For the solar energy industry to increase its competitiveness, there is a global drive to lower the cost of solar-generated electricity. Photovoltaic (PV) module assembly is material-demanding, and the cover glass constitutes a significant proportion of the cost. Currently, 3-mm-thick glass is the predominant cover material for PV modules, accounting for 10%–25% of the total cost. Here, we review the state-of-the-art of cover glasses for PV modules and present our recent results for improvement of the glass. These improvements were demonstrated in terms of mechanical, chemical and optical properties by optimizing the glass composition, including addition of novel dopants, to produce cover glasses that can provide (i) enhanced UV protection of polymeric PV module components, potentially increasing module service lifetimes; (ii) re-emission of a proportion of the absorbed UV photon energy as visible photons capable of being absorbed by the solar cells, thereby increasing PV module efficiencies and (iii) successful laboratory-scale demonstration of proof of concept, with increases of 1%–6% in Isc and 1%–8% in Ipm. Improvements in both chemical and crack resistance of the cover glass were also achieved through modest chemical reformulation, highlighting what may be achievable within existing manufacturing technology constraints. © 2020 The Authors.

Solar energy is promising renewable energy where glass is an important material and have a significant impact on the efficiency of the photovoltaic (PV) module. The cover glass of PV-modules constitutes a large part of the total weight of the unit. In a recent Solar-ERA.NET project, LIMES (www.limes.nu), have we been aiming towards developing 1 mm thin glass for PV modules by improving the indentation mechanical properties and by investigating a novel thermo-chemical strengthening method.

Starting from traditional soda-lime-silicate float composition different components was studied in a DoE fashion. The mechanical properties were studied using nano- and microindentation, the chemical durability by P98 analysis and weathering experiments. The findings resulted in a suggested composition for improving the properties of float glass by adding small amounts of zinc and titanium oxide as well as increasing the amount of aluminum and magnesium oxide. The components found to improve the chemical resistance were alumina, zirconia, zinc, lanthanum and titanium oxide. The surface hardness, crack- and scratch resistance were improved when magnesia was replaced with zinc oxide. When magnesia was replaced with titania, the hardness was increased.

Some results from the thermo-chemical strengthening experiments will be presented. Heating and quenching in a reactive gas atmosphere using aluminum precursors have resulted in chemically modified surface in addition to the thermal strengthening.

Utvinning av solenergi genom solceller är en lovande teknik för att öka andelen förnyelsebara energikällor både nu och i framtiden. Glas till solceller är en betydande del av kostnaden och en nödvändighet att utveckla för att öka livslängden och minska priset per utvunnen watt. I LIMES har man studerat dels att tillsätta optiskt aktiva komponenter som absorberar skadligt UV ljus och samtidigt konverterar det till synligt ljus som i sin tur kan konverteras till energi i solcellerna. Därmed är vinsten tvåfaldig, ökar både livslängden och effektiviteten med upp till 4%. Vidare har det studerats hur man kan optimera de mekaniska och kemiska egenskaperna av glas för att kunna öka den mekaniska och kemiska livslängden, detta genom att optimera glassammansättningen. Man har inom projektet visat att motstånd mot sprickbildning av en ny sammansättning ökar med en faktor 3 och att den kemiska resistensen ökar med en faktor 4. Termo-kemisk härdning av glas har demonstrerats i labskala som ger upphov till minst lika stor härdningsgrad samt ökar motstånd mot sprickbildning med en faktor 2. Det möjliggör användning av tunnare glas och därmed betydligt lättare solceller. Glasytans sammansättning modifieras signifikant genom att öka halten aluminiumoxid och det ger upphov till de förbättrade egenskaperna. Den termo-kemiska behandlingen ökar vattens kontaktvinkel mot glasytan vilket bidrar till ett självrengörande glas. Multifunktionella ytor på glas som är både antireflektiva och självrengörande har studerats genom två olika angreppssätt, nanostrukturerad ytmodifiering och porösa antireflektiva beläggningar med fotokatalytisk nedbrytningsförmåga. Nanostrukturerade glasytor ger upphov till en ökad ljusspridning och kan på så vis effektivt guida ner diffust ljus till solceller och samtidigt ändra vattens kontaktvinkel mot glaset. LIMES-koncepten har demonstrerats genom kvantitativa mätningar och tillverkande av små kiselsolcellsmoduler. Projektet har stått för att öka potentialen för kommersialisering ifrån TRL (Technology Readiness Level) nivå 2-4 till 4-6. Man undersöker i det närmaste hur man kan skala upp planglastillverkning för att kunna ta nästa steg mot kommersialisering.

