Andreas Schueler

Facade Integration of Solar Thermal Collectors: A Breakthrough

One main barrier to the acceptability of facade use of solar thermal collectors is their black appearance and the visibility of piping or absorber irregularities through the glazing. To facilitate facade integration, a project was set up to develop selective filters reflecting only a small part of the solar spectrum in the visible range while letting the rest of the radiation heat the absorber. These filters were successfully produced and, combined with a diffusing glass treatment, have achieved the desired masking effect with minor impact on the collector efficiency (less than 10%). Glasses of various colours combined with several diffusing finishing (acid etching, structured glass etc…) can be produced that are able to hide the absorber. Such glazings will allow the use of the same product both in front of facade areas equipped with solar absorbers (as collector external glass) and in front of the non exposed areas (as facade cladding), opening the way to a broad variety of active facade designs. The active elements can then be positioned at will on the exposed areas, and their quantity determined only by thermal needs. By freeing the dimension of the facade area that can be clad with this glazing from the thermally needed surface for collectors, a major step to help architects use solar thermal on facades has been taken.

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

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 300–800 nm reached the surface of amorphous silicon photovoltaic cells encapsulated below structural glass fiber-reinforced polymer laminates with a fiber reinforcement weight of 820 g/m2, demonstrating the feasibility of conceiving multifunctional glass fiber-reinforced polymer structures.

Integration of dye solar cells in load- bearing translucent glass fiber- reinforced polymer laminates

The encapsulation of dye solar cells in translucent, structural and lightweight glass fiber-reinforced polymer laminates was investigated with a view to designing multifunctional envelopes for daylit buildings. Small and large integrating sphere experiments and solar radiation experiments were performed to determine the light transmittance of the laminates and the electrical efficiency of the encapsulated cells. An overall cell efficiency of 3.9% (before encapsulation) only decreased to 3.4% after encapsulation below laminates of around 3-mm thickness. Thermal cycle experiments and finite element analysis allowed the thermal performance of the encapsulation for two types of cell substrates (glass and acrylic polymer) to be evaluated. Contrary to glass substrates, no delaminations were observed on acrylic substrates after 300 h of cycles +60/−20℃. A design for integrating dye solar cells into multifunctional sandwich building envelopes is proposed. A light transmittance of around 0.35 was estimated through a sandwich envelope with cell modules occupying 50% of the external face sheet. Research on the manufacturability of cells on polymeric substrates is encouraged.

Van der Waals MoS2/VO2 heterostructure junction with tunable rectifier behavior and efficient photoresponse

Junctions between n-type semiconductors of different electron affinity show rectification if the junction is abrupt enough. With the advent of 2D materials, we are able to realize thin van der Waals (vdW) heterostructures based on a large diversity of materials. In parallel, strongly correlated functional oxides have emerged, having the ability to show reversible insulator-to-metal (IMT) phase transition by collapsing their electronic bandgap under a certain external stimulus. Here, we report for the first time the electronic and optoelectronic characterization of ultra-thin n-n heterojunctions fabricated using deterministic assembly of multilayer molybdenum disulphide (MoS2) on a phase transition material, vanadium dioxide (VO2). The vdW MoS2/VO2 heterojunction combines the excellent blocking capability of an n-n junction with a high conductivity in on-state, and it can be turned into a Schottky rectifier at high applied voltage or at temperatures higher than 68 °C, exploiting the metal state of VO2. We report tunable diode-like current rectification with a good diode ideality factor of 1.75 and excellent conductance swing of 120 mV/dec. Finally, we demonstrate unique tunable photosensitivity and excellent junction photoresponse in the 500/650 nm wavelength range.

Optically-derived mechanical properties of glass fiber-reinforced polymer laminates for multifunctional load-bearing structures:

This paper demonstrates how the translucency of glass fiber-reinforced polymer (GFRP) laminates allows the derivation of their mechanical properties through optical measurements. Spectrophotometric, goniophotometric and tensile experiments were performed on unidirectional and cross-ply hand lay-up GFRP laminates with fiber volume fractions ranging from 0.15 to 0.45. An analytical model to predict the directional fiber volume fractions—and thus the mechanical properties of GFRP laminates—has been developed based on the total and diffuse transmittance and directional light scattering of the laminates. It is demonstrated that structurally optimized GFRP laminates can meet the requirements for GFRP skylights and the encapsulation of photovoltaic cells into translucent GFRP laminates.