system using solar powered Stirling engine

Proc. of the Third Intl. Conf. on Advances in Applied Science and Environmental Engineering - ASEE 2015 Copyright © Institute of Research Engineers and Doctors, USA .All rights reserved. ISBN: 978-1-63248-055-2 doi: 10.15224/ 978-1-63248-055-2-79

Comparative evaluation of optimal energy efficiency designs for solar tracking systems A.Z. Hafez, J.H. Shazly, M.B. Eteiba Abstract—The aim of this paper is to present a way in which the efficiency of solar power collection can be increased. A new design idea of a one axis tracking PV module using solar-powered Stirling engine as the power source for the tracking motor was proposed in the present study. Every PV module is mounted on an individual sun tracking frame. The new systems designed here provided good power output performance. The optimum PV-tracking axis is the E–W that corresponds to the maximum possible power. The power of PV equipped with an E–W sun-tracking system using solarpowered Stirling engine gave much better performance than that of fixed PV systems. Azimuth tracking using solarpowered Stirling engine increased annual solar irradiation incident on a surface relative to a fixed south-facing surface at optimum tilt angle. An analytical model to simulate the thermal behaviour of the solar-powered Stirling engine prototype is proposed and validated. The results are shown using simulation and virtual reality. The site of application is chosen at Giza, Egypt (31º North, 30º East). Keywords—Photovoltaic, Efficiency.

I.

Tracking,

Stirling

Engine,

Introduction

The solar energy is becoming more and more a viable source of energy for many industrial and housing appliances. The amount of power produced by a solar system depends upon the amount of sun light to which it is exposed. Therefore, Photovoltaic tracking systems are the best for increasing amount of solar irradiation in PV Systems. Increasing the efficiency and reducing the cost are the two main targets in order to increase the competitiveness of PV energy. A tracking mechanism must be reliable and able to follow the Sun with a certain degree of accuracy, return the collector to its original position at the end of the day or during the night, and also track during periods of cloud cover. There are a number of works proposed by many researchers to track the sun. The first tracker constructed was completely mechanically, done by Finster in 1962 [1]. Later, Saavedra presented a mechanism with an automatic electronic control [2]. It was used to orient an Eppley pyrheliometer. Maldonado designed and built a sun tracker at UTFSM [3]. The position of the sun was calculated with a computing program or sensed by a servo control, and the system ensured reliable automatic orientation of a pyrheliometer. Huang and Sun [4] designed the solar tracking system called ‘‘one axis three position sun tracking PV module” with low concentration ratio reflector. Abu-Khadera et al. [5] investigated the effects of multiaxes sun-tracking systems on the electrical generation of a flat photovoltaic system (FPVS) which was carried out to evaluate its performance under Jordanian climate. Abdallah S. [6] implemented four electromechanical sun-tracking systems, two axes, one axis vertical, one axis east–west and one axis

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north–south, were designed and constructed for the purpose of investigating the effect of tracking on the current, the voltage and the power, according to the different loads. Tomson T. [7] described mainly the performance of PV modules with daily two-position in the morning and in the afternoon. Ibrahim Sefa et al. [8] introduced a design and application of a novel one-axis sun tracking system which follows the position of the sun and allows investigating effects of one-axis tracking system on the solar energy in Turkey. J. Rizk et al. [9] presented a way in which the efficiency of solar power collection can be increased. It is to increase the efficiency of solar power conversion by increasing the amount of time that the solar panel is directly perpendicular to the sunlight. Ali Al-Mohamad [10] improved efficiency of photovoltaic panels using a Sun-tracking. C.S. Chin et al. [11] presented the design, modeling and testing of an active single axis solar tracker. Ahmet Senpinar et al. [12] compared the performance of two PV modules, one fixed and the other fitted with a two-axis tracking system which enables the PV collector to move and be controlled to follow the Sun’s radiation. Chang T.P. [13] considered the gain of single axis tracked panel according to following extraterrestrial radiation and found that the amount of solar radiation gains are between 36.3 percent and 62.1 percent for the four particular days of the year, between 37.8 percent and 60 percent for the four seasons and 49 Percent over all the year. Chang T.P. [14] presented a theoretical study the electrical PV module output at different azimuth and tilt angles in Taiwan. Chang T.P. [15] considered a theoretical study on the East-West oriented single axis sun tracking system. Bakos GC. [16] Performed to investigate the effect of using a continuous operation two-axes tracking on the solar energy collected. Hossein Mousazadeh [17] reviewed the principle and sun-tracking methods for maximizing solar systems output. We are present the implementation of a generalized photovoltaic simulation model using MATLAB®/GUI interface. The model is developed using basic circuit equations of the Photovoltaic (PV) cells including the effects of solar radiation and temperature changes [18].

