Applied Mechanics and Materials Vol. 283

Abstract: The solar updraft tower (SUT) concept is an exciting renewable technology with the potential to deliver high power output. A comprehensive SUT sizing computer model has been developed to determine power output and thus appropriate system dimensions for different ambient conditions. The efficient thermodynamic model performs steady-state macro-scale simulations incorporating radiation and natural convection heat transfer mechanisms. The solar collector is simulated as a discretised, axisymmetric, radial system composed of thermal components. A set of linear simultaneous equations describes the heat exchanged between these components and is solved by matrix inversion. The short computation time of the model makes it ideal for parametric analysis of SUT plants across a range of dimensions. The thermodynamic performance of the collector proves to be a limiting factor of system power output. Results from the model show that for given chimney dimensions, there is a maximum collector size beyond which no further useful heat is added to the air as the system has reached thermal equilibrium. Therefore the only way to increase power output further is to increase chimney height and diameter as well as extending the collector diameter.

Abstract: In the essay, two numerical analog study models were developed using compressible and incompressible gas models by focusing on the research of the Manzanares solar chimney power station in Spain. The simulation distributing images of air pressure, speed, temperature and density in the system were given. The comparative analysis of the results of these two models showed that in the simulation of small scale solar chimney power system the error caused by ignoring the air compressibility did not exceed 2%.

Abstract: The compressible transient model of solar chimney power plant system was proposed. It was added to the pressure equation and the ideal gas state equation basis on the heat balance equation for the solar collector model. The air flow station can be easily calculated with the improved model. The results of dynamic changes of the total pressure difference calculated in the model were in good agreement with the given actual measured values in references. The solar chimney model was considered the influence of fluid pressure on the density. The influence of the structural chimney on the chimney efficiency was analyzed with the established model. It was shown that the chimney efficiency changes significantly with the chimney height and its diameter. The chimney efficiency was decreased with a convergent chimney shape while increased with the divergent one. When the tilt angle of chimney reached a peak and then further increased, the chimney efficiency was the constant. These results will provide the important reference to improving the system efficiency.

Abstract: Solar updraft chimneys (SUCs) form as engines of solar updraft power plants tower-like shell structures of extreme height with rather thin shell walls, similar to high chimneys comprising multiple flue gas ducts. The height of pre-designed SUCs presently reaches up to 1000 m. Thus they are exposed chiefly to extreme wind-loads and thermal actions from the internal flow of warm air. As first design attempt, the structural analysis of solar chimneys generally is carried out by linear elastic models. For optimization, the typical shell-like wind stresses have to be constraint towards a more beam-like response behavior, approaching as far as possible linear stresses over the entire chimney circumference. This requires rather strong ring stiffeners, either as spoke-wheels in the designs of sbp (Schlaich Bergermann and Partners) or as external stiffeners in the designs of K&P (Krätzig and Partners). Both alternatives require considerable construction efforts leading to high investment costs. There exists an interesting simplification of this stiffening, namely applying to the SUC shell relatively soft external rings, and admitting large-widths cracking in the limit state of failure. This cracking constraints and equalizes the meridional stresses over the chimney’s cross-section, saving large amounts of reinforcement steel in the SUC. The design requires materially nonlinear analyses to verify the internal forces under crack-formations. The manuscript will derive this concept and demonstrate the crack analysis by example of a 750 m high solar chimney.

Abstract: The structure of Solar Updraft Towers is basically a circular cylinder, which may turn into a hyperboloid at lower levels in order apply benefits of shape strengthening. The height of the tower is up to 1.5 km and it is usually designed as a thin reinforced concrete shell. The wind action is the main natural hazard, which plays a decisive role for the feasibility of the technology. An extensive wind tunnel investigation has been recently performed at WiSt laboratory at Ruhr-University Bochum (Germany) and at Criaciv laboratory at University of Florence (Italy). The tests highlighted in no-efflux conditions (out-of-use of the power plant) a new phenomenon egarding cross-wind loads, induced by a bi-stable and asymmetric flow distribution. It is created by compartments between stiffening rings along the tower and enhanced by a strong interaction with free-end flow structures at the top of a finite length circular cylinder. A proper positioning of the rings should allow to avoid this phenomenon.

Abstract: A 100MW solar chimney is high as one thousand meters, belonging to ultra-high-rise structure. Considering the complicated load condition, the large scale and long period of construction process, construction analysis is important to the structure. Using element birth and death technology in ANSYS, the whole construction process is simulated in this paper. Numerical results indicate that the deformation and internal force of the structure change a lot during the construction process. Great differences exist in property and magnitude between construction status and design status. To investigate the stability of the structure under wind and gravity load, the first eigen buckling mode with a value of L/300 and construction deformation are considered as initial imperfection respectively. The results show the ultimate bearing capacity of the structure considering construction deformation is lower than that considering the first-order initial imperfection.

Abstract: The characteristics of time-varying mean wind pressure distribution on the surface of solar updraft tower (SUT, an axisymmetric structure) in a translating thunderstorm downburst is discussed based on revised Chen and Letchford’s empirical model, in which Wood et al.’s empirical model for vertical profile of radial velocity, revised Poreh and Cermak’s empirical model for horizontal profile of radial velocity by considering the full time variation of downburst jet intensity, and Holmes and Oliver’ empirical model for the time function are utilized. The results show that the time histories of mean wind pressures at the points around the circular surface are complex due to the moving of stagnation points for the SUT. The time fluctuation is driven by the summation of the moving of downburst and the characteristics of pressure distribution on the SUT.

Abstract: Until today, the biggest solar updraft tower power plant ever built and tested was the 50 kW Spain plant in Manzanares. Since then no real plant has been built, whilst many grand plans have been drawn and given up. Solar Wind Power (SWP) is an energy form in search of its destiny: it is time to find a real market for SWP. This market is currently forming and we call it ‘evening power’. SWP transforms sunlight into heat, heat into hot artificial wind, and this wind into electricity. The three steps of transformation allow SWP to delay the generation of electricity from the daily peak of solar radiation into the evening. In the evening, the greater power demand cannot be met with other renewable CO2-free energies like wind and photovoltaic. SWP has been tested once, thirty years ago - it is time for a second trial: the Intermediate Solar Wind Power Plant (ISWiPP). The goal is to develop, test and measure SWP’s potential for heat-storage and evening power output. The technology for constructing a light steel-tower with a concrete base will be tested under real-life conditions and technologies for heat storage will be developed. The ISWiPP will enable investors to prepare for large SWiPP with hybrid (concrete and steel) towers of 1000 m height or more. This development growth path is realistic and adequate to overcome the current impasse. Like all CO2-free energy forms SWP depends very much on the location chosen. Locations with strong winds, or sand- and dust-storms, are inadequate for SWP. A good location for a SWiPP is a hot, flat and rocky desert, not too far from a city with a demand for evening power.

Abstract: The upfront cost and technical difficulties of constructing a Solar Updraft Tower is its current bottleneck. Based on the case study of Wuhan New Energy Institute headquarters, this paper proposes to integrate an urban Solar Updraft Tower with a hi-rise building design. The integrated design can reduce the construction cost greatly: the solar chimney integrated with the elevator shaft can avoid large investment on a detached chimney structure; the heat collector can be integrated with the roof garden to provide shaded public space. This type of small-scale, distributed Solar Updraft Tower is relatively low-cost and easy promoting. Potentially, it can build up a distributed energy system as a supplement for the power grid. Furthermore, it can provide valuable experimental data for future researches on large scale Solar Updraft Towers.