Dr. Sébastien Huclin graduated with a thesis entitled “Medium-term technical and economic analysis of storage impacts on power systems under different scenarios with a high renewable share” at theComillas Pontifical University. 

Dr. Huclin has carried out her research FPI grant under María de Maeztu 2018-2021 project with Dr Huclin´s thesis has been supervised by BC3 researcher Mikel González-Eguino and University of Comillas researchers José Pablo Chaves Ávila and Andrés Ramos Galán.

Abstract: 

At the heart of the global efforts to combat climate change, as delineated by the Paris Agreement, lies the urgent need to curtail greenhouse gas emissions, with the energy sector playing a pivotal role. This sector, traditionally a significant contributor to carbon emissions, stands at the threshold of a transformative journey. The Agreement, through its nationally determined contributions, aims to diminish greenhouse gas emissions across various economic sectors. Within the energy domain, this commitment heralds a paradigm shift towards more sustainable, low-emission energy systems, pivoting away from the reliance on fossil fuels. This transition is not without its challenges, as integrating variable renewable energy sources (VRESs) into the energy mix introduces a new dimension of inflexibility, marked by fluctuations in energy availability vis-`a-vis electricity demand.

The quest for a sustainable energy future, characterized by a high penetration of VRES, brings to the fore the critical issue of power system flexibility. This new energy landscape, marked by the intermittent nature of VRES, necessitates a power system that can swiftly adapt its generation or consumption in response to supply or demand variability. Traditional power system regulatory frameworks, designed in an era dominated by fossil fuels, often fall short in accommodating the uncertainty and variability introduced by VRES and the emerging solutions aimed at enhancing system flexibility. The challenge lies in ensuring the power system’s flexibility and adequacy in the face of significant VRES penetration, a challenge that calls for innovative solutions in energy storage, demand response programs, and regulatory reforms to incentivize the provision of flexibility, thereby ensuring the efficient

and reliable operation of power systems.

The comprehensive review of existing studies and methodologies reveals several critical deficiencies in the current models for representing power systems with a substantial integration of VRES especially within a medium-term time scope. There emerges a pronounced need for models that adeptly manage both energy and balancing services, distinguishing clearly between the operating reserve (i.e., power) and the actual activation of the operating reserve (i.e., energy). This delineation is crucial for assessing the roles of energy storage systems (ESSs) and their impacts on power system operations in scenarios dominated by renewable energy sources.

The thesis is based on a medium-term power system operation model. Such a model must maintain the chronological sequence and coherence of input data series, a cornerstone for ensuring the accuracy and reliability of power system operation models. This requirement addresses the critical gap in modeling the operation of power systems, ensuring that the temporal aspects of energy generation and consumption are accurately represented. Additionally, the accurate modeling of diverse ESSs is highlighted, considering their different storage durations and roundtrip conversion efficiencies. This aspect is paramount for evaluating their impact on the operation of power systems. The intricacies of ESS, from short-duration batteries to long-term Pumped Storage Hydro (PSH), play a pivotal role in balancing the intermittency of renewable energy sources, thus requiring meticulous modeling to capture their operational nuances. The need to develop an intricate hydrothermal operation planning model is also underscored. Such a model

should accurately simulate market operations, especially for Hydro Storage, and model PSH as separate physical entities. This distinction is crucial for understanding the unique contributions of hydro storage technologies to the flexibility and adequacy of the power system. Moreover, there is a call for a novel approach that captures the behavior of different technologies in offering operational flexibility and adequacy. This approach should traverse various time scales and address multiple power system scarcities, which complicate the integration of VRES. Understanding how different technologies can meet these demands is crucial for optimizing the power system’s operational strategy in a renewable-dominated landscape. Lastly, an urgent call for analysis of the competition between and within technologies in providing  assorted wholesale system services is made. This analysis is vital for highlighting how technologies can optimize their roles and contributions in renewable-dominated power systems. The competition and complementarity between distinct dispatchable technologies shape the operation of power systems, influencing their ability to integrate renewable energy sources effectively. This comprehensive understanding is imperative for guiding policy, regulatory reforms, and technological advancements in the journey towards a sustainable and reliable energy future.

The innovative methodology, designed specifically for this research, aims to meticulously assess flexibility requirements, evaluate the contributions of various technologies to system flexibility, and gauge their impact on the power system’s overall adequacy. Its distinctive attribute lies in its scalability and replicability, enabling its application across diverse scarcity scenarios and suitability for any electricity system. This universal applicability is achieved through the methodology’s reliance on hourly time series data, which includes load demand, outputs from VRES, and the technical characteristics of generation and storage systems, serving as the fundamental inputs. The methodological approach begins with the ex-ante analysis, which determines the power system’s flexibility requirements. This phase sets the stage for the application of a medium-term operation model, designed to

represent the power system’s operation across a one-year time scope with an hourly time step, incorporating considerations for wholesale flexibility services. The final stage, the ex-post analysis, involves a detailed examination of the model’s outputs, focusing on calculating capacity values and contributions to flexibility. These pivotal calculations are rooted in the capacity factor approximation-based method and a novel methodology for assessing contributions to flexibility, which collectively underpin the analysis. Central to this methodology is the time series decomposition module, a sophisticated analytical tool that plays a crucial role in discerning the requirements for, and contributions to, flexibility across various time scales. This module employs a frequency analysis method, adept at identifying and quantifying the distribution of variations across different periodicities within the net load

demand and technology outputs.

