# Browsing by Author "Kocaman, Ayşe Selin"

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Item Open Access A planar facility location–allocation problem with fixed and/or variable cost structures for rural electrification(2023-06) Akbaş, Beste; Kocaman, Ayşe SelinShow more One major impediment to developing countries’ economic growth is the lack of access to affordable, sustainable, and reliable modern energy systems. Even today, hundreds of millions of people live in rural areas and do not have access to essential electricity services. In this study, we present a planar facility location–allocation problem for planning decentralized energy systems in rural development. We consider nano-grid and micro-grid systems to electrify rural households. While micro-grids serve multiple households with a common generation facility, nano-grids are small-scale systems serving individual consumers. The households served by micro-grids are connected to the generation facilities with low-voltage cables, for which we employ a distance limit constraint due to technical concerns, including power loss and allowable voltage levels. In this problem, we minimize the total investment cost that consists of the facility opening and the low-voltage cable costs. In order to capture the diversity of cost structures in renewable energy investments, we consider three versions of the objective function where we incorporate different combinations of fixed and variable cost components for facilities. For this problem, we provide mixed-integer quadratically constrained problem formulations and propose model-based and clustering-based heuristic approaches. Model-based approaches are multi-stage, in which we solve the discrete counterparts of the problem and employ alternative selection methods for the candidate facility locations. Clustering-based approaches utilize faster clustering techniques to identify the type and location of the facilities. We conduct computational experiments on real-life instances from villages in Sub-Saharan Africa and perform a comparative analysis of the suggested heuristic approaches.Show more Item Open Access Benefits of transmission switching and energy storage in power systems with high renewable energy penetration(Elsevier, 2018) Peker, Meltem; Kocaman, Ayşe Selin; Kara, Bahar Y.Show more Increasing the share of renewable energy sources in electricity generation helps address concerns about carbon emissions, global warming and energy security (i.e. dependence on fossil fuels). However, integrating intermittent and variable energy sources into the grid imposes new challenges for power system reliability and stability. To use these clean sources in electricity generation without endangering power systems, utilities can implement various control mechanisms, such as energy storage systems, demand side management, renewable energy curtailment and transmission switching. This paper introduces a two-stage stochastic programming model that co-optimizes transmission switching operations, and transmission and storage investments subject to limitations on load shedding and curtailment amounts. We discuss the effect of transmission switching on the total investment and operational costs, siting and sizing decisions of energy storage systems, and load shedding and renewable energy curtailment in a power system with high renewable penetration. An extensive computational study on the IEEE 24-bus power system with wind and solar as available renewable sources demonstrates that the total cost and total capacity of energy storage systems can be decreased up to 17% and 50%, respectively, when transmission switching is incorporated into the power system.Show more Item Open Access Bi‐objective optimization of a grid‐connected decentralized energy system(John Wiley and Sons, 2018) Altıntaş, Onur; Ökten, Büşra; Karsu, Özlem; Kocaman, Ayşe SelinShow more Motivated by the increasing transition from fossil fuel-based centralized systems to renewable energy-based decentralized systems, we consider a bi-objective investment planning problem of a grid-connected decentralized hybrid renewable energy system. In this system, solar and wind are the main electricity generation resources. A national grid is assumed to be a carbon-intense alternative to the renewables and is used as a backup source to ensure reliability. We consider both total cost and carbon emissions caused by electricity purchased from the grid. We first discuss a novel simulation-optimization algorithm and then adapt multi-objective metaheuristic algorithms. We integrate a simulation module to these algorithms to handle the stochastic nature of this bi-objective problem. We perform extensive comparative analysis for the solution approaches and report their performances in terms of solution time and quality based on well-known measures from the literature.Show more Item Embargo Deviations from commitments: Markov decision process formulations for the role of energy storage(Elsevier BV, 2022-11-11) Karakoyun, Ece Çiğdem; Avci, H.; Kocaman, Ayşe Selin; Nadar, EmreShow more We study the energy commitment, generation, and storage problem for a wind power producer who can own and operate a battery for different purposes. We