1. Only works as an adjective with a hyphen e.g. "it is an electricity-generating business" 2. It's just about OK but 4 sounds better. e.g. "the generating of electricity was an expensive business in that town" 3. OK. e.g. "Electricity generation is a lucrative business" 4. OK e.g. "The generation of electricity is a lucrative business"

Electricity generating - this should be Generating electricity, it is more common to phrase it this way as a phrase on its own. Generating of electricity - Generation of electricity, you cannot use the gerund in this form. Electricity generation - perfect Generation of electricity - perfect