Choosing the right on-site generation requires an understanding of the loads to be powered, the capability required of the engine to meet the loads, the site's access to cost-effective fuel, and the local emissions requirements.
At scale (greater than 1 MW), gas generation can be very competitive with grid power in terms of cost. Further, since the utilization may or go up or down, it is important to look at each site individually to determine the economics of placing on-site generators.