Andreas Schüler

In plants, light direction is perceived by the phototropin photoreceptors, which trigger directional growth responses known as phototropism. The formation of a phototropin activation gradient across a photosensitive organ initiates this response. However, the optical tissue properties that functionally contribute to phototropism remain unclear. In this work, we show that intercellular air channels limit light transmittance through various organs in several species. Air channels enhance light scattering in Arabidopsis hypocotyls, thereby steepening the light gradient. This is required for an efficient phototropic response in Arabidopsis and Brassica. We identified an embryonically expressed ABC transporter required for the presence of air channels in seedlings and a structure surrounding them. Our work provides insights into intercellular air space development or maintenance and identifies a mechanism of directional light sensing in plants.

High-technology glazing panes are designed to meet the need for natural light, while optimizing key functions such as reducing solar heat gain in spaces and/or redirecting daylight to the rear of the spaces. However, the actual performance in terms of both illumination and glare protection of these glazing systems is often unknown. This study aims to compare the visual comfort performance of four complex fenestration systems by means of point-in-time measurements under real sky conditions and for different seasons. The tested systems included: two glazing types with embedded seasonal solar protection, namely, MicroShade™ and Coolshade™, one prototype of daylight redirecting glazing with embedded micro-mirrors (GEMM), and one clear glazing. We conducted our tests in side-by-side nearly identical spaces in the NEST building in Dübendorf, Switzerland. Results showed a higher daylight provision for clear and daylight redirecting glazing. Discomfort glare assessment from daylight showed that MicroShade™ was substantially more efficient at addressing glare due to sunlight for high sun angles when compared to Coolshade™. The performance of the GEMM prototype was highly dependent on the glazing pane used and one pane provided a promising performance when it comes to mitigating glare risks for high sun positions. However, none of the systems were able to provide an adequate glare protection for lower sun positions. The performed measurements provide a basis for the calibration of simulation models.

The integrated performance assessment of buildings can orient their design in the early stages. Despite the wide availability of physics simulation-based, data-driven, and hybrid techniques, it is often difficult to rely on a single, appropriate technique to obtain reliable results. A set of methods, each featuring advantages and limitations, help to refine the performance assessment in an iterative comparative process until a comprehensive picture of the building is achieved. The approach was implemented on a nearly zero-energy building, recently built-up as a combined living and office space (e.g., the SolAce unit) on the NEST infrastructure in Dübendorf (Switzerland). The proposed approach showed that the unit reaches high energy performance accordingly requiring optimal cooling management, involving the control of the opening of blinds and windows. A sound convergence between the computer simulations and data-driven analysis were observed, attesting to the overall energy consumption, of around 26 kWh/m²year, in continuous decrease, aiming at an annual energy-positive balance. The unit was ranked first according to the dynamic energy exchange scheme of the energy trading hub within the NEST facility, which features high-level building modules as a testbed of future building technologies. Embodied energy is estimated at 39 kWh/m²year, which is below the commended limits of Swiss eco-building standards. By considering the carbon sequestration of the wood products during their lifespan, the unit is very close to carbon neutrality with the CO₂ emitted annually by the unit over its lifetime being compensated by those stored within wood products during the same period. Highlights: An innovative combined living/office space is connected to an ‘Energy-hub’. The unit includes novel bioclimatic developments of the building industry. Energy performance is assessed in the concept phase, construction, and operation. Used and compared simulation vs data monitoring for energy and comfort assessment. High energy performance and neutral CO₂ emission; plus-energy exported to the hub.

