Two-Axis Solar Heat Collection Tracker System for Solar Thermal Applications

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Hindawi Publishing Corporation International Journal of Photoenergy Volume 2013, Article ID 803457,7pages http://dx.doi.org/10.1155/2013/803457

Research Article

Two-Axis Solar Heat Collection Tracker

System for Solar Thermal Applications

Tsung-Chieh Cheng, Wei-Cheng Hung, and Te-Hua Fang

Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan

Correspondence should be addressed to Tsung-Chieh Cheng; tcchengme@cc.kuas.edu.tw Received 15 September 2013; Accepted 15 October 2013

Academic Editor: Teen-Hang Meen

Copyright © 2013 Tsung-Chieh Cheng et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

An experimental study was performed to investigate the effect of using a continuous operation two-axes tracking on the solar heat energy collected. This heat-collection sun tracking which LDR (light dependent resistor) sensors installed on the Fersnel lens was used to control the tracking path of the sun with programming method of control with a closed loop system. The control hardware was connected to a computer through Zigbee wireless module and it also can monitor the whole tracking process information on a computer screen. An experimental study was performed to investigate the effect of using two-axes tracking on the solar heat energy collected. The results indicate that sun tracking systems are being increasingly employed to enhance the efficiency of heat collection by polar-axis tracking of the sun. Besides, the heating power was also measured by designed power measurement module at the different focal length of Fresnel lens, and the design of shadow mask of LDR sensors is an important factor for solar photothermal applications. Moreover, the results also indicated that the best time to obtain the largest solar irradiation power is during 11:00 –13:00 in Taiwan.

1. Introduction

Because of the energy crisis and the environmental aware-ness, to develop renewable energies has become one of the important targets in the future. There are many approaches that could be developed for renewable energies. Finding energy sources to satisfy the world’s growing demand is one of society’s foremost challenges for the next halfcentury. Solar energy is clean, renewable, and abundant in every part of our world. There are two main energy types of solar energy collection. One is photoelectric conversion and the other is photothermal conversion. For photothermal application, solar stirling engine which is a photothermal engine that converts sunlight heat energy into mechanical motion to form the electrical power by using air or an inert gas as the working fluid operating on a highly efficient thermodynamic cycle is a kind of green power. For photothermal applications, in order to receive heat energy from the sunlight, the solar tracker, a device in an optimum position perpendicular to the solar radiation during daylight hours, is necessary to increase the collected heat energy. Therefore, in this paper, an experimental study was performed to investigate the effect of

using a continuous operation two-axes tracking on the solar heat energy collected.

Over the years, several researchers have studied the solar tracking systems with different modes and electromechanical module to improve the efficiency of solar systems. The design of tracker was based on some criteria: low cost, easy maintenance, modular, low energy consumption, and easy adjustment in case of different location [1]. From previous studies, there are two tracking types to track the sun. One is active type and the other is passive type [2]. In a passive system the tracker follows the sun from east to west without using any type of electric motor to power the movement, but the active type needs motor, control IC, track procedure, and detect components responding to the solar direction. Passive solar trackers are based on thermal expansion of a matter (usually Freon), on low boiling point compressed gas fluid, or on shape memory alloys. Clifford and Eastwood [3] presented the passive solar tracker design which incorporates two bimetallic strips made of aluminum and steel, positioned on a wooden frame symmetrically on either side of a central horizontal axis. The efficiency of this passive solar tracker with tracking method had the potential to increase solar panel

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2 International Journal of Photoenergy efficiency by up to 23%. Mwithiga and Kigo [4] designed and

constructed a dryer which consisted of a gauge 20 mild steel flat absorber plate formed into a topless box and the results showed that the solar dryer can be used to successfully dry grains. Poulek [5] developed a single axis passive solar tracker based on a shape memory alloy (SMA). It was concluded the efficiency of the SMA actuators (−2%) is approximately two orders of magnitude higher than that of bimetallic actuators. However, the passive tracker had many drawbacks, like low tracking efficiency than active tracker, susceptible to high winds, or sluggish in getting moving in cold temperatures. Therefore, the approach of solar tracker was trend to develop at active mode solar tracker.