A.Z. Hafez Environmental Engineering Sciences Department, Institute of Environmental Studies and Research, Ain Shams University Cairo, Egypt

J.H. Shazly, M.B. Eteiba Electrical Engineering Department, Faculty of Engineering, Fayoum University Fayoum, Egypt


Design of solar tracking system using solar powered Stirling engine

connections of photovoltaic module, Dc motor, and stand connections are shown in Fig. 2, Fig. 3 and Fig. 4 respectively.

The aim of this paper is to present a way in which the efficiency of solar power collection can be increased. It is to increase the efficiency of solar power conversion by increasing the amount of time that the solar panel is directly perpendicular to the sunlight. Efficiency is based on accurately positioning the solar panel throughout the day and thus motors and Light Dependent Resistors (LDR) have been selected as the primary driving mechanism of this system [9]. This paper presents a Sun-tracking design, whereby the movement of a photovoltaic module was controlled to follow the Sun's radiation using a Light Dependent Resistors (LDR) and the power source of PVtracking are coming from solar-powered Stirling engine. All electronic circuits and the necessary software have been designed and developed to perform the technical tasks. The results will be decrease the power for operating solar tracking system by selecting the solar-powered Stirling engine as the power source for motor of solar tracking system.

A sun-tracking system was designed and constructed consisting of an electronic circuit that processes the input signals from a set of sensors and outputs the control signal to the motor that drive the photovoltaic module actuator which is placed in the base of the solar photovoltaic module frame. The sensors are a set of photo-resistors operated using 12V power supply. When the sensors are exactly opposite the sun, the two photo-resistors have the same resistance value (Fig. 5). The movement is achieved through the activation of the appropriate motor.

II.

B.

Tracking the sun from east in the morning to west in the evening will increase the efficiency of the solar panel depending on where you are in the world. Near the equator, you will have the highest benefit of tracking the sun. For this manner, a tracking system is needed. Our aims is to offer a complete system that moves the tracking base according to the sun without outside electricity source and catch the sunlight and increase the output of the solar panel and decrease the power consumption of the driving motor using solar-powered Stirling engine as shown in Fig. 1.

Sensors and signals processing unit

Figure 1. Photovoltaic Tracking System using Solar powered Stirling Engine

The system consists of: 1. The Photovoltaic module (8.4V–2W) 2. Power supply, which supplies power to the drivers and the CPC using solar powered Stirling engine. 3. Position Sensors: delivering information about the axes position of the module 4. Control Process Circuit: (CPC), controlling the processing of the information to the module

Figure 2. Photovoltaic Module, Tracking System, 3-D Design

5. Driver "Dc Motor", which realize the system motion and the module A short description of the system follows: A.

Photovoltaic panel and electromechanical movement mechanism

Figure 3. Photovoltaic Module

The photovoltaic module used in this thesis was a ‘‘SM40_14A2’’ from Siemens. The module consists of 14 solar cells connected serially. The output voltage of each cell is 0.6 V: this produces an estimated output of about 8.4 V–2 W. This is under standard test conditions (STCs) of solar intensity=1000 W/m2, cell temperature=25 ºC and air mass=1.5. The horizontal support rod and vertical support rod are used for connecting photovoltaic module and DC Motor in the base of connection. The design is shown in Fig. 1. The

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Figure 4. Photovoltaic Module with Stand Connections for Fixed and Tracking Systems


combustion engine, and also to its non-explosive nature in converting energy into mechanical form and thus leading to silent and cleaner operation [19]. Stirling engines are thermodynamic devices working theoretically on the Stirling cycle, or its modifications, in which compressible fluids, such as air, hydrogen, helium, nitrogen or even vapors, are used as working fluids. The Stirling engine offers possibility for having high efficiency engine with less exhaust emissions in comparison with the internal combustion engine. The earlier Stirling engines were huge and inefficient. However, over a period of time, a number of new Stirling engine models have been developed to improve the deficiencies [20].

Figure 5. Operating principle of the sensor system

New technique of solar tracking using solar-powered Stirling engine as the power source for the tracking motor are presented and shown in Fig. 7. D.

