I gathered three geom_bar() plots in one plot by grid.arrange:
I removed the y axis of the two right plots (Q2,Q3) and kept the y axis of Q1 as a common axis. Subsequently, I change plot.margin a little bit to obtain a continuous x axis. Although this worked fine, it bugs me that the leftmost plot is smaller than the remaining two plots. I highlighted the difference in size by plotting the y axis again. I tried to fix this by changing plot.margin but without success. Is there any way to equalize the size of the three plots?

 
    