Systems, methods, and building block modules for modular power generation facilities are disclosed. A method of erecting a modular power generation facility includes producing a plurality of primary modules, each including a housing adapted from an intermodal shipping container having posts, rails, and sills connected together by shipping container corner castings; shipping the primary modules, which include gen-set modules and a switchgear module, to an installation location; positioning the primary modules in a vertical stack; attaching the primary modules to one another in the vertical stack; interconnecting the engine-generators of the one or more gen-set modules with the switchgear of the switchgear module; and operating the engine-generators and the switchgear to provide electricity to a transformer connected to the switchgear in response to a power load demand. The shipping, positioning, and attaching steps are carried out with engine-generators and switchgear operatively installed in the interior of the primary modules.