MES (multi-energy systems): An overview of concepts and evaluation models

The recent development of efficient thermal prime movers for distributed generation is changing the focus of the production of electricity from large centralized power plants to local generation units scattered over the territory. The scientific community is addressing the analysis and planning of distributed energy resources with widespread approaches, taking into account technical, environmental, economic and social issues. The coupling of cogeneration systems to absorption/electric chillers or heat pumps, as well as the interactions with renewable sources, allow for setting up multi-generation systems for combined local production of different energy vectors such as electricity, heat (at different enthalpy levels), cooling power, hydrogen, various chemical substances, and so forth. Adoption of composite multi-generation systems may lead to significant benefits in terms of higher energy efficiency, reduced CO2 emissions, and enhanced economy. In this light, a key direction for improving the characteristics of the local energy production concerns the integration of the concepts of distributed energy resources and combined production of different energy vectors into a comprehensive distributed multi-generation (DMG) framework that entails various approaches to energy planning currently available in the literature. This paper outlines the main aspects of the DMG framework, illustrating its characteristics and summarizing the relevant DMG structures. The presentation is backed by an extended review of the most recent journal publications and reports.

Distributed multi-generation: A comprehensive view

This paper presents mathematical optimization models of residential energy hubs which can be readily incorporated into automated decision making technologies in smart grids, and can be solved efficiently in a real-time frame to optimally control all major residential energy loads, storage and production components while properly considering the customer preferences and comfort level. Novel mathematical models for major household demand, i.e., fridge, freezer, dishwasher, washer and dryer, stove, water heater, hot tub, and pool pumps are formulated. Also, mathematical models of other components of a residential energy system including lighting, heating, and air-conditioning are developed, and generic models for solar PV panels and energy storage/generation devices are proposed. The developed mathematical models result in Mixed Integer Linear Programming (MILP) optimization problems with the objective functions of minimizing energy consumption, total cost of electricity and gas, emissions, peak load, and/or any combination of these objectives, while considering end-user preferences. Several realistic case studies are carried out to examine the performance of the mathematical model, and experimental tests are carried out to find practical procedures to determine the parameters of the model. The application of the proposed model to a real household in Ontario, Canada is presented for various objective functions. The simulation results show that savings of up to 20% on energy costs and 50% on peak demand can be achieved, while maintaining the household owner's desired comfort levels.

Optimal Operation of Residential Energy Hubs in Smart Grids

Optimal electrical and thermal energy management of a residential energy hub, integrating demand response and energy storage system

This paper focuses on the role of networked microgrids as distributed systems for enhancing the power system resilience against extreme events. Resilience is an intrinsically complex property which requires deep understanding of microgrid operation in order to respond effectively in emergency conditions. The paper first introduces the definition and offers a generic framework for analyzing the power system resilience. The notion that large power systems can achieve a higher level of resilience through the deployment of networked microgrids is discussed in detail. In particular, the management of networked microgrids for riding through extreme events is analyzed. In addition, the merits of advanced information and communication technologies (ICTs) in microgrid-based distributed systems that can support the power system resilience are presented. The paper also points out the challenges for expanding the role of distributed systems and concludes that networked microgrids in particular provide a universal solution for improving the resilience against extreme events in Smart Cities.

Networked Microgrids for Enhancing the Power System Resilience

This paper presents a project named "Vision of Future Energy Networks", which aims at a greenfield approach for future energy systems. The definition of energy hubs and the conception of combined interconnector devices represent key approaches towards a multicarrier greenfield layout. Models and tools for technical, economical and environmental investigations in multicarrier energy systems have been developed and used in various case studies

Energy hubs for the future

Introduction Many of today's energy infrastructures evolved during the second half of the twentieth century and it could be questioned if they meet the requirements of tomorrow. Besides congested transmission systems, many facilities are approaching the end of their prospected life time. In addition to that, other issues such as the continuously growing demand for energy, the dependency on limited fossil energy resources, the restructuring of power industries, and the general aim of utilizing more sustainable and environmentally friendly energy sources raise the question whether piecewise changes of the existing systems are sufficient to cope with all these challenges or a more radical change in system design be needed. Various scientific studies have investigated future scenarios based on boundary conditions given by today’s structures, such as standardized electric voltage and gas pressure levels. Although these studies provide important insights, they often result in solutions that comply with the existing systems; possibly interesting and more long-term oriented solutions are “hidden”, as they lie beyond system-given boundaries. In contrast to these studies, a project named Vision of Future Energy Networks was initiated at ETH Zurich together with partners that aims at a greenfield approach for future energy supply systems. Restrictions given by the existing systems are basically neglected in order to determine “real” optima. The consideration of multiple energy carriers, not only electricity, represents one of the key characteristic of this project. It is believed that synergies among various forms of energy represent a great opportunity for system improvements. Besides the possibilities of modern information technology, state-of-the-art as well as emerging and looming energy technologies, e.g. fuel cells, are taken into account. The time horizon for implementation is set to 30 to 50 years from now. Thus, the basic question to be answered is: “How should energy systems look like in 30 to 50 years, and what can be expected from them?” Under these conditions, two key approaches are reasonable: transformation, conversion, and storage of various forms of energy in centralized units called energy hubs, and combined transportation of different energy carriers over longer distances in single transmission devices named energy interconnectors. It was soon realized that only a few established tools are available for the integrated analysis of multiple energy carrier systems, thus the project focused in a first phase on developing a modelling and analysis framework. In the second phase, which recently started, optimal system structures and operation strategies are determined and compared with conventional infrastructures using the developed tools. The result of this phase is the greenfield approach. The final phase of the project is dedicated to identifying transition paths and bridging systems leading from today’s systems to the identified optimal structures. Figure 1 outlines this process.

Bernd Klöckl

Papers

Energy hubs for the future

The Energy Hub: A Powerful Concept for Future Energy Systems