Total Light Transmittance of Glass Fiber-Reinforced Polymer Laminates for Multifunctional Load-Bearing Structures

Glass fiber-reinforced polymer (GFRP) materials are increasingly used in building construction for the design of multifunctional structures. These composite materials allow the integration of structural functions, building physics functions (mainly thermal insulation) and architectural functions (complex forms and color) in single large-scale building components. GFRP materials also allow the fabrication of translucent structural components with high degree of transparency when optically aligned resins and glass fibers are used, i.e. their refractive indices are identical. In this study the total light transmittance of hand lay-up GFRP laminates for building construction was investigated with a view to two architectural applications: translucent load-bearing structures and the encapsulation of photovoltaic (PV) cells into GFRP building skins of sandwich structures. Spectrophotometric experiments using an integrating sphere set-up were performed on unidirectional and cross-ply GFRP specimens in the range from 20% to 35% fiber volume fraction. Results were compared with the shortcircuit currents generated by amorphous silicon (a-Si) PV cells encapsulated in GFRP laminates exposed to artificial sunlight radiation. The total amount of fibers in the laminates was the major parameter influencing light transmittance, with fiber architecture having little effect. 83% of solar irradiance in the band of 300-800 nm reached the surface of a-Si PV cells encapsulated below structural GFRP laminates with a fiber reinforcement weight of 820 g/m2, demonstrating the feasibility of conceiving multifunctional GFRP structures.

Translucent load-bearing GFRP envelopes for daylighting and solar cell integration in building construction

Carlos Pascual Agullo

This project investigates the light transmittance of load-bearing glass fiber-reinforced polymer (GFRP) laminates with a view to two architectural applications: the daylighting of buildings through load-bearing translucent GFRP envelopes and encapsulation of solar cells into the GFRP building skins of sandwich structures. The total and diffuse visible light transmittances of the laminates were experimentally investigated using a spectrophotometer coupled to an integrating sphere. The refractive indices of polymeric resin and glass fibers were also investigated and numerical ray-tracing simulations were performed to demonstrate the experimentally observed wavelength dependency of light diffusion. The total transmittance and translucency of GFRP laminates were analytically modeled as a function of the reinforcement weight, fiber architecture and fiber volume fraction. Goniophotometric experiments – performed to investigate the directional light scattering of laminates reinforced with different fiber architectures – were demonstrated as an effective method to predict the fiber architecture of translucent GFRP laminates. The optical properties of the laminates, i.e. the total and diffuse transmittances and directionality of light diffusion, were correlated with the experimentally investigated mechanical properties, i.e. the directional tensile strength and E-modulus. The experimental work demonstrated that structural skylights could be designed with GFRP laminates exhibiting a translucency of 0.9 and total light transmittance of 0.5 – minimum values recommended for daylighting of buildings through translucent envelopes – and that solar cells could be encapsulated in load-bearing GFRP laminates with a total light transmittance of around 0.83. A case study was performed using the GFRP/polyurethane sandwich roof of the Novartis Campus Main Gate Building to demonstrate the basic feasibility of integrating skylights and solar cells into the external translucent skin of optimized sandwich structures. Finally, the encapsulation of transparent and colored dye solar cells in translucent GFRP laminates has been explored. Prototype solar panels have been fabricated and a significant weight reduction, increase in structural strength and around 10% reduction of electrical efficiency compared to traditional solar panels with glass encapsulants were achieved.

EPFL2014

Total light transmittance of glass fiber-reinforced polymer laminates for multifunctional load-bearing structures

Julia De Castro San Roman Fest, Thomas Keller, Carlos Pascual Agullo, Andreas Schueler, Anastasios Vassilopoulos

The total light transmittance of hand lay-up glass fiber-reinforced polymer laminates for building construction was investigated with a view to two architectural applications: translucent load-bearing structures and the encapsulation of photovoltaic cells into glass fiber-reinforced polymer building skins of sandwich structures. Spectrophotometric experiments on unidirectional and cross-ply glass fiber-reinforced polymer specimens in the range from 0.20 to 0.45 fiber volume fraction and artificial sunlight exposure experiments on encapsulated amorphous silicon photovoltaic cells were performed. Analytical models have been developed to predict light transmittance through glass fiber-reinforced polymer structures and the percentage of solar radiation reaching encapsulated photovoltaic cells. The total amount of fibers in the laminates was the major parameter influencing light transmittance, with fiber architecture having little effect and regardless of fiber volume fraction. Eight-three percent of solar irradiance in the band of 300-800nm reached the surface of amorphous silicon photovoltaic cells encapsulated below structural glass fiber-reinforced polymer laminates with a fiber reinforcement weight of 820g/m(2), demonstrating the feasibility of conceiving multifunctional glass fiber-reinforced polymer structures.

SAGE Publications2014

Light diffusion in GFRP laminates for building construction

Julia De Castro San Roman Fest, Thomas Keller, André Gabriel Kostro, Carlos Pascual Agullo, Andreas Schueler

The light diffusion of hand lay-up glass fiber-reinforced polymer (GFRP) laminates was investigated with a spectrophotometric set-up using an integrating sphere. Reinforcement weights of the laminates ranged from 410 to 3280 g/m2 and fiber volume fractions were between 0.20 to 0.35. The influence of resin gel times on light diffusion was also studied. Experimental results showed that blue light was more diffused than other colors, particularly in laminates with longer gel times. The refractive indices of resin and glass fibers were investigated and a significant mismatch below 500-nm wavelength was observed. Numerical ray-tracing simulations were performed and the trend of the experimental total and diffuse transmittances were successfully modeled. These analyses confirmed that the spectral mismatch of refractive indices was responsible for the wavelength dependency of light diffusion in GFRP laminates.

2014

Translucent load-bearing GFRP envelopes for daylighting and solar cell integration in building construction

Carlos Pascual Agullo

EPFL2014