O.A. Jaramillo

Design, construction, and testing of a parabolic trough solar concentrator for hot water and low enthalpy steam generation

This paper reports the design, construction, and evaluation of a solar parabolic trough concentrator (PTC) with a rim angle of 45°, a length of 4.88 m, and an aperture area of 5.8 m2. The PTC is made of aluminium in such a way that both the manufacturing and assembly processes do not require complicated technology or skilled labour. Since the PTC is for low enthalpy steam generation and hot water, it is designed with an unshielded receiver and without a glass cover in order to reduce both production and transportation costs. A finite element stress analysis is conducted to determine the mechanical behaviour of the PTC under various simulated wind loads on the structure. A simple solar tracking system is employed when it is oriented in a North-to-South direction. The optical efficiency of the collector is also reported. Said efficiency depends on the optical properties of the materials involved, the geometry of the collector, and the various imperfections arising from the construction of the collector. The...

Bimodal versus Weibull Wind Speed Distributions: an Analysis of Wind Energy Potential in La Venta, Mexico

The International Standard IEC 61400-12 and other international recommendations suggest the use of the two-parameter Weibull probability distribution function (PDF) to estimate the Annual Energy Production (AEP) of a wind turbine. Most of the commercial software uses the unimodal Weibull PDF as the default option to carry out estimations of AEP, which in turn, are used to optimise wind farm layouts. Furthermore, AEP is essential data to assess the economic feasibility of a wind power project. However, in some regions of the world, the use of these widely adopted and recommended methods lead to incorrect results. This is the case for the region of La Ventosa in Mexico, where the frequency of the wind speed shows a bimodal distribution. In this work, mathematical formulations by using a Weibull PDF and a bimodal distribution are established to compare the AEP, the capacity factor and the levelised production cost for a specific wind turbine. By combining one year of wind speed data with the hypothetic power performance of the Vestas V27-225 kW wind turbine, it was found that using the Weibull PDF underestimates AEP (and thus the Capacity Factor) by about 12%.

A thermal study of optical fibres transmitting concentrated solar energy

In this paper we develop a theoretical thermal study of optical fibres transmitting concentrated solar energy. An energy equation for simultaneous conduction and radiation of heat through optical fibres is obtained. To transmit concentrated solar energy an optical fibre tip is placed in the focus of a small paraboloidal mirror. The role of aluminium and silver as the reflective surface on the mirror that allows one to concentrate the solar energy is studied. The power supply is estimated to be 26 W at the end of a 10 m long fibre with 88% transmission efficiency. The thermal study considers a wavelength-dependent absorption coefficient of the optical fibre core in order to obtain the radiative heat flux in the fibre. The time evolution of the temperature distribution is obtained by a finite-difference method. With this result we predict that the fibre can be used 6 h.

Optical fibres for a mini-dish/Stirling system: thermodynamic optimization

A thermodynamic optimization of a solar mini-dish/stirling system is presented. The solar collector heat losses by convection and radiation are diminished by using optical fibres to transport concentrated solar energy. We analyse an absorber-heater for the solar heat engine to ensure the reduction of the heat losses using the first law and the second law. Taking into account internal and external irreversibilities for the solar heat engine, the optimal operating temperature and the overall efficiency of the system are established.

A theoretical and experimental thermal study of SiO2 optical fibres transmitting concentrated radiative energy

In this work a theoretical and experimental thermal behaviour study of optical fibres with a high-purity SiO2 core transporting concentrated radiative energy is carried out. A theoretical unidimensional model for the simultaneous transport of heat by conduction and radiation in optical fibres, including the heat losses by convection at the surface, is developed. This model considers a constant linear absorption coefficient and it is solved analytically. An experimental method to determine the linear coefficient of absorption is developed. The time evolution of the axial temperature distribution of two kinds of fibres is recorded and compared with the theoretical predictions. These experimental results validate the theoretical model proposed.

