New engineering model describing how the energy-water nexus works

Electric power is required to extract, condition, convey, dispose of and recycle water for human use. At the same time, the bulk of global electricity generation capacity uses water as a heat sink or prime mover. This energy-water nexus is of growing importance due to increased demand for water and electricity; distortion of the temporal and spatial availability of fresh water due to climate change; as well as various drivers of more energy-intense water supply for example increased wastewater treatment requirements, and more water-intense electricity generation for example emissions control technologies at power plants.

There are several notable published studies on this nexus. At a technology level, there have been attempts to optimize coupling points between the electricity and water systems to reduce the water-intensity of technologies in the former and the energy-intensity of technologies in the latter. Empirical determinations of the electricity-intensity of water technologies and the water-intensity of electricity technologies have been reported and analyzed. Various models that enable the exploration of the water resource implications of defined electricity sector development pathways and thus support the analysis of various water and electricity policies have also been developed. To our knowledge however, a transparent physics-based approach that interfaces a model of the electricity system to models of the municipal water and wastewater systems enabling an input-output analysis of these three systems in unison has not been presented. Such a modeling approach would support integrated control applications as well as integrated planning without a priori specification of development pathways, for example through optimization.

A paper recently published by the LIINES in Applied Energy titled “Quantitative engineering systems modeling and analysis of the energy–water nexus”presents such a systems-of-system model. In this work, bond graphs are used to develop models that characterize the salient transmissions of matter and energy in and between the electricity, water and wastewater systems as identified in the reference architecture. Bond graphs, which are graphical representations of physical dynamic systems, were chosen as the modeling tool as they facilitate the inter-energy-domain modeling necessitated by the heterogeneous nature of the energy-water nexus. Furthermore they clearly identify causality and readily allow for model enhancement as required by applications. The developed models, when combined, make it possible to relate a region’s energy and municipal water consumption to the required water withdrawals in an input-output model.  This paper builds on another LIINES publication entitled “A Reference Architecture for the Energy-Water Nexus” found in the IEEE Systems Journal.