Cepel researcher is co-author of a technical report by Sintef Energy Research on the status and future challenges of the chain of computer models for the operation planning and programming in Brazil and Norway
The operation planning and the generation scheduling in Brazil and Norway are thems of the technical report “Scheduling Toolchains in Hydro-Dominated Systems - Evolution, Current Status and Future Challenges for Norway and Brazil”, released, on August 18th, by the Energy Markets area of SINTEF Energy Research, located in Trondheim, Norway. The document, authored by researchers Arild Helseth (Sintef) and Albert Melo (Cepel), results from a technical cooperation between Cepel and Sintef in the area of operation planning of interconnected hydrothermal systems. Click here to access the report.
Both the Norwegian and the Brazilian systems have vast hydropower resources, with numerous geographically widespread and complex reservoir systems, some of which with reservoirs having multi-year regulation capabilities. “The underlying objective of the scheduling is essentially the same for the two systems; to minimize the operational costs while meeting demands and satisfying all relevant constraints. Thus, the generation scheduling problem in hydro-dominated systems involves both the establishment of long-term strategies for efficient use of water in the entire planning horizon as well as the short-term unit commitment problem”, says Albert.
The researcher points out that, on the other hand, the systems are operated in different market contexts, where the different stakeholders and their respective objectives clearly differ. “In the deregulated Norwegian system, the producer makes bids and offers to the Nord Pool and has the responsibility of generation scheduling of its own hydropower facilities; the problem can then be reformulated and distributed to the producer in the following form: maximize the profit over the planning period while satisfying all relevant constraints. In turn, in Brazil, the National System Operator (ONS) collects technical data from generators and loads to perform a centralized cost-based dispatch and the spot prices, calculated by the Electricity Trading Chamber (CCEE), reflects, in each time period, the marginal cost of energy on the system. This leads to different uses of the models and information flow between them in both countries”, explains Albert. As of January 2020, the DESSEM model, developed by CEPEL, has officially joined the NEWAVE and DECOMP models (also developed by the Center) and started to determine the dispatch of the system on a semi-hourly basis. Learn more.
It is clear in the report that the optimization problem – with the long planning horizon and the many decision stages and time steps – becomes extremely large and complex for a realistically sized system. “As operational scheduling typically is performed on a daily basis, the computational time allowed for solving the problem is limited. This has led to the need for a scheduling toolchain that split up the overall problem along the time axis to emphasize both on the long-term uncertainties and dynamics as well as the short-term details – strategy adopted for both Cepel and SINTEF”, affirms Arild.
The report reviews the different scheduling models and their respective model toolchains developed and maintained by the two research institutions – Cepel and SINTEF Energy Research. These models are, among other tasks, used for operative scheduling in both systems. “We identify the similarities and differences in terms of toolchain design, solution methodologies and modelling details. Our aim is to represent the whole picture, not just model by model”, speaks Albert.
“Another aim is to cover some of the history of the models, to shed light on the original ideas that motivated the creation of the models and toolchains, and the mechanisms facilitating phase-in of new models in the industry. The collected references can serve as a good starting point for further digging into the details”, states Arild.
The report also discusses the current state of these models and how they are being developed through R&D. “As relevant changes in the electrical systems are taking place worldwide, we discuss the need to improve and extend the current toolchains of both countries”, adds Arild.
Finally, researcher Albert emphasizes that this report is of a strategic nature, since both countries have great similarity in relation to the high participation of hydropower plants in their systems, but the market models are different: in Norway (which is part of Nord Pool), the spot price is defined by bids, while in Brazil, by the Cepel´s chain of energy models. "Thus, the deeper knowledge of Norway and the Nord Pool is a relevant asset for the Cepel and Eletrobras, should the market model in Brazil migrate to price bids ", ponders the researcher.
