The SQL CE version is for the web access and has a limit of 4GB. To keep data longer( for a year in your case) you will want a full SQL version, and a log to database action in Kiwi Syslog. The database size depends on the volume of syslogs being received. See this link:
http://www.kiwisyslog.com/help/syslog/index.html?action_log_to_odbc_database.htm