import pandas as pd
import openpyxl

# create empty excel file
xl_file_name = 'test.xlsx'
wb = openpyxl.Workbook()
ws = wb.active
wb.save(xl_file_name)

# write to excel file
xl_writer = pd.ExcelWriter(xl_file_name, if_sheet_exists='replace', engine='openpyxl', mode='a')
book = openpyxl.load_workbook(xl_file_name)
xl_writer.book = book
xl_writer.sheets = dict((ws.title, ws) for ws in book.worksheets)
chunk = pd.DataFrame({'temp_c': [17.0, 25.0]},
                  index=['Portland', 'Berkeley'])
chunk.to_excel(xl_writer, merge_cells=False, header=False, sheet_name='Sheet')
xl_writer.save()
xl_writer.close()