Solar Tracker Circuit Using LDR

This circuit is the solar tracking circuit which monitors the position of the sun using two Light Dependent Resistors (LDR's), and makes the decision to move the solar panel to correctly orientate to the sun. The output configuration is called a H-bridge which will drive a small electric gearbox up to 50mA at the input voltage (12V), both forward and reverse. Figure 6. Controlling process Flowchart

Two symmetric photo-resistors were used to track the Sun's position. The photo-resistors were positioned on the same holder of the PV solar module, and were separated by a solid barrier to provide shadowing for one of the resistors. The physical values of the resistors decrease when the sunlight is incident on their surfaces. When the solar-radiation intensity increases, the resistivity of the photo-resistor decreases, and consequently the voltage drop across this resistor decreases. As a result, the voltage drop across the variable resistor (1K) increases. This will produce a direct relationship between the incident solar-radiation intensity and the corresponding voltage-drop across the resistor. The two output signals of this unit are connected directly to the solar tracking control circuit, which in turn compares the two signals and produces a proper output signal to activate an electromechanical Sun tracking movement are illustrated in Fig. 6. C.

A light dependent resistor also known as a LDR, photoresist or, photoconductor or photocell, is a resistor whose resistance increases or decreases depending on the amount of light intensity. LDRs (Light Dependent Resistors) are a very useful tool in a light/dark circuits. LDRs can have a variety of resistance and functions. For example it can be used to turn on a light when the LDR is in darkness or to turn off a light when the LDR is in light. It can also work the other way around so when the LDR is in light it turns on the circuit and when it’s in darkness the resistance increase and disrupts the circuit (Shown in Fig. 8). If we look at the solar tracker circuit schematic, and particularly the motor control, the forward and reverse is achieved when the outputs of IC1a and IC1b (LM1458) are in different states [21]. A truth table helps explain this as given in Table 1:

System power supply

Fig. 1 shows a solar-powered Sirling engine will be operate as power supply for the tracking system. Implementation of the low temperature Stirling engine added to generator resulted in a power-supply unit with high efficiency and low losses. The design of this unit is based solely on the amount solar radiation drops in Stirling engine and the temperature of the upper plate "will be discussed in the next section". The direct conversion of solar power into mechanical power reduces both the cost and complexity of the prime mover. Stirling engines are able to use solar energy that is a cheap source of energy. The increasing interest in Stirling engines is largely due to the fact the engine is more environmentally friendly than the widely used internal

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Figure 7. Solar Powered Stirling Engine 3-D design [22]

Proc. of the Third Intl. Conf. on Advances in Applied Science and Environmental Engineering - ASEE 2015 Copyright © Institute of Research Engineers and Doctors, USA .All rights reserved. ISBN: 978-1-63248-055-2 doi: 10.15224/ 978-1-63248-055-2-79 TABLE I.

A TRUTH TABLE FOR IC1A AND IC1B IN (LM1458)

IC1a Output

IC1b Output

Low

Low

Motor Behaviour Stop Forward *

Low

High

High

High

Stop

High

Low

Reverse *

III.

The transistors work in diagonal pairs to provide +ve & ve to the motor terminals or -ve & +ve to the motor terminals for forward / reverse. The four power diodes protect the transistors from the voltage created by the motor in the instant(s) after the motor has been stopped. As the motor still has angular momentum, it will generate a voltage and current (Power). This power is capable of destroying the transistors and is bled off via the diodes [21]. The input stage uses two operational amplifiers (contained in IC1) to decide on the direction of light. The op-amps are fed by the junction of the LDRs (LDR & LDR’). If both LDR LDR’ see the same amount of light, their resistance is equal. The junction of the LDR LDR’ would be at input voltage divided by two ie. 12V input – junction of LDR LDR’ at 6V. If the light on one LDR is greater than the other, than the voltage will move, higher or lower depending on which LDR has more light. Limits are set by the four resistors in series from +V to 0V, and adjusted by the two trimpots. If the voltage moves outside these limits, the respective op-amp will activate the motor and move the solar panel appropriately [21]. The 20K trimpot sets the sensitivity ie. the distance between these limits. The 100K trimpot adjusts so that these limits are symmetrical around +V/2 (balance point) [21]. Solar tracker circuit component layout is shown in Fig. 9. Solar tracker circuit board is shown in Fig. 10.

(b)

A Sun tracking mechanism increases the amount of solar energy that can be received by the solar photovoltaic modules: consequently this would result in a higher daily and annual output power harnessed. The use of a tracking system is more expensive and more complex than fixed mounts: however they can become cost-effective in many cases because they provide more power output throughout the year. In this section discussion the results of the thesis and equipment tools of measurements and simulation results as fellow: 1. Solar Radiation practical data for Fixed and Tracking System. 2. Temperature practical data for ambient temperature & Photovoltaic Module Temperature. 3. Photovoltaic Module (PV) Output data.

