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Photovoltaies is expanding into new market segments. Photovoltaic noise barriers (PVNB) along motorways and railways permit today one of the most economic applications of grid-connected PV w ith the additional benefits of large scale plants (typical installed power: more than 100 kWp) and no extra land consumption. The aim of this study is to reveal the large potential that can be exploited for PV on noise barriers with the overall objective of raising the share of renewable energies for the EU's electricity market. In contrast to many PV-potential studies published before, this proposal is focusing on PVNB only, as one of the cheapest ways to implement large scale grid-connected PV installations.

Rising demand for solar power generation will lead to increased land use competition, and thus to potential economic and social conflict. A solution to this challenge is to produce food and energy within an agrophotovoltaics (APV) system. Since 2017, governments in Japan, France, Massachusetts (USA), South Korea, and China have introduced policies supporting APV implementation. Governments considering APV implementation – e.g. in India and Germany – for evidence-based policy making are demanding information on how levelized cost of electricity (LCOE) of APV differs from that of conventional ground-mounted photovoltaics (PV), as well as on how additional costs associated with APV installation relate to the benefit of maintaining agricultural activity under APV. Data for a techno-economic price-performance ratio calculation has been retrieved from an inter- and transdisciplinary APV case study in Germany. We observed that the LCOE of APV with €0.0828 kWh−1 is 38% higher than that of ground-mounted PV, resulting in an annual cropland preservation price of €9,052 ha−1 a−1. The annual revenue of potato and winter wheat production under APV resulted in a performance of €10,707 ha−1 a−1 and €1,959 ha−1 a−1 respectively, leading to a beneficial price-performance ratio of 0.85 for potato production and, with a ratio of 4.62, a disadvantageous result for winter wheat. Overall, APV is not necessarily recommended in crop rotating systems. However, in combination with permanent cultures – e.g. berries, fruits, or wine grapes – as the price for these types of applications is lower, while at the same time providing higher performance by optimizing techno-ecological synergies.

In this paper, we present a novel geometry for a photovoltaic module. This novel geometry employs light trapping effects to split the solar spectrum onto two different kinds of solar cells. The two different kinds of solar cells utilize different parts of the solar spectrum most efficiently. The proposed structure is based on prisms. The different kinds of solar cells are attached to opposing surfaces of the prisms. To achieve spectral selectivity, either spectrally selective filters or the solar cells itself are used. After introducing the general concept, we discuss different possible realizations. The theoretical potential of the light trap is calculated using the concept of spectral efficiency. Based on experimental solar cell data, we calculate theoretically that conversion efficiencies exceeding 30% are possible with such a module using silicon and GaAs solar cells. First experiments show that the optical losses of the proposed geometry are as low as 2.1% relative.

In this paper, a novel type of light trap is introduced. It enables photovoltaic conversion with separate solar cells optimized for different frequency bands, which are covered by spectrally selective mirrors. Sunlight is coupled into a transparent medium and converted to diffuse radiation by randomization. It is well known that under these conditions light intensity is enhanced by a factor of 2n2 inside the medium. The unidirectional radiation at the aperture is however only n2. Two types of light trap are presented. The first one employs concentrated radiation incident on a small volume light trap. It is shown that efficiency depends on the ratio (solar cell area)/(input area). A more detailed analysis shows that under regular conditions part of the light is absorbed directly after entering the trap which results in higher efficiencies. We show that a trapping efficiency above 90% is obtainable. The second type of trap is based on a photonic structure covering the surface of the medium. It has high angular selectivity and broad spectral transmission. An analysis of efficiency and loss mechanisms is presented. If both types of trap are combined even higher efficiency is possible. Consequences for solar cell technology are investigated. It is further shown that the light trapping principle can also be applied to large area stationary modules.

This paper gives an up to date perspective of PV technology and materials. The most important material has been and still is silicon. It dominates the present world market, particularly in its crystalline form but amorphous silicon is also of importance. Crystalline silicon solar cells are still heavily dependent on the materials base of the semiconductor industry. This material still has a large potential for cost reduction in its conventional form and even more so in the crystalline thin film version. Great hope rests with the thin film materials which require only small amounts of material. A great number of new concepts and materials are still in the research stage. Some of them may lead to much higher efficiency and lower cost in the coming decades. A function was identified which can be fitted to the past development of the best laboratory efficiencies. By fitting this function to the data points the future development of efficiency can be estimated for each technology.

