This Special Issue on Multienergy Systems is motivated by the tremendous changes and opportunities in integrated planning, operation, and modeling of the energy systems, including electric, natural gas, and district heating–cooling systems together with the demand side. Traditionally, the role of electric power has been regarded as an energy carrier between the power plants and the consumers. Consequently, the focus of power system analysis, planning, and operation has been limited to those parts of the system that are between the electrical side of the power generators and the power outlets of the consumers. By expanding the system boundaries to also include the dynamics of supply of primary energy, for example, gas, and the characteristics of consumers’ power consumption, the overall efficiency and security of the power system can be improved. Furthermore, energy requirements of some consumers can be satisfied by different energy carriers. For example, heating can be achieved by electric power, gas, or, if available, district heating networks. An integrated analysis of all these systems would, therefore, offer new possibilities of providing an energy system with additional redundancy and flexibility, resulting in more efficient and resilient energy offerings to the consumers and the society, in general.

In many parts of the world, electric power systems have seen a significant shift toward generation from renewable energy and natural gas. Because of their ability to flexibly adjust power generation in real time, gas-fired power plants are frequently seen as the perfect partner for variable renewable generation. However, this reliance on gas generation increases interdependence and propagates uncertainty between power grids and gas pipelines and brings coordination and uncertainty management challenges. To address these issues, we propose an uncertainty management framework for uncertain, but bounded gas consumption by gas-fired power plants. The admissible ranges are computed based on a joint optimization problem for the combined gas and electricity networks, which involves chance-constrained scheduling for the electric grid and a novel robust optimization formulation for the natural-gas network. This formulation ensures feasibility of the integrated system with a high probability, while providing a tractable numerical formulation. A key advance with respect to existing methods is that our method is based on a physically accurate, validated model for transient gas pipeline flows. Our case study benchmarks our proposed formulation against methods that ignore how reserve activation impacts the fuel use of gas power plants and only consider predetermined gas consumption. The results demonstrate the importance of considering uncertainty to avoid operating constraint violations and curtailment of gas to the generators.

This paper evaluates different means of reducing power consumption of macro base stations (BS) and heterogeneous mobile network deployments (HetNet) considering the time dimension. These approaches are based on the same idea of reducing the load of heavily loaded macro cells and putting them to discontinuous transmission (DTX) mode during the time of inactivity by either (1) macro cell densification or (2) offloading traffic to small cells. Activity factor of a BS is defined as the fraction of time the BS is transmitting over a fixed time period. It is shown that by macro cell layer network densification, the average daily area power consumption can be reduced by up to 73 % with the use of cell DTX. However, reducing the activity factor by macro layer densification is not cost effective, as already demonstrated in previous studies. Alternatively, by adding small cells and enabling their DTX capability, power consumption can be reduced by up to 29 %. Adding small cells is especially effective in terms of energy savings, when users are distributed around hot spots, where additional coverage and capacity is required.

Aggregations of demand response resources can provide a variety of services to the power grid. To utilize them effectively, for both planning problems and real-time control, we must estimate their flexibility. However, flexibility estimates are uncertain because of issues such as model error and forecasting error. In this paper, we present a model of uncertain flexibility and describe the many causes of uncertainty. We conduct two case studies, one for electric vehicle aggregations and one for air conditioner aggregations, in order to show specific examples that illustrate the causes and magnitude of uncertainty. We find that uncertainty can be very large for small load aggregations, when models do not capture enough of the underlying dynamics, or when forecasts of other quantities, such as ambient conditions, are bad. Although the focus of the paper is on understanding uncertainty, we also briefly discuss how one might use knowledge of uncertainty distributions in planning problems to derive closer-to-optimal results.

This paper presents a generic framework for the modeling of energy systems comprising multiple-energy carriers, such as electricity, heat, gas, biomass, etc. The modeling framework is based on the so-called energy hub approach. The core idea of the energy hub is the definition of a conversion matrix capable of describing the interactions of production, delivery, and consumption in multiple-energy carrier systems. Based on the energy hub concept a broad spectrum of modeling extensions and applications is presented, such as a multiple-energy carrier optimal power flow, risk management and investment analysis tools, agent-based control schemes for decentralized generation units as well as the possibility to analyze the influence of plug-in hybrid electric vehicles (PHEVs) on future energy systems. The paper is concluded with a section presenting the key benefits of the energy hub modeling framework, followed by a discussion on the main design principles generality, scalability, and modularity as well as a discussion on the possibility to follow top-down or bottom-up modeling strategies.

This paper discusses the basic design and special applications of wide-area monitoring and control systems, which complement classical protection systems and Supervisory Control and Data Acquisition/Energy Management System applications. Systemwide installed phasor measurement units send their measured data to a central computer, where snapshots of the dynamic system behavior are made available online. This new quality of system information opens up a wide range of new applications to assess and actively maintain system's stability in case of voltage, angle or frequency instability, thermal overload, and oscillations. Recent developed algorithms and their design for these application areas are introduced. With practical examples, the benefits in terms of system security are shown.