Updraft Tower Research Articles

Emergy and Sustainability Ternary Diagrams of Energy Systems: Application to Solar Updraft Tower

To facilitate sustainable energy development, one has to understand the limited availability of nonrenewable energy resources, and the ability of the earth to renew or recover. Emergy is an instrument that measures environmental loading, ecological economics, and regional sustainable development. In this study, emergy indicators are calculated to investigate the sustainability of solar updraft tower (SUT). SUT produces energy from the hot air, utilizing a combination of a solar collector, central tower, and air turbines. The results demonstrate that the sustainability of SUT grew as the size of the plant increased. Further, emergetic ternary diagrams are drawn to facilitate the comparison between SUT and various technologies. The resources-use efficiency of wind energy and SUT, 200 MW is found to be the lowest among all energy technologies presented in this research. Scenario analysis is performed to explore the future optimization directions. The results demonstrate that the development direction of SUT systems should mainly focus on reducing the materials demanded by the manufacturing and construction of its solar collectors. This study aims to demonstrate the value of emergy as a powerful instrument for drawing long-term sustainable strategies in energy markets for a greener tomorrow.

Ma’an – a new approach to the autonomous building

The paper describes the general principles of autonomous building operation. Derived from those, a building concept, which ensures energy and water self-sufficiency, has been presented. Another important benefit is the minimization of a carbon footprint – both during construction and operation. The proposed solutions are based on a system combining the technology of a cooling tower and a solar updraft tower enhanced with reverse osmosis technology and others. All of this has been achieved by creating an original architecture that matches its place of origin and functions.

Performance evaluation of solar vortex engine and optimization of number of air entry slots and turbine location

ABSTRACT Solar vortex engine (SVE) is one of the novel alternative energy concepts which uses solar energy for creating artificial vortices. The working principle of SVE is the same as the solar updraft tower (SUT) plant. In the present study, a 3D computational model of SVE was studied to evaluate the flow parameters and power potential. The effect of the number of air entry slots (AESs) which is varied from 6 to 12 and the location of the turbine were studied and optimized. A turbulent, renormalization group (RNG) k-ɛ model was used to solve the governing equations. The flow parameters such as velocity, temperature and dynamic pressure for the optimum SVE with 8 AESs were 1.42 ms−1, 311.1 K and 1.58 Pa, respectively. The optimum height for the turbine was 0.702 m from the base plate (0.1 m from the top plate) and so that the turbine can harness maximum energy. The theoretical and actual powers for the optimum case (AESs of 8 and the turbine at 0.702 m) were 3.45 and 2.3 W, respectively. The study proved that SVE is a potential choice to replace the chimney of a solar updraft tower (SUT) plant for electricity generation.

Performance analysis of solar updraft tower using Ansys fluent

The solar updraft tower (SUT) is a renewable energy power plant design concept for generating electricity by utilizing convective air flow due to low temperature heat absorption from incoming solar radiation. A parametric study on the performance power output of the SUT at various canopy angles and different insolation levels were carried out to investigate the relationship between them with respect to key parameters i.e. in terms of updraft tower velocity, temperature, pressure and height to choose turbine position for maximum air velocity absorption and energy conversion using Ansys-fluent software version 15 for analysis. The results obtained were analyzed comparatively to draw conclusions. The results identified using simulation software mentioned above were validated with earlier results and identified significant improvement in the power generated at various collector angles, when compared with the earlier works on SUT.

Estimation of flow parameters and power potential of solar vortex engine (SVE) by varying its geometrical configurations: A numerical study

Solar vortex engine (SVE) is a novel concept for creating artificial vortices and airflow using solar energy. The working principle of SVE is similar to the solar updraft tower (SUT) plant, but SVE replaces the chimney of SUT plant. SVE consists of air entry slots (AES), guide blades and top and base plates having an outlet and base holes, respectively. In the present study, a 3D model of SVE with an external bounding structure (EBS) was developed to evaluate the flow parameters and visualize the flow and vortex generation inside the domain. The flow parameters were estimated by varying the top-hole diameter (0.2–0.5 m) and increasing inlet velocity at AES (0.2–0.7 m/s). The increase in top hole diameter from 0.2 to 0.5 m, flow parameters enhanced significantly and reached a maximum at 0.3 m and after it decreased. Higher inlet air velocity at AES enhanced flow parameters significantly. The optimum height was 0.702 m from base plate (0.1 m from the top plate) as it had the maximum velocity of 4.4 m/s and vorticity of 73.9 s−1, so that a turbine can be fixed at this location to harness maximum energy. The average velocity, temperature, dynamic pressure, theoretical and actual powers of SVE with EBS for optimum case (top hole diameter of 0.3 m, inlet velocity at AES of 0.7 m/s) were 1.4 m/s, 311.1 K, 1.6 Pa, 3.5 and 2.3 W, respectively. The preliminary study results shown that, SVE is one of the potential options to replace the chimney of SUT plant for generating electric power.