Modeling and optimization of a solar parabolic trough concentrator system using inverse artificial neural network

In this paper, an artificial neural network inverse (ANNi) model is applied to optimize the thermal performance (η) of parabolic trough concentrators. A feedforward neural network architecture is trained using an experimental database from parabolic trough concentrators operations. Rim angle ( φr), inlet (Tin) and outlet (Tout) fluid temperatures, ambient temperature (Ta), water flow (Fw), direct solar radiation (Gb), and the wind velocity (Vw) were used as main input variables within the neural network model to estimate the thermal performance with a correlation coefficient of R2 = 0.9996 between experimental and simulated values. The sensitivity analysis is carried out to verify the effect of all input variables. The optimal operation conditions of parabolic trough concentrators are established using artificial neural network inverse modeling (ANNi) to achieve optimal operation conditions of parabolic trough concentrators. The results indicated that ANNi is a feasible tool for Parabolic Trough Concentra...

Application of fiber optics in the hydrogen production by photoelectrolysis

This paper presents an alternative way to transmit concentrated solar energy which may be applied in the hydrogen production by photoelectrolysis. It is possible to obtain high efficiency in the photoelectrochemical conversion systems with a simple structural design. The basic idea is to place an optical fiber in a paraboloidal mirror receptor plane. The concentrated solar energy is transmitted for a few meters by total internal reflection. The appropriate conditions existing between a paraboloidal mirror (reflective surface, Ag or Al) and an optical fiber (low doping, commercial type) is studied. The theoretical efficiency of the conversion system is obtained and analyzed.

Wind Power Error Estimation in Resource Assessments

Estimating the power output is one of the elements that determine the techno-economic feasibility of a renewable project. At present, there is a need to develop reliable methods that achieve this goal, thereby contributing to wind power penetration. In this study, we propose a method for wind power error estimation based on the wind speed measurement error, probability density function, and wind turbine power curves. This method uses the actual wind speed data without prior statistical treatment based on 28 wind turbine power curves, which were fitted by Lagranges method, to calculate the estimate wind power output and the corresponding error propagation. We found that wind speed percentage errors of 10% were propagated into the power output estimates, thereby yielding an error of 5%. The proposed error propagation complements the traditional power resource assessments. The wind power estimation error also allows us to estimate intervals for the power production leveled cost or the investment time return. The implementation of this method increases the reliability of techno-economic resource assessment studies.

Parabolic trough concentrators for hot water generation: Comparison of the levelized cost of production

With the objective of demonstrating the technical and economic viabilities of a hybrid solar energy system applied to hot water generation, a simulation of a parabolic trough power plant with an auxiliary electrical heater system is presented. This article reports the procedure to obtain the characteristic equation of the useful heat value when N parabolic troughs are operated in series; the equation takes into account the heat loss through the pipes and the use of a heat exchanger. Additionally, this work reports a theoretical case study of a hybrid system that supplies hot water via solar energy and an auxiliary electrical system. The solar fraction and the global efficiency of the hybrid solar power plant are calculated. Using the results from the simulation, a cost analysis of the hybrid solar power plant was done where the levelized cost of thermal power generated is obtained; this in turn shows that the levelized cost of a conventional electrical heater system is one and a half times more than that ...

A Modular Linear Fresnel Reflecting Solar Concentrator for Low-Enthalpy Processes

One of the aims of solar-thermal engineering is to develop ‘medium temperature collectors’ in the range of 70–250 °C that are suitable for applications such as cleaning, drying, evaporation, distillation, pasteurization, sterilization and cooking, as well as applications with low-temperature heat demand and high consumption rates (domestic hot water, space heating and swimming pool heating), and heat-driven refrigeration and cooling. In this work, we present an applied research on the development of a modular linear Fresnel reflecting solar concentrator (MLFRC) for heating water and steam generation at low enthalpy in the temperature range of 70–110 °C. We present a simple mathematical method to determine the distance among the reflecting elements and the angle for each one in order to avoid shading between the elements during the period of operation. We designed a non-imaging CPC cusp-type collector with a cylindrical receiver as a secondary concentrator. We also evaluated the thermal performance of MLFRC according to the Standard ANSI/ASHRAE 93:2003.