Active tracking systems are powered by small electric motors and require some type of control module to direct them. The controller had two modes that can identify the active tracker to location of the sun. One is electrooptical sen-sors such as solar cell or LDR (Light Dependent Resistance) or photodiodes based on the structure of trackers (closed loop system); another is according to the function which adopted the azimuth and solar altitude angles or polar axis (open loop system). Abouzeid [6] presents a new tracking system with a firm step movement of either 15∘ or 7.5∘. The system is controlled automatically using a programmable logic array plus an EEPROM carrying all necessary commands required for different operation cases (Abouzeid, 2001). Oner et al. [7] design a spherical motor controlled by a microcontroller for a PV-tracking system with the ability to move on two axes. The spherical motors which have the linear and circular movement ability in three independent dimensions can be used for precisely tracking the sun as a solution. Roth et al. [8] has published a low-cost automatic closed-loop sun tracker, built and tested. A four-quadrant photodetector senses the position of the sun and two small DC motors move the instrument platform keeping the sun’s image at the center of the four-quadrant photodetectors. The situation of tracking under cloudy conditions, when the sun is not visible, a computing program calculates the position of the sun and takes control of the movement, until the detector can sense the sun again. Rubio et al. [9] show a hybrid tracking system that consists of a combination of open-loop tracking strategies based on solar movement models and closed-loop strategies using a dynamic feedback controller. The results have been presented that show the benefits of the new strategy with respect to a classical open-loop strategy when errors in the estimation of the sun’s position. Alata et al. [10] demonstrated the design and simulation of time controlled sun tracking system. The approach starts by generating the input/output data. Then, the subtractive clustering algorithm, along with least square estimation (LSE), generates the fuzzy rules that describe the relationship between the input/output data of solar angles that change with time. The fuzzy rules are tuned by an adaptive neurofuzzy inference system (ANFIS). This open-loop control system is designed for each of the previous types of sun tracking systems and the electrooptical trackers give very good results during good weather condi-tions. Some studies [11–13] also use four photoresistors with cylindrical shades, electrooptical unit, or electrooptical unit as a sun sensor. Its controller contains differential amplifiers,

comparators, and output components to provide fairly good accuracy and reliable operation. Abdallah and Nijmeh [14] investigated the two axes tracking and the results indicate that the two axes tracking surface showed a better performance with an increase in the collected energy of up to 41.34% compared with the fixed surface. Neville [15] presented a theoretical comparative study between the energy available to a two axes tracker, an east-west tracker and a fixed surface. It was found that the energy available to the ideal tracker is higher by 5–10% and 50% higher than the east-west tracker and the fixed surface, respectively. Sungur [16] designed aboth axes sun tracking system with programmable logic control and with the function of solar azimuth angle and solar altitude angle to follow the sun’s position. He found that the energy more than 42.6% in the two-axes sun-tracking system was obtained when compared to the fixed system. Barakat et al. [17] made a two-axes sun tracking system between closed-loop system and with complicated typical electronic control circuits. They found that the energy available to the two-axes tracker is higher by 20%. Bakos [18] developed the two-axes tracking using a continuous operation on the solar energy collected. He set the position of the photoresistors and the results indicate that solar energy on the moving surface was significantly larger (up to 46.46%) than the fixed surface. Khalifa and Al-Mutawalli [19] investigated the effect of using a two-axis sun tracking system on the thermal performance of compound parabolic concentrators (CPC). They indicated that the tracking CPC collector showed a better performance with an increase in the collected energy of up to 75% compared with an identical fixed collector. Mousazadeh et al. [20] established equations to compare the relation between tracking collector and fixed collector about energy gains. This amount of energy can be obtained from tracking collector more 57% than fixed collector.

However, for solar stirling electrical generator, the idea of concentrating solar energy to generate electricity has ingeniously made use of the concept in concentrator optics especially for designing a specific geometry of reflectors or lenses to focus sunlight onto a small receiving heating element. Many previous researches also have discussed that many existing concentrator systems will produce nonuniform focused illumination [21,22] and it will decrease the energy collection of the sun. In this paper, a concept came from a realization that the need to concentrate the solar energy with the available Fresnel concentrating lens on the heating element of stirling engine to have higher efficiency in power generation. Therefore, we design the active two-axis solar tracker with Fresnel lens to collect the thermal power of solar efficiently and to offer a steady heat source for photo-thermal applications.

2. Experiments

2.1. The Structure of Two-Axis Heat-Collection Solar Tracker System. The proposed two axes heat collection solar tracker

system as shown inFigure 1consists of the following three parts:

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International Journal of Photoenergy 7 thermal energy of the sunlight by Fresnel lens, letting the

concentrative sunlight to totally illuminate on the heating element without any heat loss is very important.

Acknowledgment

The authors would like to thank the National Science Council of Taiwan, for partially supporting this research under Con-tract no. NSC 101-2221-E-151-010.

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Two-Axis Solar Heat Collection Tracker System for Solar Thermal Applications

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