In simple words, Conventional Energy Sources are the energy sources which cannot be used again after using the resource OR which are non - recycleable OR one day or the other they may get exhausted. Eg: pertrol, diesel, and mineral oil. once we make use of these resources we cannot use them again. For eg: petrol we use in vehicles once used cannot get converted to liquify Pertroleum.
And for Non-Conventional Sources the defination is just opposite i.e. vice-versa. Eg; solar energy, wind energy ,etc. that is available in nature. solar energy can be used by us again and again.