There are web versions of the iWork applications, including Numbers, available in the iCloud.com web portal (called iWork for iCloud).
These work in Windows as well, the only thing required is a supported Windows web browser.
Browser requirements for iWork for iCloud below (from https://www.apple.com/iwork/)
iWork for iCloud works with Safari 9 or later, Chrome 50 or later, and
Internet Explorer 11 or later.
There is no need to export your Numbers document into a different format. If you save your Numbers spreadsheet document to your iCloud Drive on your Mac/iOS device, it will be available and editable in the web version. The edits you make in the web version of Numbers will then sync to your Mac/iOS device and vice versa.
This requires a free Apple ID / iCloud account. If you already set one up on your Mac or iOS device, you just use the credentials to login on the iCloud.com web portal.
Otherwise, see https://support.apple.com/en-us/HT204174 for more info about setting up iCloud.com web access.