Is there a way to schedule a python script loading data to Bigquery without having to copy the authentication code generated from a google account link for each run. 
I am currently using the windows task scheduler to achieve this.
You can create the credentials by following this link cloud.google.com/storage/docs/authentication#service_accounts.
In the python script, you can pass the json file path directly to the function you are using to read/write from/to BQ with the private_key argument.
pandas_gbq.read_gbq(query, project_id= myprojectid, ..., private_key= 'jsonfilepath', dialect=’legacy’) 
pandas.to_gbq(dataframe, destination_table, project_id, chunksize=10000, ..., private_key='jsonfilepath') 
Then you schedule the task to run the python script as you'll normally do with the windows task scheduler.
Schedule a python script loading data to BigQuery under windows 10