Elsevier

Applied Energy

Volume 102, February 2013, Pages 975-982
Applied Energy

A comprehensive approach to design and improve a solar chimney power plant: A special case – Kerman project

https://doi.org/10.1016/j.apenergy.2012.06.012Get rights and content

Abstract

The objective of this paper was to present a comprehensive analysis including analytical and numerical models which were developed to predict the performance of a solar chimney power plant in Kerman, Iran. The numerical model results including air temperature, velocity and electrical power output were validated by comparing with experimental data of the Manzanares prototype power plant. Also the mathematical model was verified with the practical power output of the Kerman pilot plant. Also in this paper, a novel approach to evaluate the influence of the site altitude on the potential of solar chimney power plants was presented and thereby a coefficient called altitude effectiveness was defined using Manzanares prototype geometrical parameters in different site altitudes. The developed model was applied to improve the performance of a solar chimney pilot power plant built in Kerman, Iran. Based on an approximate cost model, the thermo-economic optimal configurations of the pilot power plant were illustrated; and also it was found that the chimney diameter was the most important structural dimension to improve the performance of this pilot power plant.

Highlights

► A comprehensive mathematical model to analyze the solar chimney is developed. ► To evaluate effect of site altitude, altitude effectiveness coefficient is defined. ► A scheme of computation of a pilot power plant built in Kerman, Iran is considered. ► The model is reliable and applicable in design and operation of the solar chimney.

Introduction

Solar thermal power systems utilize the heat generated by a solar collector to convert the solar energy into electrical power. Sensible technology for the wide use of renewable energy must be simple and reliable, accessible to the technologically less developed countries that are sunny and often have limited raw materials resources [1]. A solar chimney power plant (SCPP) converts solar energy into electrical energy by a combination of three main parts, the collector, the chimney and the turbine. The air inside the collector is heated by the greenhouse effect. Therefore a continuous updraft in the chimney is produced by the upward buoyancy force. The airflow at the base of the chimney runs a wind turbine. Finally, mechanical energy is converted into electrical energy by using a conventional generator.

In Refs. [2], [3], [4], the basic principles and reported preliminary test results for a prototype SCPP built in Manzanares, Spain, were presented. By introducing the SCPP concept, research and development studies on the performance of the SCPP have been done increasingly. In general, a simplified mathematical model is applicable for design and performance improvement of solar chimney systems. In order to study the effect of various environment conditions and geometric parameters on the performance of the SCPP, various one dimensional mathematical models were carried out. Pasumarthi and Sherif [5] presented an approximate theoretical analysis and reported experimental data on the performance of a built solar chimney pilot plant. Padki and Sherif [6] developed a simple mathematical model to predict the performance of the SCPP. Gannon and von Backström [7] analyzed the solar chimney including chimney friction, turbine and exit kinetic losses, using a simple model of the solar collector. A case study of the SCPP in Northwestern regions of China was presented by Dai et al. [8], using a simple mathematical model. Pastohr et al. [9] conducted a CFD analysis on the SCPP and compared their results to a simple mathematical model. More thorough analyses of the solar chimney system performance were presented by Bernardes et al. [10] and later Ming et al. [11]. Pretorius and Kröger [12] evaluated the performance of a large-scale SCPP, using convective heat transfer and corresponding momentum relations. Bernardes et al. [13] made a comparison of the methods used to calculate the heat fluxes in the collector presented in earlier works [10], [12]. The feasibility of solar chimney power plants as an environmentally acceptable energy system was analyzed by Nizetic et al. [14]. Pretorius and Kröger [15] presented an approximate thermo-economic model to optimize a SCPP. Petela [16] presented a thermodynamic analysis of the SCPP, using a simplified mathematical model.