consider two main problem settings: In the first setting, the producer may choose to deviate from her commitments based on the latest available information, using the battery to support such deviations. In the second setting, the producer is required to fulfill her commitments, using the battery as a back-up source. We also consider the special cases of these settings with no battery. In these settings, the producer decides how much energy to commit to purchasing or selling, how much energy to generate in the wind power plant, and how much energy to charge into or discharge from the battery. We formulate the producer’s decision-making process as a Markov decision process (MDP) by taking into account uncertainties in the electricity price and wind speed in a market setting where the price can be negative. We analytically compare the total profits of the two main settings. We then conduct data-calibrated numerical experiments to examine the effects of system components, imbalance pricing parameters, negative prices, and wind availability on the system operations and profits. Using the battery to intentionally deviate from commitments rather than to minimize such deviations improves the total profit by 16.5%, while this change in the role of the battery increases the total imbalance by 16 times, on average, in our experiments.Show more Item Open Access Optimization of hybrid energy systems with pumped hydro storage: a case study for Turkey(Gazi Üniversitesi Mühendislik-Mimarlık, 2019) Kocaman, Ayşe SelinShow more There is a need for energy models that include renewable energy sources to reduce the role of fossil fuels in electricity generation. However, renewable energy sources are intermittent and cannot be predicted precisely. Designing hybrid systems that combine alternative resources and energy storage helps reduce the intermittency of renewable sources and result in cost effective and reliable solutions. The most widely used energy storage form in the World is to store the potential energy of water in the pumped hydroelectricity systems (PHES). Pumped hydroelectricity systems can be designed in two types: mixed systems, if there is a natural water inflow to the system and pure systems, if the system is closed to water inflow. In this study, we present two-stage stochastic programming models for both types of PHES, which take into account the uncertainty of resources and electricity demand. For the first time in the literature, we consider the sizing problem of hybrid systems that include solar generation supported by pure and mixed PHES systems separately and present the results for Turkey, which currently does not have any PHES system and highly depends on fossil fuels for electricity generation, despite of the rich renewable energy potential.Show more Item Embargo Optimization of pumped hydro energy storage systems under uncertainty: A review(Elsevier, 2023-12-20) Toufani, P.; Karakoyun, E. Ç.; Nadar, Emre; Fasso, O. B.; Kocaman, Ayşe SelinShow more This paper provides an overview of the research dealing with optimization of pumped hydro energy storage (PHES) systems under uncertainty. This overview can potentially stimulate the scientific community’s interest and facilitate future research on this topic. We review the literature from various perspectives, including the optimization problem type, objective function, physical characteristics of the PHES facility, paradigm used to capture uncertainty, and solution method adopted. We then identify several research gaps and future research directions for energy researchers. This review highlights the need for developing optimization models such as Markov decision processes that can represent uncertainties in renewable energy sources and electricity markets more accurately, constructing multi-objective models that consider not only economic but also environmental impacts, investigating underrepresented solar-PHES systems and PHES sizing problems, addressing nonlinear characteristics of PHES facilities, and optimizing bidding strategies in sequential or coordinated electricity markets.Show more Item Open Access A prize collecting Steiner tree approach to least cost evaluation of grid and off-grid electrification systems(Elsevier, 2018) Bölükbaşı, Gizem; Kocaman, Ayşe SelinShow more The lack of access to electricity in developing countries necessitates spatial electricity planning for guiding sustainable electrification projects that evaluate the costs of centralized systems vis-a-vis decentralized systems. Heuristic approaches have been widely used in such electrification problems to find feasible, cost effective solutions; however, most of the time global optimality of these solutions is not guaranteed. Our paper through its modeling approach provides a new methodology to find the least cost solution to this electrification problem. We model the spatial network planning problem as Prize Collecting Steiner Tree problem, which would be a base for a decision support tool for rural electrification. This new method is systematically assessed using both randomly generated data and real data from rural regions across Sub-Saharan Africa. Comparative results for the proposed approach and a widely used heuristic method