Large scale solar Photovoltaic (PV) deployment on existing building rooftops has proven to be one of the most efficient and viable sources of renewable energy in urban areas. As it usually requires a potential analysis over the area of interest, a crucial step is to estimate the geometric characteristics of the building rooftops. In this paper, we introduce a multi-layer machine learning methodology to classify 6 roof types, 9 aspect (azimuth) classes and 5 slope (tilt) classes for all building rooftops in Switzerland, using GIS processing. We train Random Forests (RF), an ensemble learning algorithm, to build the classifiers. We use (2 × 2) [m2 ] LiDAR data (considering buildings and vegetation) to extract several rooftop features, and a generalised footprint polygon data to localize buildings. The roof classifier is trained and tested with 1252 labeled roofs from three different urban areas, namely Baden, Luzern, and Winterthur. The results for roof type classification show an average accuracy of 67%. The aspect and slope classifiers are trained and tested with 11449 labeled roofs in the Zurich periphery area. The results for aspect and slope classification show different accuracies depending on the classes: while some classes are well identified, other under-represented classes remain challenging to detect.
High dynamic range imaging has been shown to be a reliable tool to assess luminance maps and glare risk probability in
buildings. However, there are some limitations of image capturing time, especially when dealing with highly dynamic
and contrasted daylight situations. We used a newly developed prototype of a digital camera which contains a high
dynamic range pixel array chip, with a logarithmic scale for encoding. This type of camera allows to effectively
assessing luminance, contrast and contrast directions, by taking only a single image or by performing real time
recordings. The device was equipped with a fisheye lens and V-lambda filters to adapt the camera’s spectral sensitivity
to the human eye. After spectral as well as photometric calibration and vignetting correction, the device was tested to
perform luminance mapping of real scenes. The results showed that luminance maps of a room can be efficiently
assessed under dynamic daylight and mixed day- and electric lighting conditions in a very short time (i.e. 100 ms), when
compared to classical HDR imaging techniques. This allows us to calculate glare indexes of a scene simultaneously. The
camera opens a variety of new applications as a useful tool for architects, building designers and lighting experts. The
device can be used to easily monitor daylight availability and glare indexes in existing buildings and further
developments for advanced (day-) lighting control can be envisaged.
A novel concept for an advanced fenestration system was studied and samples were produced to demonstrate the feasibility. The resulting novel glazing will combine the functions of daylighting, glare protection, and seasonal thermal control. Coated microstructures provide redirection of the incident solar radiation, thus simultaneously reducing glare and projecting daylight deep into the room in the same manner as an anidolic mirror-based system. The solar gains are reduced for chosen angles corresponding to aestival elevations of the sun, thereby minimizing heating loads in winter and cooling loads in summer. A ray-tracing program developed especially for the study of laminar structures was used for the optimization of structures with the above mentioned goals. The chosen solution is based on reflective surfaces embedded in a polymer film that can be combined with a standard doubled glazed window. The fabrication of such structures required several steps. The fabrication of a metallic mould with a relative high aspect ratio and mirror polished surfaces is followed by the production of an intermediate Polydimethylsiloxane moulds that was subsequently used to replicate the structure with a UV curable polymer. Selected facets of these samples were then coated with a thin film of highly reflective material in a physical vapour deposition process. Finally, the structures were filled with the same polymer to integrated the mirrors.
Making daylight more available in buildings is highly desirable for reasons of energy efficiency, visual comfort,
occupant well-being and health. The Anidolic Integrated Ceiling (AIC) is a highly efficient daylighting system, designed
to gather and redirect daylight from the outside of a building into its interior with minimal losses. The reflective coating
materials used within AICs have a major impact on the optical efficiency of such systems. The first part of our article
presents a new computer model of an AIC consisting of more than 30 distinct components. We discuss on which of them
the use of expensive, highly reflective coatings makes the most sense. We conclude that coating the component
"Anidolic element 1" is always a good choice and that considerable financial savings can be obtained by following an
appropriate optimization sequence.The second part of our article discusses chronobiological properties of Anidolic
Daylighting Systems (ADS). We recorded daytime irradiance values for several weeks from March to May 2009 in an
experimental office setup in our laboratory using a portable digital spectroradiometer. Our results showed to which
extent different sky conditions influenced daylight exposure of office workers in an ADS-equipped office room. We
conclude that for the tested ADS-equipped office room, daylight supply can be considered largely sufficient during long
periods on most working days. However, complementary artificial lighting with blue-enriched polychromatic fluorescent
tubes might be useful on days with predominantly overcast skies as well as before 09:00 and after 16:30 on all days.
