FO Generators vs. Diesel Generators

Costs are an internal matter for the organisation in question. These are the sorts of questions that are better addressed to the others of the "we" in that particular organisation rather than the readers of a global engineering forum.

What's an FO Generator, chief?

I THINK you are asking about the differences between a liquid fuel diesel and a gaseous fuel diesel. Is this correct?

If it is- The key differences in installation are the need for large volume storage and a day-tank (smaller and inside to allow the fuel to reach temperature closer to internal ambient during cold weather) plus feed pumps, recirculating piping and possibly some form of fuel treatment for the liquid fuel- typically No. 2 diesel oil (very similar to furnace oil) vs. a direct, moderate to high pressure gaseous fuel line- typically natural gas but could be propane with a large storage tank.

Aside from the obvious issue of having the fuel delivered by truck, using up a large amount of ground for storage, having to install a moat to contain a possible ruptured tank and the need for fire safety flooding nozzles in case of fire at or neat the tank, another issue is the air quality of the generator exhaust.

Liquid fuel units have "dirtier" exhausts- particulates, CO2 and NOx than gaseous fuel devices.

Gaseous fuel engines usually have higher wear, and/or need higher lubricating oil feeds because of the "cleaning" action of the gaseous fuel compared to liquid fuels.

Gaseous engines usually engine cost more because they need have have larger displacement because the fuel does not have as high of a thermal content as liquid fuels, so more gas/air must be burnt to get the same power.

You will have to get a design for either option and fully price out all components, then decide how long you can go without a tank refill to figure tank capacity for liquid fuel and then make a decision on what will work best for your operation.