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37th European Photovoltaic Solar Energy Conference and Exhibition; 1984-1994, The dominating solar cell technology for PV power plants is the Si based solar cell. However, solar cell technologies such as chalcogenide, organic, III-V or perovskite solar cells, all have their own niche markets or potentials. The aim of this work is to provide an overview and comparison of the different solar cell technologies for the application in integrated photovoltaics. The current statuses of the technologies are reviewed. Characteristics relevant for integrated photovoltaics are defined and each technology is discussed regarding those key influencing factors. The results of the comparison are compiled in a concise table summarizing strengths and weaknesses of the different technologies in respect of their application for integrated photovoltaics.

We review distinct features arising from the unique nature of the carrier-phonon coupling in self-assembled semiconductor quantum dots. Because of the discrete electronic energy structure, the pure dephasing coupling usually dominates the phonon effects, of which two properties are of key importance: The resonant nature of the dot-phonon coupling, i.e. its non-monotonic behavior as a function of energy, and the fact that it is of super-Ohmic type. Phonons do not only act destructively in quantum dots by introducing dephasing, they also offer new opportunities, e.g. in state preparation protocols. Apart from being an interesting model systems for studying fundamental physical aspects, quantum dot and quantum dot-microcavity systems are a hotspot for many innovative applications. We discuss recent developments related to the decisive impact of phonons on key figures of merit of photonic devices like single or entangled photon sources under aspects like indistinguishability, purity and brightness. All in all it follows that understanding and controlling the carrier-phonon interaction in semiconductor quantum dots is vital for their usage in quantum information technology.

36th European Photovoltaic Solar Energy Conference and Exhibition; 1749-1753, For photovoltaic systems that are integrated into buildings (building-integrated photovoltaics, BIPV), the aesthetical properties are crucial. While PV-modules based on (pseudo-)square crystalline silicon solar cells feature a geometrically regular and usually very technical appearance, architects and designers demand more freedom of design for PV-modules. Simultaneously, the electric efficiency and yield should stay in the focus when developing aesthetically valuable modules. In this work, we present a novel BIPV module design method aiming at high efficiency and innovative design. The novel concept is based on the idea that a PV cell can also consist of several parts that are electrically connected in parallel. These solar cell parts can vary in size and shape and be connected using a wire-based approach. A large variety of geometrical designs is possible and the modules can be aesthetically integrated into the design of a building’s envelope. The electric design of those modules is of course more challenging and we developed a simulation tool that allows for calculating the electric module properties based on an arbitrary design. The design can be given as an image, which is automatically translated via image recognition into a SPICE model. Using SPICE, the relevant electrical output (IV-curve, Jsc, Voc, FF) can be calculated and designs can be optimized electrically.

35th European Photovoltaic Solar Energy Conference and Exhibition; 1123-1126, DC-DC power optimizers present a promising approach to minimize losses in photovoltaic systems integrated into buildings (BIPV). Compared to free-standing PV plants, BIPV systems are often geometrically very complex, leading to a more complicated electric circuit and effects like partial shading and hot spots. We addressed the complex electrical design with a detailed modeling approach that includes the relevant physical quantities to analyze the time-resolved yield of a BIPV system. This comprises the calculation of the time-resolved irradiance on each individual solar cell by ray-tracing, the temperature-dependent electric performance of each solar cell, the electrical interconnection including bypass and blocking diodes and the DC/AC conversion. As each BIPV system is geometrically unique and requires detailed electrical planning, DC-DC power optimizers, which ensure that individual modules are always operated at their individual maximum power point, could simplify this planning process. However, this requires DC-DC converters that are highly efficient also under the specific operation conditions that can strongly vary between different BIPV systems, during the day or the year. In this work, we extended the Fraunhofer ISE BIPV simulation tool and included DC-DC optimizers to be able to quantify the benefits of optimizers for specific BIPV projects.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2630-2634, In order to support acceptance and attractivity of building integrated PV (BIPV), there is a rapidly increasing demand for coloured PV modules. Especially, architects and building planners wish an individual colour choice, saturated colors, a homogeneous appearance for all angles of incidence and at the same time a high module efficiency. Furthermore, it is important that glare effects can be suppressed. State of the art concepts offer a restricted choice of colours, show a strong angular dependence, cause a high efficiency loss or do not allow for an efficient industrial production. We overcome these restrictions by using the Morpho butterfly effect, a bionic concept based on 3D photonic structures. Our novel technological realization of these structures is well suited for large scale production.

