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When analyzing power systems, it is often desirable to visualize the network of buses and branches. Here, a new algorithm for producing 2-D network layouts is proposed. The method consists of two steps: first, a matrix of desired distances between all bus-pairs is computed based on base voltages and branch reactances and, second, coordinates that minimize the errors between desired and actual distances are found. The parallelization used in the latter step is particularly beneficial for interpreted languages; it is shown that layouts for relatively large systems (a few thousand buses) can be produced within seconds on a standard laptop computer using Python or Matlab. Predefined coordinates for selected buses can optionally be given as input. This can be useful, e.g., when one wants to retain some geographical aspects of the system or wish to compare a full and reduced network model. Although the focus here is on power systems, the algorithm can also be used for other types of networks., QC 20201103

Rapidly increasing levels of variable inverter-based renewable energy sources (are quickly changing electric power systems and prompting questions about how the systems will be operated when renewable generation becomes the dominant technologies. In this article, we review the status of this shifting paradigm in power systems throughout the world. We then review the implications of this shift, focusing on the rising challenges, and we provide an overview and technology-readiness classifications of some proposed mitigation strategies. Finally, we highlight outstanding questions that will require solutions to reach these ultrahigh shares of variable inverter-based renewable energy sources., QC 20201217

Due to the increased use of variable renewable energy sources, more capacity for reserves is required. Non-generating resources such as thermostatically controlled loads (TCLs) can arbitrage energy prices and provide reserves due to their thermal energy storage capacity. The quantity of reserves depends not only on the aggregate power capacity, but also on information and communication technology, exogenous parameters, and system operator requirements. Specifically, the practical limitations origin from (i) communication constraints, (ii) ambient temperature, and (iii) the dispatch time of the activation signal. This paper explores the impact of these parameters on the amount of reserves that an aggregator of TCLs can provide to the system operator based on centralized control of a TCL population. We propose a decision support tool that can be used by aggregators to decide on maximum dispatchable reserve bids. The method can accommodate the specific control algorithm and TCL population of an aggregator and is based on offline computation. It constitutes a powerful reserve bid library to be used when optimization tools become computationally intractable due to the increased number of decentralized flexible loads., QC 20201216

Non-generating resources such as thermostatically controlled loads (TCLs) can arbitrage energy prices and provide balancing reserves when aggregated due to their thermal energy storage capacity. An aggregator that wants to quantify this flexibility in order to place optimal bids before gate closure, would be affected by market timing. The market timing can be quantified by parameters such as lead time and contract period. This paper explores the impact of market timing on TCL aggregate power consumption and reserve capacity bids and quantifies trade-offs between market timing and flexibility. We first optimize the power consumption and reserve capacity offers at given lead times and contract periods, varying from 24 hours ahead to real-time. We then introduce uncertainty in prices and TCL availability, formulate a two-stage chance-constrained optimization problem of a risk-averse aggregator, implement it on a rolling horizon basis, and evaluate how the trade-offs change. The results show that shorter lead times and contract periods positively impact TCL profit as well as flexibility if the prediction horizon is sufficiently long. The proposed method can be used by aggregators to decide on optimal bids and incentive payments to consumers to reward flexibility., QC 20200214

Network reduction techniques are very useful for taming the complexity of simulating large interconnected power systems. In this paper, we present the implementation of a tool that performs a multi-area spatial network aggregation based on the generalized Radial Equivalent Independent (REI) methodology. The tool is integrated in Spine, an open source energy modelling framework currently under development. The main objective of Spine is to enable open, practical, flexible and realistic planning of future European energy grids. The validity and the efficacy of the reduction tool is investigated through a series of power flow scenarios for various test networks., QC 20211216

Hosting an increasing share of distributed generation and flexible consumers, distribution systems are being more often considered as providers of ancillary services among which are reactive power support and voltage control. For the purpose of reliable and efficient planning and operation of a transmission system, information about reactive power capabilities of connected distribution systems would be beneficial. These capabilities are subject to uncertainties especially with a presence of intermittent distributed generation and stochastic loads. To capture these uncertainties, this paper introduces probabilistic capability charts using the concept of probabilistic curves. These curves analytically represent reactive power support limits of distribution systems as a family of random variables with their associated probabilistic density functions. As such, they carry more information about states of the system than deterministic curves. The proposed capability charts can be easily applied in probabilistic studies of the overlaying transmission system. By providing analytical expressions of stochastic power injections of connected distribution systems, the use of these charts can speed up time and memory demanding probabilistic calculations of transmission systems planning and operation studies. Not containing sensitive system information, the charts can be used to exchange data between distribution and transmission system operators., QC 20200819, Volatile

