WebSolarLog uses a “single-file” SQLite3 database for data storage. The big advantage of SQLite3 database is, that you could copy/move the database at any given moment.
In the WebSolarLog admin its possible to make a copy of the database to Dropbox.
You could also make a copy of the database by making a file-based copy;
cp /path/to/websolarlog/database/wsl.sdb /backup/location/other/medium/wsl.sdb
The above command will make a copy of /path/to/websolarlog/database/wsl.sdb to and place it in /backup/location/other/medium/wsl.sdb