are presented based on computational experiments.Show more Item Open Access A risk-averse approach for the planning of a hybrid energy system with conventional hydropower(Elsevier BV, 2021-02) Çavuş, Özlem; Kocaman, Ayşe Selin; Yılmaz, ÖzlemShow more We present a risk-averse two-stage stochastic programming model for the planning of a hybrid energy system with conventional hydropower component. Using Conditional Value-at-Risk as our measure of risk-aversion, we take into consideration the dispersion of the random total cost arising due to uncertain streamflow amount. We propose an exact solution approach based on scenario decomposition to solve our large scale problem. We then present a case study for the Mediterranean Region in Turkey and gen erate scenarios using a modified k-nearest neighbor algorithm for bootstrapping the historical time series data of Manavgat River. The results of our computational study show how an optimal solution differs based on the degree of risk-aversion and demonstrate the computational power of our solution approach. Our algorithm is able to solve instances that cannot be solved by CPLEX, furthermore, CPLEX requires 5.84 times more computation time than our algorithm.Show more Item Open Access Rural electrification: An overview of optimization methods(Elsevier Ltd, 2021-12-23) Akbas, B.; Kocaman, Ayşe Selin; Trotter, P. A.; Nock, D.Show more In order to provide “affordable, reliable, sustainable and modern energy for all” by 2030 under Sustainable Development Goal 7 (SDG7), rural electrification needs significant progress as the majority of people without access to electricity reside in rural areas. Optimization methods can play a critical role in this progress, providing an analytical framework to achieve a variety of economic, social, and environmental objectives subject to budget, resources, local demographics and other constraints. This review paper presents the first overview of optimization-based solution methodologies developed or applied for rural electrification. Based on our review, we first propose four archetype problems for rural electrification, namely (i) optimal system configuration and unit sizing, (ii) optimal power dispatch strategy, (iii) optimal technology choice, and (iv) optimal network design. We discuss each problem type, and provide a systematic classification based on the problem objective, proposed solution methodology, components, scale, region as well as their relationship to the different SDG7 components. We reveal research gaps and open questions for future studies for energy researchers and aim to draw the attention of the optimization community to the challenging and unique problems that need urgent attention in this critical area.Show more Item Open Access A scalable framework to measure the impact of spatial heterogeneity on electrification(Elsevier Ltd., 2021-02) Fobi, S.; Kocaman, Ayşe Selin; Taneja, J.; Modi, V.Show more We propose a scalable computational framework to examine the effects of settlement patterns on the electrification of an entire country. We first propose a data processing strategy to convert structure locations, identified from satellite imagery, to estimated household locations using census data. Then, we present a computational framework that involves a two-level network design algorithm to find an abstract representation of the power distribution system at a national scale involving low voltage (LV) wires, medium voltage (MV) wires, and the transformers between the two levels of the system. Given the system components, we introduce three metrics for per-household connectivity requirements of LV and MV wires, and transformers to interpret our results at the administrative and the sub-administrative unit levels. With our administrative level analysis provided for 9.2 million structures in Kenya, we show that traditional rural/urban classification based on population density may not be enough and is often deceiving in estimating the cost of electrification and a new categorization based on our metrics provides more relevant estimates on the total cost. Moreover, our metrics can help determine the least-cost electrification option (e.g.,grid, mini-grid, or stand-alone systems) for expanding access in the sub-administrative unit level and create a platform to perform sensitivity analysis based on different cost components. Our work demonstrates the potential for improvements in universal electrification combining new and more detailed data sources with a scalable planning framework and helps governments achieve Sustainable Development Goal 7 (SDG7) more quickly and at lower cost.Show more Item Open Access Short-term assessment of pumped hydro energy storage configurations: Up, down, or closed?