Integrated Modelling of Urban Energy Systems: Results from a London Case Study
A Sivakumar, J Keirstead, J Polak, Imperial College London, UK
This paper presents the detailed design of SynCity, an integrated modelling framework for urban energy systems, followed by the results of a London implementation.
The majority of the world?s population now live in cities and the trend towards urbanisation is accelerating, with the global proportion of urban population expected to rise to 60% by 2030 (UN World Urbanisation Prospects). Accordingly, the challenges confronting cities are of historically unprecedented scale and complexity, creating both massive risks and enormous business opportunities. Significant innovation will be required to manage these challenges, for example, transforming the urban mobility landscape, improving waste management and recycling systems, ensuring smart and cost effective building technologies. It also requires the development and implementation of optimal urban design and planning principles based on an integrated view of urban systems.
The overall objective of the Urban Energy Systems (UES) project at Imperial College London is to develop a systematic, integrated approach to the design and operation of urban energy systems, with a view to halving the energy intensity of cities. Toward this aim a working model of an urban energy system, titled SynCity, has been developed by a multi-disciplinary research team comprising of environmental scientists, electrical engineers, civil and transport engineers, chemical and systems modelling specialists, and specialists in innovation processes and business models.
SynCity is a hierarchical model system with four layers. The first layer is a spatial layout model that describes and potentially optimises the land use configuration of the urban area; the second layer is an agent-based modelling system (ABMS) that forms the core energy demand estimation component; the third layer is a resource flow and conversion/network optimisation model; and the final layer is a model of urban energy service networks. The ABMS in turn comprises three inter-related modules -- an activity travel demand model, an urban freight logistics component, and a land use module ? and comprises a variety of agents including individuals, households, businesses, industries.
While the spatial layout and resource flow models are optimization models aimed at producing normative and potentially optimal solutions, the ABMS is a descriptive model that aims to predict realistic patterns of agent behaviour. Effectively, therefore, SynCity consists of a behavioural model sandwiched between optimisation models, which is a novel approach to modelling urban energy systems and to the best of our knowledge among the first of its kind (the proposed approach has some precedent in continuous equilibrium network design models that were developed to design optimal networks). The complexity of integrated systems modelling does not typically allow for normative models and this approach conceptually overcomes the difficulty, thus simultaneously serving as a descriptor of behaviour and a design tool.
This paper will present the detailed design of SynCity, dwelling on the benefits of the integrated modelling framework, which will be followed by a more in-depth description of the ABMS component. It then presents the implementation of SynCity for the Greater London region, specifically focusing on reconciling the normative and descriptive results. A number of policy scenarios will be examined, such as, mobility pricing through fuel surcharges or distance-based pricing, and optimal land use configurations from energy and environmental perspectives. Typical policy design would be to determine prices based on a marginal social cost curve, a curve that can be constructed, for instance, through simulation models describing behaviour under varying cost regimes. In SynCity, the descriptive models are overlaid with optimisation models and together they attempt to reconcile the behavioural results with the optimum solution. Similarly, in the case of land use configurations, the descriptive models in the ABMS predict land use processes and the resulting configurations as a result of various policies pricing mechanisms, whereas the layout model prescribes an optimum land use configuration from an energy and/or environmental perspective.
The London implementation of SynCity described in this paper is not only the first large scale empirical application of an activity-based travel demand modelling system for Greater London but goes further to tie activity and travel demand patterns to resource consumption and energy demand. More importantly, the research breaks new ground in the way that transport demand is conceptualised ? as part of a wider system of interactive social and economic relationships that are examined both from a normative and descriptive perspective.
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