Yes it is but it's not simple. If you use CumulusMX or Weather Display they can do it for you. I expect things like weewx and other pieces of software can also do it.
Because of the type of sensor you have to do quite a complex calculation as it measures global solar radiation, so you have to calculate the expected max value for the time and you location and compare the reading to that expected max,normally anything over 75% of expected is considered sunny, you then add up the minutes it has been above this level for the sunshine hours.
As I said it's easier to use some software to do it for you.
Stuart