This paper deals with the state of the art of advanced solar control devices for buildings, with the comparative evaluation of solar-control systems and with guidelines for the development of new solar control systems. It includes multifunctional systems with building integrated photovoltaic (BIPV) and/or building integrated solar thermal (BIST) energy conversion. In order to facilitate and to structure the understanding of solar control systems two multidimensional spaces are introduced: the design space and the evaluation space. The design space contains the design parameters which are to be selected by the designer when solar control devices are to be chosen for specific buildings or when new systems are to be developed, such us the color of the slat of a venetian blind or the fraction of holes (direct transmittance) of a fabric for a roller blind. The evaluation space contains the performance parameters or evaluation criteria, which indicate the design's ability to satisfy the functional and aesthetic requirements, such us passive solar gain control or visual comfort. All the design parameters and evaluation criteria are explained in detail in the paper. A chapter with examples of advanced solar control systems completes the overview of the state of the art of solar control systems.

Kohärente Phononen können die Licht-Materie-Wechselwirkung in Halbleiter Nanostrukturen stark ändern. Bei einem Ensemble von Quantenpunkten (QP) als aktivem Lasermedium sind Phononen im Stande, die Laserintensität deutlich zu verstärken oder abzuschwächen. Die Physik des gekoppelten Phonon-Exziton-Licht-Systems wird von verschiedenen Mechanismen dominiert, die im Experiment nicht eindeutig unterschieden werden können, da die komplizierte Probenstruktur zu einem komplexen Verspannungspuls führt, der auf das QP-Ensemble trifft. Hier zeigen wir durch eine umfassende theoretische Studie, wie die Laseremission durch Phononpulse verschiedener Form und QP-Ensembles verschiedener spektraler Verteilung beeinflusst wird. Dies erlaubt einen Einblick in die grundlegenden Wechselspiele des gekoppelten Gesamtsystems. Dadurch können wir zwischen zwei Mechanismen unterschieden: der adiabatischen Verschiebung des Ensembles und dem Schüttel-Effekt. Dies ebnet den Weg zu einer gezielten Kontrolle der Laser Emission durch kohärente Phononen. Coherent phonons can greatly vary light–matter interaction in semiconductor nanostructures placed inside an optical resonator on a picosecond time scale. For an ensemble of quantum dots (QDs) as active laser medium, phonons are able to induce a large enhancement or attenuation of the emission intensity, as has been recently demonstrated. The physics of this coupled phonon–exciton–light system consists of various effects, which in the experiment typically cannot be clearly separated, in particular, due to the complicated sample structure a rather complex strain pulse impinges on the QD ensemble. Here we present a comprehensive theoretical study how the laser emission is affected by phonon pulses of various shapes as well as by ensembles with different spectral distributions of the QDs. This gives insight into the fundamental interaction dynamics of the coupled phonon–exciton–light system, while it allows us to clearly discriminate between two prominent effects: the adiabatic shifting of the ensemble and the shaking effect. This paves the way to a tailored laser emission controlled by phonons.

33rd European Photovoltaic Solar Energy Conference and Exhibition; 2118-2122, Photovoltaic systems that are integrated into buildings face several challenges compared to freestanding PV plants. Besides their multi-functionality and a more complex construction process with the constraints given by a building and its facades and roof, BIPV systems are often geometrically very complex, leading to a more complicated electric circuit and effects like partial shading and hot spots. We addressed the complex electrical design with a detailed modeling approach that includes the relevant physical quantities to analyze the time-resolved yield of a BIPV system. This comprises the calculation of the time-resolved irradiance on each individual solar cell by raytracing, the temperature-dependent electric performance of each solar cell, the electrical interconnection including bypass and blocking diodes and the inverter behaviour. Beyond BIPV systems, our developed tools can also be beneficial for the planning of all PV systems, where partial shading occurs, e.g. for bifacial modules.