Dr. Arild Helseth's stay as visiting researcher at DEA / Cepel
The technical report of Sintef results from the arrival of Dr. Arild Helseth as a visiting researcher at the Department of Energy Optimization and Environment of Cepel, from September 1, 2019 to mid-March 2020. Originally, the visit should last up to 30 June this year, but due to the Covid-19 pandemic, the researcher received a call from the Norwegian government to return to his country. “With that, we continued with the discussions and the finalization of the report, both of us being on under home office regime”, says Albert.
To make this technical collaboration feasible, the research project “Study of market structures, dispatch and short-term price formation for the planning of electrical systems” was submitted and approved by CNPq - (Process No. 01300.005260 / 2019-78), where researcher Albert appears as coordinator, with Arild as a counterpart. Also, each institution paid the associated costs. In the case of the researcher and manager of the Energy Markets area at SINTEF, and also a professor at NTNU (Norwegian University of Science and Technology), his coming was financed by the Research Council of Norway.
Another result of the arrival of the researcher Arild to the DEA was the realization of a study together with the researcher André Diniz, department head of the DEA, on alternative forms of hourly electricity pricing, for operational daily programming problems of hydrothermal systems. “In this type of problem, integer variables are used to represent constraints of unit commitment of thermoelectric units, resulting in some difficulties and the need to use some hypotheses to obtain the operation marginal cost, which is the basis for determining the hourly price”, highlights André. This study resulted in the paper “Convex Approximations of the Short-Term Hydrothermal Scheduling Problem”, which was submitted and is under review for publication in the IEEE Transactions in Power Systems, leading journal in the field of power systems.
According to André Diniz, the arrival of Arild to the DEA represented an important milestone in the technical collaboration between Cepel and SINTEF/NTNU, and opens the door for the realization of other joint research projects in the future, which are essential to further train the researchers from both institutions in relation to the new challenges that the electricity sector is facing, such as the growth of intermittent energy sources, the concern with greenhouse gas emissions, distributed generation and energy storage. “This enhancement of capacity building is indispensable for the development of new products and the further improvement of the programs and tools already existing by CEPEL, to serve not only the Eletrobras System and the institutions of the electric sector, but also fostering their internationalization”, adds André.
Regarding his experience as a visiting researcher at Cepel, Arild says “It has been a pleasure to visit Cepel! Both Cepel and SINTEF have a proud history of maintenance and research-based development of scheduling models for operational use in hydro-dominated systems. The applied toolchains and the choice of methodologies for the individual models in Brazil and Norway have many similarities, indicating a certain degree of harmonization and an established best practice. Given the many common research challenges of the future, I see a great potential and need for mutual learning through exchange of experiences!”
Technical collaboration between Cepel and SINTEF/NTNU
For two decades, Cepel and Sintef have been exchanging experiences in mathematical formulations and modeling in planning the operation of interconnected hydrothermal systems. However, it was only in 2016 that a step was taken to formalize this cooperation, when the Center became a partner of Sintef and NTNU at the FME (Center for Environmentally Friendly Energy) in Hydroelectricity (HydroCen). That same year, the Norwegian Minister for Research and Education (Torbjørn Røe Isaksen) was in Brazil, accompanied by representatives of the main Norwegian universities and research centers, and met with the director general of Cepel, at the time the researcher Albert Melo. That same year, on September 23, the director of the Strategic Energy Research at NTNU, Olav Fosso, was at Cepel, where he participated in a meeting with the director general of the Center and also with researchers from the institution.
In the midst of this cooperation, more recently, in May 2019, André Diniz participated in Trondheim in the assessment committee of the doctoral thesis “Medium-Term Hydropower Scheduling - In a Multi-Market Setting”, by Martin Hjelmeland, at NTNU, supervised by Magnus Korpås and Arild Helseth. In June 2019, Maria Elvira Maceira participated in Trondheim in the assessment committee of the doctoral thesis “Unit-based Short-term Hydro Scheduling in Competitive Electricity Markets”, by Hans Ivar Skjelbred, also at NTNU, supervised by Olav Fosso.