**4. Development of MCA-based CPV prototype**

*h* = (

as given by Eq. (8):

118 Solar Panels and Photovoltaic Materials

[*OD* + (

and 34.43 mm, respectively.

a tracking error of 1o

\_\_\_\_\_\_ *ID* − *OD*

If Eqs. (6) and (7) are compared, then we can find the expression for the lower slope angle 'θ'

<sup>2</sup> )].tan(2*<sup>θ</sup>* <sup>−</sup> 90) <sup>=</sup> (

Parameter 'OD' represents the dimension for the outlet aperture of homogenizer, which is same as the size of MJC, i.e., 5.5 mm. On the other hand, a suitable value of '16' is also considered for parameter 'ID' so that ray can easily be propagated to the outlet aperture. If the value of 'ID' is small, then the height 'h' will also be small, same for 'OD'. Otherwise, the ray will have multiple total internal reflections (TIR) inside the homogenizer if the value of 'h' is higher for smaller 'ID'. Or, there may be a chance that the ray can propagate back if the value of 'h' is very big. However, the large value of 'ID' also requires a larger value of 'h', same for 'OD'. For the given value of 'ID' and 'OD', the value of 'θ' and 'h' can be calculated as 81.33o

After finalizing the design of lower tapered portion of the homogenizer, now the upper tapered portion of homogenizer is considered, which is needed to be designed to accommodate the rays which are not parallel to the axis of concentrating assembly. From the design point of view,

the homogenizer design will be able to handle the deviated ray for maximum angle of 1°. By using the graphical method and trigonometric laws, it has been shown in **Figure 5** that if there

is selected which can be handled by the homogenizer. This means that

\_\_\_\_\_\_ *ID* − *OD*

**Figure 5.** Acceptance angle calculation for multicell concentrating assembly.

<sup>2</sup> ).tan*θ* (7)

<sup>2</sup> ).tan*θ* (8)

\_\_\_\_\_\_ *ID* − *OD*

To verify and analyze the field performance of proposed and designed MCA, a prototype of CPV is fabricated as per designed concentration ratio of ×165. The prototype of fabricated MCA is shown in **Figure 6** and the MCA-based novel CPV unit is shown in **Figure 7**. The primary and secondary reflectors are machined from aluminum blocks. However, to improve the surface quality and reflection characteristics, the reflecting surface of both reflectors was coated with thin optical graded reflecting aluminum layer, using sputter-coating method. The multi-leg homogenizer was fabricated in the form of four symmetrical pieces which were joined together to form a single unit. Each homogenizer piece is similar to the half of schematic shown in **Figure 4**. The individual pieces of homogenizer were machined using N-BK7 glass material. To form a single homogenizer unit, all four pieces were joined together using optical graded UV glue. It must be noted that the machining method of fabrication is an expensive fabrication technique, and that is why smaller concentration ratio was chosen at the start to keep the overall cost minimum. However, for mass production of reflectors and homogenizers, injection molding techniques for plastic and glass materials are used.

Four MJCs were attached at the four outlet apertures of the homogenizer. However, the back side of MJCs was attached to the heat spreader and heat sink to dissipate the heat during CPV operation and to keep the cell temperature within optimum limit.

In order to test the performance of developed novel MCA-based CPV module, a twoaxis solar tracking unit was used with tracking accuracy of 0.1° [20, 21]. The developed CPV module was mounted onto the top frame of solar tracker. The tracking system is based upon the hybrid tracking algorithm which defines the solar position through both active and passive techniques. After calculating the position of sun, based upon the solar geometry model, the actual position of the sun is verified by taking the real-time feedback

**5. Results and discussion**

of the homogenizer.

In order to analyze the optical performance of proposed multicell concentrating assembly (MCA), the ray tracing simulation was conducted using TracePro software. The concentrating assembly was analyzed in terms of division of rays among four outlet apertures, uniformity of rays at the outlet aperture and investigation of deflected path of incident rays. The simulation model for proposed MCA, according to the discussed design, is shown in **Figure 8**. To conduct ray tracing simulation, a square grid of parallel rays was selected as the primary reflector is also of square shape. As the received solar radiation is not exactly parallel in nature, that is why the simulated MCA model was not only investigated for parallel ray grid but also for the grid with angle same as the solar subtended angle. The ray tracing simulation results of proposed MCA design with parallel ray grid are shown in **Figure 9**. It can be seen that a perfect division of rays among four outlet apertures of homogenizer is experienced. In addition, the rays are also uniformly distributed over the whole surface area of outlet aperture. Moreover, a concentrated collimated beam is also achieved after reflection of parallel incident rays from secondary reflector. As per discussed design, this concentrated collimated beam is being divided among four sections of homogenizer and also hitting the lower tapered portion

Multicell Design for Concentrated Photovoltaic (CPV) Module

http://dx.doi.org/10.5772/intechopen.78000

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In order to simulate the optical performance of proposed MCA in real field environment, the simulation results for grid of rays with solar subtended angle are shown in **Figure 10**. These rays are not exactly parallel to the axis of primary reflector but have a small deviation which is same as the actual solar radiations, received during real field operation. It can be seen that there is still a perfect division of received radiations among four sections of the homogenizer and uniform distribution of these radiations over the outlet apertures of homogenizer. However, one of the differences which can be seen here is that the rays are also hitting the upper tapered portion of the homogenizer, without any induced ray deviation. The reason

**Figure 8.** TracePro model of multicell concentrating assembly (MCA) for ray tracing simulation.

**Figure 6.** Developed prototype of multicell concentrating assembly (MCA)-based CPV module.

**Figure 7.** Experimental prototype of MCA-based novel CPV unit.

from solar tracking sensor. Such real-time optical feedback avoids any chance of tracking error which may arise due to passive tracking method and possible backlash in the driving assembly.