Numerical analysis on flow and performance characteristics of a small-scale solar updraft tower (SUT) with horizontal absorber plate and collector glass

A numerical analysis has been performed to examine and assess the flow and performance characteristics of the solar updraft tower (SUT) power plant. A realistic domain (geometry and mesh) of the flow model was generated and simulations were run with the help of ANSYS FLUENT 16.0 CFD package. A turbulent, realizable (k–e) and discrete ordinates radiation techniques were taken into consideration to solve the governing equation. The maximum air velocity of 3.27 m s−1 was noticed at 200 mm above the chimney base (CB). The mean velocity at CB was 1.8 m s−1. The highest air temperature of the absorber plate was 323 K, and it was at the centre of the absorber plate. The average air temperature inside the setup was 306.7 K. The power generated from the plant, chimney efficiency and overall efficiency of the SUT setup were evaluated to be 0.38 W, 0.018% and 0.005%, respectively. 24% velocity increase and 70% power output increase were noticed when solar flux increased from 650 to 1150 W m−2. Exergy analysis was performed. The results were compared with existing studies and were found to be in good agreement.

An Ignored Wind Generates More Electricity: A Solar Updraft Tower to a Wind Solar Tower

A solar updraft tower is one of the wind power generation plants which utilizes solar energy. The purpose of this study was to ascertain whether the tower was also able to utilize crosswind energy. Wind tunnel experiments and numerical simulations were conducted simulating the crosswind. The results showed that suctioned updraft speed in the tower was proportional to the crosswind speed, and its conversion rate depended on the tower configuration. A diffuser-shaped tower with a vortex generator achieved to produce the updraft whose speed exceeded the crosswind speed. It was due to the low pressure created by the vortex atop the tower and to the diffuser effect. The crosswind utilization enables the simple power generation device to generate electricity during the night, and the hybrid utilization of renewable energies contributes to the increasing wind energy market.

3D numerical study on estimating flow and performance parameters of solar updraft tower (SUT) plant: Impact of divergent angle of chimney, ambient temperature, solar flux and turbine efficiency

A 3D numerical model was made to analyse the effect of divergence angle of chimney (Φch), ambient temperature (Ta), solar flux (I) and turbine efficiency (ηtur) on wind flow and performance parameters of a solar updraft tower (SUT). A parametric study was carried out by varying Φch from 1 to 5° for different I (600–900 W/m2) and the results were compared with results for existing cylindrical chimney SUT (CC-SUT) plants. The range of Ta selected was 293–318 K and ηtur was 0.54–0.9%. Five different configurations of divergent chimney SUT (DC-SUT) plants were modelled. It was noticed that at Φch of 2°, the average velocity of air at chimney base was enhanced by 58.9% compared to CC-SUT plant. The average absorber plate temperature increased from 316.4 to 332.85 K with an increase in I from 600 to 900 W/m2 for Φch of 2°. The maximum overall efficiency, theoretical and actual power output of the DC-SUT plant were 0.0307%, 3.99 W and 2.67 W, respectively. The exergy of DC-SUT was 58% higher when Φch was increased from 1 to 2° at I = 900 W/m2. Correlations were generated to calculate performance parameters as functions of geometrical parameters.