The development of this comprehensive methodological framework is a response to the European Commission’s directives, emphasizing the critical importance of simultaneously considering flexibility aspects across multiple time scales as well as adequacy issues in the context of renewable energy integration. Moreover, it addresses the growing call from industry experts and regulatory bodies for incorporating flexibility considerations into power system adequacy assessments. By doing so, this methodology offers a robust and adaptable tool for navigating the complexities of managing modern electricity systems, particularly in scenarios characterized by high shares of VRES. This alignment with regulatory directives and the methodology’s innovative design underscore its potential to significantly contribute to the field, providing a valuable asset for enhancing the adaptability and resilience of power systems in the face of increasing renewable integration. 

This thesis meticulously crafts a series of scenarios for the year 2030, drawing inspiration from the Spanish National Energy and Climate Plan (NECP)’s scenario with its ambitious target of generating 81% of its electricity from VRES by 2030. At the heart of these scenarios is the exploration of the pivotal role that ESSs are poised to play within the future landscape of 2030. The foundation for this investigation is the construction of a Base Case (BC), which utilizes average water inflow data from 2015 as a reference point. This approach not only grounds the study in a technologically neutral framework but also paves the way for an equitable comparison of ESS across both short- and long-term operational timelines. Integral to the BC are scenarios that consider operating reserves to assess how a detailed modeling of these reserves might influence the analysis of ESS. Moreover, the thesis includes ramping services—a novel consideration in the Spanish power system—eager to uncover potential impacts and benefits these services may herald for the electricity system at large and the role of ESS within it. Additionally, a particularly compelling scenario, the Dunkelflaute (i.e., anticyclone), delves into the power system’s resilience during critical periods marked by high demand but an absence of wind generation coinciding in winter when solar radiation is low. This scenario not only tests the system’s operational robustness but also accentuates the crucial role of ESS in maintaining system reliability under such extreme condition. Finally, given Spain’s significant dependence on hydropower, the thesis embarks on a systematic exploration of the system’s sensitivity to fluctuating water inflow conditions. This sensitivity analysis is instrumental in identifying potential scarcities within the power system, which is crucial for the holistic understanding of system vulnerabilities and resilience. Collectively, these scenario analyses, rooted in the objectives laid out by the NECP, embark on a forward-looking journey to dissect the medium-term impacts of ESS within a renewables-dominated Spanish power system. By doing so, the thesis not only aligns with the overarching goals of the NECP but also charts a course for the future, envisioning a power system that is both resilient and capable of embracing the variability and uncertainty inherent in

the transition to renewable energy sources.

The study places a special emphasis on the energy storage capacity as a pivotal factor in determining the adequacy contributions of ESS technologies. It shows that Open-Loop Pumped Storage Hydro (OLPSH), with its capacity for water pumping, showcases a superior contribution to system adequacycompared to Closed-Loop Pumped Storage Hydro (CLPSH) units, which are limited by their lower energy storage capacity. Within this context, batteries, despite their relatively smaller energy capacity, are highlighted as key players in the balancing market, underpinning the system’s reliability. Indeed, according to BC’s results, the income per capacity of batteries based on the services they provide is 14% higher than that of CLPSH. Thus, although batteries play a smaller role in matching demand, their active participation in the reserve market means that other controllable technologies are still

available for critical times. This differentiation underscores the diverse roles that various storage technologies can occupy within a renewable-dominated power system, highlighting the need for a nuanced understanding of their operational and adequacy contributions. Another pivotal contribution is the detailed scrutiny of different ESS under a spectrum of critical scenarios, ranging from variations in water inflow conditions to examine the system’s resilience under the Dunkelflaute scenario. This multifaceted analysis enriches the understanding of the complex roles that storage technologies assume under varying environmental and operational conditions, offering a deep dive into how these technologies can both complement and compete within the power system to boost reliability and efficiency. 

An integral aspect of this research is the incorporation of ramping services into the operational model, marking a significant stride in understanding the complex roles of dispatchable technologies in providing an array of power system services. The novel integration of ramping services prompts a recalibration in the operation of batteries, enhancing their contributions to energy and ramping services. This adaptation, in turn, enables OLPSH to bolster its availability during critical periods, thereby supporting system adequacy and illustrating the intricate interplay within the power system. Moreover, the exploration of the economic and operational impacts of ramping services uncovers insights into the intricate relationships among dispatchable technologies within the power system and the potential for a redistribution of revenue among them. These insights accentuate the critical importance of including such services in medium-term operational planning, especially in scenarios characterized by a high penetration of renewable energy.

Thesis Committee: 

Dr. Javier Contreras Sanz – Universidad Castilla-la Mancha

Dr. Javier García González – Universidad Pontificia Comillas

Dr. Timo Gerres Universidad – Enagas

Dr. Diego Alejandro Tejada Arango – TNO

Dr. Sonja Wogrin – Graz University of Technology