To place two separate figures in one column with different captions use the following code
\begin{figure}[!h]
\begin{minipage}[t]{0.45\linewidth}
\centering
\includegraphics[width=1\textwidth]{./Graphs/Single/Experimental_temperature.png}
\caption{caption1}
\label{f1}
\end{minipage}
\hspace{0.1cm}
\begin{minipage}[t]{0.45\linewidth}
\centering
\includegraphics[width=1\textwidth]{./Graphs/Single/Experimental_temperature.png}
\caption{caption2}
\label{f2}
\end{minipage}
\end{figure}
\begin{figure}[!h]
\begin{minipage}[t]{0.45\linewidth}
\centering
\includegraphics[width=1\textwidth]{./Graphs/Single/Experimental_temperature.png}
\caption{caption1}
\label{f1}
\end{minipage}
\hspace{0.1cm}
\begin{minipage}[t]{0.45\linewidth}
\centering
\includegraphics[width=1\textwidth]{./Graphs/Single/Experimental_temperature.png}
\caption{caption2}
\label{f2}
\end{minipage}
\end{figure}
\begin{figure}
\centering
\subfloat[For different temperatures and at $ G=1kW/m^2 $]{\includegraphics[width=0.4\linewidth]{./Graphs/Single/Experimental_temperature.png}%
\label{fig_first_case}}
\hfil
\subfloat[For different values of irradiations and at $ T=25^oC $]{\includegraphics[width=0.4\linewidth]{./Graphs/Single/Experimental_irr-eps-converted-to.pdf}%
\label{fig_second_case}}
\caption{$I-V$ curve of Single Diode Model of Sanyo-HIT 215 from manufacturer}
\label{13}
\end{figure}