Extraction of solar energy through solar cells is a promising technology for increasing the share of renewable energy sources, both now and in the future. Glass for solar cells is a significant part of the cost, and a necessity to develop to increase life expectancy and reduce the cost per watt recovered. In the LIMES project have adding optically active components been studied, these absorb harmful UV light and simultaneously converts those UV photons into visible light, which in turn can be converted into energy in solar cells. Thus, the profit is twofold, increasing both the lifetime and efficiency by up to 4%. Further, it has been studied how to optimize the mechanical and chemical properties of glass by optimizing the glass composition in order to increase the mechanical and chemical lifetime. It has shown that resistance to cracking of the new composition increases by a factor of 3 and that the chemical resistance is increased by a factor of 4. Novel thermo-chemical strengthening of glass has been demonstrated in the lab and giving rise to at least equal strengthening level and increases the crack resistance by a factor of 2. It enables the use of thinner glass and thus significantly lighter photovoltaic modules. In the thermo-chemical strengthening process, the glass surface composition is modified significantly by increasing the content of aluminum oxide and thus gives rise to improved properties. The thermo-chemical treatment increases the glass surface contact angle of water, which contributes to a self-cleaning glass. Multifunctional glass surfaces that are both anti-reflective and self-cleaning have been studied by two different approaches, nanostructured surface modification and porous antireflective coatings with photocatalytic degradation ability. Nanostructured glass surfaces gives rise to an increased light scattering and can thus effectively guide diffused light to the solar cells and simultaneously change the glass contact angle with water. The LIMES-concept has been demonstrated by quantitative measurements and manufacturing of small silicon photovoltaic modules. The project has significantly increased the potential for commercialization by increasing the TRL (Technology Readiness Level) level from 2-4 to 4-6. Investigations on how to scale up manufacturing flat glass in order to take the next step towards commercialization is on-going.

Planar ground float glass surfaces and the surfaces within holes are polished using fluid jet polishing (FJP) in order to improve their visual appearance or material strength. The large flexibility of FJP makes it suitable for polishing holes and other complex geometries. The influence of polishing speed, incident angle, distance, pressure, abrasive concentration, and nozzle diameter are investigated. Al2 O 3 is the abrasive used. The surface quality is evaluated visually and also measured with an optical profiler. The mechanical strength of the polished holes are evaluated with an MTS testing machine. Planar surfaces, and the surfaces of drilled and water cut holes are greatly improved by polishing. For a planar surface the lowest root mean square surface slope, Sdq, value achieved is 0•5 deg using 50% abrasive and 1000 mesh grains. The failure load of the glass with drilled holes increased 20% with FJP.

Structural glass-timber composite beams and shear wall elements were investigated in terms of their mechanical behaviour, energy performance and their LCA performance. The load bearing components were manufactured using annealed float glass which was adhesively bonded to the timber with different adhesives. The results show, among other things, that is is possible to join the two materials glass and timber and obtaining a non-brittle failure of the beams. The shear wall elements have the potential of being used as stabilising elements and load bearing walls in buildings of up to 4 storeys height. It is possible to combine glass and timber in a load bearing shear wall without loss of energy performance of a building or without loosing LCA performance. In addition to these benefits, the timber glass composite wall has, of course the benefit of being transparent.

Osseointegration is a prerequisite for achieving a stable long-term fixation and load-bearing capacity of bone anchored implants. Removal torque measurements are often used experimentally to evaluate the fixation of osseointegrated screw-shaped implants. However, a detailed understanding of the way different factors influence the result of removal torque measurements is lacking. The present study aims to identify the main factors contributing to anchorage. Individual factors important for implant fixation were identified using a model system with an experimental design in which cylindrical or screw-shaped samples were embedded in thermosetting polymers, in order to eliminate biological variation. Within the limits of the present study, it is concluded that surface topography and the mechanical properties of the medium surrounding the implant affect the maximum removal torque. In addition to displaying effects individually, these factors demonstrate interplay between them. The rotational speed was found not to influence the removal torque measurements within the investigated range.