Computational investigation of solar updraft tower for power generation in sultanate of Oman

The current study is aimed at harnessing solar power through solar updraft tower (SUT) and explored the local environmental factors conducive to SUT installation. The SUT collects solar insolation to raise the air velocity, which is then allowed to pass through a ducted turbine. An alternator is installed with the air turbine to generate electricity. The study presents a performance analysis of SUT based on local thermal radiation and wind velocity. Three-dimensional numerical modelling of SUT is carried using computational fluid dynamics (CFD) solver. The model is validated with the experimental results available in the open literature. The collector temperature profile obtained through CFD modelling matches well with the experimental results. A maximum temperature rise of 20 ºC was ob-served in the collector modelled and solved numerically using CFD solver. The air velocity increases as the flow move from the collector periphery to the center of the SUT and reach to its maximum just before the center of the SUT. However, for the chimney, the temperature was observed to be increased continuously due to its continuous heating through the chimney walls, which receives solar radiation. The performance of SUT is examined with the change in inlet air velocity based on the local conditions in the Sultanate of Oman.

Evaluation of the experimental data to determine the performance of a solar chimney power plant

Solar chimney power plants play an important role in the field of renewable energies. The present study undertaken is related to design a solar updraft tower with all the variable geometric parameter in consideration and to optimize the performance for solar chimney power plant by means of experimental data as well as computer simulation with the formulation an approximate mathematical model. The components of the solar chimney power plant include the collector sheets, chimney and turbo generator. Solar radiation is transferred to the collector plates, air under the solar collector is heated up which is sucked vertical chimney located at the centre of the vertical cylindrical shell. The updraft is formed which drives the turbine and generator to produce the electricity with low cost as compared to other methods.

NUMERICAL ANALYSIS OF SOLAR TOWER SYSTEM UTILIZED WITH FLAT PLATE AND POROUS ABSORBER

The performance of solar updraft tower investigates numerically by comparing between two solar collectors with and without porous absorber flat plate. In this study, copper metal foam (10 and 40) PPI at the same porosity (0.9) are used as an absorber plate. The effect of the absorbing porous medium is studied to increase the air flow towards the updraft tower by tilting of the porous absorber at an angle (2° and 6°) from the horizontal line for (10 and 40) PPI and compared with the horizontal absorber flat plate. To simulate the physical quantities inside the porous medium, at steady state, symmetry, three dimensional, Darcy model and energy numerical model with local thermal equilibrium (LTE) assumption are adopted and numerical models is approximated by a RNG (Re-Normalization Group) k- ϵ turbulent model and discrete ordinates (DO) radiation model equations. The numerical study is analyzed by Fluent software package (version 18.2) to solve the governing equations. The results showed that the tilting of a porous absorber plate at an angle (2° and 6°) from the horizontal line lead to increase in the mass flow rate inside the solar updraft tower and the maximum performance is found by using 40 PPI at tilt angle 2°.The performance of solar updraft tower investigates numerically by comparing between two solar collectors with and without porous absorber flat plate. In this study, copper metal foam (10 and 40) PPI at the same porosity (0.9) are used as an absorber plate. The effect of the absorbing porous medium is studied to increase the air flow towards the updraft tower by tilting of the porous absorber at an angle (2° and 6°) from the horizontal line for (10 and 40) PPI and compared with the horizontal absorber flat plate. To simulate the physical quantities inside the porous medium, at steady state, symmetry, three dimensional, Darcy model and energy numerical model with local thermal equilibrium (LTE) assumption are adopted and numerical models is approximated by a RNG (Re-Normalization Group) k- ϵ turbulent model and discrete ordinates (DO) radiation model equations. The numerical study is analyzed by Fluent software package (version 18.2) to solve the governing equations. The results showed that the tilting of a porous absorber plate at an angle (2° and 6°) from the horizontal line lead to increase in the mass flow rate inside the solar updraft tower and the maximum performance is found by using 40 PPI at tilt angle 2°.

Additive Aerodynamic and Thermal Effects of a Central Guide Post and Baffle Installed in a Solar Updraft Tower

The solar updraft tower (SUT) is a renewable power generation system that uses natural air convection from the ground that is heated by solar radiation. Placing flow-guide structures within the collector of the SUT can enhance aerodynamic performance, and hence, increase the kinetic power. Here, we propose a central guide post (CGP) structure in the SUT that controls updraft flow. The effect of the CGP geometry on aerodynamic performance was investigated using computational fluid dynamics modeling (ANSYS Fluent 19.2) to show that a CGP can play a positive role by preventing stagnation of the airflow at the center of the collector, resulting in increased kinetic power output (up to ~2%). However, excessively long CGPs retarded airflow, resulting in a dramatic decrease in kinetic power output. We also investigated a system with both a CGP (to improve aerodynamic performance and minimize energy loss) and a heat-exchange baffle (to maximize thermal energy transfer). When installed with a proper distance between components, the CGP and baffle showed a combined effect of increasing the kinetic power output by up to 10%. We expect that our proposed method using the CGP and baffle system will contribute to the development of better future SUT technology.