This paper presents a method to evaluate the thermal impact of complex fenestration systems on the energy balance of a building zone based on directional solar heat gain coefficients (DSHGC) and bi-directional scattering distribution functions (BSDF). The proposed methodology is presented as an alternative to layer-by-layer heat transfer models. An example of a layer-by-layer heat transfer model is the ISO15099 as implemented in the EnergyPlus building simulation program. The ISO15099 model relies on a number of assumptions that are not justified in the case of three-dimensional structures, air-permeable layers and deviations from ideal geometries, which are common features in commercial daylighting and solar-control systems. In this paper, the proposed methodology is implemented in the Fener simulation engine and compared with EnergyPlus for systems for which the assumptions of the ISO15099 model are valid. Then, the Fener program is used to simulate the thermal behaviour of a zone with a fenestration system that contains sawtooth-shaped retro-reflecting interior blinds, which cannot be directly modelled with the ISO15099 model. The impact of different control strategies on the thermal performance of the zone is demonstrated for this case study.

This paper addresses the definition of a new criterion Raout-in to evaluate the color rendering of objects in a room viewed by an observer who is outdoors. This is not only relevant when outdoor observers are viewing persons in the room. It is also frequently taken into account when the color of internal solar-control or glare protection systems is selected so that they have a pleasing appearance for both indoor and outdoor observers. The relation of the new criterion to the general color rendering index Ra as applied for daylight transmitted through glazing is discussed and several solar control systems are assessed with respect to Ra and Raout-in. Both color rendering indices are based on an evaluation of the color rendering of eight moderately saturated test colors illuminated with the reference illuminant D65 and the illuminant under consideration (e.g. the same illuminant transmitted through a spectrally selective solar-control glazing). A discussion about an extension of the range of test colors by addition of strongly saturated test colors is also included in the paper. © 2016, Elsevier B.V. All rights reserved.

Seit Sommer 2013 bieten 15 m2 winkelselektive PVShade®-Verglasungen im Brüstungsbereich eines Seminarraums am Fraunhofer-Institut für Solare Energiesysteme ISE in Freiburg saisonalen Sonnenschutz und selektive Durchsicht und erzeugen Strom photovoltaisch (PV). Das PVShade®-Element wurde von einem der Autoren erfunden und patentiert. Während mehrerer Forschungsprojekte wurden die technischen, energetischen und ökonomischen Eigenschaften dieser PV-Verglasungen durch Messungen und modellbasierte Simulationsrechnungen umfassend untersucht. Zu den untersuchten Eigenschaften gehören der winkelabhängige Gesamtenergiedurchlassgrad (g-Wert), der Wärmedurchgangskoeffizient (U-Wert), die Eignung als absturzsichernde Verglasung, die Auswirkung der Verglasungen auf den Energiebedarf im Seminarraum, die Strom-Spannungskennlinien der PV-Module, der elektrische Ertrag der PV-Anlage, die Temperaturentwicklung der PV-Ebenen und die Lebenszykluskosten. In diesem Beitrag werden sowohl die Untersuchungsmethoden als auch Ergebnisse der verschiedenen Charakterisierungsansätze für diese besonderen Verglasungen jeweils kurz vorgestellt.

This paper addresses the definition of a new criterion Raout-in to evaluate the color rendering of objects in a room viewed by an observer who is outdoors. This is not only relevant when outdoor observers are viewing persons in the room. It is also frequently taken into account when the color of internal solar control or glare protection systems is selected so that they have a pleasing appearance for both indoor and outdoor observers. The relation of the new criterion to the general color rendering index R-a as applied for daylight transmitted through glazing is discussed and several solar control systems are assessed with respect to R-a and Raout-in. Both color rendering indices are based on an evaluation of the color rendering of eight moderately saturated test colors illuminated with the reference illuminant D65 and the illuminant under consideration (e.g. the same illuminant transmitted through a spectrally selective solar-control glazing). A discussion about an extension of the range of test colors by addition of strongly saturated test colors is also included in the paper.