A static, non-mechanical, self-activating sun protection system affecting the direct sunlight but not the diffuse skylight is described. It is based on the selection of direct sunlight by concentration. A lens array in front of a glass pane concentrates the direct light onto a thermotropic layer where it increases temperature beyond the switching temperature and causes the thermotropic layer to become locally quasi-opaque. Most parts of the glazing except for the small focal regions remain transparent and contribute to the illumination of the room behind. The system performance is theoretically analysed by a numerical solution of the equation of heat conduction, giving the temperature distribution within the system. Different samples of the sun protection system, using different thermotropic materials and other system components have been constructed and measurements of various temperature and transmission properties have been performed.

This paper traces briefly the history of this photovoltaic materials and it tries to look at possible future scenarios. A large part of the paper is concerned with silicon although from solid-state physics we know that silicon is not the ideal material for photovoltaic conversion. From the first solar cell developed at Bell Laboratories in 1954 photovoltaics was dominated by silicon. The reasons for this dominating position are investigated. Crystalline silicon today has a market share of 86% which is almost equally distributed between single crystal and cast silicon. Amorphous silicon has another 13%. The main endeavor is to reduce cost. Present trends in the crystalline field are reviewed. The conventional technology still has significant potential for cost reduction but this comes only with increasing volume. A problem to be solved is the supply of solar-grade silicon material. Other future possibilities include thin film crystalline silicon on different substrates. Because of the low absorption coefficient of silicon light trapping is required. True thin film materials need only 1–2 μm of material. Amorphous silicon, copper indium diselenide (CIS) and CdTe are hopeful approaches for very cost-effective solar cells. Some other, more speculative materials and concepts are described at the end of this paper

The local prebreakdown behavior of a damage etched multicrystalline silicon solar cell produced from virgin grade feedstock was characterized. At the position of micrometer-scaled prebreakdown sites, which correlate with recombination active defects found along grain boundaries, micro-x-ray fluorescence mappings revealed the presence of Fe precipitate colonies. These measurements represent direct evidence that transition metal clusters lead to decreased breakdown voltage and cause soft diode breakdown.

The use of transparent sheets doped with fluorescent dyes for the concentration of sunlight was suggested first in the 1970s [1, 2]. The principle itself is much older; it was first used in scintillation counters for atomic physics [3, 4]. Although significant advances were made in early work, after some years further progress was limited by the materials available at that time — in particular the dyes — and interest was dormant for decades. Only recently new progress in materials as well as theoretical advances rekindled interest. In this article the historic work and the present state of the art will be reviewed.

Fluorescent planar collector-concentrators are a new principle for solar energy conversion into electrical and thermal energy. Collection and concentration of direct and diffuse radiation is possible by the use of a stack of transparent sheets of material doped with fluorescent dyes. In combination with photovoltaic cells this type of collector offers the advantage of separating the various fractions of light and converting them with solar cells with different bandgaps. Theoretical estimates of the system, efficiency, real collector properties and first experimental results are given.

The paper reviews the history, the present status and possible future developments of photovoltaic (PV) materials for terrestrial applications. After a brief history and introduction of the photovoltaic effect theoretical requirements for the optimal performance of materials for pn-junction solar cells are discussed. Most important are efficiency, long-term stability and, not to be neglected, lowest possible cost. Today the market is dominated by crystalline silicon in its multi crystalline and monocrystalline form. The physical and technical limitations of this material are discussed. Although crystalline silicon is not the optimal material from a solid state physics point of view it dominates the market and will continue to do this for the next 5-10 years. Because of its importance a considerable part of this review deals with materials aspects of crystalline silicon. For reasons of cost only multicrystalline silicon and monocrystalline Czochralski (Cz) crystals are used in practical cells. Light induced instability in this Cz-material has recently been investigated and ways to eliminate this effect have been devised. For future large scale production of crystalline silicon solar cells development of a special solar grade silicon appears necessary. Ribbon growth is a possibility to avoid the costly sawing process. A very vivid R&D area is thin-film crystalline silicon (about 5-30 mu m active layer thickness) which would avoid the crystal growing and sawing processes. The problems arising for this material are: assuring adequate light absorption, assuring good crystal quality and purity of the films, and finding a substrate that fulfills all requirements. Three approaches have emerged: high- temperature, low-temperature and transfer technique. Genuine thin-film materials are characterized by a direct band structure which gives them very high light absorption. Therefore, these materials have a thickness of only one micron or less. The oldest such material is amorphous silicon which is the second most important material today. It is mainly used in consumer products but is on the verge to also penetrate the power market. Other strong contenders are chalcogenides like copper indium diselenide (CIS) and cadmium telluride. The interest has expanded from CuInSe/sub 2/, to CuGaSe/sub 2/, CuInS/sub 2/ and their multinary alloys Cu(In,Ga)(S,Se)/sub 2/. The two deposition techniques are either separate deposition of the components followed by annealing on one hand or coevaporation. Laboratory efficiencies for small area devices are approaching 19% and large area modules have reached 12%. Pilot production of CIS-modules has started in the US and Germany. Cadmium telluride solar cells also offer great promise. They have only slightly lower efficiency and are also at the start of production. In the future other materials and concepts can be expected to come into play. Some of these are: dye sensitized cells, organic solar cells and various concentrating systems including III/V-tandem cells. Theoretical materials that have not yet been realized are Auger generation material and intermediate metallic band material.