Overheating is a common problem both with the use of active and passive solar energy in thermal solar energy
systems and in highly glazed buildings. In solar thermal collectors, the elevated temperatures occurring during
stagnation result in reduced lifetime of the collector materials. Highly glazed building facades provide high solar
gains in winter, but imply in most cases high energy needs for air conditioning in summer. A solution to such
problems might be provided by "smart" thermochromic coatings. A durable inorganic thermochromic material is
vanadium dioxide. At 68°C, VO2 undergoes a reversible crystal structural phase transition accompanied by a
strong variation in optical properties. By doping the material with tungsten, it is possible to lower the transition
temperature making it suitable as a window coating. In order to simulate the optical behaviour of multilayered
solar coatings, precise knowledge on the optical material properties is necessary. Experimental data reported in
the literature are rare and controversial. We determined the complex dielectric function for VO2:W by
spectroscopic UV-VIS-NIR ellipsometry above and below the transition temperature and subsequent point-by-point
analysis of the ellipsometric psi/delta data. For a validation, the solar reflectance, absorptance and
transmittance were measured by spectrophotometry in the visible range and in the near infrared range up to 2500
nm. The experimental reflectance spectra have been compared with the computer simulations based on the
determined optical material properties. Finally, we collected optical data in a more extended wavelength range by
digital infrared imaging to detect the switch in thermal emissivity of VO2:W at around 45°C.
One promising application of semiconductor nanostructures in the field of photovoltaics might be quantum dot solar concentrators. Quantum dot containing nanocomposite thin films are synthesized at EPFL-LESO by a low cost sol-gel process. In order to study the potential of the novel planar photoluminescent concentrators, reliable computer simulations are needed. A computer code for ray tracing simulations of quantum dot solar concentrators has been developed at EPFL-LESO on the basis of Monte Carlo methods that are applied to polarization-dependent reflection/transmission at
interfaces, photon absorption by the semiconductor nanocrystals and photoluminescent reemission. The software allows importing measured or theoretical absorption/reemission spectra describing the photoluminescent properties of the quantum dots. Hereby the properties of photoluminescent reemission are described by a set of emission spectra depending on the energy of the incoming photon, allowing to simulate the photoluminescent emission using the inverse
function method. By our simulations, the importance of two main factors is revealed, an emission spectrum matched to the spectral efficiency curve of the photovoltaic cell, and a large Stokes shift, which is advantageous for the lateral energy transport. No significant energy losses are implied when the quantum dots are contained within a nanocomposite coating instead of being dispersed in the entire volume of the pane. Together with the knowledge on the optoelectronical properties of suitable photovoltaic cells, the simulations allow to predict the total efficiency of the envisaged
concentrating PV systems, and to optimize photoluminescent emission frequencies, optical densities, and pane dimensions.
Electric lighting is responsible for a significant fraction of electricity consumption within non-residential buildings.
Making daylight more available in office and commercial buildings can lead as a consequence to important electricity
savings, as well as to the improvement of occupants' visual performance and wellbeing. Over the last decades,
daylighting technologies have been developed for that purpose, some of them having proven to be highly efficient such
as anidolic daylighting systems. Based on non-imaging optics these optical devices were designed to achieve an efficient
collection and redistribution of daylight within deep office rooms. However in order to benefit from the substantial
daylight provision obtained through these systems and convert it into effective electricity savings, novel electric lighting
strategies are required.
An optimal integration of high efficacy light sources and efficient luminaries based on non-imaging optics with anidolic
daylighting systems can lead to such novel strategies. Starting from the experience gained through the development of an
Anidolic Integrated Ceiling (AIC), this paper presents an optimal integrated daylighting and electric lighting system.
Computer simulations based on ray-tracing techniques were used to achieve the integration of 36W fluorescent tubes and
non-imaging reflectors with an advanced daylighting system. Lighting power densities lower than 4 W/m2 can be
achieved in this way within the corresponding office room. On-site monitoring of an integrated daylighting and electric
lighting system carried out on a solar experimental building confirmed the energy and visual performance of such a
system: it showed that low lighting power densities can be achieved by combining an anidolic daylighting system with
very efficient electric light sources and luminaries.
Non imaging optics has established a reliable and sound framework for the design of efficient lighting systems in different application fields (nuclear physics, solar concentrators, electric lighting appliances,etc.). Based on its outstanding features, novel daylighting devices (anidolic daylighting systems)were designed in order to achieve efficient collection and redistribution of the diffuse component of daylight within deep office rooms. Several devices were set up, optimised through computer numerical simulations, built at different scales (1:10 scale models, 1:1 scale
test modules)and finally monitored under different weather conditions (clear and overcast skies).
An overview of the high luminous performance achieved by these daylighting devices --a zenithal anidolic collector, an anidolic ceiling and facade integrated anidolic systems --in 6 to 7 meters deep rooms under typical Central European weather conditions will be given in this communication. It will be shown that a very significant improvement of daylight factors monitored at a 5 meter distance from the facade is achieved by theses systems in comparison to a conventional double glazing reference facade (doubling of the daylight factors on the work plane), which corresponds to a substantial improvement of the daylight provision in the deeper part of the room.A daylighting system (anidolic slats) that shows the limits of building integration for such systems,will be considered as well.