Entropy generation analysis of convective airflow in a solar updraft tower power plant

AbstractThe main objective of this numerical investigation is to interpret the entropy generation for free convection airflow in a solar tower updraft system. The ground surface is subjected to uniform hot temperature and the collector cover is maintained at lower constant temperature while the chimney wall is adiabatic. Two dimensionless equations of steady laminar free convective airflow are discretized using the finite volume approach. Numerical solutions were accomplished for different values of the Rayleigh number. Results are given in terms of isotherms, velocity magnitude, local entropy generation associated with thermal and fluid friction, local total entropy generation and local Bejan number contours for Rayleigh number ranging between 103 and 108. The reported results show that thermal and frictional irreversibilities are proportional to the Rayleigh number. Also, it was found that, at lower Rayleigh, total irreversibility is attributable to the thermal irreversibilities and occurs essentially in the collector section. At higher Rayleigh, frictional irreversibilities are increased significantly and become the dominant source of irreversibility in the solar tower, and the chimney section is the main contributor in the total irreversibility in the system.

Design, Fabrication and Testing of Solar Updraft Tower

Design, Fabrication and Testing of Solar Updraft Tower

Thermo-Fluid Dynamic Effects of the Radial Location of the Baffle Installed in a Solar Updraft Tower

The solar updraft tower (SUT) is a renewable power generation system that uses the natural convection phenomenon of the ground’s air heated by solar radiation. The baffle is a thermo-fluid dynamic structure that improves the heat exchange efficiency and has been recently reported to be a useful tool to increase the output of the SUT. However, one of the less well-known issues is the relationship between the thermo-fluid dynamic characteristics of the flow in the collector of the SUT and the installation location of the baffle and how this affects the power output and SUT efficiency. In this study, the positive and negative thermo-fluid dynamic effects of the baffle, which vary depending on the installation location, are quantitatively analyzed, and the best location is predicted where the overall kinetic power generated by the SUT is maximized. The target SUT model consists of a chimney (12 m height and 0.25 m diameter) and a collector (1 m height and 10 m diameter), and a total of eight model cases are calculated. The results confirm that the kinetic power is lower or higher than that of the control model having no baffle, depending on the baffle installation location. When the position of the baffle is 4.5 m from the center, the increase in kinetic power is maximized by 8.43%. Two important conclusions are that the baffle should interfere minimally with the progress of the main flow into the chimney, generating kinetic power, and at the same time, the baffle should isolate the inner recirculating flow in order to accumulate the heat in the collector so that the natural convection strength is maximized. The perspective gained from the resulting data is useful for SUT design and for pursuing a higher efficiency in the future.

Computational study on the effect of collector cover inclination angle, absorber plate diameter and chimney height on flow and performance parameters of solar updraft tower (SUT) plant

A computational model is developed to investigate the influence of geometrical configurations such as chimney height (Hch), absorber plate diameter (Dap) and collector plate angle (θcr) on flow and performance characteristics of solar updraft tower (SUT) plant. The diameter of the chimney (Dch) and air entrance gap (e) selected for numerical simulations are 0.6 m and 0.1 m, respectively. Parametric study is carried out by varying Hch of 3–8 m, θcr of 20°-35° with an increment of 5° and Dap of 3.5–12 m. A turbulent model (RNG k-ɛ) is incorporated for considering turbulence effect and Discrete ordinates (DO) model incorporated for estimation of radiation heat transfer inside the setup. It is found that a slight decrease of temperature and increase of air velocity when θcr is increased. It is noticed that air velocity is enhanced (up to 44%) while the Hch is increased from 3 to 8 m. Power output, overall, chimney and exergy efficiencies are estimated. Correlations are developed to estimate the performance parameters in terms of geometrical configurations. From the parametric study, it is concluded that for the Dch and e of 0.6 m and 0.1 m, respectively, better performance can be achieved at a Hch of 7 m, θcr of 30° and Dap of 5 m.