Die Photovoltaik ist eine Energiequelle, die heute nur einen geringen Beitrag zur Stromerzeugung leistet. Sie wird heute vor allem wegen ihrer Zukunftsaussichten gefordert. Ich mochte in meinem Vortrag mit generellen Aspekten der Photovoltaik beginnen, dann kurz auf Technologien eingehen, des weiteren die Auswirkungen des neuen Einspeisegesetzes und schlieslich auch die Kostenreduktionsaussichten und Potentiale der Photovoltaik erlautern. Ich beginne mit einer Zusammenstellung der Vorteile und Probleme der Photovoltaik.

Economic operation of high-efficiency concentrator solar cells requires solar concentration ratios which up to now can only be achieved with two-axis tracking. In this paper we present a two-stage concentrator approaching concentration ratios up to 300X while being tracked around only one polar axis. Its principle is as follows: A parabolic trough focusses the direct solar radiation onto a line parallel to the polar tracking axis. The half rim angle of this first concentrating stage is chosen to be equal to the sun's maximum declination of 23.5 degree(s). The second stage consists of a row of dielectric, nonimaging 3D-concentrators, which couple the concentrated light directly into square solar cells. The proposed design makes use of the limited divergence of +/- 23.5 degree(s)) in the NS-direction which still can be concentrated by a factor of n/sin(23.5 degree(s)). The performance of the system depends sensitively on how well the angular acceptance characteristic of the second stage matches with the square-shaped angular irradiance distribution in the focal line of the parabolic trough. A new concentrator profile has been found that exhibits an almost ideal square acceptance characteristic with a very sharp cut-off. It is longer than the standard CPC and its slope is reduced towards the exit of the concentrator. A prototype two-stage concentrator has been constructed with a total geometrical concentration of 214X. In outdoor measurements a total optical efficiency of 77.5% was obtained.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In Kapitel 9.6 wurde das Prinzip der lichtdurchlassigen oder transparenten Warmedammung beschrieben und Mesergebnisse erster Experimente vorgestellt. Zwischenzeitlich wurden eine Vielzahl transparent warmegedammter Fassaden (TWD-Fassaden) realisiert. Eines der wissenschaftlich sicher interessantesten Projekte ist das Energieautarke Solarhaus, das Ende 1992 fertiggestellt wurde /70/71/. Der gesamte Energiebedarf des Hauses wird durch die auf die Gebaudehulle auftreffende Sonnenstrahlung gedeckt. Die Heizwarme wird bis auf einen berechneten Zusatzenergiebedarf von 300 kWh pro Heizperiode direkt uber die sudorientierten Fenster und TWD-Elemente bereitgestellt.

Sowohl der Weltenergiebedarf als auch der Energiebedarf der Bundesrepublik Deutschland stiegen in der Vergangenheit bis 1973 um etwa 5 % pro Jahr. Abb.1.1 zeigt diese Entwicklung fur den Weltprimarenergiebedarf. Zusatzlich ist hier das Anwachsen der Weltbevolkerung eingetragen. Man erkennt deutlich den starken Anstieg des Energiebedarfs in der Nachkriegszeit, der eng mit dem steigenden Lebenskomfort in der westlichen Welt gekoppelt und nur unwesentlich durch das Wachstum der Bevolkerung in der Dritten Welt bedingt ist. Mit steigender Industrialisierung der Entwicklungslander ware ein weiterer drastischer Anstieg des Weltenergiebedarfs zu erwarten. Abb. 1.2 gibt die Entwicklung des realen Primarenergieverbrauchs in der Bundesrepublik wieder. Ab 1973, dem Zeitpunkt der ersten Olkrise, unterlag der Verbrauch der Primarenergietrager starken Schwankungen und blieb im wesentlichen konstant. Hier zeigt sich bereits der enge Zusammenhang zwischen Energiepreis und Energieverbrauch: Die vielfaltigen Moglichkeiten der Energieeinsparung werden umso starker genutzt, je starker die Anreize durch hohe Energiekosten gegeben sind.

