Python - Stacked Bar Chart of all columns with Cumulative Sum Lineplot (across columns, down rows) - 2 axes plot

I have a dataframe with a monthly datetime index and energy data: df.info() & df.head(). Each column is its own building on a campus. The goal is to plot a stacked bar of each month (and each building) on ax1 stacked barchart photo, and a cumulative lineplot on ax2 CuSum line attemped with stacked bars on the same chart. I have started on some code (pasted below). How can I combine the stacked bar plot of building kWh by month and cumulative kWh line plot into a single overlayed plot?

Code Below:

def stacked_bar_annual_cusum(frame, year):
    
    fig = plt.figure(figsize=(10, 7))
    ax_1 = fig.add_subplot(111)
    frame_raw = frame.copy()
    
    frame_annual = frame_raw.loc[frame_raw.index.year == year]
    
    frame_annual.plot(kind='bar', 
                    stacked=True, 
                    colormap='tab20', 
                    ax=ax_1)
    ax_1.set_xlabel("DateTime")
    ax_1.set_ylabel(f"Energy [kWh]")
    ax_1.legend(loc="upper left", ncol=1)
    ax_1.yaxis.set_major_formatter(mpl.ticker.StrMethodFormatter("{x:,.0f}"))
    plt.xlim(frame.index[0], frame.index[-1])
 
    # Create the second subplot to show the CuSum as a timeseries lineplot
    ax_2 = ax_1.twinx()
    frame_annual.sum(axis=1).cumsum().plot(kind='line', ax=ax_2, color="red", label="CuSum kWh")
    ax_2.set_ylabel(f"CuSum (Energy kWh)")
    ax_2.legend(loc=4)
    ax_2.yaxis.set_major_formatter(mpl.ticker.StrMethodFormatter("{x:,.0f}"))
    # plt.hlines(MEPC_kWh_pred, xmin=frame_annual.index[0], xmax=frame_annual.index[-1])
    plt.title(f"CY{year} Campus Energy Usage")
    fig.autofmt_xdate()
    plt.grid()
    plt.show()

stacked_bar_annual_cusum(frame=Joined_energy_data_trunc, year=2021)