Is it possible to extract stream data into an excel file?

If you want to do it Server Side onto a File Repository, you can use one of this  extensions:

• CSV Parser: https://marketplace.thingworx.com/Items/csv-parser
• Data Exporter ( PDF, Excel, Word 😞 https://marketplace.thingworx.com/Items/Data%20Export%20Extension

You can save files directly to the File Repository without any extension too, with FileRepository.WriteToTextFile Service

Google Drive:

• Google Drive: https://marketplace.thingworx.com/Items/google-drive

Client Side you can use the Data Export Widget or from either client or server side you can use the REST API with Accept=text/csv