This paper presents the development and simulation of hydro power models in the open source energy modelling framework Spine. We study the market-based hourly operation of the Skellefte river in the Swedish hydro power system using the abstract representation of \textit{Spine Model}, in order to employ and demonstrate its available functionalities, focusing on the automated handling of the temporal resolution of the optimization model. The Spine temporal block is used for automating the transformation of the temporal resolution of the model in different time intervals, as well as the manipulation of various modelling parameters. After the mathematical formulation of the optimization problem and the detailed analysis of the modelling steps in Spine, various results are extracted discussing the added value of Spine., QC 20210427ISBN:nr 978-1-7281-1078-3

Simulation of large hydro-thermal power systems requires several extensive simplifications and model reductions. For hydropower systems with several interconnected power stations, these reductions can be particularly challenging and are denoted Equivalent models. The purpose of the Equivalent model is to mimic a more detailed hydropower model, while decreasing computation time, to be used in larger power system models. In this paper different Equivalent models for hydropower systems have been computed with a novel approach using a Particle swarm optimization-algorithm and are evaluated with respect to accuracy in hourly and total power generation as well as computation time. For each of the Equivalent models, computation time is decreased with over 99.99 % and the difference in power production is less than 11% compared to a more detailed model., QC 20220301Part of proceeding: ISBN 978-1-7281-7455-6

This paper investigates the coordinated scheduling of hydropower plants in a river participating in a day-ahead, regulation and reserve markets. The gains in participating in the multiple sequential electricity markets are formulated through the linear programming. In the reserve market, the possibility of proposing an unsymmetrical frequency containment reserve (FCR) is considered for two scenarios in the winter and summer. Furthermore, the impacts of active time of regulation bids are investigated. The results show a moderate revenue increase by participating in the reserve market. Also, it states that providing the unsymmetrical FCR market will even increase revenue as an incentive for the owners to participate., QC 20210628

System operators have the option to trade balancing reserves among countries and operators. In order to trade balancing reserves with other system operators the markets should be harmonized. While the spot and intraday markets are already harmonized within the Nordics, the balancing markets still display differences. The differences can be subtle, yet they may play a significant role for the planning, operation, modelling and control of the power system. In this paper, we conduct a thorough literature review on Nordic balancing markets and summarize the market rules and requirements. This review can help operators and modellers to better represent the Nordic power system., QC 20230307

This chapter presents three different methods concerning how to analyze systems with large shares of solar and wind power. The methods are applied to a Swedish case with close to 100 percent renewable power based on hydro, solar, wind and biofueled combined heat and power (CHP). The chapter shows that there are limited balancing costs for this case. The costs for curtailment of surplus as well as to keep enough capacity to cover a high load combined with low solar and low wind is comparatively small, below 0.3 Eurocent/kWh. There are several challenges regarding the handling of large amounts of wind and solar power in power systems. The overall general challenge is to maintain a continuous balance in an economical and reliable way with minimum environmental effects. The challenge for the continuous balancing process is that controllable production and consumption have to maintain the balance on all time scales., Part of ISBN 9781119508311, 9781119508281QC 20240315

In order to effectively utilize hydro production flexibility, a sufficient amount of transmission capacity has to be available between the hydro-dominated part of the system and the part that requires operational flexibility. This chapter starts with a rough categorization of “base” hydropower flexibility, investigating the types of hydropower plants installed in power systems today. The “effective” hydropower flexibility available to support the integration of variable generation is a far more complex and case-specific aspect. It is discussed through national experiences. The chapter presents potential developments that would increase the participation of hydropower and discuss the ensuing challenges. Modeling a flow-based hydro system is a complex exercise, as is modeling the power system. Especially important is the correct assessment of hydropower flexibility to support power systems with a large share of variable generation (VG) and its value for storage. With increasing uncertainty and variability, a stochastic scheduling approach should yield lower costs., QC 20240314Part of ISBN 9781119508311Part of ISBN 9781119508281

This chapter describes some of the recent research into the capacity value of wind power. It builds on previous reviews from IEEE and International Energy Agency (IEA) Wind Task 25, and examines recent work that evaluates the impact of multiple-year data sets and the impact of interconnected systems on resource adequacy. The chapter provides examples that explore the use of alternative reliability metrics for wind capacity value calculations. It shows how multiple-year data sets significantly increase the robustness of results compared to single-year assessments. The preferred method for assessing the capacity value of wind and solar generation is a probabilistic approach grounded in the well-known loss of load probability (LOLP) and related reliability metrics. While reliability-based methods are widely accepted and provide accurate measures of wind and solar capacity values, they require detailed system data and can be computationally expensive to evaluate., QC 20240711

