It will change station to station, but if you open the station details page, adjust X Range to something like 28/180 days, then tune low pass to filter out all the high frequency (daily) fluctuations, you might get your answer. Some stations don't have strong Solar contributions, and won't change much on an annual basis, you can enable the Harmonics toggle and see if any show up on the outside in yellow (disable Sun).

I did consider adding a "max finding" mode of some sort, but that's never really been my use case.