**1. Introduction**

Due to dependency of global energy need on fossil fuels, the global warming situation is hitting to an alarming level with record amount of greenhouse gas emissions. Under such circumstances, renewable energy resources are seen to be able to provide sustainable energy source to

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

meet global energy needs [1–4]. However, solar energy, being the energy source with the highest energy potential [5–7], can provide a sustainable source of future primary energy supply if captured with high efficiency and simple configuration. Photovoltaic system provides the most simple configuration to convert solar energy into high-grade energy form, i.e., electricity. However, in the current photovoltaic market with 99% share of single-junction solar cells, the multi-junction solar cells (MJCs) have yet to exploit their potential of the highest solar energy conversion efficiency. This is due to the fact that the multi-junction solar cell (MJC) can respond to a full spectrum of solar radiation, with less loss and as a result higher efficiency [8–12]. On the other hand, due to their high material cost, MJCs are not available in the form of flat-plate panels like conventional single-junction solar cells. But rather, they are utilized in the form of concentrated photovoltaic (CPV) system where low-cost solar concentrators concentrate solar radiations onto the small area of solar cell material, thereby reducing the use of expensive solar cell material by 500 or 1000 times [13–17]. This is possible because MJC can withstand high concentrations. However, all of the commercial CPV modules, available hitherto, can only accommodate single solar cell per concentrator [18, 19]. Such conventional system requires increased assembly efforts. Therefore, by keeping the cell size same, this chapter discusses a novel CPV module design which can accommodate multiple MJCs with single solar concentrator.

associated with the two axis solar tracking, during CPV operation. However, in the proposed novel multicell concentrating assembly (MCA) design, the homogenizer not only serves as part of conventional homogenizer, but it also helps to split the collimated beam received from a pair of parabolic concentrators. Such ray splitting is achieved because of the fact that the collimated beam, at the inlet aperture of homogenizer, makes an area concentration unlike conventional concentrating assembly design in which point concentration is achieved. By using the concept of concentrator photovoltaics (CPV), the expensive semiconductor multi-junction solar cell material was replaced with cheap solar concentrators. However, with the proposed multicell concentrating assembly design, the cost and assembly efforts of CPV modules will be reduced

Multicell Design for Concentrated Photovoltaic (CPV) Module

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as a less number of solar concentrators will be needed for same capacity of the system.

The theoretical design of proposed multicell concentrating assembly (MCA) is explained in **Figure 2**. It can be seen that the design is based upon the Cassegrain arrangement of two parabolic concentrators, with the intention of achieving the area concentration. Such concentrating assembly acts as a collimating reflector where the parallel solar radiations are converted into concentrated collimated beam. Both parabolic reflectors are arranged such that their focal points coincide with each other. In addition, one of the reflectors uses its inner surface for reflection, while the other uses its outer surface. The primary reflector converges the incoming parallel rays at its focal point. However, these converging rays interact with the outer surface of secondary parabolic reflector which is placed in their way to the focal point. The secondary reflector introduces the cancelation effect which converges rays and diverges them as parallel rays. However, due to smaller contact surface of secondary reflector, the diverged collimated rays become concentrated before they hit the inlet aperture of homogenizer. In order to design multicell concentrating assembly (MCA), the edge ray is traced such that it hits point 'b' of secondary concentrator after being reflected by point 'a' of primary concentrator. As the foci of both reflectors are coinciding, therefore, the edge ray become parallel again after being reflected by the outer surface of secondary reflector and enter the homogenizer through its inlet aperture. This edge ray, after entering into the homogenizer, hits point 'c', which is located at its lower tapered portion. This lower tapered portion of multi-leg homogenizer is designed such that the edge ray, after being reflected by total internal reflection from point 'c', hits point 'e' of outlet aperture of homogenizer and falls on the MJC, placed there. The distribution of such parallel ray distribution is easily explained in simple schematic shown in **Figure 2(b)**. The back surface of MJC is attached to the heat spreader and heat sink assembly, to effectively dissipate the heat during CPV operation. It can be seen that the rays, after being reflected by secondary reflector, become concentrated over an area and size of such area con-

There are three phases in which the design of proposed multicell concentrating assembly (MCA) is divided. The first phase is related to the calculations needed for the sizing of primary reflector. The main factor determining the size of primary reflector is the concentration requirement, depending upon the MJC specifications. The second phase is related to the form

**3. Theoretical design of MCA**

centration depends upon the size of secondary reflector.