Modeling solar chimney for geometry optimization

Wind energy characteristics include lack of “stability and predictability”. Solar updraft tower, also known as solar chimney SC, is a device in which wind is locally generated by the thermal effects of a solar collector which covers an area surrounding the chimney. In this work computational fluid dynamics, is applied to model the heat and transport relations in the collector and chimney area. The geometry, mesh layout and the existing analytical models are verified for consistency against the experimental data of Manzanares plant in Spain. As one of the geometrical parameters such as collector diameter is changed, an optimization process occurs, leading to a decision on the best matching size for the other dimensions. The process checks the output against the optimized profiles of temperature, velocity and pressure. Based on studying 180 cases in 15 groups for collector size against chimney height and diameter and another 130 cases in 12 groups for collector height, a table and graphs of matching dimensions are obtained. As a consequence of this work, it is possible now to make a more accurate decision on consistent dimensions for a solar chimney plant.

A complete design data and performance parameter evaluation of a pilot scale solar updraft tower

Renewable energy sources are the best alternative for giving solution to the energy shortage and CO2 emission problems. Solar updraft tower is a relative novel technology for electricity production from solar energy. It consists of three main components; a solar air collector with absorber plate, central chimney, and a turbine. The objective of this work is to present complete design parameters of individual components of a small and less expensive prototype solar updraft tower. The main contents of this study are; solar radiation calculations, chimney design, solar wind turbine design calculations, heat loss and pressure loss estimations for collector. The pilot solar chimney power plant considered in this work consists of an air collector diameter of 3.5-m, the chimney diameter and height are 0.6 and 6 m, respectively. Theoretically the maximum velocity of air is achieved at chimney base is 1.9 m/s. The overall efficiency of the plant is estimated as 0.0019%.

The effect of strong ambient winds on the efficiency of solar updraft power towers: A numerical case study for Orkney

Solar updraft tower (SUT) is a simple power plant in which ventilation of heated air inside a channel drives a turbine. This system is recognised as suitable for areas with abundant solar radiation. As a result, there is no extensive research on the performance of SUTs under mild solar radiation. Studies show that strong ambient crosswinds can affect the performance of a SUT. In this paper, the efficiency of SUTs in areas which benefit from strong winds, despite low solar radiation, is investigated through numerical modelling. Comparison is made between the efficiency of a commercial-scale SUT in Manzanares (Spain) with intensive solar radiation, and one of the same size potentially located in the windy and mild climate of Orkney Islands in Scotland. The results show that ambient crosswinds can increase internal air speed and efficiency of a SUT by more than 15% and 50%, respectively. Consequently, such a SUT in Orkney can offer more than 70% of the efficiency of the one in Manzanares. The results show that, for a given power capacity, a wind turbine enclosed in a SUT can be considered as an alternative to a number of conventional wind turbines installed at height in the open air.

A Feasibility Study on Power Generation from Solar Thermal Wind Tower: Inclusive Impact Assessment Concerning Environmental and Economic Costs

A solar thermal wind tower (STWT) is a low-temperature power generation plant that mimics the wind cycle in nature, comprising a flat plate solar air collector and central updraft tower to produce thermal wind that drives turbines to generate electricity. The development of power generation systems toward a sustainable future needs to be made taking into account the balance between environmental impact and economic feasibility. We examine the sustainability of STWT power generation technology using the inclusive impact index light (Triple I-light), which estimates whether it is good to do the project, including both the negative environmental impact and the economic aspect. Environmental disadvantages are discussed by performing a CO2 inventory analysis for the life-cycle of the STWT power plant. Evaluation of the economic feasibility is done by calculating the levelized electricity cost (LEC), which is the cost per unit of electricity generated. From the calculations, it is found that overall system efficiency is increased by enlarging the capacity, the negative environmental impact by the STWT plant comes mainly from manufacturing stage (more than 60%), and the levelized electricity cost is dramatically decreased by enlarging the capacity of the system (about 50% reduction). A negative value of Triple I (meaning it is sustainable) can be achieved for high power generation capacity (above 100 MW). Moreover, this paper discusses the implementation and the potential of constructing offshore STWTs.