Fur die Nutzung von Solarenergie in der Praxis ist es notwendig, das eine Vielzahl von Einzelvoraussetzungen erfullt werden. So erfordert ein Kollektorsystem zur Erzeugung warmen Brauchwassers z.B.: die Wahl geeigneter Kollektoren bezuglich Wirkungsgrad und Arbeitstemperatur, die Festlegung des Speichervolumens einschlieslich der Warmedammung, die Regelung des Kollektor-Speicher-Systems, die Anpassung des Kollektor-Speicher-Systems an die architektonischen Gegebenheiten und das bereits meist vorhandene Heizungssystem.

Bei vielen in der Vergangenheit gebauten Solaranlagen wurde festgestellt, das sie nicht wirtschaftlich waren. Nun ist jedoch Wirtschaftlichkeit kein sehr einfach zu definierender Begriff, wie in diesem Kapitel klar werden wird. Wegen der zentralen Bedeutung der Wirtschaftlichkeit fur Solaranlagen ist es erforderlich, sich damit auseinanderzusetzen und insbesondere die gebrauchlichen Methoden der Ertragsberechnung kennenzulernen. Zunachst ist es notwendig, zu erkennen, das die ubliche betriebswirtschaftliche Methode nur einen Teilaspekt der Gesamtwirtschaftlichkeit betrachtet. Nicht berucksichtigt werden folgende Gesichtspunkte: 1. Umweltaspekte: Der Umstand, das eine Solaranlage ohne negative Auswirkungen auf die Umwelt Energie liefert, bleibt auserhalb der Betrachtung. Allerdings sind staatliche Masnahmen, wie steuerliche Vorteile und Zuschusse, auch dadurch motiviert. 2. Volkswirtschaftliche Aspekte: Solarenergie verringert die Abhangigkeit von importierten Energietragern und reduziert die Inanspruchnahme erschopfbarer Energiequellen. Diese Beitrage, dei sehr schwer quantitative zu beziffern sind, warden ebenfalls durch die oben erwahnten staatlichen Fordermasnahmen zum Teil berucksichtigt.

Die Grundlage aller Solarenergienutzung ist die Wechselwirkung des Strahlungsfeldes der Sonne mit einem materiellen Empfanger. Zur Charakterisierung und zum Verstandnis der physikalisch-optischen Eigenschaften von Strahlungsfeld und Materie bedarf es einiger Begriffsbestimmungen und der Erlauterung der wichtigsten Zusammenhange.

Die in Kapitel 4 abgeleiteten Grenzen fur den Umwandlungswirkungs-grad von Sonnenenergie in Warme und mechanische Energie zeigen, das zum einen die Konzentration des Lichtes und zum anderen das spektrale Verhalten des Absorbers die entscheidenden Kenngrosen eines solaren Wandlersystems darstellen. Im nachfolgenden Kapitel sollen die theoretischen und experimentellen Grenzen fur die Konzentration von Licht sowie die verschiedenen Herstellungsverfahren selektiver Schichten vorgestellt werden.

Wie bereits in den Kapiteln 1 und 9 gezeigt, liegt das groste Potential zur Nutzung der Sonnenenergie in unseren Klimazonen im Bereich der Heiz- und Brauchwasserwarme. Neben dieser Niedertemperaturanwendung gibt es im Prinzip auch Hochtemperaturanwendungen in Solar-turmkraftwerken, diese werden jedoch in unseren Klimabereichen sicher nie eine grose Rolle spielen und werden daher in diesem Buch nicht detailliert behandelt /50/51/.

Die Methoden zur Messung von Strahlung unterscheiden sich entsprechend den Eigenschaften der Strahlung. Fur die Nutzung der Sonnenenergie sind es besonders zwei Kenngrosen, die man exakt kennen mochte. Dies ist zum einen die Intensitat des direkten Sonnenlichtes I sowie die Intensitat der gesamten Globalstrahlung G, die sich wiederum aus dem diffusen und dem gerichteten Anteil zusammensetzt.

Fluorescent planar concentrators have been discussed in the literature for about five years. The advantages of the system are the ability to concentrate both direct and diffuse light, and variability in transparency which offers the possibility of a manifold of hybrid applications. The best total efficiency measured for electrical conversion with a stack of two plates is 4%, the highest energy concentration factor at the output edge was ten. In addition the latest results for thermal conversion are given. The highest stagnation temperatures up to now are in the range of 550°C. Theoretical calculations of the limitations on the concentration factor are presented. The lifetime of the total system could be improved, so the first commercial applications are now being planned.

Fluorescent planar collector-concentrators are a new idea for the conversion of solar energy into electrical and thermal energy. The collection and concentration of direct and diffuse radiation is possible by using a stack of transparent sheets of material doped with fluorescent dyes. In combination with photovoltaic cells this type of collector offers the advantage of separating the various wavelengths of light and converting them using solar cells with different band gaps. Theoretical models of the system, the efficiency, the real collector properties and the experimental results are reviewed.