# Cell/Module Integration Technology with Wire-Embedded EVA Sheet
## 3 Results
In area b, the incident light from the wire is reflected on the module glass, when the refractive index of the glass used in the module is 1.5. The effective shading area decreases to approximately 35%. In c, the light reflected from the round wire is reflected back to the module glass; however, the incident angle is larger than the total reflection angle, and therefore the light is divided into reflected and transmitted parts. Accordingly, the shading area of the wire is reduced, and incident light is vertically reflected by the wire, which is re-incident to the wafer surface. Contrastingly, incident light on the rectangular-shaped conventional busbar is less re-incident to the wafer surface. To measure the contact area between the wire and the finger electrode, a cross-sectional scanning electron microscope (SEM) image of the wire and the finger electrode was performed, as shown in Figure 4. The contact area between the wire and finger electrode was reduced by 70% of the wire diameter. The diameter and number of wires should consider the shading loss and the resistance loss simultaneously, and the diameter and number of wires that can minimize both factors should be selected. Because the module manufacturing based on the simulation results can proceed without significantly deviating from the range of the experimental conditions, the wire diameter according to the number of wires was derived using simulation as in MathCAD, and the design of the optimal wire electrode for actual module fabrication was performed. To design a simulation program, an approach to theoretical equations for solar cell parameters is required. Figure 5 shows the basic structure of a solar cell [22]. \[P_{sb} =\frac{1}{m}B^{2}\rho_{smf}\frac{J_{mp}}{V_{mpp}}\frac{S}{W_{F}}\] \[P_{sb} =\frac{1}{m}A^{2}B\rho_{smb}\frac{J_{mp}}{V_{mpp}}\frac{1}{W_{B}}\]  
Figure 4: Cross-section of the SEM image between wire and finger electrode. Figure 3: Schematic of the conventional rectangle-type busbar and the wire. \[P_{sb} =\frac{W_{F}}{S}\] \[P_{sb} =\frac{W_{B}}{B}\]  
When the thickness of the electrode changes in the solar cell, the loss value of the electrode also changes. In the solar cell, the loss owing to the resistance of the electrode (\(P_{rb},P_{sb}\)) and the loss owing to the reduction of the light-emitting area by the electrode (\(P_{sb}\)) occur in the solar cell. The two losses owing to the electrodes are expressed as [22]. \[W_{B} =AB\sqrt{\frac{\rho_{smb}}{m}\frac{J_{mp}}{V_{mp}}}\] Figure 2:0  
Here, \(\rho_{smf}\) and \(\rho_{smb}\) are the sheet resistances of the fingers and busbars, respectively; \(W_{F}\) and \(W_{B}\) are the thicknesses of the fingers and busbars, respectively; \(A\) and \(B\) are the lengths of each side of the solar cell unit structure, and \(S\) is the finger spacing. \(m\) is equal to 4 when the electrode shape is a tapered shape and 3 when the electrode shape is a square shape with a uniform width. As shown in the above equation, as the thickness of the busbar increases, the loss owing to resistance decreases, although the lighting area decreases, thereby increasing the shadow loss. Therefore, it is essential to establish an optimized busbar thickness that can minimize the sum of the two losses. The thickness of the busbar that can minimize the two losses is when the loss owing to resistance and shadow loss matches. In this study, the busbar of the busbarless cell solar cell was changed to a wire instead of the existing five busbars. Accordingly, the simulation program must be modified to accommodate such changes. After confirming the effective light transmission area ratio based on the busbar shape and the changed solar cell parameters, the simulation program was modified. Based on this simulation program, a graph shows the value of the optimum wire diameter versus the number of wires derived from a simulation program designed by applying the busbar shape as a wire. Figure 6 shows the value of the optimum wire diameter based on the number of wires derived from the simulation program.