I posted it: https://forum.fortinet.com/tm.aspx?m=147363
1) Create a user with read only privilege in the Fortigate. ie: user backup, password: 1234
2) In a File Share (ie: D:\backup\), put PSCP.EXE and create a BAT file with this:
echo Y|pscp -P 22 -pw 1234 firstname.lastname@example.org:sys_config %DESTINATION%FORTIGATE%FECHA%.conf >> %LOG%
192.168.0.1 is the IP of your Fortigate.
In the BAT file the user and password is stored in clear text, so that's why is necessary a read only user, but if you don't mind, you can use the admin user.
3) Create a schedule task in windows to execute the bat.
Just check the SCP is enabled in your Fortigate:
config system global
set admin-scp enable
and of course, you have to download pscp:http://www.chiark.greenend.org.uk/~sgtatham/putty/latest.html
Hope it helps!