Detailed explanation (in the readmes) of various modding concepts, including QNP, can be found here:
http://www.spaceempires.net/home/modworks-concepts.html
An alternate model, also illustrated, is mQNP, which uses mounts to scale engine size with ship hull. This directly makes engine components larger on larger ships, rather than requiring more engine components. It does pose issues with Ionic Dispersers which should be addressed in any mQNP mod, but they are minor.
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You can also find explanations of some of these systems in the Advanced Modding Tutorials thread:
http://www.spaceempires.net/home/ftopict-312.html