A good understanding of forecast errors is imperative for greater penetration of wind power, as it can facilitate planning and operation tasks. Oftentimes, public data is used for system studies without questioning or verifying its origin. In this paper, we propose a methodology to verify public data with the example of wind power prognosis published by Nord Pool. We focus on Swedish data and identify a significant bias that increases over the forecast horizon. In order to explore the origin of this bias, we first compare against Danish forecast and then describe the underlying structure behind the submission processes of this data. Based on the balance settlement structure, we reveal that Swedish "wind power prognoses" on Nord Pool are in fact rather wind production plans than technical forecasts. We conclude with the recommendation for improved communication and transparency with respect to terminology of public data on Nord Pool. We stress the importance for the research community to check publicly available input data before further use. Furthermore, the root-mean-square error and the spatio-temporal correlation between the errors in the bidding areas at different horizons is presented. Even with this compromised data, a stronger correlation is identified in neighbouring areas., QC 20190124

In the Republic of Djibouti, due to increasing electricity demands, the government has planned to increase power supply by using renewable resources such as geothermal, solar and wind energy. This work presents the first wind resource assessment in the Republic of Djibouti using measured wind speed data for the period of three years by meteorological stations at eight locations. The results confirmed that three of the eight locations (i.e. GaliMa-aba, Ghoubbet and Bada Wein) have the best resource, with mean annual wind speeds of more than 6.0 m/s. Wind simulations using NCEP-CFSR and ERA5 models reanalysis shows that the seasonal variations are stable between different years and are broadly consistent with the observed wind speed. The feasibility of three wind farms with total capacity of 275 MW at GaliMa-aba, Ghoubbet and Bada Wein is examined. Using the WindPRO program and two commercial wind turbines in according to IEC 61400-1 design criteria, the electricity generation were technically assessed. These wind farms can produce 1073 GWh of electricity per year, approximately equal to Djibouti's expected average annual electrical demand in 2030. The economic evaluation using the present value cost (PVC) method estimate that the generation cost per kWh at these locations varies from 7.03 US.$ cent/kWh to 9.67 US.$ cent/kWh. Elsevier Ltd. All rights reserved., QC 20191010

Generation adequacy is a concern in today's electricity market where intermittent renewable energy sources are rapidly becoming a greater share of the generation mix. This paper focuses on the North-European power system that is comprised of the system areas of the Nord Pool spot market. Sequential Monte Carlo Simulation is applied to assess the generation adequacy of this multi-area system for several future scenarios defined within the Nordic Flex4RES project. The paper gives insights into the characteristics of these adequacy problems that the system could face in a more sustainable future and quantifies their magnitude. Finally, some solutions based on the demand flexibility of residential electric heating are discussed., QC 20200217

A rising penetration of renewable energy sources in electric power grids is both a challenge and an opportunity to utilize its potential to stabilize operation of future power systems. Bi-directional flows between distribution and transmission systems can cause significant problems with keeping the voltages and reactive power in grids within permissible levels. This paper addresses the problem of reactive power exchange between the distribution system of Öland and the mainland Swedish electricity grid. Wind turbine generators with the capacity that highly exceeds total demand in Öland, are used to minimize absolute reactive power exchanged at the point of connection. This is done by applying droop control functions for reactive support to the wind turbines. Results indicate that the controllability of the reactive power support from wind turbine generators can keep the reactive power flow minimized at the point of connection and simultaneously diminish the active power losses in the system. The analysis in this paper has been done using the PSS/E software., QC 20191220

Increasing penetration of renewables and focus on cost efficiency means that power systems are operated closer to security limits. It has been suggested that the traditional N-l approach to security is unsatisfactory as it does not consider the likelihood and severity of contingencies. In this paper we investigate a stochastic version of security-constrained optimal power flow (S-SCOPF), which considers outage probabilities when deciding the optimal dispatch. Both a priori dispatch costs and realized real time costs are considered to evaluate the usefulness of the S-SCOPF a s opposed to the deterministic SCOPF (D-SCOPF). For low outage probabilities the S-SCOPF gives lower total costs, achieved by reducing the security for contingency situations. For high outage probabilities the two methods give the same dispatch. The robustness of the S-SCOPF to errors in the outage probability is also investigated. Underestimating the true outage probability results in the S-SCOPF giving higher total costs., QC 20191017

Electric vehicles (EV) can be considered as energy storage with availability, energy and capacity constraints that can provide flexibility to the power system in the form of balancing products when aggregated. In this paper, we develop a two-stage stochastic optimization problem that maximizes the profit of a risk-averse EV aggregator for bids on the day ahead in both energy and Frequency Containment Reserve (FCR) markets. Unidirectional charging is examined, while we take into account uncertainty from prices and vehicle availability. Case studies are carried out in different Nordic bidding areas based on historical EV charging data. We identify a strong temporal alignment of EV availability and high FCR-N prices. Results show that consumption is shifted largely towards early hours of the morning. When compared to a reference cost of charging case, up to 50% of the cost of charging can be recovered in Norway, and 100% in Sweden., QC 20190710. QC 20191203

