CHAPTER 3 PROBLEM DEFINITION AND OBJECTIVE

Transcription

1 49 CHAPTER 3 PROBLEM DEFINITION AND OBJECTIVE 3.1 MOTIVATION Concentrating solar power is a principle of increasing solar power density. It can be demonstrated to set a piece of paper on fire by using a magnifying glass which is the basic principle of concentrated solar power. Sunlight shining on the curved glass or reflector is concentrated to a small point and combust. Paraboloidal is a geometric surface whose section parallel to two coordinate planes is parabolic and in this work two dimensional Parabolic Dish Concentrator is Paraboloidal Dish Concentrator(PDC). The point focusing in parabolic dish concentrator can have concentration ratios ranging from 100 to a few thousand and can yield temperature up to 2000 C (Mo wang & Kamaran 2010). These require continuous two-axis tracking. These involve surfaces of double curvature which reflects or incoming rays into a small region and solar energy conversion takes place. Review from collected literature shows that not much of work were developed, investigated in Solar PDC in tracking techniques and using different reflecting material as aluminum and glass reflector. Parabolidal is a surface produced by rotating a parabola about its optical axis. Azimuth-elevation and tilt-roll tracking mechanism are among the most commonly used sun-tracking methods for aiming the solar collector towards the sun at all times. It has been many decades that each of these two sun-tracking methods has its own specific sun tracking formula and they are

2 50 not interrelated. The general form of sun tracking that embraces all the possibilities in tracking of sun in two axis east-west and north-south that are required and commonly used in practice(chong &Wong 2009), but this investigations are interested to eliminate the drawbacks as there is no tracking in east-west, optimized with intermittent tracking has to be developed in the north south directions attracted by using two different reflecting medium and it is always placed to the incoming solar radiation rays to obtain higher efficiency and to get more energy to be captured throughout the year. In this research engrossed to carry out the experimental investigation to plot temperature in the solar trace, fluid temperature at different time interval and plot the graphs of aluminum reflector and glass reflector to analyze the heat transfer fluid and phase change status by the two experimental setup, interested to design of absorber size of different solar altitude angle period It is also paying attention to know that the solar thermal power applied efficiently in use of cooking, water distillation An economic solar power by parabolic dish concentrating system can provide rural areas with electricity and cater energy needs to dramatically to improve their quality of life. Many under-developed areas around the world receive large amounts of sunlight but it has not been harvested. This is a great opportunity to use solar power to provide basic energy needs in those regions. The two most prominent solar energy technologies are photovoltaic and parabolic dish concentrated, solar power photovoltaic systems are beneficial because they can be scaled to any size, but they are costly and solely produce electricity but parabolic dish concentrated solar power systems can provide electricity from solar energy conversion technology through solar thermal power.

3 DEFINITION OF THE PROBLEM Sun-tracking system plays an important role to ensure that the solar collector can receive maximum solar radiation at all times. Concentrator should be oriented more precisely towards the sun to get higher concentration. More importantly, for either imaging or non-imaging solar concentrator, inaccurate sun-tracking will directly deteriorate the quality of solar flux distribution at the absorber (Chen et al 2008) and thus affect the performance of the solar collecting system. Generally, a good tracking mechanism must be reliable and able to track the sun at the right angle even in the periods of cloud cover however more sophisticated and expensive tracking mechanism have to be used for the purpose. Sun-tracking systems are available as either a passive tracking system using open loop approach or an active tracking system using closed loop approach. For the passive tracking system, the tracker will perform calculation to identify the sun s position and to determine the rotational angles of the two tracking axes using a specific sun-tracking formula in order to drive the solar collector towards the sun. On the other hand, for the active tracking system, the sun tracker normally will sense the direct solar radiation falling on a photo-sensor as a feedback signal to ensure that the solar collector is tracking the sun all the time. Abdurrakhamanov et al (2012) studied photo electric station with two axis sun tracking estimated about 30% to 40% to cost for support and rotating facility. In this work there is no cost involved because design itself incorporated the tracking technique and absorber have been designed receive solar radiation for all times.

