\documentclass{article}

\usepackage{graphicx}
\usepackage{subcaption}

\begin{document}

\begin{figure}[!h]
\begin{subfigure}[b]{0.49\textwidth}
\includegraphics[width=0.99\linewidth,keepaspectratio]{Power_int.pdf}
\caption{Power dispatch}\label{fig:Power_int}
\end{subfigure}
\begin{subfigure}[b]{0.49\textwidth}
\centering
\includegraphics[width=0.99\linewidth,keepaspectratio]{Heat_int.pdf}
\caption{Heat dispatch}\label{fig:load}
\end{subfigure}
\caption{Power and heat dispatch in the integrated market framework}
\label{fig:image2}
\end{figure}

\end{document}