Naveed ur Rehman

Performance Model and Sensitivity Analysis for a Solar Thermoelectric Generator

In this paper, a regression model for evaluating the performance of solar concentrated thermoelectric generators (SCTEGs) is established and the significance of contributing parameters is discussed in detail. The model is based on several natural, design and operational parameters of the system, including the thermoelectric generator (TEG) module and its intrinsic material properties, the connected electrical load, concentrator attributes, heat transfer coefficients, solar flux, and ambient temperature. The model is developed by fitting a response curve, using the least-squares method, to the results. The sample points for the model were obtained by simulating a thermodynamic model, also developed in this paper, over a range of values of input variables. These samples were generated employing the Latin hypercube sampling (LHS) technique using a realistic distribution of parameters. The coefficient of determination was found to be 99.2%. The proposed model is validated by comparing the predicted results with those in the published literature. In addition, based on the elasticity for parameters in the model, sensitivity analysis was performed and the effects of parameters on the performance of SCTEGs are discussed in detail. This research will contribute to the design and performance evaluation of any SCTEG system for a variety of applications.

Critical Concentration Ratio for Solar Thermoelectric Generators

A correlation for determining the critical concentration ratio (CCR) of solar concentrated thermoelectric generators (SCTEGs) has been established, and the significance of the contributing parameters is discussed in detail. For any SCTEG, higher concentration ratio leads to higher temperatures at the hot side of modules. However, the maximum value of this temperature for safe operation is limited by the material properties of the modules and should be considered as an important design constraint. Taking into account this limitation, the CCR can be defined as the maximum concentration ratio usable for a particular SCTEG. The established correlation is based on factors associated with the material and geometric properties of modules, thermal characteristics of the receiver, installation site attributes, and thermal and electrical operating conditions. To reduce the number of terms in the correlation, these factors are combined to form dimensionless groups by applying the Buckingham Pi theorem. A correlation model containing these groups is proposed and fit to a dataset obtained by simulating a thermodynamic (physical) model over sampled values acquired by applying the Latin hypercube sampling (LHS) technique over a realistic distribution of factors. The coefficient of determination and relative error are found to be 97% and ±20%, respectively. The correlation is validated by comparing the predicted results with literature values. In addition, the significance and effects of the Pi groups on the CCR are evaluated and thoroughly discussed. This study will lead to a wide range of opportunities regarding design and optimization of SCTEGs.

A novel method for determining sky view factor for isotropic diffuse radiations for a collector in obstacles-free or urban sites

A novel method for computing sky view factor for isotropic diffuse radiations on tilted collectors located in obstacle free and urban sites has been introduced in this paper. The proposed method involves disintegrating the hemispherical sky vault around collector into small portions (sky elements). Collector is a flat receiving surface, positioned at a particular tilt angle and facing a specific azimuthal orientation. The three-dimensional celestial vault is transformed into a two-dimensional plane. This plane is converted into a computer graphic raster image for computing. Each pixel of raster image represents a sky element. Color (gray shade) of every pixel describes specific weight which depends upon sky elements solid angle and incidence angle with respect to collector. Sky view factor is evaluated by taking ratio of the sum of color codes of all the pixels for tilted collector to that of horizontal collector. Sky view factors at different tilt angles for obstacle free sites are evaluated and results...

Solar energy potential estimation by calculating sun illumination hours and sky view factor on building rooftops using digital elevation model

The detailed and precise estimation of solar energy is a major requirement for solar applications on building roof tops. These estimations help in sustainable development, energy policy making, and renewable energy consumption. In this paper, a methodology was devised to estimate the solar radiation components. This methodology is easily accessible using a simple measuring tape to form a digital elevation model with a cell size of 1 × 1 sq. ft. Liu and Jordans model [Liu and Jordan, “The interrelationship and characteristic distribution of direct, diffuse and total solar radiation,” Sol. Energy. 4(3), 1–19 (1960)] was modified for the urban environment and programmed in MATLAB to estimate solar potential. To validate the developed algorithm and modified model, the roof-top area of the postgraduate laboratories of the Mechanical Engineering Department (NED University) was selected as a case study. Measurements were carried out on different days, which showed good agreement with the proposed work. Within t...

The proper interpretation of analytical sky view factors for isotropic diffuse solar irradiance on tilted planes

The consistency of well-known analytical models used for determining the sky view factor ( SVF) in comparison with the theoretical definition of SVF is quantified in this paper. A general formula for SVF is derived, which can be configured to use various methods of computing solar irradiance approaching from all directions in a hemispherical vault around an arbitrarily tilted plane. The true model is then derived by choosing the receiving plane as the reference plane in a general formula. The true model most accurately follows the radiation theory. Different settings are then proposed for adapting the general formula to depict the response of each of the analytical models over the range of tilt angles. These settings realistically represent the analytical model, as there is satisfactory agreement between the results from an appropriately configured general formula and those from the corresponding analytical model. Simulations of the true model are performed to compare with the analytical models. The resul...