Ecological network analysis of an urban energy metabolic system

Analysis of the structure and function of urban energy metabolic systems is an important tool to facilitate compliance with China's current energy-conservation policy. In this study, we used network throughflow analysis and network utility analysis to analyze the structure of an urban energy metabolic system and the complex relationships among its components. Using weight distributions in the network flow matrix, we determined the system structure; using the sign distribution in the network utility matrix, we determined the relationships between pairs of components. We then developed an ecological network model using Beijing in 1995, 2000, 2005, and 2007 as an example of how the model can be used to understand the system's structure and function. The model's components were the energy exploitation, transformation, consumption, and recovery sectors. Network throughflow analysis revealed that the energy transformation and consumption sectors had high weights (34-45%) in all 4 years, whereas the energy recovery sector had small weights (<5%) and the energy exploitation had low to intermediate weights (which decreased from 23% in 1995 to 11% in 2007). Network utility analysis revealed that the ecological relationships between the energy transformation and exploitation sectors, the energy consumption and transformation sectors, and the energy consumption and exploitation sectors did not change, but that the ecological relationships between the energy recovery sector and other sectors changed greatly. Our analysis of Beijing's urban energy metabolic system provided guidance for optimizing the system's structure and adjusting the relationships among the sectors.