The power degradation and failure of photovoltaic (PV) modules can be caused by changes in the mechanical properties of the polymeric components during the module lifetime. This paper introduces instrumented nanoindentation as a method to investigate the mechanical properties of module materials such as polymeric encapsulants. To this end, nanoindentation tests were carried out on ethylene vinyl acetate (EVA) surfaces, which have been separated from the glass panel. Two types of time-dependent indentation cycle modes, the time domain (creep mode) and frequency domain (dynamic mode) were performed to determine the viscoelastic behavior. For each mode, a corresponding model was applied to calculate the main mechanical properties. The general capability of nanoindentation as cross-linking determination method is investigated with the methodological advantages over bulk mechanical characterization methods. A large number of Glass/EVA/Backsheet laminates were built using different lamination conditions resulting in different degrees of curing. Both indentation modes indicate good modulus sensitivity for following the EVA crosslinking in its early stages but could not reliably differentiate between samples with higher EVA branching. Additional dynamic mechanical analysis (DMA) characterization was used as an established method to validate the indentation measurements. Both nanoindentation and DMA tensile mode produce similar quantitative viscoelastic responses, in the form of the damping factor parameter, demonstrated for three different frequencies at room temperature. A statistical study of the data reveals the advantages for the investigation of multilayer PV laminates by using nanoindenation as a surface method while also being applicable to field aged modules.

Long-term photovoltaic (PV) module reliability is highly determined by the durability of the polymeric components (backsheet and encapsulation materials). This paper presents the result of experiments on encapsulant degradation influenced by the backsheet permeation properties. Towards this goal, one type of ethylene/vinyl acetate copolymer (EVA) was aged in glass/EVA/backsheet laminates in accelerated aging tests (up to 4000 h for Damp-Heat (DH) and up to 480 kWh/m² for UV and UV-DH combined). The samples contained three backsheets with different permeation properties to examine their impact on EVA degradation. Thermal and chemical characterization shows that the EVA degradation is stronger with the glass–EVA–polyamide (PA)-based backsheet than with the polyethylene terephthalate (PET)-based backsheets. The higher oxygen transmission rate (OTR) of the PA-based backsheet may increase photo-oxidation and aggravating the degradation of EVA in the laminates. Furthermore, FTIR results were used to demonstrate the effect of damp heat exposure on the EVA interfaces, showing an accelerated degradation at the glass–EVA interface. The comparison of accelerated aging stress factors reveals that EVA suffers the strongest chemical and optical degradation when high UV, high temperature and high relative humidity are combined simultaneously.

The present paper deals with the deposition of Cu-Co-Mn oxides thin film by magnetron sputtering to produce a black selective coating for solar Parabolic Trough Collector (PTC) systems. The effect of temperature was studied between the nominal temperature range of 300-600°C, using both in-situ heating and post annealing. The optical behavior was investigated by advanced spectrophotometry devices in visible, near and infrared spectral ranges. Scanning Electron Microscopy (SEM) was used to show the microstructure, and X-ray Diffraction (XRD) to identify the phases and to compare the samples’pattern prepared at different temperatures.

Novel glazing with embedded micro-mirrors can significantly reduce the energy consumption due to cooling and lighting in buildings. Especially promising are large arrays of periodic micro compound-parabolic-concentrators (CPCs) with angular-selected transmittance. For the production of micro CPCs, curved sidewall grooves with a controlled optical surface and an aspect ratio of about 2.3 are fabricated on polycarbonate substrates by scanning nanosecond 248-nm excimer laser ablation. The likewise obtained microstructures can be used as master mold for replication. The cross-sections of the micro grooves are characterized by confocal microscopy, and the extracted morphologies are used for the ray-tracing simulation of the optical devices. Prior to the scanning ablation using a suitable mask in the optical path, the depth profiles under static ablation are investigated to identify ablation rate, imaging resolution and produced surface. Interestingly for the width of the mask opening being less than 6 μm, the ablation rate is increased due to optical interference and /or less shielding by debris. Concerning the scanning ablation, the depth of the curved sidewall grooves ranges from 48 μm to 114 μm, corresponding to the width of the groove opening being in the range from 20 μm to 50 μm. The observed final shapes in cross-sections are in good agreement with the design of the mask. For both theoretical and fabricated groove shapes, the angular-selected transmittance profiles predicted from ray-tracing simulations are highly similar. Scanning nanosecond excimer laser ablation is therefore a promising approach for the realization of high-quality micro CPCs.