4 52 Instead of the above options, some researchers have done few work, also designed a hybrid system that contains both the active and passive tracking system to achieve a good tracking accuracy Two most commonly used configurations in two-axis sun-tracking system are Azimuth-elevation and tilt-roll (or polar) tracking system. Inspired by an ordinary optical mirror mount, Azimuth-elevation system is among the most popular sun-tracking system employed in various solar energy applications In the azimuth-elevation tracking, the collector must be free to rotate about the zenith-axis and the axis parallel to the surface of the earth. The tracking angle about the zenith-axis is the solar azimuth angle and the tracking angle about the horizontal axis is the solar elevation angle Therefore, the accuracy of the azimuth-elevation tracking system highly relied on how well the azimuth-axis is aligned to be parallel with the zenith-axis. Alternatively, tilt-roll (or polar) tracking system adopts an idea of driving the collector to follow the sun-rising in the east and sun setting in the west from morning to evening as well as changing the tilting angle of the collector due to the yearly change of sun path (Strebkov et al 2008). Hence, for the tilt-roll tracking system, one axis of rotation is aligned parallel with the earth s polar-axis that is aimed towards the star Polaris. This gives it a tilt from the horizon equal to the local latitude angle. The other axis of rotation is perpendicular to this polar-axis (Poulek & Libra 2000). The tracking angle about the polar-axis is equal to the sun s hour angle and the tracking angle about the perpendicular axis is dependent on the declination angle. The advantage of tilt-roll tracking is that the tracking velocity is almost constant at 15 degrees per hour and therefore the control system is easy to be designed

5 53 (Clifford Ho 2008). The accuracy of the tilt-roll tracking system relies strongly upon how well the roll-axis can be aligned in parallel with the polaraxis, which is also latitude dependant. It was observed from the survey that not much of the tested works, developed the tracking techniques and were not investigated such as optimal tracking in north- south due to the solar altitude angle development of a optimal period tacking towards sun and elimination of tracking in east- west direction variation of hour angle changing period towards east to west and design the absorber based on the above. In this research work fabricated two experimental setup using different reflecting materials aluminum reflector and glass mirror and test was carried out analyzing direct steam generation by solar paraboloidal dish concentrating system by non tracking in east west and optimal tracking in north south for given solar altitude angle. Therefore the present work is carried out to reveal the theoretical and experimental investigation of the potential and the extent to which optimal tracking in one direction and non tracking in another direction. The effect of these tracking performance and characteristics and conversion efficiency analysis are studied. In order to reduce the overall weight of the PDC, the material for the reflecting surface of PDC glass mirror and polished aluminum sheet have been used because of its reflectivity more than 85% and comparison of two types have been used with performance analysis. Several researches on simple water heating, using solar energy have been carried out by flat plate collector and other thermal collector has been used as well though on a smaller scale. Nazir (2004) constructed a

6 54 experimental study of the thermal performance of a parabolic cylindrical collector. Fared et al (2012) tested the portable solar dish collector, Lokeswaran & Eswaramoorthi (2012) experimentally studied the PDC, but not much of work carried out direct steam generating possibility with the novel tracking technique. PDC has the highest efficiency in terms of utilization reflector area because of in a fully steerable dish system as there are no losses due to aperture projection effects (Ibrahim ladan Mohamed 2012). Radiation losses are very small, because of the small area of the absorber at the focus. Fareed et al (2012) studied that solar heat flux concentration ratio obtained in the range of , , for trough, tower, and dish systems. Conventional flat plate collector are capable of producing heat up to C (Kaushika 1992) due to high heat losses proportional to the absorber area. More recent efforts have been taken by Folaranmi (2009) who destined the PDC for steam generation system with manual tracking. So the present work carried out in PDC with using novel tracking techniques and performance analysis. 3.3 SCOPE AND OBJECTIVES investigation are: Based on the review focused the objectives of the present To design and fabricate the experimental setup using reflecting materials like aluminum and glass mirror in two axis tracking east-west and north-south.

7 55 To investigate theoretically in no tracking in east-west, optimized with intermittent tracking in the north -south directions. To develop the program to design the absorber with different solar altitude angle period. To carry out the experimental investigations of obtaining higher efficiency and to get energy capturing to be captured throughout the year. To find out solar altitude angle at different locations using a program. To examine the performance of reflecting materials of aluminum and glass mirror dish technology. To compare the two reflective systems of aluminum and glass parabolic concentrating system. To carry out the performances analysis of a parabolic collector both types of equipment to achieve the phase change of the heat transfer fluid at the solar trace in the simultaneous movement of the sun. To examine the direct steam generation with collector efficiency from two test equipment. To study the drawback of present work and suggestions for further study and carry out the research.

8 METHODOLOGY AND APPROACH Literature Survey Definition of the Problem Design of Paraboloidal Dish Concentrator Using Aluminum Reflector Using Glass Mirror Reflector Fabrication of Paraboloidal Dish Concentrator Using Aluminum Reflector Using Glass Mirror Reflector Experimentation Experimentation Results Results Comparison and Analysis Conclusion Figure 3.1 Methodology and approach