Are scarifiers available with both petrol and electric power?

Yes. Scarifiers can be found in both electric and petrol versions. The differences are pretty much the same as in any piece of gardening equipment. 

Electric Scarifiers - are low or no maintenance, lightweight, with no emissions and low noise. 

Petrol Scarifiers - are generally more powerful, free of the restrictions of cables, can be used more freely and where there is no mains power available.