The generated electricity of a rather complex building-integrated photovoltaic system, installed in the main building of the Fraunhofer Institute for Solar Energy Systems, is analyzed in detail. For this purpose, the measured irradiance on the tilted surface, the temperatures of the PV modules, the DC power and the AC power are compared with the results of an advanced electricity yield simulation program that has been developed at the institute. The chosen building-integrated photovoltaic (BIPV) system allows detailed investigation of complex shading patterns, improved electrical cell connection and the temperature characteristics of building-integrated photovoltaic modules when they simultaneously function as insulating glazing units with a low U value.

The indoor environment in retrofitted pilot demonstration offices, equipped. with advanced radiant ceiling panels that were used for heating and cooling, is evaluated in the paper. comprehensive analyses based on various sets of real case measurements were carried out in order to assess the efficiency and adequacy of the proposed retrofitting concept. It was established that the entire system for tempering the offices operates well, and that the range of indoor air temperatures ensures the highest level of comfort.

Um den Kühlenergiebedarf von Gebäuden zu senken und den ""heat island"" Effekt in Städten einzugrenzen, werden im Rahmen der amerikanischen LEED®-Vorschriften auch die optischen Eigenschaften von Baumaterialien wie Dach- und Bodenbedeckungen einbezogen. Nach der Norm ASTM E 1980-11 werden opake Bedeckungsmaterialien, die horizontal oder mit geringer Neigung verlegt werden, durch einen sogenannten ""Solar Reflectance Index - SRI"" charakterisiert. Er wird aus dem solaren Reflexionsgrad (SR) und dem thermischen Emissionsgrad berechnet und stellt ein Maß für die relative Erwärmung der Materialien bei Berücksichtigung der absorbierten Sonneneinstrahlung und der gegen den Himmel abgestrahlten Wärme dar. In diesem Beitrag wird die Bedeutung des SRI-Wertes von Bedeckungsmaterialien für das Stadtklima dargelegt. Darüber hinaus werden die Herleitung des SRI-Wertes aus gemessenen Reflexionsspektren, SRI-Beispiele für Betonproben unterschiedlicher Farbe und Zusammenhänge mit anderen aus Reflexionsspektren abgeleiteten Werte wie Solar- und Lichtreflexionsgrade vorgestellt.

This study presents and demonstrates a methodology for calculating the economic potential of photovoltaic installations in urban areas including the previously often disregarded potential on building façades. The analysis of a 2km2 urban area has shown that building façades there provide almost triple the area of building roofs. However due to non-optimal inclination and orientation, they receive only 41% of the total irradiation. From this, the economic potential under present market conditions was calculated, resulting in 17% of all analyzed building surfaces, i.e. 0.3km2 of roof surfaces being economically exploitable for photovoltaic installations already now which corresponds to an installed capacity of 47MWp. Considering further a material substitution from the building integration of the photovoltaic installations, an economic potential of up to 56MWp or 0.4km2 results, of which up to 6MWp or 0.04km2 are economically installable on building façades. Façade-mounted installations would then account for 13% of the economic potential. The calculation of an economic potential and additionally considering the material substitution from building integration both constitute an extension to many existing renewable energy potential studies just focusing on the technical potential. However, only the economic potential allows forecasts of the future diffusion of this technology.

With the aim of reducing the cooling energy demand of buildings and limiting the urban heat island effect, the optical properties of building materials such as roofing and pavers are taken into account in the U.S. American LEED® Green Building Rating Systems. According to the ASTM E1980-11 standard, opaque roofing or paving materials which are installed horizontally or at a low tilt angle can be characterised by the so-called ""Solar Reflectance Index - SRI"". It is calculated from the solar reflectance (SR) and the thermal emissivity, and is a measure for the relative heating of such materials when absorbed solar radiation and heat emitted to the atmosphere are considered. The paper illustrates why the SRI value of surface-covering materials is significant for urban climates. It will also present the derivation of the SRI value from measured reflectance spectra, SRI examples for concrete pavers of differing colours and correlations with other quantities which can be derived from the reflectance spectra, such as solar and visual reflectance.

