Is it possible to write from csv to an existing Excel file without closing it?

Question

I have a program outputing a large pandas dataframe. The program is used in a monitoring application and so the end user must continuously see the output of the program in a given excel workbook ex "Output.xlsx". I want to make the program as fast as possible, so I write the dataframe to a csv file "Speed.csv" and then convert the csv file to "Output.xlsx".

from openpyxl import Workbook
import csv

def speed_writing(df):
    df.to_csv(r'Speed.csv')

def csv_to_excel():
    wb = Workbook()
    ws = wb.active
    with open('Speed.csv', 'r') as f:
        for row in csv.reader(f):
            ws.append(row)

        wb.save('Output.xlsx')

speed_writing(df)
csv_to_excel()

Now, this works well only when "Output.xlsx" is closed. If I open the file, run the code I get the following traceback:

Traceback (most recent call last):
  File "trade_export.py", line 140, in <module>
    csv_to_excel()
  File "trade_export.py", line 130, in csv_to_excel
    wb.save('Output.xlsx')
  File "C:\Users\AppData\Local\Programs\Python\Python36\lib\site-packages\openpyxl\workbook\workbook.py", line 391, in save
    save_workbook(self, filename)
  File "C:\Users\\AppData\Local\Programs\Python\Python36\lib\site-packages\openpyxl\writer\excel.py", line 282, in save_workbook
    archive = ZipFile(filename, 'w', ZIP_DEFLATED, allowZip64=True)
  File "C:\Users\AppData\Local\Programs\Python\Python36\lib\zipfile.py", line 1113, in __init__
    self.fp = io.open(file, filemode)
PermissionError: [Errno 13] Permission denied: 'Output.xlsx'

Is this because of local settings or because I cannot save opened files with openpyxl? Any hints, solutions are welcome!