• Energy Research

Thermostatic loads are expected to support the transition to low-carbon systems by providing an array of ancillary services. The delivery of energy-intensive services requires the thermostatic appliances to payback the deployed thermal energy via extra power consumption at a later time. This is made available by conventional generators providing contingency reserve. Previous works acknowledged the interplay between secondary response and contingency reserve. However, the structure of the payback period was fixed and did not fully consider the capabilities of generators providing contingency reserve, e.g., modelling only spinning generators while neglecting standing units. This paper introduces a novel methodology that allows to optimally coordinate the energy recovery of thermostatic loads and the allocation of contingency reserve among spinning and standing units. To do so, the commitment times and structures of secondary response and contingency reserve can be optimally chosen depending on system needs and current availabilities at each time step. The model is applied to the Great Britain network, which is connected to the power system in Continental Europe via a high-voltage direct-current link. Results illustrate the techno-economic advantages stemming from the proposed methodology.

In the Great Britain power system, reduced system inertia (particularly during low demand conditions) and larger possible infeed loss would make grid frequency regulation extremely challenging in future. Traditional primary frequency response could be insufficient to limit the frequency variation within acceptable range. This paper shows that thermostatically controlled loads (TCLs) (domestic refrigerators) can be controlled without real-time communication and in a non-disruptive way to collectively enhance the network frequency response. The aggregated power consumption of TCLs, distributed across the system, could be controlled as a â€∼linear’ function of the locally measured frequency and its rate of change. Alternatively, their aggregated consumption could be made to follow a â€∼pre-set’ power profile depending on the estimated infeed loss. A novel technique for accurate estimation of infeed loss and consequent post-fault TCL power reduction is also proposed. The effectiveness of the two TCL control strategies are compared for primary and secondary frequency response through a case study on a 36 busbar reduced equivalent of the Great Britain power system. The effect of spatial variation of transient frequencies and the time delays in frequency measurement and filtering are considered to show how the TCLs can realistically provide rapid frequency response.

Renewable integration into the electricity system of Great Britain (GB) is causing considerable demand for additional flexibility from plants. In particular, a considerable share of this flexibility may be dispatched to secure post-fault transient frequency dynamics. Pursuant to the unprecedented changes to the traditional portfolio of generation sources, this work presents a detailed analysis of the potential system-level value of unlocking flexibility from nuclear electricity production. A rigorous enhanced mixed integer linear programming (MILP) unit commitment formulation is adopted to simulate several generation-demand scenarios where different layers of flexibility are associated to the operation of nuclear power plants. Moreover, the proposed optimisation model is able to assess the benefit of the large contribution to the system inertial response provided by nuclear power plants. This is made possible by considering a set of linearised inertia-dependent and multi-speed constraints on post fault frequency dynamics. Several case studies are introduced considering 2050 GB low-carbon scenarios. The value of operating the nuclear fleet under more flexible paradigms is assessed, including environmental considerations quantified in terms of system-level CO2 emissions’ reduction.

Thermostatically controlled loads (TCLs) such as refrigerators and air conditioners are natural candidates for short term demand response. In this paper we quantify the value associated with the TCLs' ability to provide system security and transmission constraint management services. The analysis builds on recent results that enable the aggregate control of TCLs as a leaky storage unit. We incorporate this model in a security constrained economic dispatch (SCED) that minimizes the system operational cost of a two bus-bar system, subject to frequency response and transmission constraints. Further sensitivity studies assess the impact of different penetration levels of controllable loads and transmission flow constraints.

This paper proposes a novel distributed solution for the operation of large populations of thermostatically controlled loads (TCLs) providing frequency support. A game-theory framework is adopted, modeling the TCLs as price-responsive rational agents that schedule their energy consumption and allocate frequency response provision in order to minimize their operational costs. The novelty of this work lies in the use of mean field games to abstract the complex interactions of large numbers of TCLs with the grid and in the introduction of an innovative market structure, envisioning distinct price signals for electricity and response. Differently from previous approaches, such prices are not designed ad hoc but are derived instead from an underlying system scheduling model.

This paper analyses the potential benefits for flexible operation of interconnectors in cross-border power systems. The underlying modelling approach enables the simultaneous cross-border exchange of power and inertiadependent frequency response services through the interconnector. Two main operational paradigms are adopted. The first considers the interconnectors as centrally-operated assets; the latter envisages them as profit-seeking private entities. Furthermore, the proposed work adopts a samplingbased method to assess the impact of wind and demand variability on the short-term operation of the interconnectors, evaluating the sensitivities of relevant operational and economical metrics with respect to wind availability and demand levels. A comprehensive set of case studies is developed considering the Great Britain (GB)-France interconnected systems. The studies show significant value for interconnectors under a wide range of system conditions.

The paper proposes a novel generalized formulation of the energy-power dynamics of aggregate thermostatic loads to include power profiles that linearly increase/decrease with time within scheduling intervals. It extends previous models admitting only constant profiles. A MILP optimization problem is built to optimize the dispatch of the devices’ energy/power and the simultaneous allocation of multiple frequency services. Case studies, tailored on the Great Britain electricity context, validate the proposed formulation.

The decarbonization of many heavy power-consuming industries is dependent on the integration of renewable energy sources and energy storage systems in isolated autonomous power systems. The optimal energy management in such schemes becomes harder due to the increased complexity and stability requirements, the rapidly varying operating conditions and uncertainty of renewable sources, the conflicting objectives across different timescales, the limited amount of reliable power sources and energy storage. The state of charge management when energy storage is used for multiple services, such as optimal scheduling and frequency support, is one of the most notorious problems in this context. To address this issue, an optimal energy management system is proposed in this paper. It co-optimizes the primary frequency control layer and the dispatch schedule of conventional generators and energy storage by taking advantage of an algorithm that provides adaptive active power demand uncertainty quantification, theoretical guarantees for frequency stability, and bounds for the reserves for frequency support assigned to the energy storage system. A convex reformulation is derived enabling the efficient solution of the involved optimization problem, being a test case of an isolated offshore oil and gas platform presented for validation.