A.



Photovoltaic Module (PV) practical output data for Fixed and Tracking Systems.



Photovoltaic Module (PV) comparison practical output data between Fixed and Tracking Systems.



Maximum Data for Photovoltaic Module for Fixed & Tracking Systems.



Input Power to Photovoltaic Module.



Efficiency of Photovoltaic Module systems.

Solar Radiation Data for Fixed and Tracking System

The solar radiation measurement experiments took place on 2 March from 07:00 AM to 5:00 PM by pyranometer Sensor and data acquisition (NI USB 6008) and the solar radiation for photvoltaic fixed system was varying from 130, 220, 550, 700, 860, 900, 820, 680, 310, 120, 25 W/m2, and the solar radiation for photvoltaic tracking system was varying from 200, 340, 690, 770, 880, 910, 890, 750, 430, 210, 30 W/m2. The solar radiation measurement experimental results are shown in Fig. 11. The solar radiation gain data between Fixed System and Tracking System during day hours are shown in Fig. 12. During the experiment the solar radiation after the noon hours was decreased due to the appearance of clouds in late afternoon hours.

Figure 8. Solar Tracker Circuit - Schematic Diagram

(a)

RESULTS

It can be seen that after the decrease of solar radiation intensity, the developed controlling circuit is helping the photovoltaic to follow the Sun up to the end of the day, even though the solar intensity is inadequate to switch on the sensors.

(c)

Figure 9. Solar Tracker Circuit Component Layout (a) Front & Back Layout (b) Front Layout (c) Back Layout

B.

Temperature Data for ambient temperature & Photovoltaic Module Temperature

The temperature measurement experiments took place on 2 March from 07:00 AM to 5:00 PM by LM35 Sensor and data acquisition (NI USB 6008) and the ambient temperature Figure 10. Solar Tracker Circuit Board

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was varying from 27.2, 27.7, 28.1, 29.4, 30.5, 31.9, 32.4, 31.7, 31.5, 29.8, 28.4 ºC, and the photovoltaic temperature was varying from 31.3, 33.7, 34.1, 35.7, 36.3, 36.9, 39.6, 36.7, 36.1, 31.7, 31.6 ºC. During these experiments the weather conditions were very good and were almost no clouds in the sky else from 4:00 PM to 5:00 PM. The experimental results are shown in Fig. 13.

C.

Photovoltaic Module (PV) Output data

1) Photovoltaic Module (PV) Electrical output data for Fixed and Tracking Systems From the experimental results sections III.A & III.B, it can be noticed an increased efficiency of the new technique tracking due to the variation of Sun orbit (East–West movement) using solar powered Stirling engine as the power source. The efficiency is improved when the Sun inclination is increased with respect to 30º inclination of fixed surface and, in any case, when the photovoltaic base is tracking East—West, particularly during early morning and late afternoon hours. The solar energy collection efficiency of the PVs, due to the application of the developed tracking system compared to fixed surface inclination, is given in the following figures. Measurements ((Current-Voltage) characteristics) on the fixed PV system sloped to the south at different hours conditions are shown in Fig. 14. Measurements ((PowerVoltage) characteristics) on the fixed PV system sloped to the south at different hours conditions are shown in Fig. 16. The present experiments were performed for several hours (from 7:00 AM to 5:00 PM) under different climates.

Figure 11. Solar radiation data for Fixed System and Tracking System during day hours at Giza on 2 March

Measurements ((Current-Voltage) characteristics) on the PV sun tracking system with solar powered Stirling engine at different hours conditions are shown in Fig. 15. Measurements ((Power-Voltage) characteristics) on the fixed PV system sloped to the south at different hours conditions are shown in Fig. 17. The present experiments were performed for several hours (from 7:00 AM to 5:00 PM) under different climates.

Figure 12. Solar radiation gain data between Fixed System and Tracking System during day hours at Giza on 2 March

(a)

Figure 13. Ambient Temperature and Photovoltaic Module Temperature during day hours at Giza on 2 March

(b) Figure 14. (Current-Voltage) characteristics of photovoltaic fixed system at Giza on 2 March from (a) 7:00 AM to 12:00 PM (b) 12:00 PM to 5:00 PM

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(a)

(a)

(b)

(b)

Figure 15. (Current-Voltage) characteristics of photovoltaic tracking system at Giza on 2 March from

Figure 17. (Power-Voltage) characteristics of photovoltaic tracking system at Giza on 2 March from

