Safety, maintainability, efficiency, code compliance and economics play crucial roles in determining the topology of a power-generation system, according to an article on the Consulting Specifying Engineer website.

Specific requirements for power vary based on building occupancy type, facility use and critical function. The decision that might be expected to have the greatest environmental impact is the selection of the fuel source for the generating system. 

Natural gas has lower emissions of almost every type at the point of use, with the exception of water vapor.

Natural gas engines are somewhat less efficient than diesel engines, though that gap appears to be closing. In terms of carbon dioxide emissions, the advantage of natural gas over diesel is therefore less pronounced when comparing equal amounts of energy delivered at the generator terminals, as opposed to equal heat content.

Read the article.