As informal urban settlements grow in size and population across the developing world, the issue of how to design and implement effective policies to provide for the needs and the aspirations of dwellers becomes ever more pressing. This paper addresses the challenge of how to characterise in quantitative terms the complex and fast-changing phenomenon of informal urban settlements without falling into oversimplification and a narrow focus on the material deficits of informal settlements. Energy policies are taken as an example to illustrate the shortcomings of oversimplification in producing policy relevant information. We adopt a semantically open representation of informal settlements that can capture the diversity of adaptive strategies used by different settlement typologies, based on the societal metabolism approach. Results show that as settlements grow in size and complexity, they remain economically and politically marginalised and fail to integrate into the city. We argue that in the case of energy policy, the analysis must go beyond the definition of problems such as access to energy at the level of the individual, and focus on a multi-scale assessment including the household and community levels studying the capacity of the household to increase it energy throughput through exosomatic devices and infrastructure.