclature. When US flat-glass and module makers or certifiers discuss the strength of the glass, they are referring to surface compression only. In Europe, however, the term is used to mean bending strength, which is a measurement combining both surface compression and inner (core) tensile strength.  In the case of thin glass tempered via the LiSEC method, the difference between what is measured/calculated can be significant:  by the US definition, strength of the glass is ~10,000 PSI, but by the European definition, the “corrected” value is 17,404 PSI as proven during bending tests.  Hence the industry needs to tighten up what it is referring to and how that value is measured in order for parties in all geographies to be sure the same property is being discussed.  There is no doubt that industry and certification organisations have work ahead of them to deal with the implications of this new technology.

According to Paul Stassen, TULiPPS Solar inventor and managing director: “When I first saw this very-thin glass made by LiSEC tempering equipment, I was simply amazed by its flexibility and strength. At just 2mm thick, it literally offers the same strength as conventional low-iron solar glass at 3.2 and 4.0 mm, yet it is half the thickness and far lighter. I quickly realized that it was the perfect complement to TULiPPS’ frameless COSMOS PV module design.  You cannot take full advantage of thin solar glass if you use a rigid aluminum frame. Even more importantly, with this special glass we achieve a new standard in transparency – 95 per cent vs. typical 91 peer cent seen with thicker, low-iron solar glass – so our modules not only weigh less, but they are also more energy efficient – the holy grail of the solar PV market.  This means a faster return on investment for module owners.  The combination of LiSEC’s special tempering process, which preserves strength even in very-thin glass, Ducatt’s exceptional glass clarity and transparency, and TULiPPS’ patent-pending module construction method means that the new COSMOS modules represent innovation to the power of three.”

Notes Roel Bollen, chief-executive officer, Ducatt NV: “We are very excited to be working with a visionary company like TULiPPS, because their unique module design is the best technology platform we have seen to showcase the many benefits of our singular solar glass.  Literally and figuratively, the COSMOS module allows Ducatt to fulfill its mission to help our customers harvest the energy of the sun while saving on energy costs.  We feel this product sets a new gold-standard in solar glass.”

Ing Leopold Mader, managing director-Development & Technical Division, LiSEC continues, “We applaud management’s vision at both companies. Ducatt’s new tempering line is the world’s leading example of what our process and equipment can achieve. We are so proud that a new company has chosen to fill a new hall with a complete LiSEC machine path.  Now our equipment will be used all together, the way it was meant to be, so the full benefits of the technology will really shine. Ducatt’s investment means its customers can be assured of the thinnest, strongest tempered solar glass possible.  And by selecting Ducatt glass, TULiPPS has guaranteed that its modules will not only be very light and break resistant, but also more energy efficient, which will help solar PV achieve grid parity faster.”

Johann Weixlberger, manager-Business Development at LiSEC adds: “We predicted the growth in demand for thin tempered solar glass for thin-film, glass/glass modules.  However, we never anticipated a module design that would use a single layer of thin glass by itself with silicon cells. With the approach that TULiPPS has taken, they have literally opened up a new market for thin solar glass, and that makes us very happy.”

Stassen concludes, “The world is about to change. The cost of solar PV is declining rapidly with residential costs already comparable in price to electricity generated from fossil fuels in Italy, the Netherlands, and five US states. It will not be too long before economies of scale will make solar PV energy cheaper than non-renewable sources.  COSMOS module technology will change the game for solar PV because it offers the unbeatable combination lowest cost, highest output, longest service life, and lowest carbon footprint. Our systems will achieve the highest ROI because we will have the lowest installed cost base and the highest conversion efficiencies of any PV module technology.  And our partnership with Ducatt is vital to help us achieve these goals.”

 New patent-pending COSMOS module technology from TULiPPS Solar BV – available in standard 72- and larger 120-cell configurations – has carefully been designed to address deficiencies with conventional PV systems in order to bring greater value to all members of the solar PV supply chain – from the PV module manufacturers and module installation companies to building owners and investors. Developed in partnership with leading companies in the automotive composites, roofing, and PV industries, and with financial support from the Province of Noord-Brabant and assistance from the Brabantse Ontwikkelingsmaatschappij in the Netherlands, the modules reduce weight, production costs, installation time and maintenance, as well as increase revenues, and lower system costs (Watt-peak installed) for the next generation of solar PV modules. 

Key to the success of the system is the combination of tough but lightweight automotive-grade composites, a frameless support system with plug-¢n-play functionality, a proven roof-anchor system that does not penetrate the roof membrane, and special thin 2mm/0.08 inch, single-layer toughened solar glass from Ducatt NV that provides improved break resistance and industry’s highest light transparency and therefore offers greater energy conversion per unit area.  COSMOS module technology can be used for roof- or ground-mounted solar arrays and building-integrated PV (BIPV) modules in all existing PV module factories.

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