Maximizing intermittency in 100% renewable and reliable power systems: A holistic approach applied to Reunion Island in 2030☆
Introduction
Power systems are complex man-made infrastructures involving millions of of transmission and distribution lines and hundreds of power plants. Power system generation needs to adapt to consumption in real time, involving strong fluctuations that are only partly predictable. Two intricate time-based issues are of concern to grid operators and utilities [1] in order to: maintain power system quantities within security margins under normal and transient operations, notably frequency and voltage plans [2]; handle the evolution of power systems, which is driven by political, economic, social and environmental issues addressed through long-term energy planning models.
Tackling the considerable challenge of grid decarbonization and the subsequent massive introduction of intermittent electricity production requires a general framework that aggregates the space characteristics of the power grid and reconciles the short-term dynamics of power system management with long-term prospective analysis.
The integration of renewable energy sources in electricity production has been widely studied and several publications have centered on an increased share of renewable energy sources in power production. Some have focused on how to meet future global or regional demand [3], [4], others [5], [6] have included cost optimization criteria to study the feasibility and/or design of solar- and wind-based power system using storage technologies. Cost-effective studies of the integration of high amounts of RES for Europe have focused on a suitable grid [7], [8], [9], [10], [11]; others have looked at RES penetration objectives in different countries such as Germany [12], [13], [14], [15], Belgium [16], Ireland [17] United States [18] and France [19], [20], [21]. However, the scenarios generated by these long-term planning models cannot guarantee reliable power system operations. As a result, numerous methodologies [22], [23], [24] have been developed to bridge the gap between highly detailed operational power system models and long-term planning models. Their aim is to better capture the economic and technical challenges related to the integration of short-term variations resulting from the integration of variable renewable energy systems, and to assess the flexibility of the system.
To our knowledge, this work is the first contribution in which reliability conditions are enforced over time in a long-term planning exercise addressing both space-consolidation and time-reconciliation of all scales involved in power management. It is based on prospective studies combined with a quantitative assessment of power supply reliability based on a bottom-up, long-term investment planning model coupled with an analysis of short-term power system dynamics. This allows us to reconcile the long-term prospective analysis with the short-term power systems management in line with [25], [26].
Thus, this paper proposes to derive a set of conditions based on which the reliability and robustness of the power grid could be discussed and endogenized in prospective studies. This analysis is demonstrated by the case of Reunion Island which aims to produce electricity using renewable energy sources in 2030. Reunion Island is a relevant example because in addition to biomass resources (bagass, the residue from processing sugar cane after the juice is extracted, and wood), the power system will need to foster a broad range of renewable energy sources including ambitious penetration targets for photovoltaics and ocean energy, resulting in a high level of intermittency. This large share of intermittent sources jeopardizes the reliability of the power supply.
Section 2 describes the general conditions for reliable operations under transient regimes underlining the role of synchronism in aggregating all of the kinetic energy embedded in the power system, and deriving two reliability indicators. Section 3 presents the methodology adopted: the main principles of the TIMES model for Reunion Island are described, with the implementation of flexibility solutions and kinetic reliability indicators. The fourth section derives a prospective analysis for the Reunionese power system, based on the previous methodology. The results of the scenarios are discussed and their relevance analyzed from an economic perspective and the long-term evolution of supply reliability.
Section snippets
Power system description and operations
To describe the general conditions for reliable operations under transient regimes requires a detailed understanding of the dynamics of the phenomena involved in the power system.
For local design or power management purposes, electrical power is expressed (see [1]) from the power deviation in the domain , typically surrounding an electrical machine to:
locally enforce the integral form of Poynting’s conservation equation
globally satisfy:
The TIMES-Reunion model
In order to provide plausible options for the long-term development of power systems, TIMES models are useful tools as they offer a technology-rich representation of the electricity system.
Each step of the energy chain, from raw materials to final energy demand, is represented in the model (Fig. 1) by processes (i.e. fridges, electricity distribution, coal power plants) and commodities (i.e. underground gas, electricity). Each process is defined by a set of attributes (i.e. investment costs,
Results
We use the TIMES-Reunion model to assess long-term scenarios for achieving this rapid change (Fig. 2) and assess the level of reliability associated. The future electricity production mix obtained for the Reunion Island strongly relies on intermittent sources, mostly obtained from photovoltaics as shown in Fig. 3.
Based on the stored level of kinetic energy according to the power plant’s type and capacity in the power mix [1], the future electricity system cannot maintain the kinetic indicator
Conclusion
The relevant scales to operate a power system have been reviewed in this paper. A second-order Kuramoto model was adopted to assess the synchronism condition over the whole power grid, with an emphasis on the role of kinetic energy to ensure the power system’s transient reliability to handle sudden disturbances. So far, two indicators have been introduced to analyze a power system’s reliability and robustness:
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The kinetic indicator is related to the kinetic energy embodied in the power system.
Acknowledgements
This research was supported by the Chair Modeling for sustainable development, led by MINES ParisTech, Ecole des Ponts ParisTech, AgroParisTech, and supported by ADEME, EDF, GRTgaz, SCHNEIDER ELECTRIC and the French Department for Climate and Energy.
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This paper was presented at the 8th International Conference on Applied Energy (ICAE2016), October 8–11, 2016, Beijing, China (Original paper: “Power system synchronism in planning exercises: From Kuramoto lattice model to kinetic energy aggregation ” and paper N°: 673).