NORTH-SOUTH HORIZONTAL AXIS WEIGHTED AVERAGE ALTITUDE TRACKING A.V.N.Rao & K.Jnanand rao

1. NORTH-SOUTH HORIZONTAL AXIS WEIGHTED AVERAGE ALTITUDE TRACKINGA.V.N.Rao & K.Jnanandrao

2. THEORETICAL ANALYSIS Set up showing the directions of X, Y and Z-axes

3. Contd…. Vectorial representation of incident ray

4. Contd…… Incident ray and reflected ray vectors

5. Incident ray I in the coordinate system (X, Y, Z) can be expressed as Ix = - cos αs cos γs Iy = cos αs sin γs Iz = - sin αs Contd….

6. After giving a rotation ξ about X-axis the (X,Y,Z) co-ordinate system transfers to a new (X1,Y1,Z1) co-ordinate system as shown in figure . This angle ξ equals to the hour angle which equals to 7.5° for every half an hour. Contd…. The new co-ordinate system after giving a rotation of ξ about X- axis

7. Incident ray in the co-ordinate system (X1,Y1,Z1) can be expressed as Ix1 = Ix Iy1 = Iy cos ξ – Iz sin ξ Iz1 = Iy sin ξ + Iz cos ξ Contd….

8. In order to obtain the direction of the reflected ray vector, a new coordinate system (X2, Y2, Z2 ) is defined by giving a rotation of (90-β) about Y-axis where β is the angle made by the mirror with the receiver in the direction of the opening of the receiver irrespective of the receiver orientation which is fixed at 120°, such that the axis x2 is normal to the mirror plane. Contd….

9. Contd….. 90-β 90-β Receiver and Mirror after a rotation of (90-β) about Y- axis

10. After giving the rotation (90-β) about y-axis, the unit vector I of the incident ray can be expressed in (x2, y2, z2) coordinate system as Ix2 = Ix1 sin β+ Iz1 cosβ Iy2 = Iy1 Iz2 = -Ix1 cos β + Iz1 sinβ Contd..

11. Contd.. In order to obtain the direction of the reflected ray vector in the tilted receiver plane, a rotation βc about y2 axis results the new coordinate system (X3,Y3,Z3) as shown in figure New co-ordinate system after receiver tilted to an angle of βc about Y- axis

12. After giving the rotation of βc about y2 axis, the incident ray vector I can be expressed in the new coordinate system (X3, Y3, Z3) as Ix3 = Ix2 cos βc+ Iz2 sinβc Iy3 = Iy2 Iz3 = -Ix2 sin βc + Iz2 cosβc Contd…

13. For north facing mirror, The vector equations for the north facing mirror can be obtained by rotating the entire system with south facing mirror by 180° about Z-axis. Then for north facing mirror the vector equations are Ix4= - Ix3 Iy4 = Iy3 Iz4 = Iz3 Contd…..

14. The resultant vectors with both the mirrors can be obtained by adding the vectors that are obtained from south facing mirror and north facing mirror Contd….. =

15. By using the derived equations the computer code is generated. The theoretical values which are obtained by the code are compared with experimental values on the days of 2nd and 3rd February,2010 and the results are discussed in results chapter. Contd….

16. photograph OF THE RECEIVER-MIRROR SYSTEM

17. EXPERIMENTAL PROCEDURE The measurements were performed in solar energy laboratory during the year 2009 to 2010. The solar energy laboratory is located on NIT campus in Warangal, India (longitude 79.50 E, latitude 17.95 N at an elevation of 275m above mean sea level). The readings were recorded from 10A.M. to 3:30P.M. on days when the sky is clear without any clouds for 25 days. The following procedure was followed during the course of experiments to achieve the results in the most accurate manner.

18. The receiver angle (βc) is adjusted every day before the starting of the experiment which is taken as the weighted average of the altitude on that day as shown below.. βc= ∑(Ibαs) / ∑ Ib Where, αs= Altitude of the sun on a particular day Ib= Theoretically calculated beam radiation(W/m²). Contd…

19. The system is tracked towards west so that the receiver is fully illuminated by any one of the mirrors attached to it, since the receiver angle is fixed to the horizontal. The tracking is done in such a way that the receiver is illuminated always and no shadow is appeared on the receiver The global radiation incident on the receiver was measured by the pyranometer at three different positions of the receiver for better results and took the average of the three measured values. Contd…..

20. For comparison the readings were recorded on a static horizontal plane, tracking horizontal plane, an inclined plane without mirrors, an inclined plane with south facing mirror, an inclined plane with north facing mirror and an inclined plane with both the mirrors. • The readings were recorded for every half an hour. • The readings with south facing and north facing mirror were obtained by covering one of the mirror with black cloth, which will not reflect or allow any radiation to pass through it. Contd..

21. The angle of tracking is adjusted by rotating the shaft which is discussed earlier and locked by means of the screw. The system as a whole will be rotated and hence the energy contribution can be calculated without disturbing the system every time. After all the readings completed on a day the system is kept in horizontal position to avoid any damage during winds..etc. Contd….

22. RESULTS The variation of insolation values with LAT for various receiver positions on 27th January, 2010

23. Contd…. The variation of insolation values with LAT for various receiver positions on 2nd February, 2010

24. Contd….. The variation of insolation values with LAT for various receiver positions on 3rd February, 2010

25. Contd…. The variation of insolation values with LAT for various receiver positions on 5th February, 2010

26. Contd….. The variation of insolation values with LAT for various receiver positions on 9th February, 2010

27. COMPARISION WITH THEORETICAL VALUES: Comparison of insolation values on tilted tracking receiver with both mirrors on 2nd February, 2010 with Theoretical values

28. Contd… Comparison of insolation values on tilted tracking receiver with both mirrors on 3rd February, 2010 with Theoretical values

29. From the results on daily total basis it can be summarised that • The increase in the insolation on a tracking horizontal receiver over a non-tracking horizontal receiver is around 6% • For inclined tracking plane the increase is about 26% • For inclined tracking receiver with north facing mirror the increase is about 52% • For inclined tracking receiver with south facing mirror the increase is about 65% • For inclined tracking receiver with both mirrors was found to increase the insolation at about 83%. SUMMARY

30. The south facing mirror contributes more energy than north facing mirror because the angle of incident and reflected rays are higher than north facing mirror. Hence the losses will be more in case of reflected rays on north facing mirror. Contd…

31. From the results it is evident that the plane receiver tracked on North-South horizontal axis is making the energy flux distribution more flatter when compared to a fixed horizontal plane. The flatter energy flux is desirable in the case of photo voltaic applications. Contd…

32. Theoretically it was found that there is an increase in energy is about 85% of daily total insolation with the weighted average altitude tracking plane over horizontal plane. The theoretical values which are obtained by the computer code are also in good agreement with the results obtained experimentally. Contd…

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