The mass flow rate through the solar chimney system is one of the most important factors to analyze the system. Due to the pressure distribution in the system influences the mass flow rate, previous investigations proposed pressure equations to analyze the system. Ref [9] obtained that static pressure increases along the flow direction inside the collector, which is in opposition with the basic flow theory in the solar chimney system. Ref. [11] illustrated that the relative static pressure decreases along the flow direction inside the collector, using the Bernoulli equation. But due to solar radiation, there is a difference in mechanical energy per unit mass between sections inflow and outflow in the collector and therefore, the Bernoulli equation is not appropriate to obtain the pressure difference in the collector. In Refs. [1], [2], [3], [10], [17], [18], analyses for finding the optimal ratio of turbine pressure drop to available pressure drop to predict power output of the SCPP were presented. According to these studies, for evaluation the ratio different values in the range of 2/3–0.97 have been suggested. Therefore, no unified value of the factor exists in works previously performed by researchers. In Ref [18], for predicting the power output of the SCPP, an optimal velocity of air at the chimney inlet was estimated with the assumption that temperature rise in the collector is constant. This approach is improved in the present work by deriving the velocity distribution equation in the flow field based on the optimal velocity of air at the chimney inlet and conservation equation for energy to obtain temperature distribution in the collector.

The purpose of this study is to present a comprehensive analytical and numerical model to predict the performance of the solar chimney power plant at any solar insolation in a specific site altitude. In this model, based on the optimal velocity of air at the chimney inlet, the velocity distribution equation in the collector is analytically derived. The numerical solution of the energy conservation equation provides the temperature distribution in the flow field. Then, to calculate performance of the system basic principles of the SCPP are employed. Using the developed model, a scheme of computation and improvement of a pilot SCPP built under specified meteorological conditions in Kerman, Iran, have been considered. Also, in this paper for the first time an approach to determine the influence of altitude of the geographical location (the site altitude) on the SCPP performance due to the effect of the buoyancy force is presented and a coefficient called altitude effectiveness is defined, by simulation the Manzanares prototype geometrical parameters in different site altitudes.

Section snippets

Influence of the site altitude

As altitude increases, barometric pressure of atmospheric air decreases smoothly from the sea level. The change in pressure due to changes in the site altitude affects buoyancy that is the driving force of airflow in the SCPP. Therefore, the performance of the SCPP decreases by increasing the site altitude of the SCPP. The expression for pressure in terms of altitude in the standard atmosphere is:p=p0·(1-LS/T0)gM/RL

It is based on a subset of the International Standard Atmosphere (ISA) model

Governing equations in the collector

While the collector air is heated, the buoyancy force aids the airflow, the velocity near the roof and ground surface is increased, heat transfer by convection is increased with regard to that for forced convection. Hence, the flow and heat transfer are extremely difficult to calculate. To solve strongly coupled set of conservation equations of mass, momentum and energy, a one dimensional flow field is assumed to be in the sense that the velocity, temperature, density, etc. are uniform over any

Numerical results of the model

Eqs. (2), (4), (5), (6), (7), (8) are discretized using finite difference approximations and are solved simultaneously by a computer simulation program to obtain distributions of air velocity and temperature through the collector. Then, to calculate the power output and thermo-economic analysis Eqs. (15), (16), (17), (18), (19), (20), (21), (22), (23) are employed.

Based on the results of computational simulation for the mathematical model (so-called the model results), performance of the SCPP

Conclusions

In this study a comprehensive analytical and numerical model to predict the performance of the SCPP was developed. Based on a novel approach for evaluating the influence of the site altitude on solar chimney power generation, a coefficient called altitude effectiveness was defined. This formula is not unique and it is not easy to demonstrate the formula for the altitude effectiveness, but the approach is informative for comparing the potential of solar chimney power plants in regions at

Acknowledgement

The authors thank the anonymous reviewers who made valuable suggestions that helped us to improve the article.

References (22)

  • N. Pasumarthi et al.

    Experimental and theoretical performance of a demonstration solar chimney model. Part I: Mathematical model development

    Int J Energy Res

    (1998)
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