The paper describes procedures for the direct calorimetric measurement of the solar heat gain coefficient g in detail. g is also called SHGC, solar factor, g-value or total solar energy transmittance TSET. All these terms are used synonymously in this document although there are some differences in the details of the definitions of these properties (e.g. different reference wind conditions or reference solar spectra). The document aims to summarize more than 25 years of experience in g-value testing at Fraunhofer ISE, Freiburg, Germany, which includes many different transparent and translucent building materials ranging from transparent insulation materials to daylighting and solar control systems and active solar energy harvesting facade components like building-integrated PV systems (BIPV) or building-integrated solar thermal collectors (BIST). The document focuses on methods for the calorimetric measurement of g under steady-state laboratory conditions. Transient outdoor measurements are beyond the scope of this paper. It also describes the corresponding error analysis and methods to correct experimentally determined values gexp to reference conditions, if it is not possible to reproduce the reference boundary conditions exactly in the laboratory.

Transparent solar thermal collectors (TSTC) represent a new development. An adequate model is needed to predict their performance. This paper presents a collector model with an advanced calculation of the transmission of diffuse radiation and a connection to the building which allows analysis of the collector gains and of the g value, also called " solar factor" , " solar heat gain coefficient (SHGC)" or " total solar energy transmittance" The model is implemented as a TRNSYS Type and a coupled simulation between a collector and a room is presented for different façade constructions. Façade areas with glazing and venetian blinds are simulated with a second new TRNSYS Type which introduces high modelling accuracy for façades with solar control systems. An HVAC system is presented together with a first estimate of possible reductions of primary energy. It indicates primary energy savings of about 30% by replacing opaque walls with transparent collectors. The g values prove to depend not only on the irradiation, but also on the operation of the solar collectors and vary e.g. between 0.04 and 0.21. Detailed modelling of active façades like TSTC is therefore essential for accurate predictions of the collector gain, the heating and cooling loads and the thermal comfort.

The authors investigate the effect of the coating of various internal blinds on the operative room temperature in an office space. It is very important to correctly evaluate the impact of solar protection and daylight/glare systems on building comfort, and the resulting influence on human behaviour. Many building energy simulation programmes consider the Mean Radiant Temperature (MRT) independently of the actual emissivity of the internal surfaces. This approximation is acceptable for normal constructions with emissivity close to 1, but leads to considerable errors if low-emissivity paint or coatings are used. Starting from the theory of the net-radiation in a grey enclosure, the authors evaluate the MRT, assuming that the incoming flux and the radiated flux are the same. This method is based both on an ESP-r integrated whole-building-simulation programme and on an analytical method which allows for the correct evaluation of the thermal radiant field induced by considering the presence of surfaces with low-e coatings. The method can be used either 'stand-alone' for comparisons of different façade variants or within a building simulation. The simulations carried out indicate that when an 'absorptive blind' surface faces outwards, the summer temperature can be reduced by about 1 K at a position close to the façade.

26th European Photovoltaic Solar Energy Conference and Exhibition; 4094-4098, A new methodology of simulating the electricity yield of complex BIPV systems is presented. The methodology allows a detailed optical analysis of the surroundings of the BIPV system by separating the time-independent ray-tracing of the given geometry from the time-dependent sky simulation when the radiation incident on a photovoltaic element is calculated. This separation is achieved through the discretization of the sky and by calculating the contribution of every sky region on the incidence-angle-dependent irradiance. The method allows the impact of shading, reflected light from other buildings, shading of the ground, and many other effects to be analyzed. The time-dependent results of the optical simulation under the assumption of a power spectral density function dependent on the air mass are forwarded to the PV device simulator ASA that calculates the generation profile in the photovoltaic layers. Taking material parameters into account, ASA calculates the I-V characteristics of every cell of the BIPV system at each point in time. Under the assumption of linear resistive losses within the modules, these functions are coupled to a system I-V function.