High penetrations of renewable energy sources (RES) in distribution grids lead to new challenges in voltage regulation. These challenges are not just limited to the steady-state voltage rise, but they are extended to rapid voltage changes due to wind speed variations and moving clouds, casting shadows on photovoltaic panels. According to EN50160 in low-voltage (LV) grids, the steady-state voltage should not exceed 1.1 pu (static characteristic), and rapid voltage changes should be kept less than 0.05 pu (dynamic characteristic). These two characteristics may limit the maximum amount of RES that can be installed in LV grids, called, respectively, the static hosting capacity (SHC) and dynamic hosting capacity (DHC). Although existing research just evaluated SHC in distribution grids, high-penetrated RES grids can be faced with such large voltage changes, which cause a smaller DHC than the SHC. This paper studies both SHC and DHC in distribution grids and proposes an adaptive controller for static synchronous compensators to regulate the steady-state and dynamic voltage while avoiding the unnecessary increase in the reactive power. The simulation results in some German distribution grids show considerable effects of the proposed adaptive controller on improving both SHC and DHC., QC 20190327

A zero-emission pathway for the Nordic and Baltic region in Europe is described based on the comprehensive policy and scenario analyses, accompanied by energy system modelling. The analyses show that a least-cost strategy would massively employ renewable energy, particularly in the power sector. Through strong coupling across energy sectors and countries, electricity would play a central role in the decarbonization of the main energy sectors. In particular power-to-heat conversion, where heat storage appears important in addition to existing hydropower. Technical and regulatory barriers in front of increased sector coupling and flexibility were identified, and policy measures are proposed to overcome these. In addition to a high carbon price, dynamic tariffs and taxation of electricity would be important to allow market signals for flexibility to reach end-users. A stronger power transmission connection from the Nordics to the mainland-Europe and the United Kingdom would be beneficial for the emission reductions and renewable energy use. The transition pathway analysis points out socio-technical issues such as social acceptance of large-scale new infrastructures (e.g., wind, cables). The energy system optimizations indicate that most of the investments needed for the zero-emission pathway until 2050 would take place already by 2030., QC 20191029

As the amount of wind power in power systems has increased, it has become necessary to curtail wind power in some high-penetration situations. In order to assess the need for curtailment arising from voltage stability considerations the authors develop a security constrained optimal power flow (SCOPF) for minimising the expected curtailment. The authors find that with a very high wind penetration and wind farms operating at unity power factor curtailment becomes necessary to satisfy voltage limits. In this case, the optimal solution in the studied system is to curtail at a single bus rather than curtailing by a smaller amount at several buses. However, allowing for reactive power production from wind farms reduces the need for curtailments., QC 20190930

The integration of renewable energy sources, including wind power, in the adequacy assessment of electricity generation capacity becomes increasingly important as renewable energy generation increases in volume and replaces conventional power plants. The contribution of wind power to cover the electricity demand is less certain than conventional power sources; therefore, the capacity value of wind power is smaller than that of conventional plants. This article presents an overview of the adequacy challenge, how wind power is handled in the regulation of capacity adequacy, and how wind power is treated in a selection of jurisdictions. The jurisdictions included in the overview are Sweden, Great Britain, France, Ireland, United States (PJM and ERCOT), Finland, Portugal, Spain, Norway, Denmark, Belgium, Germany, Italy and the Netherlands., Energy & Industry

A zero-emission pathway for the Nordic and Baltic region in Europe is described based on the comprehensive policy and scenario analyses, accompanied by energy system modelling. The analyses show that a least-cost strategy would massively employ renewable energy, particularly in the power sector. Through strong coupling across energy sectors and countries, electricity would play a central role in the decarbonization of the main energy sectors. In particular power-to-heat conversion, where heat storage appears important in addition to existing hydropower. Technical and regulatory barriers in front of increased sector coupling and flexibility were identified, and policy measures are proposed to overcome these. In addition to a high carbon price, dynamic tariffs and taxation of electricity would be important to allow market signals for flexibility to reach end-users. A stronger power transmission connection from the Nordics to the mainland-Europe and the United Kingdom would be beneficial for the emission reductions and renewable energy use. The transition pathway analysis points out socio-technical issues such as social acceptance of large-scale new infrastructures (e.g., wind, cables). The energy system optimizations indicate that most of the investments needed for the zero-emission pathway until 2050 would take place already by 2030.