# Numerical Investigation of Thermal Efficiency of a Solar Cell
## 3 Results and Discussion
### Experimental Results
\begin{table}
\begin{tabular}{c c c c} \hline \hline \(Q_{\textit{net\ input}}\) **(W)** & \(Q_{\textit{connection}}\) **(W)** & \(Q_{\textit{radiation}}\) **(W)** & \(Q_{\textit{total},\textit{\ cross section}}\) **(W)** \\ \hline
197.16 & 6.75 & 1.67 & 8.42 \\
208.54 & 4.87 & 1.23 & 6.1 \\
167.44 & 3.52 & 0.87 & 4.39 \\
212.21 & 3 For different heat input, the heat transfer because of convection takes place from different cross sections of the PV cell. It can be observed that the majority of the heat transfer because of convection took place through glass and substrate. Similar patterns in \begin{table}
\begin{tabular}{c c c c c} \hline \hline \(Q_{net\ input}\) **(W)** & \(Q_{I}\) **(W)** & \(Q_{II}\) **(W)** & \(Q_{III}\) **(W)** & \(Q_{total,\ convection}\) **(W)** \\ \hline
197.16 & 2.98 & 65.51 & 33.35 & 101.83 \\
208.54 & 2.12 & 46.74 & 23.79 & 72.65 \\
167.44 & 1.51 & 33.28 & 16.94 & 51.74 \\
212.21 & 1.57 & 34.54 & 17.58 & 53.69 \\
118.44 & 0.82 & 17.95 & 9.14 & 27.91 \\
90.86 & 0.60 & 13.26 & 6.75 & 20.62 \\
59.95 & 0.73 & 16.08 & 8.18 & 24.99 \\
21.06 & 0.22 & 4.82 & 2.45 & 7.49 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Heat transfer due to convection from pipe surface to atmosphere. \begin{table}
\begin{tabular}{c c c c} \hline \hline \(Q_{net\ input}\) **(W)** & \(Q_{I}\) **(W)** & \(Q_{II}\) **(W)** & \(Q_{III}\) **(W)** & \(Q_{total,\ radiation}\) **(W)** \\ \hline
197.16 & 0.13 & 1.09 & 0.61 & 1.84 \\
208.54 & 0.10 & 0.80 & 0.45 & 1.34 \\
167.44 & 0.07 & 0.55 & 0.31 & 0.93 \\
212.21 & 0.07 & 0.56 & 0.31 & 0.95 \\
118.44 & 0.04 & 0.29 & 0.16 & 0.49 \\
90.86 & 0.03 & 0.21 & 0.12 & 0.36 \\
59.95 & 0.03 & 0.26 & 0.14 & 0.43 \\
21.06 & 0.01 & 0.08 & 0.04 & 0.13 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Heat transfer due to radiation from pipe surface to atmosphere. Figure 7: Variation of incident solar radiation during day time. \begin{table}
\begin{tabular}{c c c c} \hline \hline \(Q_{net\ input}\) **(W)** & \(Q_{I}\) **(W)** & \(Q_{II}\) **(W)** & \(Q_{III}\) **(W)** & \(Q_{total,\ radiation}\) **(W)** \\ \hline
197.16 & 0.13 & 1.09 & 0.61 & 1.84 \\
208.54 & 0.10 & 0.80 & 0.45 & 1.34 \\
167.44 & 0.07 & 0.55 & 0.31 & 0.93 \\
212.21 & 0.07 & 0.56 & 0.31 & 0.95 \\
118.44 & 0.04 & 0.29 & 0.16 & 0.49 \\
90.86 & 0.03 & 0.21 & 0.12 & 0.36 \\
59.95 & 0.03 & 0.26 & 0.14 & 0.43 \\
21.06 & 0.01 & 0.08 & 0.04 & 0.13 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Total heat transfer from the surface of the pipe. heat transfer because of radiation was observed. Still, heat transfer because of radiation was comparatively lower than heat transfer because of convection. The heat transfer from the back surface because of radiation was approximately 50% as that of heat transfer because of convection. The heat transfer from the pipe surface to the atmosphere because of convection took place mostly from surface II and then from surface I. Radiation heat transfer from the pipe surface was very low. Thus, the majority of heat transfer from the pipe surface was also because of convection. Table 9 shows the heat gained by water for different heat input calculated using Equation (12), while Table 10 shows the heat balance with uncertain heat loss magnitude. It was observed that of the total heat input, large amounts of heat were carried away by the water and pipe surface. Some amount of heat transfer takes place through the cross section and back surface of the PV cell. Thus, the heat input is balanced by the total heat lost after considering a few amounts in uncertain heat loss. As seen in Table 10, the uncertain magnitude of heat loss is below 6% of total heat input. Hence, the heat balance can be successfully concluded.