• Energy Research

Abstract Solar updraft power technology will generate highly sustainable electricity in world-wide deserts in future. It will overcome certain deficits of present renewable energy technologies. In several countries, such power plants are in pre-design stage, forming an important contribution of structural engineering to future energy supply. The present manuscript starts with the working principles of solar updraft power plants, followed by explaining climatic and wind-technologic design assumptions. Then the central solar updraft chimney – the power tower – is treated in more detail: a thin ring-stiffened RC shell of extreme height, forming the utmost structural challenge of such plants. This part is followed by technical requirements for the collector constructions, by far the largest glass-covered areas ever built, and of the wind-loading on the glazing. Then, further design aspects are extracted by the durability requirements for at least 100 years of operation in extreme desert climates. The paper closes with some cost estimates for the generated electricity.

Abstract Concrete shell collectors offer an alternative to conventional parabolic trough collectors. The principle design concept is derived from existing barrel rooves that effectively bridge large spans in halls or buildings with minimum material usage. The concrete troughs merge the bearing structure and mirroring surface to just one shell of a few centimeters. They are made of high-strength concrete and track the sun via pure axial rotation or lateral movements that avoid any lifting works. In the present contribution, basic constraints in materials, geometry, and static calculation are derived and converted into a framework of possible designs. This contribution thereby presents a survey of concepts that range from small-scale prototypes to full-scale realizations of 140 m2 apertures and large-aperture concepts with a 10 m width. Design concepts with bearing and drive systems as well as optimization-based form findings are introduced to elaborate shells of minimum weight with solid sections, stiffeners, and hollow cores.

Abstract Up to now modules of parabolic trough collectors are usually made from steel frames carrying curved mirror elements. With these, the crucial disadvantage is the separation between supporting structure and reflecting surface. Here, the independent parts are merged to a very thin and light-weight but solid concrete shell having a highly precise inner surface that serves as substrate for mirror elements. Since concrete is originally very brittle and weak in tension, a special high-strength concrete with remarkable tensile strength is developed. Based on numerical analyses employing linear elastic material behaviour and limiting stresses below the tensile strength, two alternative module candidates have been designed with geometries close to already existent modules. Their design accounts for operation states by means of analytically and experimentally derived actions and constraints as well as time-dependent material effects. A first prototype on novel concrete supports demonstrates general feasibility. Highly accurate surfaces of the concrete shell, having a few centimetres of thickness only, prove structural stiffness and full optical efficiency in tests employing digital close range photogrammetry and analytically derived precision rates based on the surface slope error.

AbstractSolare Aufwindkraftwerke stellen eine Technologie zur Erzeugung solar‐basierter elektrischer Energie in den Wüsten unserer Erde dar, die verschiedene Defizite bisheriger Konzepte überwindet. Weltweit sind derartige Kraftwerksprojekte in der Vorplanung. Der vorliegende Beitrag beginnt mit der Skizzierung des Arbeitsprinzips solarer Aufwindkraftwerke. Es folgen klimatologische und wind‐technologische Planungsvoraussetzungen, wobei die Windlastermittlung im Grenzschicht‐Windkanal näher begründet wird. Sodann wird der zentrale Solarkamin behandelt, eine dünne, ringversteifte Stahlbetonschale extremer Höhe, die größte bautechnische Herausforderung dieses Kraftwerkstyps. Weiter folgt die Erläuterung grundlegender bautechnischer Anforderungen an den Solarkollektor, der die größte jemals überglaste Fläche darstellt, sowie der Windeinwirkungen auf die Verglasung und die Tragkonstruktion. Einen wichtigen Aspekt bilden Anforderungen an die Dauerhaftigkeit der eingesetzten Baustoffe für eine mindestens 100‐jährige Nutzung des Turms in einem extremen Wüstenklima. Der Artikel endet mit Kostenschätzungen für den produzierten Strom und einem Technologieausblick.Solar updraft power plants: A structural engineering contribution for sustainable and economic power generationSolar updraft power technology serves to generate electricity in the world‐wide deserts, overcoming several deficits of present renewable energy technologies. In several suited countries such power plant projects are in preparation. The present contribution starts with an explanation of the working principle of solar updraft power plants, followed by their climatic and wind‐technologic design assumptions, terminated by the wind‐load determination in boundary layer wind‐tunnels. Then the central solar chimney – the power tower – will be treated, a thin ring‐stiffened RC shell of extreme height forming the utmost structural challenge of such power plants. This part is followed by an explanation of technical requirements for the collector construction, which represents by far the largest glass‐covered area ever built, and of the wind loading at the glazing and the supporting structure. Further important aspects are formed by the durability requirements of the applied construction materials for at least 100 years of service‐duration of the tower in extreme desert climates. The paper closes with cost estimates for the generated electric power and with a technology outlook.

Abstract Green energy structures are subject of on-going optimization, which involves the shape contours and the wind sensitivity of the structure. Current developments of parabolic troughs show that the aperture width increases to save assembling and operating costs to be more competitive on market compared to conventional power plantsis increased. Alternative structural concepts based on thin-walled, high-performance concrete shells combine structural stiffness and low self-weights despite large apertures to high-potential technologies. This paper presents wind tunnel tests on 3D-printed shell-like parabolic trough collector modules with an aperture width of 10 m and a module length of 30 m. Experimental investigations are performed on solitary modules (1:75 and 1:150) and on modules arranged in arrays (1:150). Pressure, pitching moment and force coefficients are determined for various pitch angles and wind directions. The coefficients are applicable to full-scale large-aperture collector modules. Subsequent numerical analysis shows trends towards effects of e.g. scaling, shadowing in solar fields regarding maximum internal forces for operation and stow mode. Results reveal that wind directions of 0 ° / 30 ° / 150 ° / 180 ° and pitch angles of 0 ° / 45 ° / 60 ° are most significant. By means of the numerically determined internal forces and identified shadowing effects the solar field can be categorized into four characteristic sectors in which trough modules are mainly equally stressed.