(Elsevier Ltd, 2022-11-09) Toufani, Parinaz; Nadar, Emre; Kocaman, Ayşe SelinShow more We study the energy generation and storage problem for various types of two-reservoir pumped hydro energy storage facilities: open-loop facilities with the upper or lower reservoir fed by a natural inflow and closed-loop facilities. We formulate this problem as a stochastic dynamic program under uncertainty in the streamflow rate and electricity price. We include the streamflow rate and electricity price as exogenous state variables in our formulation. We compare the short-term total cash flows obtained by running different pumped hydro energy storage configurations in a market setting where the electricity price can be negative. We first derive theoretical bounds on the revenue gains and losses from switching from one configuration to another. We then conduct numerical experiments by employing time-series models to formulate the evolution of our exogenous state variables. We consider three distinct seasons with different streamflow rates, different negative price occurrence frequencies, and different reservoir capacities. Our results show that: (1) The open-loop facility with the upstream flow can yield cash flows that are up to four times as large as those of the closed-loop facility; (2) The cash flow from operating a large closed-loop facility can be achieved by operating an open-loop facility with 10 times smaller reservoirs; and (3) The open-loop facility with the downstream flow can be more advantageous than the open-loop facility with the upstream flow (with an improvement of more than 10% in the cash flow) if the negative electricity price occurs more than 30% of the time.Show more Item Open Access A stochastic framework to evaluate the impact of agricultural load flexibility on the sizing of renewable energy systems(Elsevier, 2020) Kocaman, Ayşe Selin; Özyörük, Emin; Taneja, S.; Modi, V.Show more Pumping of water for agriculture can be a flexible component of electric demand. In this study, a framework that involves scenario based stochastic programming models is developed to examine the effect of load shifting on the renewable energy system sizing for agricultural load. With the help of this framework, alternative load shifting policies are evaluated to observe how the intrinsic flexibility of agricultural load reduces the amount of investments while designing a renewable system. Using real data from India’s Gujarat region, solar and wind cases are evaluated separately to understand the coherency between these sources and the agricultural demand. The value of using a dispatchable source to help with the intermittency of the renewable sources in the systems is discussed. It is also shown that energy storage can be a convenient control mechanism for the integration of renewables; however, is an expensive substitute for demand response programs for agricultural load. Benchmarks for the incentive amounts that can be provided for alternative load shifting policies are presented.Show more Item Open Access Towards the sustainable development goals: A bi-objective framework for electricity access(Elsevier Ltd, 2021-02-01) Karsu, Özlem; Kocaman, Ayşe SelinShow more Traditionally, the main focus of evaluation in universal electricity access problems has been cost. However, additional criteria such as increasing renewable penetration due to environmental concerns or grid penetration due to reliability concerns, have become increasingly important. We acknowledge the importance of additional criteria and propose a bi-objective framework so as to help decision makers investigate the trade-offs between potentially conflicting criteria in rural electrification. We consider two objective space based exact approaches using the Prize Collecting Steiner Tree (PCST) formulation and two metaheuristic algorithms to find Pareto solutions, and investigate their performances on real life problem instances. This study is expected to be an important decision support tool for the electrification of underdeveloped communities, having the potential of contributing to their socio-economic development.Show more Item Open Access A two-stage stochastic programming approach for reliability constrained power system expansion planning(Elsevier, 2018) Peker, Meltem; Kocaman, Ayşe Selin; Kara, Bahar YetişShow more Probabilistic realizations of outages and their effects on the operational costs are highly overlooked aspects in power system expansion planning. Since the effect of randomness in contingencies can be more prominent especially when transmission switching is considered, in this paper we introduce contingency-dependent transmission switching concept to ensure N-1 criterion. To include randomness of outages and the outputs (i.e. flow on the lines/generation amounts) during the outages, we represent each contingency by a single scenario. Status of transmission lines, generation amounts and power flow decisions are defined as recourse actions of our two-stage stochastic model, therefore, expected operational cost during the contingencies are taken into account in a more accurate manner. A solution methodology with a filtering technique is also proposed to overcome the computational burden. The model and the solution methodology are tested on the IEEE Reliability Test System and IEEE 118-bus power system and the results show that the solution method finds the solutions for these power systems in significantly shorter solution times. The solution method is also tested on a new data set for the 380-kV Turkish transmission network. Suggestions for possible extensions of the problem and the modifications of the solution approach to handle these extensions are also discussed.Show more