(a) 7:00 AM to 12:00 PM (b) 12:00 PM to 5:00 PM

(a) 7:00 AM to 12:00 PM (b) 12:00 PM to 5:00 PM

2) Maximum Data for Photovoltaic Module for Fixed & Tracking Systems Maximum electrical output data for photovoltaic fixed and tracking systems are showed Fig. 18. The gain of maximum power between photovoltaic fixed system and tracking system during day hours at Giza on 2 March are presented in Fig. 19. 3)

Input Power to Photovoltaic Module

The solar radiation fall in photovoltaic is presented as the input power to the photovoltaic module depending on: (a) solar intensity (b) area of the module. The results of input power and solar radiation are shown in Fig. 20, and Fig. 21. During the experiment the solar radiation after the noon hours was decreased due to the appearance of clouds in late afternoon hours.

(a)

A: Area of Module = 15x15 cm Pin=G.A=G*0 .15*0.15= G*0.0225

(b) Figure 16. (Power-Voltage) characteristics of photovoltaic fixed system at Giza on 2 March from (a) 7:00 AM to 12:00 PM (b) 12:00 PM to 5:00 PM

Figure 18. Maximum power data for Photovoltaic Fixed System and Tracking System during day hours at Giza on 2 March

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Figure 22. Output Power data for Photovoltaic Fixed System and Tracking System during day hours at Giza on 2 March

Figure 19. Gain of Maximum power between Photovoltaic Fixed System and Tracking System during day hours at Giza on 2 March

Figure 20. Input Power and solar radiation data for Photovoltaic Module during day hours at Giza on 2 March

Figure 23. Efficiency of Photovoltaic Fixed System and Tracking System during day hours at Giza on 2 March

Figure 21. Solar radiation data during day hours at Giza on 2 March

Figure 24. Gain of Efficiency between Photovoltaic Fixed System and Tracking System during day hours at Giza on 2 March

4) Efficiency of Photovoltaic Module systems From the experimental results in sections III.A, III.B, and III.C, it can be noticed an increased efficiency of the new technique tracking due to the variation of Sun orbit (East–West movement) using solar powered Stirling engine as the power source. The efficiency is improved when the Sun inclination is increased with respect to 30º inclination of fixed surface and, in any case, when the photovoltaic tracking base is tracking East—West, particularly during early morning and late afternoon hours. Output power data for photovoltaic fixed system and tracking system during day hours at Giza on two march is given in Fig. 22. The solar energy collection efficiency of the photovoltaic

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tracking system PTS, due to the application of the developed tracking system compared to fixed surface inclination is given in Fig. 23. The gain of efficiency between photovoltaic fixed system and tracking system during day hours at Giza on 2 March are shown in Fig. 24. IV.

Conclusion

This paper presents a Sun tracking design, whereby the movement of a photovoltaic module was controlled to follow the Sun's radiation using a Light Dependent Resistors LDR sensors and the power source of PV tracking are coming from solar-powered Stirling engine. One axis


tracking using solar-powered Stirling engine resulted in an average irradiation increase relative to the fixed surface. New technique of solar tracking using solar-powered Stirling engine as the power source for the tracking motor are presented in this paper. The results will be decrease the power for operating solar tracking system by selecting the solar-powered Stirling engine as the power source for motor of solar tracking system. The results indicate that the measured collected solar energy on the moving surface was significantly larger than that on a fixed surface. The (E-W) tracking using solar-powered Stirling engine showed a better performance with an increase in the collected energy compared with the fixed surface.

[9]

All electronic circuits and the necessary software have been designed and developed to perform the technical tasks. Also, this paper presents the modelling for a prototype of the solar-powered Stirling engine working at the low temperature range. A mathematical model for the thermal analysis of the solar-powered low temperature Stirling engine with heat transfer is developed using Matlab program. The place of implementing the tracking process is selected at Giza, Egypt, for times beginning at 7:00 am and ending at 5:00 pm on 2 March.

[15]

 

[3]

[4]

[5]

[6]

[7] [8]

[13] [14]

[18]

[19]

A significant increase occurs in the overall output power of the PV module.

[20]

Due to motors powers, tracking system can moves lots of arrays with increased in temperature.

[21] [22]

Output power has good performance and gain as it works at MPPT,

About Author (s):

References

[2]

[12]

[17]

While one-axis tracking PV system using solar-powered Stirling engine is more expensive than the fixed system, it can be made more economical by connecting a numbers of PV modules in series or parallel and using the single computer as controller.

[1]

[11]

[16]

In comparison to the fixed unit, the observable benefits of one-axis tracking PV system using solar Stirling engine can be summarized as follows: 

[10]

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