This paper describes a new general method for building simulation programs which is intended to be used for the modelling of complex facades. The term 'complex facades' is used to designate facades with venetian blinds, prismatic layers, light re-directing surfaces, etc. In all these cases, the facade properties have a complex angular dependence. In addition to this, such facades very often have non-airtight layers and/or imperfect components (e.g. non-ideal sharp edges, non-flat surfaces, EL). Therefore building planners often had to neglect some of the innovative features and to use 'work-arounds' in order to approximate the properties of complex facades in building simulation programs. A well-defined methodology for these cases was missing. This paper presents such a general methodology. The main advantage of the new method is that it only uses measureable quantities of the transparent or translucent part of the facade as a whole. This is the main difference in comparison with state of the art modelling based on the characteristics of the individual subcomponents, which is often impossible due to non-existing heat- and/or light-transfer models within the complex facade. It is shown that the new method can significantly increase the accuracy of heating/cooling loads and room temperatures.

Wenn PV-Module die Funktionen der Gebäudehülle übernehmen und klassische Bauteile dadurch entfallen, können Baukosten eingespart werden. Deshalb, und weil die ästhetischen Anforderungen immer mehr steigen, wird die funktionale und ästhetische Gebäudeintegration in Zukunft eine immer größere Rolle spielen. Der folgende Beitrag ist dem Themenheft 2008 des ForschungsVerbunds Erneuerbare Energien entnommen.

In der Photovoltaik-Branche werden derzeit erhebliche Anstrengungen unternommen, um den Preis der Solarzellen zu senken. Ein Ansatz: PV-Module übernehmen die Funktion der Gebäudehülle, so dass klassische Bauteile entfallen können.

Wie entwickeln sich photovoltaische und solarthermische Systeme, was eignet sich für das Dach, was für die Fassade und warum? Was tut sich am Markt? Der Autor vom Fraunhofer Institut für solare Energiesysteme hat die Antworten recherchiert.

A general method for realistic performance evaluation of solar control properties of facades with sun-shading or other solar control systems has been developed. It is particularly designed to be used for venetian blinds. It can be used 'stand-alone' or within building simulation programs. The new method has proven to be of great practical value to planning teams of huge office buildings in Germany, Austria and Switzerland. The method is presented in detail in [4]. It can be used either 'stand-alone' (without building simulation) for comparisons of different facade variants or within building simulation programs. In this publication the extension of the methodology for the case of facades with solar control systems between the panes of an insulating glazing unit (IGU) is presented. Some parts of the proposed methodology could be used in standards (e. g. EN 13363) or to improve the accuracy of building simulation programs which are currently on the market Practical experience with the new methodology led to insights which are the basis for the design of two new products. These new products are compared with state of the art products in [5] on the basis of the new methodology. We are currently linking the new method with the building simulation program ESP-r in a project which is funded by the Veluxstiftung.

A general method for realistic performance evaluation of solar control properties of facades for facades with sun-shading or other solar control systems has been developed. It is particularly designed to be used for venetian blinds. It can be used used 'stand-alone' or within building simulation programs. The new method has proven to be of great practical value to planning teams of huge office buildings in Germany, Austria and Switzerland. The method is presented in detail in this paper. It can be used either 'stand-alone' (without building simulation) for comparisons of different facade variants or within building simulation programs. Some parts of the proposed methodology could be used in standards (e.g. EN13363) or to improve the accuracy of building simulation programs which are currently on the market. Practical experience with the new methodology led to insights which are the basis for the design of two new products. These new products are compared with state of the art products in [T.E. Kuhn, Solar control: comparsion of two new systems with the state of the art on the basis of a new general evaluation method for facades with venetian blinds or other solar control systems, Energy and Buildings, in press] on the basis of the new methodology.