1)What happen if a PV array of 30 Vmp is connected to a 12 volt battery(lead acid)? 2)Do i need a buck converter to 12 volt between the pv array and the battery to connect them together?
If you are not worried about efficiency or the life of the batteries, a buck regulator with a decent size capacitor on the PV side would do. Set to 13.8V to float charge the batteries.
Bare in mind that lead acid batteries can deliver 100's of amps, so are a potential fire hazard when things go wrong if not suitably fused.
To do it properly, find a commercial maximum power point tracking (MPPT) solar controller