The pathway towards decarbonisation in Europe requires a dramatic increase in Variable Renewable Energy (VRE) production in the upcoming years. In order to achieve a reduction of 80–95% in greenhouse gas emissions by 2050, the European Union (EU) expects that Renewable Energy Sources (RES) hold a share around 97% of the European power generation mix, considering the high RES scenario envisioned for the decarbonisation trend.
To succeed in such an important endeavour, a deep transformation of the EU Electric Power System (EPS) is taking place by massively integrating non-dispatchable RES, such as wind and solar photovoltaics, wide deployment of high-energy efficient technologies, a stronger effort for electrifying the economy and eliminating coal as a source of energy.
The process of decarbonisation of power systems mainly consists of decommissioning traditional generating units sourced by fossil fuels, and the installation of clean energy sourced generators to meet the growing energy demand. This means a significant transition from classical fossil fuel generators to non-dispatchable RES-based ones.
The traditional generators are typically synchronous rotating machines that are controllable and dispatchable in terms of power output, and are capable of providing a suite of services to the power grid — such as inertia and power balancing (capacity of providing regulating power to the grid to ensure the load/generation balance). Transmission System Operators (TSO) are ultimately responsible for assuring a secure operation of the grid and, to do so, they rely heavily on balancing services (self-provided or contracted to specific providers such as utilities). With the increasing penetration of non-dispatchable RES in the EPS, and the decreasing number of flexible dispatchable power plants, it is crucial to expand and enhance these services to support the proper operation of future EPS.
From the system perspective, system operators must constantly balance demand and supply to keep the EPS secure and stable. However, with the growing levels of non-dispatchable RES — such as wind and solar sources — the complexity of this task increases tremendously across time scales ranging from real-time, in terms of hours and even days. The challenge will also increase as thermal power plants close down, leading to a reduction in the capacity to provide regulating power to the grid.
From a technical viewpoint, the solution relies on more flexibility requirements that must be procured among multiple providers. Then, the main challenge becomes the definition of innovative strategies for operating future EPS with a high share of non-dispatchable RES, which combining multiple flexibility requirements, as well as possible providers.
XFLEX HYDRO: improving hydropower potential
In 2018, hydropower accounted for about 15% of the total electricity generated in the European interconnected transmission system (562.4 TWh out of 3,659.1 TWh). Dispatchable hydropower will, most likely, play a key role in supporting the power grid balancing and extending the flexibility of the European EPS, for the ambitious future scenario of almost 100% share in the generation mix by RES.
It is within this context that the XFLEX HYDRO project was developed: XFLEX HYDRO aims to materialise and improve hydropower potential concerning plant efficiency, availability, and provision of flexibility services to the European EPS. Hydroelectric Power Plants (HPP) are already instrumental providers of flexibility to the system, namely regarding regulation capability, frequency and Volt/var control, among others.
XFLEX HYDRO purpose is to deliver new and effective methods to incorporate state of the art hydroelectric technologies capable of not only enhancing flexibility services, but also optimising HPP maintenance schedules, increase the availability of HPP and maximise their performance. XFLEX HYDRO’s technologies are expected to be engineered and assessed in detail across seven demonstration sites in Portugal, France and Switzerland. These will enable a better understanding of the technical and economic benefits, as well as the challenges of each solution under evaluation:
• Digitalisation tools (Smart Power Plant Supervisor): using plant health monitoring and data capture to reduce maintenance needs and plant outage time, while also increasing efficiency and helping to minimise stresses on equipment under increased flexible operation. This will ultimately support hydro plant operators in their decision-making, regarding the provision of regulation services to the grid.
• Integration of Pumping and Generating Power regulation using Hydraulic Short Circuit (HSC): through the tandem operation of the pumping and generating modes, HSC can enhance the power regulation services and operating ranges offered by pumped storage plants.
• Integration of advanced control for battery storage system: hybridising a battery storage system at a run-of-river hydro power plant, with the aim of increasing plant availability, while also providing extended flexibility and fast response services to the grid.
• Integration of Doubly Fed Induction Machine (DFIM) variable speed technology: aiming to extend operating range, and add flexibility capabilities for the grid, while also improving annual efficiency and residual lifetime. Enhancing the power regulation range by running DFIM in HSC mode will be also assessed.
• Integration of Full-Size Frequency Converter (FSFC) variable speed technology: upgrading hydropower potential by integrating FSFC variable speed technology, using its high flexibility capability and enhanced functionalities for plant operation.
Within the scope of the R&D activities of the project, the first step has been developing a comprehensive framework to evaluate the technologies and improvements planned in the XFLEX HYDRO project, establishing a crucial baseline. This sets out the flexibility and system support services (or ancillary services) required by future EPS, with a strong link to the hydropower technologies being demonstrated. Market mechanisms (both current and expected) are also considered. This has been documented in an Ancillary Services Matrix (ASM), depicted below, which maps the hydro technologies, flexible power services and emerging power markets in Europe. This will help inform different stakeholders of the available technology options, providing a reporting framework for the project. The first stage of the Matrix presents the baseline case, i.e. the degree each hydropower demonstration currently meets or complies with the defined ancillary services. As the project progresses, the Matrix will be populated and updated to show the expected technological improvements with respect to the ancillary power services and corresponding markets.
Future scenarios of the power generation mix published by the European Network of Transmission System Operators (ENTSO-E), indicate that hydropower (including pumped storage) could increase to approximately 280 GW by 2040, under their National Trends scenario. This suggests an increase of around 50 GW new-build capacity over the next two decades. Moreover, much of Europe’s existing hydropower capacity was commissioned over 40 years ago, before 1980. The data suggests that, unless already addressed, over 125 GW, may need to be refurbished or modernised. With these figures in mind, the market potential for the flexibility technologies and methods explored in XFLEX HYDRO, at both new hydro plants and existing facilities, is expected to be of high significance.
About the author:
Carlos Moreira graduated in Electrical Engineering in the Faculty of Engineering of the University of Porto — FEUP (2003) and completed his PhD in Power Systems in November 2008, also from the University of Porto. He is a Senior Researcher in the Centre for Power and Energy Systems of INESC TEC since September 2003. In February 2009 he joined the Department of Electrical Engineering of FEUP as Assistant Professor. His main research interests are related to microgrids operation and control, dynamics and stability analysis of electric power systems with increasing shares of converter interfaced generation systems and grid code development.